Abstract:Institute of Petroleum Geology，Petroleum Exploration & Production Research Institute，SINOPEC，Wuxi City，Jiangsu Province，214126，China；3.Guangzhou Institute of Geochemistry，Chinese Academy of Sciences，Guangzhou City，Guangdong Province，510640，China；） Nitrogen adsorption method and mercury injection experiment were applied to characterize the joint pore distribution，porosity and fractal characteristics of Permian shales in south Anhui Province，the Lower Yangtze region. The results illustrate that：the pores in the Permian shales are dominated by micropore and macropore，and the volume of micropore accounts for 33.63% to 81.08% of the total pore volume with an average of 56.45%；the joint porosity is significantly higher than the porosity obtained by mercury injection method with an average increase of 96.06%；both the micropore and transition pore to macropore could generate obvious fractal characters for the Permian shales，and the fractal dimensions of the micropores are more dispersed than those of the transition pores to macropores，which indicates that the degree of heterogeneity and complexity of the micropore are higher than that of the transition pore to macropore；the porosity and fractal dimension of the micropore have positive correlation with TOC，specific surface area and hydrocarbon generation potential but negative correlation with quartz content；while the porosity and fractal dimension of the transition pore to macropore have negative correlation with TOC and quartz content，and no correlations with clay mineral content and specific surface area. With the increase of buried depth，the porosity and fractal dimension have no obvious variations for the micropore，but a certain decrease for the transition pore to macropore. The fractal dimension is more sensitive than the porosity to the buried depth.

Abstract:Based on comprehensive analysis of geological data，well logging and seismic interpretation，the main carrier systems（including sand bodies and faults）in the Yanchang Formation in Honghe oilfield were studied，and the characteristics of carrier systems and their important effect on hydrocarbon accumulation were analyzed. By the method of basin simulation，the palaeodynamics generated at the key period of hydrocarbon reservoiring were recovered in this area. The results obtained show that the reservoirs of Chang8 member in Yanchang Formation were situated in an overpressured system during the key reservoiring period，and the overpressure became the main driving force for hydrocarbon migration. Based on the analysis of petroleum migration mechanism and migration and accumulation regularities in Chang8 member，it is determined that the carrier system is composed of effectively connected active faults and carrier beds，which makes a composite fault-fracture-sand carrier system. Oil and gas migrates along the direction of pressure drop and entrapped in effective low potential zone. The next favorable exploration targets are lithologic and structural-lithologic traps with better lateral sealing conditions or physical property“sweet point”and effective low potential.

Abstract:In recent years，there are many discoveries of oil and gas in Neozoic in Bohai oilfield，but the exploration degree is relatively low for Paleozoic carbonate buried hill. There is a good oil discovery in Paleozoic in Well Bozhong21-2-A.Lithologic types of Paleozoic carbonate were determined as mainly dolomite，limestone，dolomitic limestone，calcite dolomite and mudstone through analyzing data of drilling，coring，logging and testing from Well Bozhong21-2-A in Paleozoic carbonate buried hill of Bozhong21-2 structure and by combing with petrology，mineralogy，geochemistry and other experimental data，it was concluded that the physical properties of dolomite are better than that of limestone. There are three types of storage space which are pore，karst cave and fracture. The main reservoir type is karst cave reservoir which can be divided into three sections in vertical，and the karst cave reservoir mainly develop in upper and lower Paleozoic，while the karst cave-fracture reservoir mainly develop in middle Paleozoic，and the sedimentary facies，karstification and structure regmagenesis control the development of reservoir. The research shows that the favorable sedimentary facies of intra-platform and beach develop in Bozhong21-2 structure. The center of buried hill locates at the highland of karst plateau and karst slope without Mesozoic covering，which is easy to be karstified and become favorable paleo-karst reservoir.

