Volume 23,Issue 3,2016 Table of Contents
2016, 23(3):1-7.
Abstract:
In order to analyze the particularity of diagenetic evolution law of the upper part of 4th member of Shahejie Formation in saline lacustrine basin of Bonan subsag，detailed research on diagenetic environment and evolution law has been carried out with comprehensive application of casting，scan electron microscope and X-ray diffraction data of clay minerals. The result shows that clastic rock，carbonate rock and gypsum salt beds were mainly developed in the upper part of 4th member of Shahejie Formation of Bonan sag. Under the influence of alkali fluid from gypsum and organic acid during early and middle-late stage of diagenetic period，the reservoirs in the study area experienced alkali and acid diagenetic environment in turn. The intensity of early-stage alkali diagenesis affected the occurrence time of acid diagenesis during middlelate stage. The early-stage strong cementation often caused small contact area between organic acid and diffluent mineral in late stage when organic acid entered into reservoir in the middle-late stage. Therefore，the beginning time of extensive dissolution would be delayed. Because of that，the reservoir follows the diagenetic evolution law that reservoirs in middle alkali diagenetic environment at early stage would be dissolved later at middle-late stage；and if they were in weak alkali diagenetic environment at early stage，they would be dissolved earlier at middle-late stage. The alkali-acid alternation of diagenetic environment in saline lacustrine basin caused the particularity in reservoir diagenetic evolution. Under the controlling of this special diagenetic evolution law，the secondary pore developed with large depth in the late time，resulting in a good match between the timing of high quality reservoir formation in deep layers and late hydrocarbon reservoiring.
In order to analyze the particularity of diagenetic evolution law of the upper part of 4th member of Shahejie Formation in saline lacustrine basin of Bonan subsag，detailed research on diagenetic environment and evolution law has been carried out with comprehensive application of casting，scan electron microscope and X-ray diffraction data of clay minerals. The result shows that clastic rock，carbonate rock and gypsum salt beds were mainly developed in the upper part of 4th member of Shahejie Formation of Bonan sag. Under the influence of alkali fluid from gypsum and organic acid during early and middle-late stage of diagenetic period，the reservoirs in the study area experienced alkali and acid diagenetic environment in turn. The intensity of early-stage alkali diagenesis affected the occurrence time of acid diagenesis during middlelate stage. The early-stage strong cementation often caused small contact area between organic acid and diffluent mineral in late stage when organic acid entered into reservoir in the middle-late stage. Therefore，the beginning time of extensive dissolution would be delayed. Because of that，the reservoir follows the diagenetic evolution law that reservoirs in middle alkali diagenetic environment at early stage would be dissolved later at middle-late stage；and if they were in weak alkali diagenetic environment at early stage，they would be dissolved earlier at middle-late stage. The alkali-acid alternation of diagenetic environment in saline lacustrine basin caused the particularity in reservoir diagenetic evolution. Under the controlling of this special diagenetic evolution law，the secondary pore developed with large depth in the late time，resulting in a good match between the timing of high quality reservoir formation in deep layers and late hydrocarbon reservoiring.
2016, 23(3):8-13.
Abstract:
Poor understanding on sedimentary system of Dongying Formation in Jiyang depression，the stratigraphy deposited at the end of basin faulting and depressing，has caused uncertainty in its reservoir distribution，reservoir type and hydrocarbon accumulation rule，which restricts the exploration of Dongying Formation. Based on the principle and methods of sedimentology，combining with data of comprehensive mud logging，logging and seismic data，it is determined that a large braided river delta sedimentary system formed crossing the east depression under the monocline structural background during the sedimentary period of Dongying Formation in Jiyang depression through analyzing geologic structure features and palaeogeography. A braided delta developed mainly at the third period of Dongying Formation. The lacustrine basin began to regress and the sedimentary area became smaller and smaller at the second period of Dongying Formation，in which shallow beach lacustrine facies formed in the east combining with depositions of small proximal fans and subsea aprons，and fluvial facies deposited mainly in the east. The lake regressed continuously at the last period of Dongying Formation，and fluvial facies and shallow beach facies developed widely. In the plane，sedimentary patterns changed from braided-delta plain subfacies and delta front sub-facies in Dongying sag in the south to pro-delta sub-facies in Zhanhua-Tanhai area in the north. Slump turbidite fans developed at the front of delta. The sedimentary model establishment of Dongying Formation not only perfects the Jiyang depression’s sedimentary evolutionary sequence of Cenozoic era and guides the direction of reservoir prediction in Dongying Formation，but also lay a foundation for the study on reservoir forming condition of Dongying Formation.
Poor understanding on sedimentary system of Dongying Formation in Jiyang depression，the stratigraphy deposited at the end of basin faulting and depressing，has caused uncertainty in its reservoir distribution，reservoir type and hydrocarbon accumulation rule，which restricts the exploration of Dongying Formation. Based on the principle and methods of sedimentology，combining with data of comprehensive mud logging，logging and seismic data，it is determined that a large braided river delta sedimentary system formed crossing the east depression under the monocline structural background during the sedimentary period of Dongying Formation in Jiyang depression through analyzing geologic structure features and palaeogeography. A braided delta developed mainly at the third period of Dongying Formation. The lacustrine basin began to regress and the sedimentary area became smaller and smaller at the second period of Dongying Formation，in which shallow beach lacustrine facies formed in the east combining with depositions of small proximal fans and subsea aprons，and fluvial facies deposited mainly in the east. The lake regressed continuously at the last period of Dongying Formation，and fluvial facies and shallow beach facies developed widely. In the plane，sedimentary patterns changed from braided-delta plain subfacies and delta front sub-facies in Dongying sag in the south to pro-delta sub-facies in Zhanhua-Tanhai area in the north. Slump turbidite fans developed at the front of delta. The sedimentary model establishment of Dongying Formation not only perfects the Jiyang depression’s sedimentary evolutionary sequence of Cenozoic era and guides the direction of reservoir prediction in Dongying Formation，but also lay a foundation for the study on reservoir forming condition of Dongying Formation.
2016, 23(3):14-19.
Abstract:
There are a lot of theoretical studies of conventional and unconventional oil and gas. However，the study of the relationship between conventional and unconventional oil and gas is still rare. In view of this，from the aspects of formation time，space distribution and the amount of oil and gas resources，research results of conventional and unconventional oil and gas were summarized；the problems in the research of conventional and unconventional oil and gas were pointed out，and the development trend of the conventional and unconventional oil and gas was analyzed. The results show that there are three types of relationships between conventional oil and gas and unconventional oil and gas characterized of reservoirsource contact：reservoir getting tight prior to hydrocarbon charging，reservoir getting tight after hydrocarbon charging and reservoir getting tight contemporaneous with hydrocarbon charging. Conventional oil and gas are mainly distributed in the higher part of the structure，and unconventional oil and gas are generally distributed in the center of the basin or the general slope. The relationships between conventional and unconventional oil and gas resources are consistent with those in the triangle diagram of oil and gas resources distribution. But there are still problems for the conventional and unconventional oil and gas：the formation time，the transition belt of oil and gas distribution，the relationship of oil and gas resources between different structural units and the determination of unconventional oil and gas boundary. In the future，more attention should be paid on the researches of whole process of hydrocarbon generation and expulsion，fine-grained sedimentology，oil and gas resources evaluation and accumulation of oil and gas.
