Abstract:To reveal the hydrocarbon accumulation law in Chengdao buried hill and thus optimize favorable targets for oil and gas exploration in the buried hill，we systematically studied the fine oil-source correlation，reservoir characteristics，and hydrocarbon migration and accumulation in Chengdao buried hill，depending on organic geochemistry，isotope，and physical properties of crude oil. Research demonstrates that Chengdao buried hill is governed by Fault Chengbei 20 and North Fault Chengbei 30，which is divided into three zones：west，middle，and east buried hills. Influenced by accumulation conditions such as source-reservoir configuration and migration patterns，the sources，migration，accumulation and enrichment of hydrocarbon in the three zones are different. Fault Chengbei serves as the oil source for west buried hills，which connects with the source rock of Chengbei Sag and traps hydrocarbon（mainly migrating and accumulating vertically）in the faulted nose and faulted blocks on the uplifted side. The oil-bearing area is small and independent，and the top weathering crust is enriched by hydrocarbon. In middle buried hills，Fault Chengbei 20 and a series of NNE strike-slip faults can transport oil from sources. Oil and gas generated in Bozhong Sag migrate and accumulate along the strike-slip fault and then travel laterally to the adjacent traps for accumulation，presenting as an overall distribution along large-scale strike-slip faults. Moreover，in east buried hills，oil and gas originate from source rocks in the Lower Submember of the third Member of Shahejie Formation in Huanghekou Sag. They are enriched in multiple strata through diversified sets of composite transport systems consisting of unconformities and faults. Differential hydrocarbon migration and accumulation in buried hills determine their orientation of exploration.

Abstract:The Lower Paleozoic buried hills，as important exploration targets in Jiyang Depression，have the good geological conditions of hydrocarbon enrichment and forming reservoir. A series of large and medium buried hill oilfields（reservoirs）such as Zhuangxi buried hill and Chengdao buried hill etc. have been discovered successively. With the high degree of hydrocarbon exploration，some discoveries have been made with the improved understanding of reservoir forming conditions，and a breakthrough in the exploration of the Lower Paleozoic buried hill have been made as well. Through the analysis of fault property，active time and trap effectiveness，it is considered that the NE strike slip faults with characteristics of inactivity after Paleogene and compression torsion property have certain seal performance，which points out the direction for exploration of negative structural and slope buried hills. Based on the study of the migration ability of the fault connecting to oil source，it is believed that hydrocarbon can transport laterally along the fault under overpressure environment，which activates the exploration of buried hills without directly connections to source rocks. Based on the study of pressure system of hydrocarbon source and vertical transport ability of fault，it is proposed that hydrocarbon can migrate downward along the fault while being in block of migrating upward under the unfavorable environment of overpressure，which makes the exploration of buried hill under the source promising. Under the guidance of new understanding，Well Chengbei 313，Well Chengbeigu xie 14，Well Zhuanggu 65 and Well Chegu 27 have been successively drilled，and a series of hidden buried hill reservoirs have been discovered，by which new prospects for the exploration of the Lower Paleozoic buried hill in Jiyang Depression have been opened up.

Abstract:Based on the core，logging，thin section and cathodoluminescence data，etc.，the main rock characteristics，lithofacies types，differential diagenesis characteristics and sequences of each lithofacies，multi-stage dolomitization characteristics and their genetic models in Mishrif Formation of X Oilfield are systematically sorted out，and then the control of each diagenesis on reservoir quality is analyzed. The results show that the bioclastic limestone in Mishrif Formation can be divided into 12 rock types and 5 lithofacies types according to bioclastic types and structural characteristics. It has undergone many diagenetic events such as the dissolution，cementation，dolomitization，compaction and pressure solution. The types and intensity of diagenesis of different lithofacies are compared and distinguished，and the mutual sequence and development characteristics of multi-stage atmospheric fresh water cementation，seawater cementation，formation water cementation and dolomitization are analyzed emphatically. Four kinds of dolomitization at the early，middle and late stages of bioclastic limestone are developed in the study area. Based on the analysis of the characteristics of dolomites in different lithofacies，it is concluded that the first type at the early stage is percolation-reflux dolomitization，the second is dorag dolomitization at the early stage，and burial dolomitization is at the middle and late stages. The genetic model of dorag dolomitization is discussed. In terms of controlling the difference in reservoir quality，the early cementation between bioclastic particles in some lithofacies is beneficial to the preservation of pores and the improvement of reservoir quality. The early dolomitization is generally beneficial to the improvement of local percolation，while the late dolomitization occupies the residual pores of the reservoir and reduces the quality of the reservoir.

