Abstract:Alluvial fans，which are important reservoirs for hydrocarbon accumulation，are characterized by complex internal structures and strong heterogeneity. Three alluvial fans（Quanjihe Fan，Shaliuhe Fan，Lanniwan Fan）developed in the north of Qinghai Lake were divided into several subfacies and several microfacies based on field surveys and analysis of remote sensing images. For Quanjihe Fan and Shaliuhe Fan，braided channel，main channel and interchannels were identified at the fan roots；braided channel，channel bars，sheet flood and noncohesive debris flow were identified at the fan middle；sheetflood and mudflat were identified at the fan margin. Two periods of debris flow and one short period of traction flow happened during the development of Lanniwan Fan. According to the sedimentary characteristics，the evolution processes of Shaliuhe Fan and Quanjihe Fan can be divided into 4 stages：the initial debris flow deposition and the development of main channel，noncohesive debris flow deposition，extensive development of braided channel and migration of channels and development of the delta. And the evolution processes of Lanniwan Fan can be divided into 3 stages：the early debris flow deposition，the intermittent traction flow deposition and the late debris flow deposits. The results show that the differences in provenance are the main causes for the differences in sedimentary characteristics for the 3 modern alluvial fans.And climatic factors，including humidity and wind field，control fan deposition too.

Abstract:The evaluation of brittleness of tight sandstone gas reservoir is of great significance in guiding fracturing construction. In view of the problems that the brittle minerals could not be determined in the evaluation of the brittleness and ignorance of influence of diagenesis on the rock brittleness，first of all，the relationship between the mineral components and the brittle index was systematically analyzed according to information of thin sections，core data and the triaxial compressive stress under formation condition based on 26 samples from the block in the northeastern Ordos Basin. The quartz and feldspar are the main brittle minerals in the study area. Secondly，based on two different correlations of brittle index with the main brittle minerals，the influence of diagenesis，pore size and brittle mineral difference on the brittle index was determined. And then the influence of the diagenetic minerals on the pore size and the degree of diagenesis was synthesized to classify tight sandstone reservoirs into two types ofⅠreservoir andⅡreservoir by using ratio of quartz and debris to feldspar content. Finally，the brittleness evaluation method for tight sandstone reservoirs based on mineral compositions and diagenesis was proposed and the corresponding brittle index evaluation model was established. The results show that the brittle index evaluation model based on mineral compositions and diagenesis can obtain more accurate brittle index of tight sandstone reservoir，which can provide parameter basis for the identification and stimulation of high-brittle fracturing target layer.

Abstract:In recent years，the exploration and development of shale gas in Southeast Chongqing has become the focus of oil and gas exploration in China. In this article，the geologic characteristics of shale gas accumulation in Longmaxi Formation in the southeast of Chongqing were systematically analyzed in terms of stratigraphic sedimentation，geochemistry，reservoir characteristics and reservoir pattern. The results show that the shale thickness of the Longmaxi Formation in the southeast of Chongqing is larger，ranging from 30 to 130 m. The sedimentary center，where the organic carbon content of shale is high （about 0.05%-17.4%），is in the Shizhu-Pengshui area，so it is the area with high organic carbon in Pengshui. The type of organic matter is dominated by amorphous sapropelic matter，and the degree of thermal evolution reaches high-over maturity. The mineral composition of the reservoir is complex. The clay minerals are composed of illite，mixed-layer minerals of illite and montmorillonite and chlorite. The brittle minerals include quartz，feldspar and carbonate minerals and the brittleness index is high. The storage space is dominated by organic pores，intergranular pores，intragranular pores，pores between interlayered clay minerals and fractures. Shale gas accumulated in situ to form a gas reservoir，and the gas was mainly generated from crude oil cracking and organic matter pyrolysis.

Abstract:Reservoir development of Liuhua reef limestone is complex，and its heterogeneity was very strong in the Pearl River Mouth Basin. Based on seismic，well logging，sedimentary and geological data in A Oilfield，the impact of sedimentary microfacies，interlayer，physical properties and seepage dynamic information of the reef limestone on the reservoir heterogeneity was analyzed，and then the reservoir heterogeneity was evaluated quantitatively under conditions of sedimentary facies constraint using the entropy weight method，and a stochastic model of the comprehensive reservoir heterogeneity evaluation was established under different constraint conditions. The results show that this method can quantitatively characterize reservoir quality parameters and reservoir geometry parameters. According to the result of comprehensive evaluation of reservoir heterogeneity and reservoir dynamic data，the distribution of remaining oil potential area is predicted in the area with heterogeneous synthetic index 0.5-0.7，and the remaining oil is mainly enriched in the northwest wing，southeast wing and the structural high position near the fault. Nine horizontal wells were deployed in the predicted potential areas where the average daily oil output was at least 50 m3/d higher than that of the ODP design production. And the average water saturation increased relatively slow. The potential areas had longer stable time for daily production. The predicted results evaluated by entropy weight method match well with the actual spatial heterogeneity of reservoir.

