Abstract:There are two types of layers sealing the oil and gas. One is generally known as the caprock，and the other is the cap shell discussed in this paper. The cap shell is an interface of a certain level of stratigraphic sequence. It is known that the sequence boundary is a sedimentary discontinuity. Before new deposits，rock was lithified when the discontinuous sedimentary surface was exposed or near the surface. This resulted in calcium shells or the formation of seepage barriers，which blocked the pores and throat of the surface stratum and made the permeability reduced. For example，the permeability of the calcareous siltstone at the sequence interface between the Minghuazhen Formation and the Guantao Formation of Well Gang-225 in Dagang Oilfield is 0.63 mD，but the permeability of the reservoirs above and below the interface are hundreds or thousands millidarcy. The top boundaries of many reservoirs，such as the main oil-reservoirs of Gangdong and Liaohe Oilfields in China，and the main gas-reservoirs of Elmorth Gasfield in Canada and Naimat Gasfield in Pakistan，are all stratigraphic sequence interfaces. The rock covering on the top of the oil reservoir or gas reservoir is not a regular cap rock such as mudstone or shale，but a layer of permeable sandstone that is interpreted as an aquifer. Oil-water inversion or gaswater inversion seems like a strange phenomenon. In fact，the upper layer of water and the lower layer of oil（gas）are separated by the impermeable sequence interface，named as cap shell，sealing the oil and gas in reservoirs. Although the thickness of a cap shell is thin，it has great significance in sealing oil and gas. A number of domestic and foreign large oil（gas） reservoirs are sealed by the cap shell.

Abstract:Based on cores data and gravity flow theory，the sedimentary characteristics and models of early Silurian gravity flow deposits were systematically analyzed in Baojing area of Hunan Province，which intends to reveal formation mechanism of shale gas reservoir and determine its temporal and spatial distribution and thus guide the shale gas exploration. The results show that there are three types of gravity flow developed during the early Silurian in Baojing area of Hunan Province，including turbidity currents，debris flow and liquid flow. Among them，the turbidite current results in incomplete Bouma sequence，which is composed mainly of progradational strata formed by superposition of multiple single-section or twosection turbidite at the bottom and aggradational strata formed by superposition of multiple three-section turbidite at the top.Massive fine sandstone is the dominant lithology developed from debris flow. Thick layer of argillaceous siltstone and silty mudstone are the dominant lithology developed from liquid flow，in which deformation bedding develops. From the deposition of Longmaxi Formation to the deposition of Majiaochong Formation in the early Silurian，submarine fan，off-shore underwater fan and slump-slip fan developed intermittently in Baojing area of Hunan Province. Turbidity current mainly results in fan-end turbidite sand and fan-end mud of submarine fan，braided channel，channel edge and front sheet sand at mid submarine fan and channel edge and front sheet sand at off-shore subaqueous fan. The debris flow results in braided channel at off-shore underwater fan. The liquid flow results in slump-slip channel at mid fan and bay at inter channels.

Abstract:Through analyses of TOC，Rock-Eval，biomarker compositions and drill and seismic data，this study was undertaken to investigate the hydrocarbon generation potential，organic matter types，organic matter input and sedimentary and preservation environment of source rocks in the Baxian Sag. Based on source-related biomarker parameters of the source rocks and oil，a detailed oil-source correlation was conducted to identify the origin of oil and to evaluate hydrocarbon contributions of each set of source rocks. The result shows that there are four sets of high-quality source rocks developed respectively in the fourth member of Shahejie Formation（E2s4），the lower third member of Shahejie Formation（E2s3L），the middle third member of Shahejie Formation（E2s3M）and the lower first member of Shahejie Formation（E3s1L），among which hydrocarbon source rocks in E2s4，E2s3L and E2s3M are distributed widely and the source rocks in E3s1L are only distributed in the southern of the studied area. And these source rocks are characterized of good type of organic matter and great potential for hydrocarbon generation and expulsion. The four sets of hydrocarbon source rocks have entered into hydrocarbon generation threshold and are thermally mature. The characteristics of biomarker parameters reveal that the original input and sedimentary preservation environments of organic matter are different. The source rocks in E2s4 and E2s3L have more abundant organic matter supply than those in E2s3M and E3s1L，however，sedimentary preservation conditions at the stages of E2s3M and E3s1L are relatively poor. From the oil-source correlation，three oil families were derived from the source rockes in E2s4，E2s3L and E3s1L respectively，and two types of mixed oil were identified. By analysis of hydrocarbon generation potential of the source rocks，their spatial distribution and distribution of their related traps，it is concluded that the main hydrocarbon source rocks for traps that have found are developed in E2s3M-L. The source rocks in E2s4 have high quality and great potential for hydrocarbon generation and expulsion. E2s4-derived oils migrated for a short distance and dispersedly accumulated in the deep or buried-hill traps near the kitchen，but only a few of them have been found. Such a petroleum distribution pattern has important implications for future exploration. There is considerable exploration potential for E2s4-derived oils in the deep traps and buried-hill traps in the Baxian Sag.