There are a lot of theoretical studies of conventional and unconventional oil and gas. However，the study of the relationship between conventional and unconventional oil and gas is still rare. In view of this，from the aspects of formation time，space distribution and the amount of oil and gas resources，research results of conventional and unconventional oil and gas were summarized；the problems in the research of conventional and unconventional oil and gas were pointed out，and the development trend of the conventional and unconventional oil and gas was analyzed. The results show that there are three types of relationships between conventional oil and gas and unconventional oil and gas characterized of reservoirsource contact：reservoir getting tight prior to hydrocarbon charging，reservoir getting tight after hydrocarbon charging and reservoir getting tight contemporaneous with hydrocarbon charging. Conventional oil and gas are mainly distributed in the higher part of the structure，and unconventional oil and gas are generally distributed in the center of the basin or the general slope. The relationships between conventional and unconventional oil and gas resources are consistent with those in the triangle diagram of oil and gas resources distribution. But there are still problems for the conventional and unconventional oil and gas：the formation time，the transition belt of oil and gas distribution，the relationship of oil and gas resources between different structural units and the determination of unconventional oil and gas boundary. In the future，more attention should be paid on the researches of whole process of hydrocarbon generation and expulsion，fine-grained sedimentology，oil and gas resources evaluation and accumulation of oil and gas.
2016, 23(3):20-25.
Abstract:
On the basis of seismic data and vertical fault displacement method，the growth process of Xi’nanzhuang fault in Nanpu sag was quantitatively inverted. It shows that the boundary fault had the characteristic of segmentation in the early stage and jointed together in the later stage during the sag evolution period. The segmentation of the fault were apparent at the beginning of the depositional period of the Shahejie Formation，and each segment had individual distribution of normal fault displacement. During the depositional period of the first member of Shahejie Formation，the segments showed the trend of linkage and in the depositional period of the Dongying Formation，the segments finally linked together to become a large fault. It also reveals that the spatiotemporal diversity of Xi’nanzhuang fault segmentation has great influence on sedimentary system of rifted-basin and its distribution. The maximum fault displacement formed by segmentation is at the center of fault，and controlled the formation of half graben where nearshore subaqueous fans easily developed under the background of half-deep lake and deep lake. Meanwhile，the segmentation points located where the fault segments connected，and structural accommodation zones of strike slope and transverse anticline developed as the main channels for sand body being transported into the depression and thus facilitate the development of fan delta sedimentary system.
On the basis of seismic data and vertical fault displacement method，the growth process of Xi’nanzhuang fault in Nanpu sag was quantitatively inverted. It shows that the boundary fault had the characteristic of segmentation in the early stage and jointed together in the later stage during the sag evolution period. The segmentation of the fault were apparent at the beginning of the depositional period of the Shahejie Formation，and each segment had individual distribution of normal fault displacement. During the depositional period of the first member of Shahejie Formation，the segments showed the trend of linkage and in the depositional period of the Dongying Formation，the segments finally linked together to become a large fault. It also reveals that the spatiotemporal diversity of Xi’nanzhuang fault segmentation has great influence on sedimentary system of rifted-basin and its distribution. The maximum fault displacement formed by segmentation is at the center of fault，and controlled the formation of half graben where nearshore subaqueous fans easily developed under the background of half-deep lake and deep lake. Meanwhile，the segmentation points located where the fault segments connected，and structural accommodation zones of strike slope and transverse anticline developed as the main channels for sand body being transported into the depression and thus facilitate the development of fan delta sedimentary system.
2016, 23(3):26-32.
Abstract:
The Bonan oilfield，developing large low permeability reservoirs，suffers serious water flood after fracturing because of its poor reservoir property and not considering the influence of current stress during exploitation. It is necessary to research the distribution of current stress systematically in the further development. Taking the Es3 of the 5th block of Bonan oilfield as an example，the current stress for the Es3 of the 5th block of Bonan oilfield and its direction were identified by means of laboratory core test method，such as differential strain method，acoustic emission method and velocity anisotropy method；and the relationship between dynamic and static rock mechanical parameters was established by logging data interpretation. The relationship between rock dynamic and static mechanical transformation parameters was extracted through logging data interpretation to pick up accurately rock mechanical parameters and establish the geologic model，and then the stress distribution characteristics and influence factors were analyzed combining with the finite element numerical simulation. The result shows that the current terrestrial stress exists regionally in the 5th block of Bonan oilfield. The maximum horizontal principal stress direction is N61.4°E in the east and S58°E in the west. The maximum horizontal principal stress is low at the center，high in the boundaries with a ring-shaped distribution pattern. The minimum horizontal principal stress decreases from north to south. The regional stress is higher in the study center. The abnormal direction of in-situ stress is mainly resulted from symmetric lateral shear forces which are formed when the V-shaped fracture system is squeezed by nearly east-west stress. The section stress is mainly influenced by depth and mechanical parameters.
The Bonan oilfield，developing large low permeability reservoirs，suffers serious water flood after fracturing because of its poor reservoir property and not considering the influence of current stress during exploitation. It is necessary to research the distribution of current stress systematically in the further development. Taking the Es3 of the 5th block of Bonan oilfield as an example，the current stress for the Es3 of the 5th block of Bonan oilfield and its direction were identified by means of laboratory core test method，such as differential strain method，acoustic emission method and velocity anisotropy method；and the relationship between dynamic and static rock mechanical parameters was established by logging data interpretation. The relationship between rock dynamic and static mechanical transformation parameters was extracted through logging data interpretation to pick up accurately rock mechanical parameters and establish the geologic model，and then the stress distribution characteristics and influence factors were analyzed combining with the finite element numerical simulation. The result shows that the current terrestrial stress exists regionally in the 5th block of Bonan oilfield. The maximum horizontal principal stress direction is N61.4°E in the east and S58°E in the west. The maximum horizontal principal stress is low at the center，high in the boundaries with a ring-shaped distribution pattern. The minimum horizontal principal stress decreases from north to south. The regional stress is higher in the study center. The abnormal direction of in-situ stress is mainly resulted from symmetric lateral shear forces which are formed when the V-shaped fracture system is squeezed by nearly east-west stress. The section stress is mainly influenced by depth and mechanical parameters.