Abstract:In order to study the characteristics and genesis of dolomite in the main gas reservoirs of the Lower Paleozonic submember Ma55 in the Sudong region，methods such as thin section observation，X-ray diffraction，scanning electron microscopy，cathodoluminescence and trace elements analysis were used to analyze the dolomite samples. The results show that the Lower Paleozoic submember Ma55 in the Sudong region are characterized by dolomitization，which can be concluded as follows：There are three types of dolomite：penecontemporary dolomite，reflux seepage dolomite and buried dolomite in submember Ma55 of the Majiagou Formation. The original intergranular pores developed well in the dolomite reservoirs，and they are dominated by intercrystal pores and suintercrystal dissolved pores. Occasionally，some non-constitutive disso? lution pores，residual intergranular pores and a small amount of paste pores were observed. Cathodoluminescence experimental results show the presence of light-emitting micrite dolomite（containing sand-gravel clastics）indicating the development of muddy gravel dolomite in the study area. The X-ray diffraction results show that the order degree of penecontemporary dolomite is not high，average 0.443，and reflux seepage dolomite has a high degree of order，average 0.574. The ordered degree of buried dolomite is as high as 1. The dolomite composition is simple，and the ratio of Ca2+ and Mg2+ is close to the stoichiometric CaMg（CO3）2，which verifies the accuracy of the order degree of dolomite obtained by X-ray diffraction.And the main trace element characteristics indicate that the reflow infiltration dolomite mainly occurs in seawater diagenetic medium.

Abstract:The major and minor elements of source rocks in the Shahejie Formation drilled by Well Fanye-1 in Dongying sag were analyzed systematically in order to clarify the element geochemical characteristics of the source rocks and their geological significance. According to the relation of contents of different elements with Al2O3 and CaO，the elements are classified into 3 different types. The elements of the first class，including Al，Ti，K，Co，Cr，Ga and V，are mainly sourced from terrestrial debris；those of the second class，which consist of Ca，Mg，Mn and Sr，are mainly sourced from lacustrine water；and those of the third class，including Na，Fe，Cd，Ni，Pb，Ba and Zn，are sourced from multiple and complex sources.Based on the genetic difference of the elements，4 parameters including CaO/Al2O3，Sr/Al2O3，Sr/Ba and V/（V+Ni）were preferably selected to set up a vertical comprehensive geochemical section，and the sedimentary environment evolution of the Shahejie Formation was discussed according to the changes of the parameters in the geochemical section. It shows that from the upper Es4 to the middle Es3，the enrichment of the elements sourced from the water gradually decreases and the salinity of the lake water gradually drops，and the reducibility of bottom water is gradually weakened. Based on the variation tendency，both the upper Es4 and the lower Es3 can be subdivided into four smaller sedimentary units where the palaeo-salinity and bottom water redox condition are obviously different.

Abstract:In recent years，much attention has been focused on the braided fluvial delta reservoir in which reservoir architecture directly controls hydrocarbon enrichment and distribution. Take the lower oil layer in the1st block of Tahe Oilfield as an example，a set of systemic methods to analyze the architecture of the braided fluvial delta reservoir were proposed by combining modern sedimentation measurement with empirical formula for forecasting. Based on the sedimentary facies analysis，according to comprehensive analysis of core data，well logs，seismic and mudlog，different hierarchical levels of architectural interfaces and the corresponding architectural elements were identified. After the identification of barrier-intercalations，using the analytic hierarchy process，the reservoir in the study area was explored into three hierarchial levels including single channel，channel bars and single accretion of channel bars，which were then characterized quantitatively. The results show that the single braided channels are 128-690 m wide，underwater distributary channels are 144-386 m wide，single channel bars are approximately 244 m wide and 594 m long of the lower oil layer in the study area. The channel bars are characteristics of well-developedinterlayerswith inclined angle of 2°-4° on the meeting water side and less than 1° on the back water side in the long axis.