Abstract:The reservoir of Block Sudong41-33 in Sulige Gas Field has the characteristics of low porosity，low permeability and high heterogeneity. The carbonate reservoir in Lower Ordovician Majiagou Formation were subjected to multi-stage multi-type construction，sedimentary and other effects，which makes the lithology complex and diverse，and thus the accurate identification of lithology has become a difficult problem of development in this area. In recent years，more and more attention has been focused on the use of decision tree method in machine learning in the field of geoscience，especially in lithology prediction. Based on the data of well logging and the analysis of lithological parameters，six kinds of well logging parameters that are sensitive to lithology were selected，which includes acoustic time difference（AC），natural gamma ray （GR），photoelectric absorption cross section index（PE），density（DEN），deep lateral resistivity（RLLD）and compensated neutron（CNL）. Through the analysis of the six well logging parameters，a multi classifier was constructed based on decision tree method，and the information of lithology and rock characteristics were fused. Compared with the lithologic data of well logging，the recognition accuracy is over 80%. When compared with the Naive Bayesian，the accuracy of lithology recognition is improved by 13%.

Abstract:The reservoir architecture characterization is an important means to exploit the residual oil in the later stage of development. The braided river sand body is an important oil and gas reservoir. However，due to the complex mechanism of the braided river sedimentation and multiple superimposition patterns of sandbodies，the mode of the inner reservoir architecture is complex and variable. In view of the study of reservoir architecture of braided river，many achievements have been made in geologic outcrop analysis，logging curve interpretation，characterization and analysis using ground penetrating radar and laboratory experiments. According to the analytical hierarchy process（AHP）of reservoir architecture，the main structure of the braided river reservoir was graded into 6 levels of architecture units，among which the 3rd level unit and the 4th level unit were the main objects to be studied focusing on their sedimentary model of single sandbodies，characterization of architecture parameters and development model of inner accretion sandbody of braided river bar and interbed and their architecture parameters. The braided river reservoir architecture are mainly affected by four aspects including tectonic movement，river water energy，climatic conditions and sedimentary datum change.

Abstract:The Sulige Gas Field in Ordos Basin has the characteristics of low permeability and low porosity，which is the most typical tight sandstone reservoir in China. According to core data from the Lower Shihezi Formation，Shanxi Formation and Taiyuan Formation of Permian system in the eastern Sulige Gas Field of Ordos Basin，experimental observations and statistical analysis were carried out on tight sandstone reservoir from the respects of geological genesis，petrological characteristics，reservoir space types and reservoir physical properties by using scanning electron microscopy，casting thin section analysis and so on. This research shows that the main reason for the formation of tight sandstone reservoir in the eastern Sulige Gas Field is strong compaction caused by deep burial depth. The reservoir pore evolution process is mainly influenced by compaction and authigenic cementation. The kaolinite has the highest content among all the clay minerals，which is easier to fall off and fill the intergranular pore and thus plugs the pore throat. The flaky illite and chlorite can fill pores，which leads to the formation of tubular throat or the segmentation of the throat. The cementation of other minerals and the strong water sensitivity of montmorillonite reduce the gas permeability. In addition，the proportion of primary pore is very low. The rock particle sorting is poor and the clay minerals fill the intergranular pores，which leads to complex relationship between pore and permeability and the reduction of the formation permeability in tight sandstone gas reservoir. The tight reservoir space are mainly lithic dissolved pore，the intercrystal pore and feldspar dissolved pore in the eastern Sulige Gas Field.

