新疆石油地质

Sedimentation Model and Exploration Significance of Large-Scaled Shallow Retrogradation Fan Delta in Mahu Sag

TANG Yong, XU Yang, LI Yazhe, WANG Libao

2018, 39 (zk(English) ): 1-8.

摘要 ( 86 )

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The upper Wuerhe formation of Permian and Triassic Baikouquan formation in Mahu sag and its adjacent areas are a set of near-source coarse deposits under the background of depression basin that are large-scaled shallow retrogradation fan-delta deposits under the background of gentle slope, and 13 lithofacies and 7 sedimentary microfacies are identified based on core observation. Multiple fan deltas are developed on the slope of the sag, and the fan bodies connect with each other. The formation of this kind of large-scaled shallow retrogradation fan delta is closely related to 3 geological conditions. The first is that continuously uplifting periphery ancient mountains and stable river systems provided sufficient provenance for each fan during deposition; the second is that there was a good paleogeographic background such as large basin, shallow water and gentle slope; the third is that continuous lake transgression and multi-stage slope-break are significant conditions for large-sized superposition and merging of sand bodies. A sedimentary model of large-scaled shallow retrogradation fan delta is established, which provides guidance for petroleum prospecting and reserves estimation in Mahu sag.

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Hierarchical Architectural Element Analysis for Sandy Conglomerate Deposits of Baikouquan Formation, Mahu Sag

ZHANG Changmin, LIU Jiangyan, PAN Jin, ZHU Rui

2018, 39 (zk(English) ): 9-20.

摘要 ( 81 )

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Enormous petroleum resources have been discovered in the Lower Triassic Baikouquan formation of Mahu sag, Jungar basin since the year of 2010, but reservoir evaluation and efficient development are difficult due to the complicated internal structure and serious reservoir heterogeneity of the sandy conglomerate in Baikouquan formation, so profound analyses on sedimentary genesis and architectural structure of the sandy conglomerate are needed. The paper utilizes hierarchical architectural element analysis method to delineate the architectural structure of the sandy conglomerate in Baikouquan formation of Mahu sag. Based on the detailed description of cores of 1,922 m long obtained from 82 wells, the paper presents a multi-attribute lithofacies denomination program which is dominated by 4 attributes i.e., rock grain size, sedimentary structure, color and grain support mode and 227 lithofacies are identified in the sandy conglomerate of Baikouquan formation. According to core, logging and seismic data, depositional interfaces of 11 orders are classified in the studied interval and architectural elements of 11 orders are identified correspondingly, and the corresponding architectural elements to lithofacies and sedimentary microfacies are analyzed. Taking the 9th order architectural element as a basic unit, the evolution processes of the sedimentary systems in Huangyangquan fan and Xiazijie fan are characterized through well-tie correlation constrained by seismic data. It is considered that the Baikouquan formation in both Huangyangquan fan and Xiazijie fan belongs to coarse-grain sandy conglomerate deposits and takes river as the main transportation force. The depositional system of Huangyangquan fan is of relatively small scale and has more characteristics of alluvial fans and fluvial fans; the depositional system of Xiazijie fan is of large scale and has more characteristics of river fans. From the first member to the third member of Baikouquan formation, the depositional system gradually changed from alluvial and fluvial fans to fan delta with the rise of water level of lake. Medium-fine conglomerate with low content of matrix is good lithofacies, seasonal channel deposits and underwater distributary channel deposits are favorable sedimentary microfacies, the second member of Baikouquan formation is the most favorable interval for oil accumulation.

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Tectonic Simulation Experiment of Fault Forming Mechanism in Kunbei Fault Terrace Belt

WANG Haiqi, DOU Xiaoyu, WANG Lin

2018, 39 (zk(English) ): 21-27.