Abstract:Based on the thin section and cathodoluminescence，a comprehensive study of the filling sequence of diagenetic minerals in T2l4 is carried out by using the geochemical data of diagenetic minerals fluid inclusions and Sr，C，O isotopes，etc.，to clarify the sequences and sources of diagenetic fluid in Leikoupo Formation，Western Sichuan Basin. The results show that the filling minerals of different grain sizes in T2l4 in Western Sichuan Basin can be divided into three stages with filling sequences as follows：micro-powder dolomite and calcite（the first stage）→fine-grained dolomite and calcite（the second stage）→meso-crystalline dolomite，calcite and intercalated dolomite（the third stage）. The three stages by which fluid accumulating are roughly corresponding to the early to late of Late Triassic（232-214 Ma），the end of Late Triassic to the end of Late Jurassic（212-145 Ma），and early Cretaceous to the end of late Cretaceous（142-70 Ma），respectively. The C，O，Sr isotopes of matrix dolomite and pore fillings in T2l4 show that the diagenetic fluid has the geochemical characteristics of normal marine carbonate rocks，and it is revealed that the high value of 87Sr/86Sr diagenetic fluid in T2l4 is from the fluid intrusion of capillary concentration，infiltration and backflow in the syngenetic-quasi syngenetic period under the environment of evaporating tidal flat，and the release of sealed seawater during the burial period.

Abstract:Small-scale fracture-cavity carbonate reservoirs in Tahe Oilfield have great exploration and development potential，but there are few related data and poor research in the early stage. In order to provide a reference for the exploration and development of this type of fracture-cavity carbonate reservoirs，this paper begins with the concept of small-scale fracture-cave and analyzes imaging data and core characteristics. It is considered that small-scale fracture-cavity reservoirs can be divided into three types：fractured type，vuggy type（including small-scale caves）and fractured-vuggy type（including karst channels between caves）. The comprehensive well seismic calibration of two kinds of reflection characteristics of “disorderly weak”and“weak small string beads”is conducted，and it is considered that although the single well logging interpretation mainly focuses on a single small-scale fracture-cave，there are a large number of small-scale fracture-caves，forming a group of interconnected small-scale fracture-caves，and the overall scale is large. Based on the fracture-cavity system characteristics and genetic evolution process of carbonate reservoirs in Tahe Oilfield，the evolution process of smallscale fracture-caves is divided into topographic infancy，adolescence，maturity and topographic old age. Among them，the fractures and the vugs associated with fractures are mainly formed in the topographic infancy stage. The karst channels and small-scale caves are mainly formed in the adolescence and maturity aged. The small-scale residual caves of cave collapses of various scales and residual karst channels between caves are mainly formed in the topographic old age.

Abstract:Rich in hydrocarbon resource，Oman Basin develops multiple sets of hydrocarbon accumulation. The previous studies mainly focused on the source-reservoir assemblages in the Paleozoic and Mesozoic reservoirs，but less on those in Cenozoic reservoirs. In this paper，the Paleogene Umm Er Radhuma carbonate reservoir in the north of Oman Basin had been studied to analyze the reservoir characteristics，hydrocarbon resource，migration path，and accumulation features and establish hydrocarbon accumulation patterns to discuss the main controlling factors based on data about crude oil composition，core，logging，and seismic combined with documents on regional tectonic evolution，source rock distribution and burial history. The results show the favorable reservoir-cap conditions. On one hand，the Paleogene Umm Er Radhuma carbonate formation in the north of Oman Basin is buried shallowly and compacted weakly with developed pores. On the other hand，the Rus gypsum horizon in the upper part can be used as the high-quality caprock. Also，according to the results，the hydrocarbon source is the organic-rich marl in the Cretaceous Natih carbonate formation and the hydrocarbon generation center is located in the Fahud salt basin in the eastern work area. In accordance with the geochemical analysis of core，the hydrocarbon source in the work area is not mature；the crude oil in the Umm Er Radhuma carbonate reservoir is from the Fahud salt basin in which the generated hydrocarbon is migrating upwards and westwards along the fault and plane of unconformity. The plane of unconformity on top of the Cretaceous system，the collapse channel of dissolution fault，and local microstructure are the key factors for hydrocarbon accumulation in the Paleogene Umm Er Radhuma carbonate reservoir in the north of Oman Basin and are characterized by“fault communication，migration along the plane of unconformity，and local microstructure in control”.