Abstract:As the oilfield development entered the middle and late stage，difficulty of tapping residual oil increases when the relationship between oil and water becomes more and more complex. Fine geological research based on reservoir architecture becomes the key to tap residual oil. The hierarchy interface analytical method was applied in the article to analyze the internal architecture characteristics of sandy braided-river in the 4th area of L Oilfield in Bohai Bay Basin based on outcrop，core，modern deposits and dense well logging data. On the basis of architecture reverse classification scheme，the architecture interface of braided-river in the study area was divided into 6-12 levels considering positive sequence classification. Based on the experience formula for sandy braided-river reservoir，modern deposits constraints and stratigraphic correlation between closely spaced wells，single braided channel belt，braided bar and braided channels and interlayers within braided bar were quantitatively characterized by grade. A set of methods for quantitatively characterizing different levels of sandy braided-river were developed，and the characteristics of single braided channel belt，braided bar and braided channels and interlayers within braided bar were determined as the three levels of the architecture. There are four filling patterns for the braided channels，including sand filling，half-mud filling，mud filling and remaining mud filling，and then the genesis of different filling patterns was analyzed.

Abstract:Fractures developed well in the Lower Silurian Longmaxi Formation in DS area，southeast Sichuan. The development characteristics and controlling factors of shale fractures were studied based on the experimental results of field geological survey，core observation of typical well，homogeneous temperature of inclusions and X-ray diffraction. The results show that there are 2 periods of fracture development in the area. The first period is at the middle-late Yanshan movement，which was dominated by NW compression induced by the rise of Jiangnan Xuefeng uplift，and near EW and SSE X-type conjugate shear fracture in plane and NE longitudinal shear fracture developed. The second period is from the end of Yanshan movement to the Himalayan period，which was dominated by NE compression as a combined effect of the rise of central Sichuan paleo-uplift，Jiangnan Xuefeng uplift and central Guizhou uplift. As a result，NNE and NEE X-type conjugate shear fracture in plane and NW longitudinal shear fracture developed. The development of fractures is mainly controlled by tectonic movement，structural position，rock mechanical properties，lithology and mineral composition. The degree of fracture development is closely related to the distance from the fault，the content of brittle mineral and clay mineral of rock，Young’s modulus and Poisson’s ratio.

Abstract:In order to achieve high and stable production and improve oil recovery，waterflooding plan is used in the most sandstone oilfields of China. However，most oilfields have entered the production decline stage with water breakthrough and water cut increasing. In order to slow down the decline and improve the development status and the oil recovery，well pattern infilling and interlayer adjustment were carried out. It is well known that the recoverable reserves and remaining recoverable reserves of oilfields are the basis of development programs and adjustment programs. At present，the recoverable reserves and the remaining recoverable reserves of Chinese oilfields are evaluated by international assessment company. The method used is the classical production decline method proposed by Arps in 1945，and mainly based on the exponential decreasing method. Based on the generalized Arps decline form，a method was proposed to evaluate the recoverable reserves， remaining recoverable reserves，reserves production ratio（RPR）and decline rate before and after the infilling adjustment of the oilfield. The practice application indicates that the technical recoverable reserves and economical recoverable reserves have been increased by 409.1×104 and 412.8×104 t respectively after infilling adjustment in Maling Oilfield.