摘要 ( 49 )

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Various conditions and stress mechanisms result in the complicated tectonic settings of the Kunbei fault terrace belt. Two series of tectonic simulation experiments are designed for the primary-order and second-order main faults, and the third-order and other secondary order faults, respectively. The first series of experiments simulate the primary-order and second-order main faults and the results reveal that a series of unbalanced thrust fault systems are developed on the Kunbei fault terrace belt under the continuous compression of N-S trending tectonic dynamics during Himalaya orogeny, which highly matches with the 5 seismic interpretation sections in the study area. The second series of experiments simulate the third-order and other secondary order fault structures and suggest that these faults are controlled by the maximum shear stress, in which 2 fault systems including conjugate reverse fault and tearing reverse fault are developed, which matches with the characteristics of fault systems displayed on the time slices in the study area. The numerical simulation results can further verify the conclusions of the 2 series of experiments and show that the secondary fault systems can improve the accumulation properties of reservoirs. Wellblocks of Qie-16, Qie-6, Qie-12 and Qie-4 in Kunbei oilfield have been proved to be the hydrocarbon enrichment areas, which well matches with the experiment results and can be the guidance and references for oil and gas exploration.

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Lower Limits of Reservoir Physical Properties and Controlling Factors of Baikouquan Formation on the Northern Slope of Mahu Sag

GUO Huajun, SHAN Xiang, LI Yazhe, ZOU Zhiwen, WANG Libao

2018, 39 (zk(English) ): 28-34.

摘要 ( 46 )

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Based on the comprehensive application of the data on formation test, core analysis and logging interpretation, the low limits of physical properties of effective sandy conglomerate reservoirs in the Lower Triassic Baikouquan formation on the northern slope of Mahu sag are determined by using the distribution function curve method and formation test method, and regression analysis method is used to match the lower limits of physical properties with depth. Based on which, lithofacies, sedimentary microfacies and diagenesis are analyzed by using the differences of reservoir physical properties. The results show that the lower limits of effective reservoir physical properties exhibit a trend of gradual decrease with the increase of depth in the study area; the development of effective reservoirs is mainly controlled by sedimentary microfacies and lithofacies, and weakly influenced by diagenesis. Microfacies of underwater distributary channel and braided channel are the most favorable areas for effective reservoir development, and tabular cross-bedding and trough cross-bedding are the most favorable lithofacies for effective reservoir development; the sandy conglomerate in the study area is mainly in the A stage of the middle diagenetic period, the secondary pores result from feldspar dissolved by organic acid which is liberated from thermal evolution of organic matter, which can improve reservoir physical properties, the effective reservoirs with the diagenetic faices of weak-compaction-weak-corrosion and unstable component corrosion are the most developed.

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Research and Identification of Gas and Water Characteristics in Ma-5₅ Submember in the Southern District of Sulige Gas Field

ZHENG Xiaopeng, WANG Shujie, HAO Long, HU Weiwei, LIU Daotian, WANG Ye

2018, 39 (zk(English) ): 35-39.

摘要 ( 61 )

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Marine carbonate reservoirs are developed in Ma-5₅ submember of the Lower Ordovician Majiagou formation in the southern district of Sulige gas field, which have no obvious gas-water interface. But gas wells produce water during the development process. Based on in-depth analysis of chemical characteristics of formation water, logging curve overlapping and cross-plot methods, the paper determines the formation water type and distribution pattern. The results show that the formation water in Ma-5₅ submember belongs to well-sealed ancient residual seawater and 3 distribution patterns exist in the submember including retained water at the bottom, gas and water in the same layer and lenticular water, among which the boundary of deep lateral resistivity between aquifer and gas-water zone is 266 Ω·m and that between gas-water zone and gas zone is 710 Ω·m.

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Geometrical and Kinematic Characteristics of Selibuya Fault Belt, Tarim Basin

ZHANG Yong, CUI Yongping, LIU Changlei

2018, 39 (zk(English) ): 40-53.