Abstract:The reservoir that produces water at high structure and oil at low structure maybe present phenomenon of oil/water inversion in super-heavy oil reservoir in the lower member of Guantao Formation of Block Cheng911-Ping1，Chengdong Oilfield. Its reason is not clear yet. Based on the well logging，experiment and dynamic data of development，the characteristics of oil/water inversion and its genesis were analyzed comprehensively. The ground crude oil density ranges from 1.007 6 to 1.024 8 g/cm3，which is higher than the formation water density in this area. The heavy oil migrates to the lower structure against the buoyancy and capillary force under the action of gravity，and it is the main reason of the oil/water inversion. This viewpoint was confirmed by mud logging and well logging data. The oil/water distribution law in reservoirs featured by oil/water inversion is very different from that in the conventional oil reservoir. Some principles and methods for delineation of the oil-bearing area in the conventional oil reservoir are not applicable to reservoirs featured by oil/water inversion. Taking proven oil-bearing area as an example，the corresponding delineated principle and the key points in delineation of oil-bearing area in the super-heavy oil reservoirs were proposed aiming at the complex oil-water distribution.

Abstract:Due to the use of staged or volume fracturing technology in the area of ultra-low permeability or tight reservoirs，the area around the horizontal well will form a complex fracturing network and the oil reservoirs are divided into matrix blocks with different shapes，and the fracturing fluid or water will contact with the matrix blocks in a large area when flowing in fractures. Dynamic counter current imbibition will occur and is dominant in the mass transfer process between matrix and fracture under the capillary force. In order to simulate dynamic counter current imbibition properly，the radical integration boundary element method（RIBEM）was used. A mathematical model suitable for the counter current imbibition was established. By comparing the result of RIBEM simulation with those of differential method, numerical calculation,experimen? tal data and analytical solution，the accuracy of the model was proved. This method is suitable for the calculation of cumulative recovery efficiency of a single matrix block with complex shape. Compared to traditional differential method，RIBEM does not need to divide network in the matrix block and the calculation process becomes easy，efficient and more suitable to the practice.

Abstract:Present threshold pressure gradient test cannot characterize the present situation of real threshold pressure gradient. After back pressure control system with high precision was introduced，experimental approaches were carried out to evaluate the threshold pressure gradient in the tight gas reservoir under reservoir conditions. Compared with the measured result under normal pressure，the threshold pressure gradient obtained by the new method is lower under the condition of same permeability and the difference becomes larger when core permeability is lower. Results show that the threshold pressure gradient is not a constant during the development of reservoir，but varies with the pore fluid pressure，and it is called dynamic threshold pressure gradient. New concepts of threshold pressure gradient sensitivity and threshold pressure gradient sensitive coefficient were proposed and defined to describe the dynamic threshold pressure gradient in the tight gas reservoir. The influencing factors of dynamic threshold pressure gradient were experimentally studied as well. Results indicate that the threshold pressure gradient of the tight cores show a linear increase with the decrease of pore fluid pressure. When the core permeability is lower and the water saturation is larger，the threshold pressure gradient becomes larger under the condition of reservoir and the variation range of the threshold pressure gradient during the development is larger. The threshold pressure gradient sensitivity is stronger and the dynamic variation of threshold pressure gradient is more obvious.

Abstract:In the process of bottom water reservoir development，the bottom-water cresting of the horizontal well is the key factor affecting the development effect，while the research on the influential factors of the water cresting morphology is relatively few. The numerical conceptual model of bottom water reservoir was established based on the actual reservoir parameters of M oilfield using the technology of reservoir numerical simulation. Quantitative description formula for the water cresting morphology was built by regression according to the formulas of the horizontal well productivity proposed by Cheng Linsong et al. The influence of horizontal well spacing，horizontal and vertical permeability ratio，liquid production of single well，vertical position of horizontal well，oil-water viscosity ratio and water cut on the recovery percent and water cresting morphology was analyzed. Analysis results show that along with the increase of horizontal well spacing，the recovery percent and the maximum water cresting radius decrease，but the water cresting volume presents a tendency of increase in general at the same water cut；along with the increase of horizontal and vertical permeability ratio and oil-water viscosity ratio，the recovery percent decreases and the maximum water cresting radius and volume decrease gradually at the same water cut；along with the increase of liquid production of single well，the recovery percent, the maximum water cresting radius and volume were increasing in general at the same water cut, but the maximum water cresting radius and volume slightly decreased at certain liquid production；if the vertical position of the horizontal well is closer to oil-water interface，the recovery percent and the maximum water cresting radius and volume decrease；the maximum water cresting and volume increase gradually along with the increase of water cut. Box-Behnken experimental design method was used to obtain the order of influential factors of each control factor，and the interactive effects of each factor on water cresting morphology. The results show that the order of degree of the influential factors on water cresting morphology was concluded as horizontal and vertical permeability ratio>oil-water viscosity ratio>vertical position of horizontal well>liquid production of single well>horizontal well spacing. The interaction of horizontal and vertical permeability ratio，liquid production of single well，oil-water viscosity ratio and horizontal well spacing on the cumulative oil production is the most obvious.