Abstract:The black shale of Longmaxi Formation in the Sichuan Basin is a set of important source rock for the large and medium-sized gas reservoirs. The organic matter in the shale absorbs a great quantity of shale gas，so it is of great significance to describe the distribution of organic matter accurately for shale gas reservoir development. Based on the scanning electron microscope（SEM）images of field core samples obtained from shale gas wells at Sichuan Basin in China，the morphological characteristics of organic matter distribution were analyzed quantitatively taking area，perimeter，compactness and elongation as key indicators. The interrelationship of organic matter obtained from samples was characterized by evaluating their distribution distances and angles. The dispersion degree described by a quantitative method was provided and used to denote the organic matter clumps having clustering. Laws between dispersion distance and dispersion angle were summed up statistically. Finally，according to the morphological characteristics and dispersion degree performance，a reconstruction model of organic matter distribution was established based on probability statistics technique and was verified reliable. The organic matter distribution strategy in different scales and their position relationships can be visualized through the model. It can also reflect accurately the strategy of the organic matter area dispersion and characterize quantitatively the heterogeneity of the organic matter. The real internal situation of core can be reflected and a foundation model can be provided for simulating shale internal micro-seepage features.

Abstract:Mishrif reservoir in the Rumaila oilfield is a typical giant reef-bank carbonate reservoir in the Middle East. Injected water breakthrough occurs easily and too early along the high permeability thin layers，thief zones，because of severe heterogeneity of reservoirs，resulting in the drop of swept efficiency of the injected water. So，the thief zone identification and the corresponding development countermeasures are the key of enhancing water flooding effect in the studied area. A method based on geological data and production performances was taken to identify thief zones. The origin of thief zones can be determined according to the core and imaging logging data. Dynamic reservoir permeability was calculated through single-well liquid production profile and other dynamic data. The thief zone can be identified after comparison of the static permeability obtained by logging interpretation and dynamic permeability. At last，development mode of the thief zone in the studied area was determined combined with sequence classification and other static data. Optimized perforation strategies of oil and water wells in various development modes of massive and layered reservoirs were put forward and applied to the flooding pilot in the Mishrif reservoir achieving expected effect after reservoir numerical simulation.

Abstract:Carbonate reservoir space is mainly fracture or dissolution cave in Nanpu offshore，Bohai Bay basin，the formation of which is controlled mainly by paleo-karst. The paleo-karstification and models of paleo-karst for the target stratigraphy were characterized in detail based on core description，mud-logging，imaging logging and outcrop investigation. The lithology of the Cambrian-Ordovician carbonate reservoir in buried hills consists of micritic limestone，argillaceous micritic limestone，grainy pelsparites and mudy pelsparites. Based on core descriptions，there are calcareous sandstones and conglomerates，calcareous breccias，bauxitic mudstones and collapse breccias formed by paleo-karstification. Logging shows large quantities of mud losses and nothing is drilled. The FMI loggings show large amounts of pores，caves and fractures generated by dissolution during paleo-karstification. Outcrop investigations show that a paleo-karst system can develop in the target interval of the Ordovician stratigraphy. These evidences manifest that the paleo-karstification occurred in the buried hills of Nanpu offshore，and the development of a large amount of vertical and horizontal caves indicates the formation of vadose zone and phreatic zone respectively. Faults and fault-associated fractures play positive role in paleo-karstification. A model of the buried-hill paleo-karst was established based on the model of outcrop karst and the characteristics of the buried-hill paleo-karst，which can visualize the distribution of the buried-hill reservoirs and have directive significance to the further petroleum development.

Abstract:In order to further deepen the study of oil and gas accumulation and to point out the direction for exploration of the limestone reservoir in the 4th member of the Shahejie Formation of the northern step-fault zone of Shaojia area，the transport system and the model for oil and gas accumulation were studied deeply based on the analysis of petroleum geological characteristics and according to the theory of petroleum geology and differential hydrocarbon accumulation theory. The results show that 4 kinds of transportation systems are found in the limestone reservoir in the 4th member of the Shahejie Formation of the northern step-fault zone of Shaojia area. The first one is the primary migration system where hydrocarbon source and reservoir rock connected laterally at the fault upthrown and downthrown. The second one is the vertical migration system where primary migration occurs in the overlying medium to high maturity source rocks. The third one is the vertical deep fracture migration system where secondary migration of hydrocarbons occurs. The fourth one is the lateral unconformity migration system for secondary migration of hydrocarbons. There are 3 kinds of oil and gas accumulation models under the influence of 4 kinds of oil and gas transportation system. In the first model，oil and gas migrate vertically and are accumulated in the structural trap. In the second one，oil and gas are accumulated in the lithological trap after migrating laterally for a short distance. The third one is the differential hydrocarbon accumulation model that hydrocarbons are trapped after migrating laterally for a long distance.