摘要 ( 55 )

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The Selibuya fault belt is one of the boundary faults on the southern margin of Bachu uplift, in which complex fault structures formed under the influence of multi-period tectonic activities in the basin. Studying the geometrical and kinematic characteristics of the Selibuya fault belt is of great significance in exploring the nature and forming time of Bachu uplift and exploring the causes of structural deformation in the craton. Using fault-related fold theories and other seismic interpretation methods, the paper detailedly interprets and analyzes 8 2D seismic profiles nearly perpendicular to the strike of the Selibuya fault belt, redepicts the geometry of the fault belt, establishes the 3D shape of the fault belt with 3D modeling techniques, and resegment the fault belt according to fault assemblages and their distribution patterns. Combining the development characteristics of growth strata and unconformities, the paper also discusses the periods and relative intensities of the structural activities. The study suggests that the Selibuya fault belt is characterized by deep faulting whose activity is the main reason leading to the uplifting of the strata at the northern side of the fault belt. The Precambrian structure proves that the activities of the Selibuya deep faults were tensional at the early stage; according to fault assemblages and their distribution patterns, the Selibuya fault belt can be divided into the northern, middle and southern segments, all of which show stratified deformation patterns. Paleogene gypsum and the Middle Cambrian salt bed are detachment layers of Cenozoic and Paleozoic faults, respectively. The morphology of the growth strata indicate that the Cenozoic faults started their activities during the Quaternary and continued to the present. The development of the unconformity indicates that the basement faulting was active during the Middle-Late Permian with the activity intensity showing stronger in the north and weaker in the south in the fault belt. The Paleozoic active fault period occurred in the Miocene-Late Pliocene and its activity intensity showed weaker in the north and stronger in the south. The basement fault led to the overall rise of the strata, while the faults of Paleozoic and Cenozoic resulted in the strong fold deformation of the strata.

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Controls of Abnormal Fluid Pressure on Tectonic Deformation in Northeastern Sichuan Basin

FAN Huida, HE Dengfa, ZHANG Xuliang

2018, 39 (zk(English) ): 54-65.

摘要 ( 51 )

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To investigate the influences of abnormal fluid pressure on structural deformation in the northeastern Sichuan Basin, on the basis of drilling and logging data obtained from 40 wells in the study area, the paper uses equivalent depth method to calculate fluid pressure in the shale section and corrects the pressure by combining with the actual measured fluid pressure to characterize the characteristics of the overpressure development in the study area and to match the variations of the fluid pressure with depth. The pore-fluid pressure ratio of different detachment layers in the northeastern Sichuan Basinare calculated. The calculated pore-fluid pressure ratio is 0.38-0.72 for the gypsum-salt detachment layer in the Lower Triassic Jialingjiang formation, 0.48-0.78 for the shale detachment layer in the Lower Silurian Longmaxi formation, 0.61-0.87 for the gypsum-salt detachment layer in the Lower Cambrian Longwangmiao formation and 0.71-0.84 in the basement detachment layer, showing a feature of “lower in the east and higher in the west”. The pore-fluid pressure ratio of each detachment layer is used to obtain effective friction coefficient and the calculated effective friction coefficient of each detachment layer is 0.170-0.530, 0.130-0.320, 0.110-0.330 and 0.090-0.180 for Jialingjiang formation, Longmaxi formation, Longwangmiao formation, and basement, respectively. Based on the through-well seismic profile interpretation, the intensity of the basement detachment layer is calculated as 0.060-0.110 by using structural wedge-related theories. Comparing the intensity with the effective friction coefficient, it is found that they are identical with each other, which can prove that the calculated effective friction coefficient of the basement detachment layer is reliable. When the fluid overpressure is not developed in the study area, the effective friction coefficient of the basement detachment layer should be 0.372-0.527, which indicates that the widely-developed fluid overpressure in the study area results in the reduction of the effective friction coefficient of the basement detachment layer by 79.1%-83.9%, indicating that the tectonic stress needed by shear action along the basement detachment layer significantly decreases.