2016, 23(3):33-39.
Abstract:
Reservoir with high porosity still developed at the second member of Yingcheng Formation in Yingtai faulted depression when sedimentary pyroclastic rocks buried underground deeper than 3 000 m. Relationships of reservoir space composition with lithology，buried depth and structural position were analyzed in order to determine reservoir characteristics and its influential factors，and the control factors of reservoir were studied from two aspects：diagenesis and the formation of high porosity zone. The results show that reservoir space of sedimentary pyroclastic reservoir in the second member of Yingcheng Formation in Yingtai faulted depression is composed of primary porosity such as intergranular pore and intraparticle pore，secondary porosity such as dissolution pore and intercrystal pore and fracture. There are three zones with high porosity：interlayers at 2 000-2 100，2 500-2 550 and 3 300-3 700 m. Reservoir is controlled by deep compaction，filling，metasomatism，corrosion-dissolution and recrystallization. The main factors about improvement of deeply buried sedimentary pyroclastic reservoir are corrosion-dissolution and matrix recrystallization. The plane porosity can increases 0.6%-5.3% through corrosion-dissolution of unstable plagioclase in this area，and the plane porosity can increases 0.9%-8.3% through recrystallization of unstable matrix. The sedimentary pyroclastic rocks have high content of unstable ingredients，which can provide material for diagenesis. So dissolved and recrystallized sedimentary pyroclastic rocks in uplift area with buried depth less than 3 700 m should be paid more attention by the exploration.
Reservoir with high porosity still developed at the second member of Yingcheng Formation in Yingtai faulted depression when sedimentary pyroclastic rocks buried underground deeper than 3 000 m. Relationships of reservoir space composition with lithology，buried depth and structural position were analyzed in order to determine reservoir characteristics and its influential factors，and the control factors of reservoir were studied from two aspects：diagenesis and the formation of high porosity zone. The results show that reservoir space of sedimentary pyroclastic reservoir in the second member of Yingcheng Formation in Yingtai faulted depression is composed of primary porosity such as intergranular pore and intraparticle pore，secondary porosity such as dissolution pore and intercrystal pore and fracture. There are three zones with high porosity：interlayers at 2 000-2 100，2 500-2 550 and 3 300-3 700 m. Reservoir is controlled by deep compaction，filling，metasomatism，corrosion-dissolution and recrystallization. The main factors about improvement of deeply buried sedimentary pyroclastic reservoir are corrosion-dissolution and matrix recrystallization. The plane porosity can increases 0.6%-5.3% through corrosion-dissolution of unstable plagioclase in this area，and the plane porosity can increases 0.9%-8.3% through recrystallization of unstable matrix. The sedimentary pyroclastic rocks have high content of unstable ingredients，which can provide material for diagenesis. So dissolved and recrystallized sedimentary pyroclastic rocks in uplift area with buried depth less than 3 700 m should be paid more attention by the exploration.
2016, 23(3):40-46.
Abstract:
There is a phenomenon of geothermal anomaly which is inconsistent with the basement structure of Fushan sag.The characteristics and forming mechanism of geothermal anomaly were discussed through geothermal data analyses and palaeogeothermal simulation of the basin. The results indicate that the geothermal gradient stratification between the upper and lower formations is caused by the difference of lithology. The geothermal anomaly，inconsistent with the basement structure，was related to the strong volcanic activity in the east of Fushan sag since Holocene. The deep magma pocket，the typical anticline structure and the accumulation of hydrocarbon are the reasons for the geothermal anomaly in Fushan sag. The formation time of the geothermal anomaly，happened 10 000 years ago，was relatively short and had little effect on organic matter maturity. However，a large number of palaeo-oil reservoirs were thermally pyrolyzed into condensate gas reservoirs at the center of geothermal abnormal area，which had huge effect on palaeo-oil reservoir in Fushan sag.
There is a phenomenon of geothermal anomaly which is inconsistent with the basement structure of Fushan sag.The characteristics and forming mechanism of geothermal anomaly were discussed through geothermal data analyses and palaeogeothermal simulation of the basin. The results indicate that the geothermal gradient stratification between the upper and lower formations is caused by the difference of lithology. The geothermal anomaly，inconsistent with the basement structure，was related to the strong volcanic activity in the east of Fushan sag since Holocene. The deep magma pocket，the typical anticline structure and the accumulation of hydrocarbon are the reasons for the geothermal anomaly in Fushan sag. The formation time of the geothermal anomaly，happened 10 000 years ago，was relatively short and had little effect on organic matter maturity. However，a large number of palaeo-oil reservoirs were thermally pyrolyzed into condensate gas reservoirs at the center of geothermal abnormal area，which had huge effect on palaeo-oil reservoir in Fushan sag.
2016, 23(3):47-52.
Abstract:
Gubei sag has abundant hydrocarbon resources，and the overpressure zones are widely developed in this area.According to the drilling stem test data，present-day overpressure commonly occurs at the depth ranging from 2 800 to 3 800 m. As the sonic transit times have obvious responses to overpressure in both sandstone and mudstone with similar range of variation and trend，the Eaton method was used to predict overpressure in sandstone reservoir. In addition，the distribution characteristics and the controlling factors of the pressure distribution were analyzed combining the drilling stem test data. On the whole，two overpressure systems were identified in the vertical including an upper system distributed in lower Ed and Es1 and a lower system in Es3 and Es4 which is also the main overpressure zone. In plane，overpressure distributes in the east and the west subsags，and it decreases gradually from the center to the uplift and boundary faults. The distribution pattern of reservoir overpressure is mainly influenced by faulting，mudstone thickness and content and hydrocarbon generation of source rock.
Gubei sag has abundant hydrocarbon resources，and the overpressure zones are widely developed in this area.According to the drilling stem test data，present-day overpressure commonly occurs at the depth ranging from 2 800 to 3 800 m. As the sonic transit times have obvious responses to overpressure in both sandstone and mudstone with similar range of variation and trend，the Eaton method was used to predict overpressure in sandstone reservoir. In addition，the distribution characteristics and the controlling factors of the pressure distribution were analyzed combining the drilling stem test data. On the whole，two overpressure systems were identified in the vertical including an upper system distributed in lower Ed and Es1 and a lower system in Es3 and Es4 which is also the main overpressure zone. In plane，overpressure distributes in the east and the west subsags，and it decreases gradually from the center to the uplift and boundary faults. The distribution pattern of reservoir overpressure is mainly influenced by faulting，mudstone thickness and content and hydrocarbon generation of source rock.
2016, 23(3):53-57.