Abstract:Relatively regular areal well pattern has been applied in most oilfields nowadays. But under the influence of reservoir heterogeneity，the development effect of different oilfields varies a lot. To solve this problem，a method of artificial fracturing for oil wells in low permeability zone was proposed，which aims to achieve the purpose of equilibrium displacement in well patterns. Targeting on the rectangular five-spot well pattern，the calculation formulas of water breakthrough time in the fractured oil well and the non-fractured oil well were derived. Besides，aiming at the target that the injected water reaches to different oil wells at the same time，a calculation method of the optimal fracture half-length of the fractured well in the low permeability zone of heterogeneous reservoir was established on the basis of stream line integral method and equivalent well diameter method. The influence of the permeability ratio，well spacing，the difference betwecn two injection-production pressure differences and the fracture conductivity on the optimal fracture half-length was analyzed. The optimal fracture half-length decreases with the difference between two injection-production pressure differences and fracture conductivity. However，when the permeability ratio and the well spacing are large，the required optimal fracture half-length will be relatively long.

Abstract:The stress sensitivity of permeability is always an important research topic in the area of tight oil and gas reservoir development. Six fractured samples were prepared from the downhole core samples in the ultra-deep tight sandstone gas reservoir，which were used to conduct the stress sensitivity evaluation experiment in the ultra-deep tight sandstone reservoir. Before and after the experiments of stress sensitivity，laser scan imaging was made on fracture wall. SEM was used to observe the micro-structure of the fracture wall. The research results show that the stress sensitive coefficients of the fractured samples of the ultra-deep tight sandstone reservoir range from 0.41 to 0.72，and the degree of stress sensitivity is from medium and weak to strong，which is significantly lower than that of the typical tight sandstone reservoir in China. The results of three-dimensional laser scanning imaging present that sand particles drop off from the fracture wall before and after stress sensitivity experiments. SEM image shows that the structure of most of the fracture wall is loose and weak before the experiment. During the stress sensitivity evaluation experiments of the fractured samples in the ultra-deep tight sandstone reservoir，the sand particles are separated from the walls of fractures under the effect of erosion，which is caused by drag force and particle erosion. Under the effect of drag force，the particles move and deposit in narrow place of the fractures.Due to a certain strength of particles，the deposited sand particles play a role on propped fractures with the increase of effective stress，which can weaken the stress sensitivity to some extent. The degree of influence of sand production from fracture wall on decreasing stress sensitivity are different for fractures with different widths. The degree of weakening effect for fractures with medium width，relatively large width and relatively small width falls in turn.

Abstract:Stimulated reservoir volume fracturing is the key technology for effective development of shale gas，which uses hydraulic force to create hydraulic fracture and connect natural fracture. But it is not capable of increasing the permeability of shale matrix. As a result，some problems still exist in shale gas wells such as short valid period，fast production decline，etc. The products of reductive environment in shale deposition such as organic matter and pyrite were analyzed and the adsorption ability of organic matter was measured. The effects of organic matter and pyrite oxidation on gas transmission were discussed，and the geological conditions and engineering feasibility of oxidative stimulation to increase shale permeability were analyzed. Results shows that shales generally have organic matter and pyrite and other reductive contents that can be easily oxidized. Oxidation of organic matter and pyrite in shale can affect shale gas transmission capacity. Organic acid can be generated after organic matter oxidization and its solution pH can be as low as 3 after the oxidization，which can dissolve calcite and other carbonate minerals. Oxidation has been used in superheated steam drilling，elimination of filter cake，fracturing fluid breaking glue，thermal recovery production processing，sterilization，etc. These applications provide important experience to engineering application of oxidative stimulation in shale gas reservoir. By using oxidation to stimulate organic-rich shale reservoir，the organic matter and pyrite and some carbonate minerals can be consumed，which brings about the formation of dissolution pore and seam and high temperature and high pressure environment. This can change the mineral composition，pore structure and adsorption/desorption characteristics of the shale reservoir. Therefore，the goal of reforming shale gas reservoir can be achieved.