Abstract:Technology of stimulated reservoir volume fracturing brings higher initial oil production in the ultra-low permeability and tight oil reservoir，but rapid decline of oil production，low cumulative oil production and poor economic effect in the depletion development and waterflooding will result in watered-out oil wells rapidly. Therefore，it is necessary to explore new effective development method of supplying energy to the reservoir. Waterflood huff and puff in the oil reservoir with stimulated reservoir volume fracturing is a new method. Three-stage model of waterflood huff and puff were built to explore the development mechanism of imbibition and unsteady driving and to deduce the corresponding oil productivity formulas. Obvious development effect of the waterflood huff and puff was studied theoretically. The major influential factors of the waterflood huff and puff were researched by oil reservoir engineering method and laboratory experiment，and the feasibility of the waterflood huff and puff was certified combined with field practice. Research results show that exchange rate and quantity of fluid between fracture and matrix has changed qualitatively in network fracturing system formed by the stimulated reservoir volume fracturing，so waterflood huff and puff has been changed from a supplementary method to a new economical and effective development method. Therefore，a new thought for effective development of ultra-low permeability and tight oil reservoir has been formed. It can be a potential development method of energy supply in the ultra-low permeability and tight oil reservoir considering its low additional cost for development and high investment benefit.

Abstract:The multi-stage Ordovician carbonate condensate gas reservoir in Tazhong M area has the characteristics of multi-type of reservoir spaces，multi-phase fluids and multi-type of water，which brings great difficulty to development.The characteristics of reservoirs，fluid，natural energy and water drive of 14 Ordovician carbonate condensate gas reservoirs were analyzed and evaluated comprehensively. Three types of reservoir spaces，three types of fluids，three types of natural energy and three types of water drive were classified，which respectively include“caves type，fracture-vug type，vug type”，“reservoir with oil rim，mid-high condensate oil without oil rim，low（minor）condensate oil without oil rim”，“sufficient natural energy，less sufficient natural energy，insufficient natural energy”and“rigid water drive，elastic strong water drive，elas? tic medium water drive”. On this basis，twelve combination types were classified comprehensively. Based on the comprehensive classification results，well location and well pattern optimization，rational utilization of natural energy，pressure maintaining by water injection and gas injection and other strategies were proposed to achieve good results.

Abstract:Thickening rules of HPAM seawater solutions from the South China Sea with magnetic treatment were studied by apparent viscosity measurement. Shear resistance，anti oxidative degradation，magnetic memory effects and flooding property of simulated core of viscosified HPAM seawater solutions were also investigated. The results show that the viscosity of HPAM seawater solution with mass concentration of 2 000 mg/L increased from 14.2 mPa?s to 18.1 mPa?s under the conditions of magnetization temperature of 30 ℃，magnetic intensity of 60 mT，magnetization time of 1.5 h and magnetization speed of 800 r/min，and the thickening rate reached to 27.5%. Shear resistance to 50-200 mesh and anti oxidative degradation of viscosified HPAM seawater solution with magnetic treatment at 30 ℃ were obviously superior to those of untreated HPAM seawater solution at the same temperature. The magnetic memory time of the viscosified solution could last for 9 d.After HPAM seawater solution flooding，3.9 times the pore volume of simulated core of viscosified HPAM seawater solution with magnetic treatment were injected and the injection pressure was increased by 35 kPa. Therefore，the swept volume was improved and the oil efficiency was enhanced.

Abstract:After waterflooding development for several decades，the majority of old offshore oilfields have entered the stage of high water cut，low production and serious invalid water cycle. Therefore，it is necessary to study the remaining oil distribution and enhancing oil recovery technology for low producing degree. CO2 immiscible flooding is usually implemented after water flooding，so the effect of injected water remained in the pores on gas injection development needs to be taken into account. Based on the traditional method of researching the remaining oil distribution，the combination experimental method of online CT scan of core and micro-model simulation of core was proposed to qualitatively and quantitatively analyze the characteristics of water flooding，gas drive and remaining oil distribution from core scale and micro pore scale at different times. The start-up mode and migration process of the remaining oil after water，gas and WAG injection were revealed. The mechanism of water injection and gas-oil displacement and macroscopic and microscopic distribution characteristics of remaining oil after oil displacement were researched quantitatively and qualitatively from the aspects of macroscopic core scale and microscopic pore structure. The start-up mode and migration process of the remaining oil during gas drive after water flooding and water alternating gas flooding were revealed. The three-phase flow rules of oil，gas and water under the action of movable water have been further described，which provides theoretical basis and experimental basis for the development of CO2 immiscible flooding.