Abstract:Thick tight sandstones in the Silurian period in the eastern Manjiaer sag have broad prospects for natural gas exploration，but there are few studies on reservoir characteristics of the tight sandstone at present. Based on comprehensive utilization of thin-section identification，EPMA，SEM，X-ray diffraction，mercury injection and physical property analysis，the reservoir characteristics of the tight sandstones were studied. Compared with conventional sandstone reservoirs in the eastern Manjiaer sag，the tight sandstone reservoirs have the following characteristics：①great burial depth；②low compositional maturity，low textural maturity，high content of debris and interstitial material；③poor physical properties（porosity is 5%-10%，permeability is 0.1×10-3-1×10-3 μm2）；④reservoir space types mainly include primary intergranular pore，intergranular dissolution pore and micropore，and the pore structure is poor in general；⑤clay mineral composition are dominated by reticular illite smectite mixed layer，chlorite and illite；⑥severe diagenesis and the diagenetic stage is from B substage of middle diagenetic stage to late diagenetic stage. The physical property of the reservoirs is influenced by various factors such as deposition，diagenesis and structure. The factors such as near source deposition，low compositional maturity，low textural maturity and argillaceous matrix filling are not favorable for the preservation of the most of primary pores. The compaction is the main factor resulting in the loss of porosity，and calcite cement and quartz secondary enlargement lead to porosity reduction. Partial dissolution and a few structural fractures improve the reservoir physical property.

Abstract:The oil shale of Dongying sag shows excellent exploratory potentiality. However，recent research on the shale is little，and the sequence boundary is difficult to be identified based on seismic and logging data，which restricts sequence framework to be built. The sequence boundary of shale was identified by making full use of the traditional division method of progradation and retrogradation sequence according to the change of palaeobathymetry. By associating element sequence with GR sequence，a method was developed for shale sequence division to establish sequence framework of shale in Dongying sag. Combined with the palaeoenvironment analysis，lithofacies and abundance of organic matter，it is determined that the laminated facies with abundant organic matter respectively deposited between the parasequence boundaries of GRPS3 and GRPS4，GRPS6 and GRPS7 are favorable segments with good lateral continuity. And a reasonable drilling design was also put forward to improve the economic benefits of further exploration and development of oil shale.

Abstract:Fracture development zone prediction is the key to efficient exploration and development of sand-gravel body in the third member of Shahejie Formation in northern zone of Chexi area in Jiyang depression. The single seismic attribute，such as coherence or curvature attribute，cannot function well in reflecting the fracture development accurately and finely due to its ambiguity. Attemptions were made to accurately predict fracture of sand-gravel body in the third member of Shahejie Formation in northern zone of Chexi area in Jiyang depression by using multi-attribute fusion technology based on seismic imaging theory，and good effect was obtained. Research shows that the attributes of similarity，maximum positive curvature and dip curvature are sensitive to fracture of sand-gravel body in northern zone of Chexi area in Jiyang depression. The multi-attribute volume calculated by RGB-IHS transformation can be used to display clearly the location and distribution shapes of fractures in vertical and lateral planes. The predicted results show that netted fractures resulted from structure fracture interlacing with overpressure fracture develop due to effect of structure activity and abnormal high pressure in the area of Che7-Che57. The development of overpressure fractures is due to effect of abnormal high pressure in all directions in Chegu25 area. The successful application of multi-attribute fusion technology based on seismic imaging theory in fracture prediction of sand-gravel body，which expands the range of application further，has reference significance to fracture prediction in other types of reservoir.