Abstract:Steam assisted gravity drainage（SAGD）technology is applied to develop heavy oil reservoirs. CO2 can reduce the viscosity of heavy oil and the heat loss of the steam chamber can be reduced，and thus oil recovery may be enhanced by this technology. Due to the limitation of experimental environment and equipment，the maximum temperature of reaction kettle is no more than 150 ℃. Thus the solubility of CO2 in super heavy oil and its impact on decreasing viscosity beyond 150 ℃still require further discussion. In terms of these issues，a high temperature and high pressure resistant heavy oil mixing apparatus was designed，and the solubility of CO2 in the super heavy oil and the effect of dissolved CO2 on the density and viscosity of the super heavy oil were measured at different temperatures and pressures. Laboratory tests show that the solubility of CO2 becomes significantly low at reservoir temperature of 200 ℃，and the viscosity and relative density of the super heavy oil will not change with the pressure. The viscosity and density of the super heavy oil saturated with CO2 are much lower than those of the degassed crude. The dissolution characteristics of CO2 and the mining effect of heavy oil were numerically simulated by CMG software，and the recovery rate of heavy oil reservoir was improved remarkably. It shows that the super heavy oil reservoir can be developed at reservoir temperature of 200 ℃.

Abstract:Bohai LD Oilfield is developed by commingling production in thick layers. Due to the field test at early polymer injection and the effect of gravity on developing the thick reservoirs，the remaining oil in the period of middle and high water cut is relatively complicated. In order to further study the remaining oil distribution of oil reservoir after the polymer flooding，laboratory core displacement experiment was carried out. Combined with the reservoir properties，physical simulation parameters were designed according to the similarity principle，and the effect of different stratum rhythm on remaining oil distribution in the early polymer injection and the production performance was researched. The research results indicate that due to gravitational differentiation，the oil reservoir is flooded at the bottom under the condition of homogeneous rhythm，and early polymer injection can slow the gravitational differentiation to a certain extent，so the remaining oil is mainly concentrated at the top of the reservoir near the production well；under the condition of positive rhythm，influenced by the gravitational differentiation and the reservoir heterogeneity，the high permeability layer is flooded at the bottom and the remaining oil is concentrated in the lower permeability layer at the top；early polymer injection can effectively drive the remaining oil in the medium and low permeability layer，and the remaining oil is concentrated in the low permeability layer near the production well；under the condition of reverse rhythm，the swept degree of water flooding is relatively uniform，and the remaining oil is mainly concentrated in the locally non-swept region，and the early polymer injection can further extend the swept degree；under the condition of composite rhythm，the displacement situation of water drive and the polymer drive are similar to that of the homogenous rhythm，and the remaining oil is concentrated in the low permeability layer near the production well.

Abstract:The bottom water coning is the key which restricts the effective development of bottom water reservoirs. Stimulation potential of nitrogen foam anti-water-coning technology in high-temperature and high-salinity bottom water reservoirs was investigated. Property analyses of foam system show that the cocoamido propyl hydroxy sulfobetaine（CHSB）has high salt tolerance and temperature resistance，and the foam formed from CHSB can achieve the effect of selective blocking water channel with its sensitivity to light crude oil. Physical simulation experiments present that nitrogen foam injection at the top of the water cone can effectively control water coning，increase the sweep efficiency of the bottom water and replace the residual oil at the top reservoir. As foam rupture occur frequently in the water cone when it is stable，shutdown days should not last long. At the same time，the lower yield of opening production of the wells could weaken the erosion of the nitrogen foam by the bottom water and enhance the foam effectiveness of reducing water production. Compared with shut-in coning control and compound coning control of nitrogen foam and nitrogen，nitrogen foam coning control can yield an extra recovery rate of 16.45% and 8%，respectively.