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Characteristics and Hydrocarbon Accumulation Models of Carboniferous Inside-Type Volcanic Reservoir in Xiquan Area, Junggar Basin

FAN Guangxu, ZHU Ka, WANG Libing, CHEN Hong, LI Hui

2018, 39 (zk(English) ): 66-73.

摘要 ( 70 )

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The strong heterogeneity, unclear controlling factors and reservoir accumulation rules of the Carboniferous inside-type volcanic reservoir constrain its exploration in the Xiquan area, eastern Junggar Basin. Based on the data of geophysical prospecting, geology and drilling, the paper studies the characteristics of the Carboniferous inside-type volcanic reservoir in the Xiquan area. The inside-type volcanic reservoir in the study area is characterized by low porosity, low permeability and strong heterogeneity, which belongs to fracture-pore reservoirs. The study shows that lithology and lithofacies are the basis for high-quality reservoir forming, the development degree of fractures is an important factor affecting the physical property and effectiveness of the reservoir, and dissolution can improve the physical properties of the Carboniferous inside-type volcanic reservoir. Based on the configuration relationships between hydrocarbon source rocks and reservoirs, 3 hydrocarbon accumulation models of the Carboniferous volcanic rocks in the study area are established - the reservoir of weathering crust type is mainly developed in Batamayineishan Formation; 2 kinds of inside-type gas reservoirs are found in Songkaersu Formation, i.e., the lithological gas reservoirs in the b member of Songkaersu formation and the structural oil and gas reservoirs in the a member of Songkaersu Formation. The shallow Carboniferous strata with high exploration degree are the areas where oil reservoirs are developed, and the deep slope zones are the favorable areas for natural gas exploration which has good prospecting potential and low exploration degree.

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Quantitative Characterization of Organic Matters with Different Occurrences in Argillaceous Source Rocks: A Case of Shahejie Formation, Dongying Sag

ZHAO Yue, CAI Jingong, LEI Tianzhu, YANG Yan

2018, 39 (zk(English) ): 74-81.

摘要 ( 65 )

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The organic matters retained in argillaceous source rocks are of various occurrences, including free state and mineral-binding state organic matters which have quite different geochemical natures and different significance in detailed source rock evaluation. However, a comprehensive quantitative characterization technique for both occurrences has not been established yet. With the argillaceous source rocks sampled from the middle Es₃, the lower Es₃ and the upper Es₄ of the Shahejie Formation, Dongying sag, and based on the analysis on the changes of pyrolysis parameters during the processes of solvent extraction and sequential chemical treatment including the variations of free hydrocarbon, cracked hydrocarbon and TOC, the paper measures the abundance of the organic matters with different occurrences quantitatively and establishes a quantitative characterization method of retained organic matters with different occurrences. The results show that the quantity of soluble organic matters of mineral-binding state is quite large in the organic matters retained in source rocks. Traditional evaluation methods such as Rock-Eval pyrolysis method and chloroform bitumen A method have some limitations. Profound study on the geochemical characteristics of the organic matters of mineral-binding state will widen the knowledge of hydrocarbon generation theory and retained hydrocarbon occurrences.

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Diagenetic Facies Characteristics of Chang 6₃ Reservoir in Huaqing Oilfield, Ordos Basin

LI Pan, SUN Wei, LI Changzheng

2018, 39 (zk(English) ): 82-88.

摘要 ( 50 )

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Exploration and development of Chang 6₃ reservoir of Yanchang formation in Huaqing oilfield, Ordos Basin, has been challenged by strong heterogeneity and complicated microscopic pore structures. Based on the data of cast thin section, SEM, high-pressure mercury injection and constant-rate mercury injection experiments, the paper studies different diagenetic facies and the pore structures of Chang 6₃ reservoir in Huaqing oilfield. Moreover, logging responses of different diagenetic facies are summarized by combining with production test data. The results show that the throats of the reservoirs of chlorite cementation-intergranular pore facies and illite + chlorite cementation-intergranular pore facies are best developed; the pore throat radius of the reservoirs of illite cementation-intergranular pore facies and illite + chlorite cementation-corrosion facies are relatively small and the reservoir connectivity is poor to medium; the pore structures of tight reservoirs of illite cementation-corrosion facies, illite cementation facies and carbonate cementation facies are poorly developed. Different diagenetic facies have different microscopic pore structure characteristics. Throat radius is the major factor influencing reservoir flowing and storage capacity. The distribution of high-quality diagenetic facies is influenced by sedimentary facies, diagenesis and microscopic pore throat characteristics.