Abstract:Accurately identifying karst channels between injection and production wells is a key issue to the treatment of water channeling in fracture-cavity reservoirs，expansion of waterflood swept volume，and further achievement in balanced displacement of such strongly heterogeneous reservoirs. Taking karst fracture-cavity reservoirs in the palaeo-subterranean river as the research object，we propose a method for identifying karst channels in such reservoirs. Through comparison between the results obtained respectively from the time domain simulator and the frequency domain simulator，the accuracy and high efficiency of the latter are verified，and the formation characteristics reflected by the parameter changes in karst channels are obtained. Research shows that harmonic pressure response analysis can identify karst channels with resistance to interference，low cost，and high accuracy. Pressure is transmitted in fracture-cavity reservoirs mainly via karst channels. For head responses at different positions，the amplitude drops and the phase shifts to different degrees. Through comprehensive analysis of amplitude reduction and phase shift of the head response at each position to the harmonic signal，we can identify the area where the test point is located. The results show that for the response with an amplitude of almost 0，the test point is located in matrices；for the amplitude response with slight phase shift，the test point is located in karst channels；for the amplitude response with pronounced phase shift，the test point is located in the matrices close to karst channels.

Abstract:The fracture-cavity reservoirs have many types of reservoir spaces，large differences in pore，fracture，and karst cave sizes，and are macroscopically characterized by coupling of multiple flow patterns. The reservoir and permeability conditions and development models are very different from those of clastic sandstone reservoirs. Considering the special geological conditions and flow patterns of fracture-cavity reservoirs，and based on the classic fluid potential theory，the theoretical model of development fluid potential for different reservoir types and different development stages of fracture-cavity reservoirs is established. It also explains the calculation methods of potential energy，pressure energy，kinetic energy，interface energy and viscous energy in the mathematical model of fluid potential. Based on this，the improved streamline method is used to develop the numerical simulation program for the development fluid potential of fracture-cavity reservoirs. Research on the control effect of fracture-cavity reservoirs in Tahe Oilfield shows that the control method based on calculation of fluid potential is suitable for the three types of karst backgrounds：fault-controlled karst，weathered shell karst and composite karst. The production strength is greater，and the effect of fluid potential control in fracture-cavity reservoirs is better when the water body multiple is less than 10 times and the liquid production ratio is 4-6.

Abstract:Nowadays，Abu Dhabi X carbonate oilfield is confronted with serious heterogenity water-flooding problems caused by abnormally high temperature and high salinity as well as severe heterogeneity. It is difficult to solve these problems with conventional water shutoff & profile control and EOR methods. In this work，a novel Soft Microgel（SMG）aqueous dispersion was selected as the displacement phase for the water-flooding sweep control technique. The natural core and crude oil from Abu Dhabi X carbonate oilfield and simulated formation water were used in the experiment to perform the analysis of SMG physical and chemical performance，research on SMG oil displacement mechanism and physical simulation experiment on oil displacement. The results indicate that the SMG aqueous dispersion has the characteristics of low viscosity，easy injection，easy deep migration，and excellent ability of retention and shutoff. To some extent，it can make up for the defect of traditional polymer flooding mechanism and overcome the limitation of oilfield application. The excellent thermal stability of SMG has been proved by six months of abnormally high temperature and high salinity aging test，demonstrating its outstanding resistance to high temperature and high salinity under reservoir conditions. Furthermore，the SMG after aging is still able to improve the water-flooding swept volume and enhance the integrated recovery of the reservoir. According to the results，the EORs of submillimeter-scale SMG and micron-scale SMG increased by 6.70% and 5.67%，respectively. To sum up，the water-flooding sweep control technique with SMG aqueous dispersion as the displacement phase can effectively control the sweep direction of water-flooding in reservoirs and improve the sweep efficiency of water flooding，for which it is expected to solve the development problem of uneven water-flooding in abnormally high temperature and high salinity reservoirs in Abu Dhabi.