Abstract:Compared with the onshore oilfield，Bohai Oilfield has great differences in reservoir geological characteristics，injection-production parameters and completion methods. In order to solve the technical problem of the fluid channeling in Bohai Oilfield，the experimental study on the composition selection and performance evaluation of the plugging agent was carried out based on the reservoir characteristics and fluid properties in Bohai Oilfield. The results show that the plugging agent is a dark gray compact solid，which consists of main agent，curing agent，thickener and retarder. It is a kind of plugging agents for large-size prefenrential channels which have the characteristics of high compressive strength and low permeability. Little correlation between total mineralization degree of the solvent and curing time，however，the CO32- and HCO3- in the solvent are beneficial to prolong the curing time. From the technical and economic point of view，the mass fraction of main agents is no less than 30% and the mass fraction of retarder ranges from 0.05% to 0.1%. Construction time can met the requirements by adjusting the the mass fraction of the retarder. When the formula of the plugging agent is made up of “thickener 5% + curing agent 0.15% + retarder 0.1% + main agent 30%”，the curing time is about 20 h.

Abstract:In order to investigate the EOR mechanism of CO2 huff and puff for the single well in the carbonate fracturedcavity reservoir，a pressure-resistant physical model which contained three different well completion positions（upper position，middle positon and lower position）was designed and fabricated. The dynamic production performance of CO2 huff and puff in three completion positions with strong bottom water was studied firstly. And the effect of producing pressure drop，CO2 injection volume，and huff and puff cycles on CO2 huff and puff was researched. The xperimental results show that the middle completion position was the most suitable position for CO2 huff and puff，in which the recovery degree was 6.15% and the gas utilization factor was 0.887 mL/mL. CO2 injected from the middle positon could diffuse and dissolve in the heavy oil from two directions，which could expand the swept volume. Furthermore，there exists a suitable producing pressure drop during CO2 huff and puff. And the reasonable CO2 injection volume was then determined according to the producing pressure drop. Thus the highest recovery degree could be obtained. During the whole huff and puff，the ultimate recovery degree at the second cycle was the highest，and oil production of the previous four cycles of CO2 huff and puff accounted for 57% of the total oil production，which is the main oil production stage.

Abstract:There are two types of oil reservoir in the Well Block Qie12 in Kunbei Oilfield of the Qaidam Basin，which are the basement oil reservoirs at the bottom and the E31 glutenite reservoir above the unconformity surface. There are no stable intercalations between them and they are a unified oil and gas system. Water flooding was done in E31 oil reservoir and oil test evaluation was made in the basement oil reservoir at the beginning of development in this area. In order to achieve effective production replacement of E31 oil reservoir，three main controlling factors of the basement oil reservoir productivity were summed up from the aspects of lithology，the degree of fracture development and the water flooding characteristics based on the understanding of the characteristics of the basement oil reservoir. And then the development mode of horizontal wells in this area was determined. The geological model of massive oil reservoir was established，and the well deployment plan was made and the tracking-while-drilling technology was formed. The research proved that both slate and granite are favorable reservoirs which have high weathering degree and well-developed fractures at the top of the basement. The water flooding in the E31 oil reservoir indicates advanced water injection in the basement oil reservoir. The analysis of the main controlling factors on the productivity is the theoretical basis of the efficient development in horizontal wells. Development results of the basement oil reservoir in the recent two years show that high efficient production with less wells has been realized under the background of low oil price，and large-scale development has been carried out in the basement oil reservoir for the first time in the Qaidam Basin.

Abstract:The continental tight oil reservoirs in China have poor physical properties and strong heterogeneity. Large-scale stimulated reservoir volume（SRV）fracturing often induces complex fractured networks，and the influence of secondary fractures on productivity cannot be ignored. An ellipsoid fracture network including main fractures and secondry fractures was designed by local grid refinement，and the production dynamic of fractured horizontal wells in Xinjiang X Oilfield was simulated by numerical simulation. The influencing factors of the productivity of the fractured horizontal wells were analyzed.The results show that the productivity of horizontal well increases with the increase of length of the horizontal section，fracturing scale，SRV，fracture network complexity and fracture conductivity，but the trend of increasing gradually decreases.There is an optimal range for each parameter. The orthogonal experiment was also used to sort the influencing degree of each engineering parameter on the productivity，and it is shown that the SRV has the greatest influence on the productivity of the fractured horizontal well in tight oil reservoirs，which is followed by fracture scale，fracture network complexity，horizontal well length and fracture conductivity.