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Channel Architecture Element and Its Controls on Hydrocarbon Accumulation: A Case Study from Chang-8 Member in Huaqing Area, Ordos Basin

XIAO Zhenglu, CHEN Shijia, LIAO Jianbo, LI Yong, WANG Pan, DING Zhengang

2018, 39 (zk(English) ): 89-94.

摘要 ( 60 )

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The oil-water differential accumulation in the Chang-8 member in Huaqing area of the Ordos Basin is the primary problem that has constrained the further development and deployment of the oilfield for a long time. The sand bodies in the underwater distributary channel are the dominant oil reservoirs in Huaqing area, and the fine description for the underwater distributary channel is conducive to solving the complex problems on oil and water accumulation. Based on the concepts and knowledge of channel architecture, the paper selected the typical rock samples of river main body and flanks of the Chang-8 member in Huaqing area, and performed microscopic identification and statistical analysis on lithology and microcapillary mercury injection data. The results reveal the physical properties and pore structures of the main channel sand bodies are far better than those of channel flanks; under the same conditions the main channel sand bodies are more favorable for crude oil charging, channel flanks make reservoir’s heterogeneity strengthened, which influences the differential distribution of oil and water. Based on the establishment of sand body profile and reservoir model, the composite channel sand bodies can be classified into 4 types. The thickness of the main channel sand body is an important index to determine the scale of a reservoir, and the size of the sand body determines the migration and accumulation of crude oil. Limited crude oil migrated along the large-scale channel sand bodies and accumulated at pinchouts or the higher positions of structures.

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Comparison Between Two Types of Slope-Break Belts in Pearl River Mouth Basin

ZHANG Shangfeng, CAO Yuanting, ZHANG Changmin, SHI Hesheng, WANG Yaning, YIN Yanshu, ZHU Rui

2018, 39 (zk(English) ): 95-102.

摘要 ( 57 )

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Slope-break belt is the basis of sequence stratigraphic classification and correlation, stratigraphic architectural analysis and sequence model establishment. A lot of researches have been done on different types of slope-breaks, however, most of them focused on the analysis of a single slope-break belt. The stratigraphic sequence analysis of the Pearl River Mouth Basin in the northern South China Sea shows that there are double slope-breaks since the Neogene in the basin, that is, the sedimentary slope-break belt of the continental shelf and the geomorphic slope-break belt of the shelf edge exist simultaneously, and the controls of different slope-break belts on sedimentary sequence are various. Based on the comparison between the two types of slope-break belts from the aspects of formation background, development and evolution, topography and geomorphology characteristics, and sedimentary systems, it is believed that the formation of the geomorphic slope-break belt is closely related to the tectonic action, as a result, three types of stratigraphic sequences are formed including four partitioned, three partitioned and two partitioned system tracts, respectively. The formation of sedimentary slopes is obviously controlled by paleogeomorphology, sediment supply process and unbalance unloading, and the last two types of stratigraphic sequences are dominant.

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Rock Mechanical Characteristics and Fracture Propagation Mechanism of Sandy Conglomerate Reservoirs in Baikouquan Formation of Mahu Sag

LIU Xiangjun, XIONG Jian, LIANG Lixi, YOU Xincai

2018, 39 (zk(English) ): 103-110.