Abstract:
Based on the measured element content of outcrop samples and drilling cutting samples of the Ordovician Wufeng Formation shale and Silurian Longmaxi Formation shale, chemical elements and oxide-geochemistry features of the shale in the Jiaoshiba area were researched. The results show that the shale formations have a higher SiO2 content overall, and the chemical indexes of alteration (CIA) are between 55 and 77 which indicates the shale developed under a warmhumid climate. The elements characteristics of different shale samples are significantly different, which show a huge difference in the quality of shale. The excess SiO2 content of the drilling cutting samples are very low in the upper of Longmaxi shale and the value of U/Th is less than 0.75, which indicates that the shale formed under an energetic and oxygen-enriched environment, and the organic matter is difficult to be saved, so the shale quality is poor. The excess SiO2 content of the drilling cutting samples is between 6.6% and 12.9% in the lower of Longmaxi shale and the value of U/Th is between 0.75 and 1.25, which indicates that the shale formed under an oxygen-poor and comparatively calm-water environment, so the quality of shale which is characterized by high organic matter content and good compressibility is good. The excess SiO2 content of the outcrop samples of the Wufeng Formation shale is between 11% and 24% and the value of U/Th is between 0.76 and 1.34, which indicates that the shale formed under an oxygen-poor or anaerobic environment. The organic matter content is so high that it is easy for the shale to develop natural fracture or to be fractured. So the shale quality is excellent.
Based on the measured element content of outcrop samples and drilling cutting samples of the Ordovician Wufeng Formation shale and Silurian Longmaxi Formation shale, chemical elements and oxide-geochemistry features of the shale in the Jiaoshiba area were researched. The results show that the shale formations have a higher SiO2 content overall, and the chemical indexes of alteration (CIA) are between 55 and 77 which indicates the shale developed under a warmhumid climate. The elements characteristics of different shale samples are significantly different, which show a huge difference in the quality of shale. The excess SiO2 content of the drilling cutting samples are very low in the upper of Longmaxi shale and the value of U/Th is less than 0.75, which indicates that the shale formed under an energetic and oxygen-enriched environment, and the organic matter is difficult to be saved, so the shale quality is poor. The excess SiO2 content of the drilling cutting samples is between 6.6% and 12.9% in the lower of Longmaxi shale and the value of U/Th is between 0.75 and 1.25, which indicates that the shale formed under an oxygen-poor and comparatively calm-water environment, so the quality of shale which is characterized by high organic matter content and good compressibility is good. The excess SiO2 content of the outcrop samples of the Wufeng Formation shale is between 11% and 24% and the value of U/Th is between 0.76 and 1.34, which indicates that the shale formed under an oxygen-poor or anaerobic environment. The organic matter content is so high that it is easy for the shale to develop natural fracture or to be fractured. So the shale quality is excellent.
2016, 23(3):58-61.
Abstract:
The hydrocarbon source and reservoir conditions of the gas reservoir of the second member of Xujiahe Formation in Sumatou structure are good. So oil and gas preservation conditions are the key factors to exploration in this area because the reservoir experienced multi-tectonic movement. On the basis of previous research results，factors related to hydrocarbon preservation conditions were analyzed comprehensively such as caprock condition，fault activity periods，pressure exerted on fault zone and geochemical characteristics，etc. The results show that the sealing ability of regional caprock of the second member of the Xujiahe Formation in Sumatou structure is excellent and the macroscopic seal of the direct caprock is good.The vertical sealing of different control gas faults is different，and the vertical sealing of the Fault M① is the best. Based on comprehensive analysis on the factors of caprock，fault and geochemical characteristics，etc.，it is concluded that the preservation condition of the gas reservoir of the second member of Xujiahe Formation is mainly controlled by the fault in Sumatou structure. Due to the destruction of the Fault M④，the preservation condition of the gas reservoir of the second member of the Xujiahe Formation in the upper wall of the Fault M① is poor，but that of the gas reservoir of the second member of the Xujiahe Formation in the footwall of the Fault M① is relatively good.
The hydrocarbon source and reservoir conditions of the gas reservoir of the second member of Xujiahe Formation in Sumatou structure are good. So oil and gas preservation conditions are the key factors to exploration in this area because the reservoir experienced multi-tectonic movement. On the basis of previous research results，factors related to hydrocarbon preservation conditions were analyzed comprehensively such as caprock condition，fault activity periods，pressure exerted on fault zone and geochemical characteristics，etc. The results show that the sealing ability of regional caprock of the second member of the Xujiahe Formation in Sumatou structure is excellent and the macroscopic seal of the direct caprock is good.The vertical sealing of different control gas faults is different，and the vertical sealing of the Fault M① is the best. Based on comprehensive analysis on the factors of caprock，fault and geochemical characteristics，etc.，it is concluded that the preservation condition of the gas reservoir of the second member of Xujiahe Formation is mainly controlled by the fault in Sumatou structure. Due to the destruction of the Fault M④，the preservation condition of the gas reservoir of the second member of the Xujiahe Formation in the upper wall of the Fault M① is poor，but that of the gas reservoir of the second member of the Xujiahe Formation in the footwall of the Fault M① is relatively good.
2016, 23(3):62-66.
Abstract:
The sedimentary microfacies and sand body distribution of the upper Es4 submember in Qingdong5 Block is not clear，which has restricted the fine prediction of the reservoir and the development of the production plan. Based on the analysis of lithology，electrical characteristics and paleontological characteristics，the upper Es4 submember in Qingdong5 Block were divided into three sand groups. By using drilling，logging，seismic data and test data and integrating geologic facies，logging facies and seismic facies，the results show that the upper Es4 submember in Qingdong5 Block is fan delta deposition with well-developed fan delta front subfacies and fan prodelta subfacies and poorly-developed fan delta plain. The main reservoirs in the study area are underwater distributary channel，estuarine sand bar and front sheet sand developed in the fan delta front，clastics beach and bar and carbonate beach bar developed in the front delta，among which the midstream and downstream of the main water diversion channel，mouth sand bar and offshore beach sands are favorable reservoirs.The development of sandbodies in the upper Es4 submember of Qingdong5 Block are controlled by contemporaneous faults and sedimentary microfacies.
The sedimentary microfacies and sand body distribution of the upper Es4 submember in Qingdong5 Block is not clear，which has restricted the fine prediction of the reservoir and the development of the production plan. Based on the analysis of lithology，electrical characteristics and paleontological characteristics，the upper Es4 submember in Qingdong5 Block were divided into three sand groups. By using drilling，logging，seismic data and test data and integrating geologic facies，logging facies and seismic facies，the results show that the upper Es4 submember in Qingdong5 Block is fan delta deposition with well-developed fan delta front subfacies and fan prodelta subfacies and poorly-developed fan delta plain. The main reservoirs in the study area are underwater distributary channel，estuarine sand bar and front sheet sand developed in the fan delta front，clastics beach and bar and carbonate beach bar developed in the front delta，among which the midstream and downstream of the main water diversion channel，mouth sand bar and offshore beach sands are favorable reservoirs.The development of sandbodies in the upper Es4 submember of Qingdong5 Block are controlled by contemporaneous faults and sedimentary microfacies.