Abstract:Fracture-cavity carbonate reservoir is characterized by strong horizontal and vertical heterogeneity，and the conventional injection-production well pattern has low production and poor economic benefits. At present，scholars have proposed a variety of development modes suitable for this kind of reservoirs，but they have not put forward a set of systematic optimization process for the development modes of fracture-cavity carbonate reservoirs. In order to select the development modes of fracture-cavity carbonate reservoirs more accurately and improve the recovery and actual economic benefits，this article takes a typical fracture-cavity carbonate reservoir（Block A）for example，and comprehensively analyzes the applicability of different development modes in reservoirs with different properties and configurations of by numerical simulation. The results show that the horizontal well can achieve a higher production rate and better economic benefits in dense parts of small-and medium-scale fracture-cavity bodies. Specifically，small-scale“fixed-point development”is a more effective development mode than areal pattern well in reservoirs with low matrix permeability. The water-flooding development of connected fracture-cavity bodies has a higher ultimate recovery than the depletion development. Both water-flooding and gas huff and puff can be effective ways of energy supplement. Finally，the idea of optimizing the development mode of this kind of reservoirs is put forward through analysis of the scale，matrix permeability，and connectivity of the fracture-cavity body.

Abstract:The conductivity of the acid etched fractures is one of the key parameters to evaluate the acid fracturing effect.At present，the experimental research on acid etch of fractures in carbonate reservoirs focuses mainly on limestone reservoirs，and the related research on dolomite reservoirs is rarely reported. The acid-rock reaction characteristics of limestone and dolomite reservoirs are obviously different. In order to study the acid etch morphology and microscopic reaction mechanism of dolomite reservoir fractures，we carried out experimental study on the acid etch conductivity of fractures with the core of dolomite reservoir in a block as the object and comparatively analyzed the micro-morphology of acid etch of limestone and dolomite slates by 3D laser scanning. Through the short-term conductivity experiment，the trend in conductivity of acid etched fractures under the influence of physical properties of the reservoir and acid concentration was analyzed.Compared with limestone，dolomite has a lower surface reaction rate. Moreover，its acid-rock reaction rate is an order of magnitude less than that of limestone. The acid solution of dolomite leads to less etch and its dissolution is mainly along the joint surface. High acid concentration is conducive to the solutions’deep permeation through the acid etched joint surface，so as to connect matrix and fracture. In addition，the acid solution of a high concentration can more fully etch the wall surfaces of acid fractures to improve the non-uniform etch degree and obtain fractures of greater conductivity. Through numerical simulation，it was found that alternating acid injection could effectively improve the non-uniform etch degree of dolomite slates，the conductivity of acid etched fractures，and the acid fracturing effect.

Abstract:Ordos Basin is rich in hydrocarbon resources，in which the organic-rich shale in Chang7 Member of Yanchang Formation is an important stratum for shale gas exploration. The previous studies lack systematic analysis of the shale in Chang7 Member in the southeast of Ordos Basin，which fail to accurately reflect the real exploration potential of shale.Based on the analysis of development characteristic，we take the shale in Chang7 Member in the southeast of Ordos Basin as the research object to evaluate its exploration potential from three aspects：gas generation potential，gas storage potential，and development potential by petrographic analysis and the five-index methods. The petrographic analysis is used to evaluate gas storage potential. In terms of total organic carbon content，content of brittle minerals（quartz，feldspar，carbonate，etc.），and relative content of clay minerals，the shale in Chang7 Member is divided into four categories，among which dark organic-rich brittle shale has the highest development potential. The five-index method is adopted to evaluate gas generation potential and development potential through the combination of five indexes. The indexes for evaluating gas generation potential are gas absorption ratio，organic-matter conversion rate，gas drying coefficient，total organic carbon content，and vitrinite reflectance；those for development potential are shale thickness，content of brittle minerals，formation pressure coefficient，total organic carbon content，and vitrinite reflectance. Finally，the data obtained by the two methods are combined to select five horizons with the most favorable exploration potential of shale in Chang7 Member：N3，N5，N6，N7，and N10.