Abstract:Effect of steam flooding is not good for easy steam channeling and low steam sweep efficiency. In order to seek out a new way to enhance recovery factor in heavy oil reservoirs，a field test of foam-assisted steam flooding was made in Zhongerbei Ng5 Block of Gudao，Shengli Oilfield. According to the high temperature of steam flooding，a new type of foaming agent DHF-1 was developed. The agent has good performance of temperature resistance and plugging，and resistance factor under 300 ℃ is more than 20. Laboratory experiment result of oil displacement shows that foam-assisted steam flooding can improve sweep volume and oil displacement efficiency. Field experiment of the foam-assisted steam flooding was made in October，2010. The injecting pressure of the steam injection well rose by 1.6 MPa averagely. All oil wells achieved good results. The application result of tracer show that the flooding sweeping is more homogenous，and the average oil displacement efficiency rose to 62.4% based on the data of sealed coring wells. It shows that the foam-assisted steam flooding can improve the stability of steam front，control steam breakthrough and improve development effect obviously. By the end of June，2016，the cumulative oil production has been 23.6×104 t and the recovery degree is 52.1% in the pilot area，and the recovery efficiency has been improved by 16.8% compared with steam huff and puff.

Abstract:The displacement characteristic curve of water drive is still used in CO2 immiscible flooding. There are not standard displacement characteristic curve and mathematic description method for gas drive. Piecewise relations were theoretically derived to determine the relationship between cumulative gas production and cumulative oil production. Based on displacement characteristics，the displacement characteristic curve of CO2 immiscible flooding for low permeability reservoir was obtained. Combined with laboratory experiments and pilot tests，the double logarithmic piecewise linear relations were proved effective to explain displacement characteristics of CO2 immiscible flooding. The constants of the linear relations can be regressed through production data. And they can also be used to predict the effects of CO2 immiscible flooding. Additionally，gas channeling time can be obtained by the gas displacement characteristic curve. The adjustment measures can be determined quickly through the relations. Pilot tests of CO2 immiscible flooding in Yaoyingtai Oilfield show that the gas channeling happened 12 months after gas injection. According to the gas displacement characteristic curve，the slope of gas channeling section decreased sharply after WAG applied. And the extent of gas channeling was reduced.

Abstract:Channel fracturing is the key technology to develop low and ultra-low permeability reservoirs with high efficiency and low cost. The key of channel fracturing is to create the unimpeded channel network in the fractures for oil and gas flow. However，researches on the proppant shape and channel characteristics in channel fracturing are in the initial stage. A large-scale visual slot equipment was used to simulate the proppant transport process in the channel fracturing. The effects of fiber，fracturing fluid，proppant，pumping velocity and pulse time on proppant transport and flow channel were studied.The experimental results show that the fiber and fracturing fluid determine whether the flow channel can be formed within the propped fracture，and the pump velocity and pulse time have a great influence on the flow channel morphology. The proppant density and size have less influence on the flow channel morphology. The molecular chain of guar gum is wound on the fiber surface，which makes the range of fiber network increase and the strength enhance. The fiber network and molecular chain together improve the stability of the slurry pulse in the transportation process. The flow channels can be divided into three categories and the flow channel morphology is controlled by product of pump velocity and pulse time. When the injection parameter of pulse unit is 2.5-5 L，the flow channel morphology obtained is optimal and the conductivity of propped fracture is the largest.

Abstract:Under the low oil prices，much attention has been paid to radial drilling because of its low cost，short time and high efficiency. In view of the present situation of its complex fracture system，various types，great difficulty and poor effect of conventional development of the remaining oil in the high position of the fault block reservoir，the radial drilling technology was proposed to realize the effective exploitation of the remaining oil. The productivity prediction model for radial drilling was built and its accuracy was verified by coupling of the expression of radial drilling potential and the equation of flow in the hole which was established according to the principle of mirror reflection and potential superposition. The results show that the radial drilling can realize the economic and effective exploitation of the remaining oil in the high position of the fault block reservoir. The error between the calculated oil production of the new model and that of the numerical simulation is less than 10%，which shows that the formula can be used to predict the productivity of the fault block reservoirs that use radial drilling technique. The larger the radial drilling length is，the better the simulation effect is. The effect of vertical multi-branch development becomes better with the increase of reservoir thickness. With the increase of reservoir thickness，the oil production index decreases gradually，and the radial drilling technique is more suitable for the thin oil reservoir exploitation.