Abstract:In order to reveal the effects of impermeable interlayer on steam assisted gravity drainage（SAGD）production process for dual horizontal well，four physical simulation experiments were carried out. According to the characteristics of SAGD in the dual horizontal well，the dimensionless Subcool was proposed for boundary similarity，which provides a control criterion for physical simulations. A two-dimensional physical model of dual horizontal well SAGD was built based on the reservoir parameters in Mackay River oil sands block. Four experiments were conducted to probe the effect of interlayers on SAGD production. Among them，test 1 was a homogeneous model and served as a basic case and test 2-4 were heterogeneous models with interlayers. The results show that the development of steam chamber in the homogeneous model may be classified into three stages，which correspond to the stages of incremental production，stable production and decreased production respectively. Comparisons among test 1 and test 2-4 indicate that the existence and distribution pattern of the interlayer cause some effects on the development of steam chamber and production performance. It is indicated that the higher the interlayer is located，the less the steam chamber is suffered and the less the production performance is influenced. If there is an interlayer between the injector and the producer，it is hard to form an effective flowing path from the injector to the producer. The single well SAGD（SW-SAGD）technology was proposed as a new preheating method.

Abstract:Inaccessible pore volume and adsorptive retention exist when polymer solution flows in porous media. The influence of inaccessible pore volume was often ignored in previous studies of the seepage law of the polymer solution in porous media. With regard to this，the inaccessible pore volume of the polymer flooding，rheological curve and effective viscosity in the porous media of the polymer solution were determined through the experiment. Parallel capillary model was established considering the influence of the inaccessible pore volume. The effect of the inaccessible pore volume of cores with different permeabilities on resistance factor，effective viscosity，shear rate and depleted layer effect of the polymer solution was analyzed. Results show that the inaccessible pore volume derived from the cumulative polymer quality curve can be more accurate. The inaccessible pore volume can lead to lower resistance factor and effective viscosity and higher shear rate and depleted layer thickness for the polymer solution. The lower the core permeability is，the larger the inaccessible pore volume will be，and a larger error will be introduced to the calculation results of resistance factor，effective viscosity，shear rate and depleted layer thickness.

Abstract:Unconventional gas reservoirs with micro-nano pore radius have been a hot spot with the increasing contradiction between supply and demand of natural gas. These reservoirs are always stress-sensitive. Besides，the small pore may lead to the existence of gas slippage when gas flows in unconventional reservoirs. Both of the above two properties would result in complex seepage characteristics and influence the inversion process for hydraulic fracture. However，there is not an existing method which takes both permeability stress-sensitivity and slippage into consideration for stress-sensitive reservoir with micro-nano pores and views the slippage factor as a function of pressure. Therefore，based on experiments，the error，caused by traditional product dynamic data analysis under different seepage，was analyzed and the traditional method was modified by introducing new pseudo-parameters to propose a new inversion method for stress-sensitive formation with micro-nano pores finally. The results show that a new linear relationship can be extracted through the method to provide a probability for determination of the fracture length of the reservoir.

Abstract:Miscible，near-miscible and immiscible state coexist during CO2 flooding in low permeability reservoirs due to the large injection-production pressure difference between injection well and production well. It is not suitable to utilize MMP to evaluate CO2 flooding effect. So traditional capillary number theory was modified for the low permeability oil reser? voirs considering diffusion effect，swelling，viscosity reduction，interfacial tension reduction，variation on viscosity ratio， density ratio and wettability. In combination of PVT phase behavior and displacement experiments of CO2 flooding in low permeability long cores before and after CO2 solution，the modified capillary number theory was utilized to optimize the in? jection-production parameters of CO2 flooding in Yaoyingtai low permeability reservoirs. The results show that the critical capillary number exists and ranges from 4.5×10-7 to 6.0×10-7，and the optimum injection rate is 0.4 mL/min and the average injection pressure is 28.84-33.43 MPa for CO2 flooding. The optimized injection-production parameters have been applied in CO2 flooding pilot test in Yaoxi block in Yaoyingtai oilfield since April 2011. Till to March 2015，incremental CO2 injec? tion has achieved 16.7×104 m3，incremental oil production has surpassed 19 253 tons，which indicates the good develop? ment effect and economic benefit of CO2 flooding.