2016, 23(3):67-71.
Abstract:
The microbe-assisted air flooding is a new oil displacement method. Its mechanism is that the rate of microbial growth and metabolism can be increased by the help of oxygen in the air，which makes air flooding safer. Experiments of microbe growing and oxygen consumption were conducted under different initial concentrations of dissolved oxygen，and experiment of oil removing efficiency of the microbe under different concentrations of dissolved oxygen as well. The results show that the growth of experimental strains experience lag phase，logarithmic phase，stable phase and degenerating phase under conditions of oxygenation and non-oxygenation. When the initial concentration of dissolved oxygen is 4.5 and 5.5 mg/L，the maximum concentration of the microbial growth is 3 times of that under non-oxygenation；the concentration of dissolved oxygen declines logarithmically at the logarithmic phase，and that declines linearly at the stable phase and degenerating phase. The decreased oxygen in the oil reservoir is due to the oxygen consumption caused by microbe degeneration，and oil removing efficiency of the microbe may increase along with the increase of the initial concentration of the dissolved oxygen. Base on the law of oxygen consumption of the microbe and reservoir flow，mathematical model was set up to calculate the oxygen concentration distribution in the oil reservoir under different injection parameters. The result shows that the oxygen concentration decreases exponentially with increased reservoir radius；the whole well area have sufficient oxygen concentration for microbe growing and the reservoir has become a favorable environment for microbe；and the oxygen concentration in the air is reduced to safe level for air flooding and the minimum oxygen consuming radius is about145 meters.
The microbe-assisted air flooding is a new oil displacement method. Its mechanism is that the rate of microbial growth and metabolism can be increased by the help of oxygen in the air，which makes air flooding safer. Experiments of microbe growing and oxygen consumption were conducted under different initial concentrations of dissolved oxygen，and experiment of oil removing efficiency of the microbe under different concentrations of dissolved oxygen as well. The results show that the growth of experimental strains experience lag phase，logarithmic phase，stable phase and degenerating phase under conditions of oxygenation and non-oxygenation. When the initial concentration of dissolved oxygen is 4.5 and 5.5 mg/L，the maximum concentration of the microbial growth is 3 times of that under non-oxygenation；the concentration of dissolved oxygen declines logarithmically at the logarithmic phase，and that declines linearly at the stable phase and degenerating phase. The decreased oxygen in the oil reservoir is due to the oxygen consumption caused by microbe degeneration，and oil removing efficiency of the microbe may increase along with the increase of the initial concentration of the dissolved oxygen. Base on the law of oxygen consumption of the microbe and reservoir flow，mathematical model was set up to calculate the oxygen concentration distribution in the oil reservoir under different injection parameters. The result shows that the oxygen concentration decreases exponentially with increased reservoir radius；the whole well area have sufficient oxygen concentration for microbe growing and the reservoir has become a favorable environment for microbe；and the oxygen concentration in the air is reduced to safe level for air flooding and the minimum oxygen consuming radius is about145 meters.
2016, 23(3):72-76.
Abstract:
Impact of compression and reinjection of the produced gas on displacement efficiency was studied and its mechanism was analyzed to solve the problem of how to recycle and make use of the large amount of CO2-rich associated gases during CO2 flooding. Based on CO2 flooding pilot test in Gao89 Block of Zhenglizhuang oilfield of Shengli oil province，the minimum miscibility pressure（MMP）between formation oil and CO2 was measured by long slim tube test method. The displacement efficiency of CO2 miscible flooding was determined by long core displacement experiment using pure CO2 and produced gases at various stages. The results show that when the CO2 content is 72.59%，the displacement efficiency is up to 76.9%，similar to that of pure CO2 miscible flooding. Moreover，the components of produced gas at different stages were analyzed，and the influence mechanism of gas composition on the displacement efficiency was investigated. The results suggest that the produced gas during CO2 flooding can be directly reinjected without purification. It provides a new and feasible solution to treat produced gas in the middle and late period of CO2 flooding.
Impact of compression and reinjection of the produced gas on displacement efficiency was studied and its mechanism was analyzed to solve the problem of how to recycle and make use of the large amount of CO2-rich associated gases during CO2 flooding. Based on CO2 flooding pilot test in Gao89 Block of Zhenglizhuang oilfield of Shengli oil province，the minimum miscibility pressure（MMP）between formation oil and CO2 was measured by long slim tube test method. The displacement efficiency of CO2 miscible flooding was determined by long core displacement experiment using pure CO2 and produced gases at various stages. The results show that when the CO2 content is 72.59%，the displacement efficiency is up to 76.9%，similar to that of pure CO2 miscible flooding. Moreover，the components of produced gas at different stages were analyzed，and the influence mechanism of gas composition on the displacement efficiency was investigated. The results suggest that the produced gas during CO2 flooding can be directly reinjected without purification. It provides a new and feasible solution to treat produced gas in the middle and late period of CO2 flooding.
2016, 23(3):77-82.
Abstract:
The oil-water transition zone of heavy oil reservoir is relatively wide，which has considerable amount of remaining oil and great development potential. However，restricted by economic and technical conditions，it is hard to build up the well pattern and produce reserves effectively for low control degree of well pattern. Through quantitative study of the influence of viscosity on the distribution in oil-water transition zone，the oil saturation distribution of the oil-water transition zone and oil-producing law of oil wells in the heavy oil reservoir were analyzed. Based on this，considering the influence of economic factors，a method of determining economic and technical limits of oil well production in the oil-water transition zone was proposed. According to practical oilfield characteristics and development requirements，economic and technical limits chart of the oil well production in W oil reservoir were established. The chart will provide guidance to the effective disposition of infilled adjustment well in the oil-water transition zone of W oil reservoir.
The oil-water transition zone of heavy oil reservoir is relatively wide，which has considerable amount of remaining oil and great development potential. However，restricted by economic and technical conditions，it is hard to build up the well pattern and produce reserves effectively for low control degree of well pattern. Through quantitative study of the influence of viscosity on the distribution in oil-water transition zone，the oil saturation distribution of the oil-water transition zone and oil-producing law of oil wells in the heavy oil reservoir were analyzed. Based on this，considering the influence of economic factors，a method of determining economic and technical limits of oil well production in the oil-water transition zone was proposed. According to practical oilfield characteristics and development requirements，economic and technical limits chart of the oil well production in W oil reservoir were established. The chart will provide guidance to the effective disposition of infilled adjustment well in the oil-water transition zone of W oil reservoir.