Abstract:The microscopic pore structure is an internal factor controlling percolation characteristics，and percolation characteristics are the external manifestation of the microscopic pore structure. Through the technique of mercury injection capillary pressure，the microscopic pore structure parameters characterizing pore throat size，distribution，and connectivity were obtained. The contributions of pore throats on different scales to the percolation capacity of the shale oil reservoir were analyzed. The single-phase percolation curve of shale oil was established with the steady flow method to analyze the influence of rock permeability and in-place oil viscosity on the law of percolation in shale oil reservoirs. The results show that the pore structure of the shale oil reservoir in Jiyang Depression characterized by significant heterogeneity is mainly composed of submicron and nanometer pore throats. In terms of volume，most pores are connected by nanometer pore throats，but percolation is transported mainly through micron（bedding fractures）and submicron pore throats. Nonlinear percolation and starting pressure gradient in shale oil reservoir can be attributable mainly to submicron and nanometer pore throats.The relationship between the starting pressure gradient rises as fluidity falls，which can be expressed by a power function.The formula estimating maximum drainage radius of the shale oil reservoir is established to predict the longest flow distance according to rock permeability and in-place oil viscosity under a certain production pressure difference，which provides a parameter basis for well spacing design or fracture spacing optimization.

Abstract:On the basis of the outcrop profile measurement and sample collection，through casting sheet identification，cathodoluminescence analysis，X-ray diffraction analysis，scanning electron microscopy analysis，geochemical analysis of total organic carbon content and vitrinite reflectance，the characteristics of shale reservoirs in the Ordovician Wufeng FormationSilurian Longmaxi Formation（Wufeng-Longmaxi Formation）were discussed combined with the regional geological background and previous research results in Yanzikou area，northwestern Guizhou with the following results obtained：①The rock types of Wufeng-Longmaxi Formation are dominated by silty shale，dolomitic/calcareous shale，and argillaceous siltstone deposited in shallow water-deep water shelf environment，and the black carbonaceous/siliceous shale in Wufeng Formation and lower Longmaxi Formation are potential source rocks. ②The mineral composition mainly includes clay minerals （22%-51%），quartz（21%-41%），and carbonate minerals（10%-35%），with a small amount of pyrite and gypsum，of which clay minerals mainly include illite/smectite mixed layer and illite. Generally，it has a large proportion of brittle miner? als（average 59.4%），strong heterogeneity，and great vertical variation. ③Reservoir space consists mainly of interlayer cracks，dissolution pores，and bedding fractures.Carbonate and feldspar dissolution phenomena are especially obvious，but organic pores are underdeveloped. ④The effective thickness of source rocks with a total organic carbon content of more than 1% in the Wufeng-Longmaxi Formation is about 20 m. ⑤The equivalent vitrinite reflectance of the Wufeng-Longmaxi Formation is around 2.5%，showing its high degree of thermal evolution. It is in the stage of overmature dry gas and is still capable of hydrocarbon generation.

Abstract:CH4 isothermal adsorption curves of 83 coal samples were systematically analyzed，and the statistical model between coal rank and parameters related to adsorption-desorption characteristics were established to reveal the influence of coal rank on CBM adsorption-desorption characteristics in the western Guizhou-eastern Yunnan region. Also，its implications on the optimization of production-layer combination were discussed. The analysis shows that a higher coal rank leads to denser coal，much larger specific surface areas of micropores，and further better adsorption to CH4，resulting in higher desorption pressure at key nodes（starting，turning，and sensitive points）and greater overburden pressure differences at every desorption stage（inefficient，slow，fast，and sensitive stages）. When vitrinite reflectance is more than 3.0%，the pore-fracture system and CBM adsorption-desorption characteristic parameters of coal tend to be stable. This differential distribution of coal rank in the study area and the spatial differentiation of the superimposed pressure system further complicate the desorption of different coalbeds. The high desorption efficiency of each production layer before coalbed exposure is an important prerequisite to ensuring the commingled production and gas productivity of each layer. Based on this，the seven constraints on the feasibility of the production-layer combination are identified to guide the future project design of commingled production.