Abstract:With some engineering geology features of low-porosity and permeability，high capillary pressure，developed natural cracks and ultra-low water saturation，the tight sandstone gas reservoirs have strong imbibition phenomenon，which could lead to water phase trapping damage due to countercurrent capillary imbibition of water in reservoir even under conditions of negative pressure difference. Some typical tight sandstone core samples from Ordos basin with different permeabilities of less than 0.2×10-3 μm2，between 0.2×10-3 and 0.5×10-3 μm2 and higher than 0.5×10-3 μm2 were selected to evaluate the counter current capillary imbibition and water flow-back during gas driving. The process of water phase trapping damage was simulated under negative pressure difference and the effect of countercurrent water imbibition on the gas permeability was discussed to know the damage degree. The results indicate that the decrease of gas permeability caused by the countercurrent imbibition under the negative pressure difference is more likely to have some characteristics of step change controlled by the physical properties of cores. The permeability damage ranges from 26.5% to 34.9% with the average of 29.8% under the same negative pressure difference. The lower the negative pressure difference is，the stronger the countercurrent imbibition is，which leads to deep entrance of water and more serious water phase trapping damage. So，safe operation，water flow-back in reservoir and other factors should be considered when the drawdown pressure is fixed during underbalanced drilling and completion and development.

Abstract:After waterflooding，a great deal of attic oil and by-pass oil was trapped underground in Tahe fractured-cavity carbonate reservoir. Nitrogen flooding can recover part of the remaining oil for its characteristic of low density，prominent gravitational differentiation and so on. Full understanding of the distribution of remaining oil after nitrogen flooding has the vital referential significance to the design optimization of gas drive scheme. Visible physical models were designed and built for nitrogen flooding simulation experiment. The experiment were conducted to intuitive display the distribution of remaining oil after gas drive in the fractured-cavity reservoir，and then the related influencing factors were discussed. Experimental results show that nitrogen flooding can effective enhance oil recovery of the remaining oil after waterflooding，but some oils were still entrapped including oil，called channel-flow oil in this article，held up in the middle of the cave due to the gas channeling and low energy of bottom water，and oil film and small oil slug entrapped in the fractures because of the low displacement efficiency of nitrogen. In the meanwhile，human factors，such as injection modes，injection well type and injection rate，had influence on the remaining oil after gas drive. This study could provide experimental basis for enhancing oil recovery with gas drive and after gas drive. Unbalanced injection mode such as WAG and nitrogen injecting with moderate rate in complex area could improve the effect of gas drive. The shape of caves，the distribution of fracture-cavity and other objective factors were realized to be the important points of further study.

Abstract:The shale gas reservoirs are featured as low porosity and ultra-low permeability. Nowadays，the key approach to enhance oil production in shale gas reservoirs and other unconventional reservoirs is multistage hydraulic fracturing in hori? zontal wells. However，the mature analysis method of pressure decline fit for fractured vertical wells cannot be applied to the pressure decline analysis after multistage fracturing directly，owing to the differences in flowing characteristic of fractur? ing fluid between several cracks closure in the horizontal wells and single crack closure. Considering stress sensitivity caused by natural crack closure and geological features of natural micro-fractures development in the shale gas formations， dual-pore media model was adopted to simulate the process of fracturing fluid filtration. Meanwhile，pseudo-three dimen? sional fracture model based on elastic-plastic theory was applied to obtain volume conservation equation of the cracks. Con? sequently，pressure decline model during shut-in period under the condition of natural closure of the fractures in the shale gas reservoir was established. The porosity of matrix，the permeability of fracture and the stress sensitivity coefficient are the main factors influencing pressure decline in the shut-in period.