2016, 23(3):83-88.
Abstract:
Water flooding is one of the most important ways to develop oilfields currently. Influenced by reservoirs，fluid，well pattern and other conditions，water displacement in different directions are obviously different from each other. When water flooding reservoir entered to high and extra-high water cut stage，the remaining oil distribution becomes more and more complex，and traditional development adjustment methods may not be applicable. Practices of oilfield development indicate that the production performance is closely related to the equalization degree of displacement by injected water. The equilibrium displacement concept was proposed and used to guide the design of production plan. However，the relationship between the displacement equalization degree and the development performance was mainly studied on the basis of qualitative analysis but lacking of quantitative and theoretical analysis. Based on reservoir engineering and seepage flow mechanics theory，the relationship between the cumulative water injection and cumulative oil production in various injection-production directions during the water flooding was derived to describe the displacement dynamics. Then the relationship between the net present value and the displacement dynamics was derived and analyzed. Moreover，formulas for well spacing and optimization design of injection-production pressure difference was given to achieve equilibrium development.
Water flooding is one of the most important ways to develop oilfields currently. Influenced by reservoirs，fluid，well pattern and other conditions，water displacement in different directions are obviously different from each other. When water flooding reservoir entered to high and extra-high water cut stage，the remaining oil distribution becomes more and more complex，and traditional development adjustment methods may not be applicable. Practices of oilfield development indicate that the production performance is closely related to the equalization degree of displacement by injected water. The equilibrium displacement concept was proposed and used to guide the design of production plan. However，the relationship between the displacement equalization degree and the development performance was mainly studied on the basis of qualitative analysis but lacking of quantitative and theoretical analysis. Based on reservoir engineering and seepage flow mechanics theory，the relationship between the cumulative water injection and cumulative oil production in various injection-production directions during the water flooding was derived to describe the displacement dynamics. Then the relationship between the net present value and the displacement dynamics was derived and analyzed. Moreover，formulas for well spacing and optimization design of injection-production pressure difference was given to achieve equilibrium development.
2016, 23(3):89-94.
Abstract:
Obvious threshold pressure gradient exists during the development of low-permeability common heavy oil reservoir in Oudeh oilfield of Syria，which affects the producing degree of reserves. It is very important to study the influence of threshold pressure gradient on limit drainage radius of horizontal wells in the oil reservoir developed by natural energy and horizontal well. In order to comprehensively study the effect of the threshold pressure gradient on reservoir development law，first of all，the threshold pressure gradient was determined by the laboratory experiment，and its relation with mobility was known. Secondly，based on the quasi-three-dimensional ideas on ellipse flow in horizontal well，pressure gradient model of horizontal well in xy and yz plane considering threshold pressure gradient was set up. Finally，the limit drainage radius of the horizontal wells in oil reservoir was determined by using the method of steady state approximating non steady state.At the same time，the limit drainage radius chart of the horizontal wells in the quasi-three dimension was established. The research results show that the threshold pressure gradient of low-permeability common heavy oil reservoir is another major factor of low producing degree besides the factor of high viscosity of crude oil. The fluid flow of horizontal well in the xy plane is a linear flow，and that in the yz plane is a radial flow. The limit drainage radius of the horizontal well in the xy plane was larger than that in the yz plane. During the development by horizontal well in the low-permeability common heavy oil reservoir，the matching relationship between the reservoir thickness and the limit drainage radius of the horizontal well in the xy plane and yz plane should be considered fully in order to achieve the purpose of expanding the scope of producing reservoir.
Obvious threshold pressure gradient exists during the development of low-permeability common heavy oil reservoir in Oudeh oilfield of Syria，which affects the producing degree of reserves. It is very important to study the influence of threshold pressure gradient on limit drainage radius of horizontal wells in the oil reservoir developed by natural energy and horizontal well. In order to comprehensively study the effect of the threshold pressure gradient on reservoir development law，first of all，the threshold pressure gradient was determined by the laboratory experiment，and its relation with mobility was known. Secondly，based on the quasi-three-dimensional ideas on ellipse flow in horizontal well，pressure gradient model of horizontal well in xy and yz plane considering threshold pressure gradient was set up. Finally，the limit drainage radius of the horizontal wells in oil reservoir was determined by using the method of steady state approximating non steady state.At the same time，the limit drainage radius chart of the horizontal wells in the quasi-three dimension was established. The research results show that the threshold pressure gradient of low-permeability common heavy oil reservoir is another major factor of low producing degree besides the factor of high viscosity of crude oil. The fluid flow of horizontal well in the xy plane is a linear flow，and that in the yz plane is a radial flow. The limit drainage radius of the horizontal well in the xy plane was larger than that in the yz plane. During the development by horizontal well in the low-permeability common heavy oil reservoir，the matching relationship between the reservoir thickness and the limit drainage radius of the horizontal well in the xy plane and yz plane should be considered fully in order to achieve the purpose of expanding the scope of producing reservoir.
2016, 23(3):95-100.
Abstract:
Fractures and severe heterogeneity commonly exist in the low permeability reservoirs，which will cause varying degrees of gas channeling phenomena during CO2 flooding. In order to study the effect of heterogeneity and fractures on CO2 flooding efficiency，four experimental models of homogeneous model，heterogeneous model with various permeability ratios，high-capacity gas channeling model and fracture model were built in the laboratory to simulate the heterogeneity and fracture of the low permeability reservoirs. Waterflood and continuous CO2 flooding were conducted firstly，followed by gas channeling control experiments using different gas channeling control systems in different types of experimental models correspondingly. Experimental results showed that the oil recovery of continuous CO2 flooding had a power function negative correlation with permeability ratios and the gas channeling phenomena became more severe as the increase of heterogeneity，resulting in the poor displacement efficiency of CO2. Gas channeling control can be achieved using different gas channeling control systems in different types of experimental models. The gas channeling control in heterogeneous models with the permeability ratio of less or equal to 100 can be achieved by ethylenediamine system plugging high permeability layers，while gas channeling control in high-capacity gas channels and fracture can be achieved by modified starch gel and ethylenediamine.