Abstract:With the advancement in China’s shale gas industry and the large-scale production of shale gas wells，how to effectively forecast the production rate and recoverable reserves of shale gas wells and has become a crucial subject of oil and gas reservoir engineering. It is also a matter of great concern to shale gas production and management departments. As shale gas is stored in the ultra-tight shale matrix and the secondary fracture system in the adsorption state and the free gas state，respectively，it can be polluted by mud during the drilling，completion，logging，and fracturing. Therefore，the shale gas wells that have been put into production show obvious independence，diversity，and complexity. More importantly，shale gas wells are brought into production by desorption after pressure drops and energy consumption featured by the decreasing production at the moment it starts. Consequently，the production decline method has become the first choice for evaluation.In this paper，the generalized single peak cycle model proposed by Chen Yuanqian et al.is simplified into a pan exponential decline model（PEDM）that can forecast the production rate and recoverable reserves of shale gas wells. The decline exponent m ranges from 0 to 1. At m=1，it is the famous exponential decline model. At m=0.5，it is the 0.5-PEDM of practical value. For specific unconventional shale gas wells，it is necessary to use production data to determine the values of a，c，and m by linear iterative trial and error method in actual forecasting. The application of production data from two wells in the Marcellus shale gas reservoir，Pennsylvania，the US，elicits the effectiveness of the PEDM in forecasting the production rate and recoverable reserves of shale gas wells.

Abstract:The migration law of CO2-crude oil miscible zone has an important influence on the effect of CO2 miscible flooding，but the influence has not been systematically understood yet. Through the compositional numerical simulation and mathematical derivation，this paper studies the migration law of the miscible zone and its influence on the recovery factor.The results show that the dimensionless area and the sweep efficiencies at the leading and trailing edges of the miscible zone increase linearly before the leading edge of the miscible zone is broken through. At the same time，the dimensionless width gradually decreases after reaching a peak value of 0.14 and the fingering coefficients at the leading and trailing edges grow faster and faster；the miscible area reached a maximum of 0.22 when the leading edge of the miscible zone is broken through. The rising speed of the sweep coefficient at the leading and trailing edges drop significantly after the trailing edge of the miscible zone is broken zone through. Meanwhile，the dimensionless area，dimensionless width，and fingering coefficients go down gradually and then stabilize. The oil displacement efficiency and expansion coefficient remain approximately constant before the breakthrough of the leading edge and after the breakthrough of the trailing edge，which means that the increase in the sweep efficiencies of the miscible zone is the primary factor affecting the development effect of CO2 miscible flooding. For this purpose，before the miscible zone is broken through，measures such as soaking，water-alternating-gas injection，injection-production coupling，and plugging of the main flow line should be adopted to expand the sweep efficiency.

Abstract:During hydraulic fracturing，the pulsed injection of fiber-containing proppant clumps effectively preserves their integrity during fracture transport and settling，resulting in columnar propped fractures. Through our experiment，the integrity of fiber-containing proppant clumps was shown. The fracturing fluid-fiber-proppant mixture was treated as a singlephase fluid. The physical property of the mixture was obtained via corrected rheological property. The gravity，buoyancy，wall friction and flow resistance of fiber-containing proppant clumps in static settling were considered to establish the formula of settling velocity and its substitute algorithm for numerical calculation. By comparing the settling velocities of the fiber-containing proppant clumps，we found that the predicted results of the model were in good agreement with the experimental results. The settling velocities affected by proppant density，proppant volume fraction，clump diameter and fracture width were further calculated. As a result，the settling velocity rises with the increase in proppant density，proppant volume fraction and fracture width. However，it is little influenced by clump diameter. This model provides an effective method to calculate the static settling velocity of fiber-containing proppant clumps and a theoretical basis for the calculation of their transport.