Abstract:Tight oil reservoir has narrow and small pore throat and strong heterogeneity. There is a high capillary resistance between oil and water two phases，so the water phase will firstly break through the pore throat with the lowest capillary force in the water flooding process. Along with the continuous breakthrough of the larger pores，a water channel will be formed gradually，and then the injected water will flow along the channel and lose the effect of oil displacement. This phenomenon will be more obvious when there is a series of micro-cracks in the reservoir. Pore structure of reservoirs and possible capillary force distribution during the water flooding in the tight oil reservoir were researched. According to pressure drop features of oil-gas-water capillary force during WAG，a new WAG method was proposed using the injection of trace gas slug and large amount of water slug to plug the natural cracks and larger pores in the tight oil reservoir. A new trace gas injection experiment was designed，and the injection intensity，injection cycle and injection times were optimized. The changes of the recovery efficiency were observed. The results show that trace gas-altering-water method is effective for enhancing development effect in the tight oil reservoir after the formation of water channel in water flooding.

Abstract:Aiming at the disadvantages of mathematical models for foamy-oil flow at present，the concepts of pseudo-bubble-point pressure and relaxation time in pseudo-bubble-point model and supersaturation model were introduced，and three depletion experiments of long cores were conducted. On this basis，a new mathematical model for foamy-oil flow was established. In this model，foamy oil is viewed as pseudo-single-phase flow，and the effective permeability of porous media varies with pressure depletion rate，oil viscosity and gas saturation，and thus an mathematical expression of effective permeability was put forward by analysis of the experimental data. The viscosity of foamy oil is approximately equal to that of saturated oil under the same conditions. The compression factor of foamy oil is treated as a linear combination of the compression factors of oil and gas phase. During foamy oil flows，the supersaturation in the depletion process has been considered as well. In order to verify the correctness of the model，results from the proposed model，the pseudo-bubble-point model，the supersaturation model and the black oil model were compared with the experimental data respectively. It shows that the new model fits the experimental data well，however，the other three models’calculations deviation is large.

Abstract:Technology of horizontal well for thermal recovery has been widely applied in heavy oil reservoirs. However，heterogeneity of the reservoirs results in the problem of uneven inflow distribution along the horizontal wellbore，which has influence on the development effect of the horizontal well for thermal recovery in the heavy oil reservoir. So a novel method for balanced production was put forward through variable-density hole in central tube. Based on pressure drop analysis of actual reservoir flow，throttle of drainage hole and pipe flow of the central tube，a mathematical model of the balanced production of horizontal well for thermal recovery in the heavy oil reservoir was built and its solution method was determined.Optimization design was made combined with a case. The results show that the inflow profile of horizontal section can be regulated effectively by optimizing the hole density distribution in the central tube，thus balanced production of the horizontal well for thermal recovery may be realized and the producing degree of reserves in the heavy oil reservoir will be improved.

Abstract:Fracabilty evaluation of shale gas reservoir is a key technique to improve fracturing results. Resent research of fracability assessment focuses on the effect of brittle minerals content and rock mechanical parameters as important basis for treatment section optimization of horizontal wells in shale gas formation. However，complex fracture network can only be created by connection and propagation of natural fractures. Therefore，forming condition of multi-stranded fractures constitutes the important part of the fracability assessment of shale gas reservoir，bringing more accuracy to favorable interval selection. After analyzing the mechanical condition of intersection between hydraulic and natural fractures，calculation method of initiation pressure of the multi-stranded fractures was put forward. Dilation mode of multi-stranded fractures can be established and applied as critical ingredients by dimensionless process to realize fracability synthetic assessment for shale gas reservoir based on pressure in the hydraulic fractures and in situ stress state of oil reservoir. Based on favorable interval analysis of the Longmaxi Formation on geophysics and logging data of the shale gas well，Wx2，in the southern Sichuan basin，evaluation results can determine the perforation and fracturing location. Compared with other vertical shale gas wells evaluated by conventional appraisement in this block，the test production of Well Wx2 is higher after the treatment. This case study demonstrates the reliability and practicability of the method for optimal selection of fracturing section，which can increase stimulation effectiveness and reduce treatment risk and cost.