Fractures and severe heterogeneity commonly exist in the low permeability reservoirs，which will cause varying degrees of gas channeling phenomena during CO2 flooding. In order to study the effect of heterogeneity and fractures on CO2 flooding efficiency，four experimental models of homogeneous model，heterogeneous model with various permeability ratios，high-capacity gas channeling model and fracture model were built in the laboratory to simulate the heterogeneity and fracture of the low permeability reservoirs. Waterflood and continuous CO2 flooding were conducted firstly，followed by gas channeling control experiments using different gas channeling control systems in different types of experimental models correspondingly. Experimental results showed that the oil recovery of continuous CO2 flooding had a power function negative correlation with permeability ratios and the gas channeling phenomena became more severe as the increase of heterogeneity，resulting in the poor displacement efficiency of CO2. Gas channeling control can be achieved using different gas channeling control systems in different types of experimental models. The gas channeling control in heterogeneous models with the permeability ratio of less or equal to 100 can be achieved by ethylenediamine system plugging high permeability layers，while gas channeling control in high-capacity gas channels and fracture can be achieved by modified starch gel and ethylenediamine.
2016, 23(3):101-105.
Abstract:
In order to solve the problem of“difficult to inject，difficult to produce”under the condition of thermal recovery in low permeability carbonate heavy oil reservoir of Syria O oilfield，experiments of self-imbibition and oil displacement were conducted for the cores in O oilfield. Imbibitions rule and displacement effect of formation water and thin film spreading agent（TFSA）solution were researched under 50 and 150 ℃. The self-imbibition experiment result shows that the wettability of the carbonate cores in O oilfield turns from obvious oil-wet or weak oil-wet under original conditions to waterwet or weak water-wet after TFSA imbibition，and thus wettability inversion is realized. The displacement experiment result shows that compared with steam injection at 150 ℃，the thermal compound chemical technology，steam injection with TFSA，can significantly reduce steam injection pressure by about 2 MPa and the displacement efficiency is increased by about 10%. After wettability inversion of the rocks，water is easy to enter the pore of the rocks under capillary force which is a driving force during water displacing oil and the difficulty of“difficult to inject”may be solved. High temperature can reduce crude oil viscosity and the percolation ability of crude oil is improved，and the difficulty of“difficult to produce”may be solved. Therefore，the thermal compound chemical technology is a feasible method for enhancing oil recovery in O oilfield and similar low permeability carbonate heavy oil reservoirs.
In order to solve the problem of“difficult to inject，difficult to produce”under the condition of thermal recovery in low permeability carbonate heavy oil reservoir of Syria O oilfield，experiments of self-imbibition and oil displacement were conducted for the cores in O oilfield. Imbibitions rule and displacement effect of formation water and thin film spreading agent（TFSA）solution were researched under 50 and 150 ℃. The self-imbibition experiment result shows that the wettability of the carbonate cores in O oilfield turns from obvious oil-wet or weak oil-wet under original conditions to waterwet or weak water-wet after TFSA imbibition，and thus wettability inversion is realized. The displacement experiment result shows that compared with steam injection at 150 ℃，the thermal compound chemical technology，steam injection with TFSA，can significantly reduce steam injection pressure by about 2 MPa and the displacement efficiency is increased by about 10%. After wettability inversion of the rocks，water is easy to enter the pore of the rocks under capillary force which is a driving force during water displacing oil and the difficulty of“difficult to inject”may be solved. High temperature can reduce crude oil viscosity and the percolation ability of crude oil is improved，and the difficulty of“difficult to produce”may be solved. Therefore，the thermal compound chemical technology is a feasible method for enhancing oil recovery in O oilfield and similar low permeability carbonate heavy oil reservoirs.
2016, 23(3):106-110.
Abstract:
Taking thin-bed heavy oil reservoir with edge-bottom water in Panyu oilfield as an example，water cut increase of the horizontal wells was classified into four types：open drowning type，rapid drowning type，rising ladder type and hillclimbing type. Influencing factors of the water cut rising type were analyzed according to the geological condition，fluid characteristic and production performance of the horizontal well. The effect sequence was given by the gray correlation method. Results indicate that the effect sequence is interlayer range＞oil viscosity＞distance between wellbore and water oil contact＞ratio of water layer thickness to overall thickness. The larger the interlayer range is and the smaller the oil viscosity is，the slower the water cut rises in single horizontal well；the smaller the distance between wellbore and water oil contact and the larger the ratio of water layer thickness to overall thickness，the faster the water cut rises in single horizontal well. The type of water cut rising is the result caused by the combination effect of drive patterns，oil viscosity，distance between wellbore and water oil contact and ratio of water layer thickness to overall thickness. Quantitative combination table of the influencing factors was given and can be used to predict production performance type of single horizontal well，to determine whether there is engineering problem and in historical-matching iterative modeling for the horizontal wells.
Taking thin-bed heavy oil reservoir with edge-bottom water in Panyu oilfield as an example，water cut increase of the horizontal wells was classified into four types：open drowning type，rapid drowning type，rising ladder type and hillclimbing type. Influencing factors of the water cut rising type were analyzed according to the geological condition，fluid characteristic and production performance of the horizontal well. The effect sequence was given by the gray correlation method. Results indicate that the effect sequence is interlayer range＞oil viscosity＞distance between wellbore and water oil contact＞ratio of water layer thickness to overall thickness. The larger the interlayer range is and the smaller the oil viscosity is，the slower the water cut rises in single horizontal well；the smaller the distance between wellbore and water oil contact and the larger the ratio of water layer thickness to overall thickness，the faster the water cut rises in single horizontal well. The type of water cut rising is the result caused by the combination effect of drive patterns，oil viscosity，distance between wellbore and water oil contact and ratio of water layer thickness to overall thickness. Quantitative combination table of the influencing factors was given and can be used to predict production performance type of single horizontal well，to determine whether there is engineering problem and in historical-matching iterative modeling for the horizontal wells.
2016, 23(3):111-115.
Abstract:
Shengtuo oilfield has entered the late extra-high water cut stage. Dynamic heterogeneity is becoming more and more serious，and the distribution of remaining oil is becoming more and more complex and diverse. So traditional development techniques is hard to achieve good results. Six modes of remaining oil distribution including edge micro phase enrichment，edge sand enrichment，non-main streamline enrichment，non-main layer enrichment，top thick layer enrichment and interbed control enrichment were presented based on the study of the remaining oil，and 3 main modes are edge micro phase enrichment on the plane，non-main layer enrichment in multilayer reservoir and thick layer reservoir and top thick layer enrichment on the vertical. Based on the idea of vector development，three modes were established respectively for the above three types of remaining oil distribution as follows：planar phase control vector development adjustment mode，layers recombination vector development adjustment mode and thick layer cooperation vector development adjustment mode.Field application effect proves that vector development modes in late extra-high water cut stage of Shengtuo oilfield can improve the recovery rate by more than 4%.
Shengtuo oilfield has entered the late extra-high water cut stage. Dynamic heterogeneity is becoming more and more serious，and the distribution of remaining oil is becoming more and more complex and diverse. So traditional development techniques is hard to achieve good results. Six modes of remaining oil distribution including edge micro phase enrichment，edge sand enrichment，non-main streamline enrichment，non-main layer enrichment，top thick layer enrichment and interbed control enrichment were presented based on the study of the remaining oil，and 3 main modes are edge micro phase enrichment on the plane，non-main layer enrichment in multilayer reservoir and thick layer reservoir and top thick layer enrichment on the vertical. Based on the idea of vector development，three modes were established respectively for the above three types of remaining oil distribution as follows：planar phase control vector development adjustment mode，layers recombination vector development adjustment mode and thick layer cooperation vector development adjustment mode.Field application effect proves that vector development modes in late extra-high water cut stage of Shengtuo oilfield can improve the recovery rate by more than 4%.
2016, 23(3):116-119.
Abstract:
The occurrence of water breakthrough is inevitable in the development process of bottom water reservoirs，and it is difficult to control the water cut after water breakthrough for the multilateral wells. Therefore，it has great importance to prolong the water breakthrough time. There are a few studies on the water breakthrough laws for the horizontal wells，but no studies for the multilateral wells. Relationship between the water breakthrough time and related parameters was obtained by numerical simulation so as to provide theoretical foundation for parameter adjustment and longer water breakthrough time.Experiment results indicate that the water breakthrough time has positive correlation with the water avoidance height，the control area for single well，the area and position of interlayer，the horizontal permeability and the three multilateral well parameters including branch length，branch angle and branch number. On the other hand，the water breakthrough time has negative correlation with the pressure difference，the fluid production rate，the vertical permeability and the ratio of oil and water. The observation of the water ridge morphology of the bottom water reservoir developed by herringbone wells and radial multilateral wells indicates that the main water breakthrough point of the herringbone well is at the intersection of the main wellbore and the branches，and the shape of the water ridge is related to the shape of the branch. So the intersection may be the position of bottom water breakthrough. The heel of the radial multilateral well may has earlier water breakthrough than the toe. While the first water breakthrough point for the radial multilateral well is the intersection of the branches，and punctiform water breakthrough occurs at first，followed by the planar water breakthrough. The shape of the water ridge is related to the shape of the branch. Therefore，the position of water breakthrough is at the heel of the radial multilateral well，which is different from that in the herringbone well.
The occurrence of water breakthrough is inevitable in the development process of bottom water reservoirs，and it is difficult to control the water cut after water breakthrough for the multilateral wells. Therefore，it has great importance to prolong the water breakthrough time. There are a few studies on the water breakthrough laws for the horizontal wells，but no studies for the multilateral wells. Relationship between the water breakthrough time and related parameters was obtained by numerical simulation so as to provide theoretical foundation for parameter adjustment and longer water breakthrough time.Experiment results indicate that the water breakthrough time has positive correlation with the water avoidance height，the control area for single well，the area and position of interlayer，the horizontal permeability and the three multilateral well parameters including branch length，branch angle and branch number. On the other hand，the water breakthrough time has negative correlation with the pressure difference，the fluid production rate，the vertical permeability and the ratio of oil and water. The observation of the water ridge morphology of the bottom water reservoir developed by herringbone wells and radial multilateral wells indicates that the main water breakthrough point of the herringbone well is at the intersection of the main wellbore and the branches，and the shape of the water ridge is related to the shape of the branch. So the intersection may be the position of bottom water breakthrough. The heel of the radial multilateral well may has earlier water breakthrough than the toe. While the first water breakthrough point for the radial multilateral well is the intersection of the branches，and punctiform water breakthrough occurs at first，followed by the planar water breakthrough. The shape of the water ridge is related to the shape of the branch. Therefore，the position of water breakthrough is at the heel of the radial multilateral well，which is different from that in the herringbone well.
2016, 23(3):120-126.
Abstract:
Aimed at the difficulty of achieving high and stable production in the tight carbonate gas reservoir，the feasibility of volume acid fracturing to lower Paleozoic tight carbonate gas reservoir in Ordos basin was analyzed with reference to the volume fracturing for shale gas in foreign countries. Firstly，stimulation mechanism of the volume acid fracturing in the tight carbonate gas reservoir was introduced. Based on this，the advantage and limitation of the volume acid fracturing for the development of the tight carbonate gas reservoir were analyzed on reservoir fracturing probability，natural fracture development，horizontal principal stress difference，intersection angle of natural fracture and hydraulic fracture，and the solution for the limitation was put forward. The study results show that the volume acid fracturing can form complex fracture network，and gain larger stimulated volume of reservoir. The stimulation effect of the volume acid fracturing is closely related to the reservoir fracturing probability，natural fracture development，intersection angle of natural fracture and hydraulic fracture.The large horizontal principal stress difference will has disadvantage impact on the fracture network formation，which may be removed by the degradable fiber diversion technology or self-diverting acid fracturing. The results of pilot test indicate that gas production of 18 gas wells after volume acid fracturing exceed that of adjacent gas wells of conventional acid fracturing by more than 60%，and the daily gas production of volume acid fracturing in 7 wells exceed that of conventional acid fracturing by more than 41% after one month. It shows that stimulation effect of the volume acid fracturing is better than that of the conventional acid fracturing for lower Paleozoic carbonate gas reservoir in Ordos basin，and the volume acid fracturing has a good prospect of application in future.
Aimed at the difficulty of achieving high and stable production in the tight carbonate gas reservoir，the feasibility of volume acid fracturing to lower Paleozoic tight carbonate gas reservoir in Ordos basin was analyzed with reference to the volume fracturing for shale gas in foreign countries. Firstly，stimulation mechanism of the volume acid fracturing in the tight carbonate gas reservoir was introduced. Based on this，the advantage and limitation of the volume acid fracturing for the development of the tight carbonate gas reservoir were analyzed on reservoir fracturing probability，natural fracture development，horizontal principal stress difference，intersection angle of natural fracture and hydraulic fracture，and the solution for the limitation was put forward. The study results show that the volume acid fracturing can form complex fracture network，and gain larger stimulated volume of reservoir. The stimulation effect of the volume acid fracturing is closely related to the reservoir fracturing probability，natural fracture development，intersection angle of natural fracture and hydraulic fracture.The large horizontal principal stress difference will has disadvantage impact on the fracture network formation，which may be removed by the degradable fiber diversion technology or self-diverting acid fracturing. The results of pilot test indicate that gas production of 18 gas wells after volume acid fracturing exceed that of adjacent gas wells of conventional acid fracturing by more than 60%，and the daily gas production of volume acid fracturing in 7 wells exceed that of conventional acid fracturing by more than 41% after one month. It shows that stimulation effect of the volume acid fracturing is better than that of the conventional acid fracturing for lower Paleozoic carbonate gas reservoir in Ordos basin，and the volume acid fracturing has a good prospect of application in future.
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