摘要 ( 161 )

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Taking the rock of the sandy conglomerate reservoirs of Baikouquan formation in Mahu sag as the study objects, the mechanical characteristics and fracture propagation mechanism of the sandy conglomerate reservoirs with different lithologies are studied through various rock mechanical experiments. Based on which, a 2D model containing true gravels is established by using numerical modeling method, the dynamic process of fracture propagation in the sandy conglomerate are investigated, and the influence of gravel strength on fracture propagation mechanism is discussed. The results indicate that the sandy conglomerate are seriously heterogeneous, resulting in the obvious differences of mechanical characteristics in sandy conglomerates with different lithologies, among which the mechanical strength of fine conglomerate is higher than that of coarse conglomerate; the differences between gravel and matrix compositions have significant influence on rock mechanical characteristics of the sandy conglomerate; the failure mode of the sandy conglomerate is dominated by splitting failure in uniaxial compression and by splitting failure, single shear failure and dual shear failure etc. in triaxial compression; gravel particles have shielding effect on the extension of fractures and the fracture propagation during rock failure process in the sandy conglomerate mainly contains 3 types such as going-through gravel, bypassing gravel and embedded in gravel. The strength of gravels and the matrix reflects the mechanical properties of glutenite. The larger the strength difference between gravel and matrix is, the stronger the shielding effect of the gravels is, the stronger the received resistance of fracture will be, causing that the fracture propagation would transfer from going-through gravel to bypassing gravel.

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Identification of Thin Interlayer and Potential Tapping of Residual Oil in Channel Sand Bodies

JIANG Zhenhai

2018, 39 (zk(English) ): 111-115.

摘要 ( 65 )

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Inefficient or invalid circulation of the injected water occur in partial high-permeable zones within channel sand bodies after long-term waterflood development in reservoirs, and remaining oil accumulates near interlayers. It is still difficult to identify thin interlayer in channel sand bodies, which goes against the remaining oil potential tapping. Taking the western area of District Beier of Daqing placanticline oilfield as an example and using the data obtained from sealed coring wells with small well spacings, the paper carries out fine description of thin interlayer within channel sand bodies, classifies and evaluates the logging response characteristics of the interlayer and determines its controls on residual oil distribution. The study results show that the interlayers in the study area can be divided into lithological interlayer and physical-property interlayer, both of which are dominated by mudstone and siltstone, mainly distributed at the top of the sedimentary cycle vertically and mainly located in the sedimentary facies transformation zones in the plane. The remaining oil concentrates in the vicinity of the interlayers. Based on the identification results of the thin interlayers and according to the characteristics of the residual oil distributed in different channel sand bodies, different methods are adopted to realize the adjustment of potential tapping in thick sand layers, and the effects of increasing oil production and decreasing water production are significant, which can be the references for the secondary development in similar blocks.

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Phase Behavior and Rheological Properties of Emulsions Based on Janus SiO₂/PS Nano-Particles

CHEN Xi, MA Desheng, TIAN Maozhang, SONG Xinmin, WU Chaodong, HAN Lu, LIANG Fuxin

2018, 39 (zk(English) ): 116-123.

摘要 ( 74 )

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Regarding microstate and rheological property, the paper studies the phase behaviors of the emulsions formed by the crude oil obtained from 81# combination station of Karamay oilfield and the aqueous dispersion system of Janus SiO₂/PS nano-particles under the conditions of different mass fraction (C_S) and different water-oil volume ratio (R_WO). Setting C_S=0.100%, when R_WO≤7/3, stable water-in-oil emulsion is formed by the aqueous dispersion system of Janus SiO₂/PS nano-particles and the crude oil, and both the droplet size and viscosity of the emulsion increase with the rise of the water-oil volume ratio; when R_WO>7/3, the oil-water miscible liquid has 2 phases—the upper is water-in-oil emulsion and the lower is dominated by water, the viscosity of the emulsion decreases with the increase of the water-oil volume ratio. Setting R_WO=7/3, when 0.080%≤C_S≤0.300%, oil and water are mixed completely, with the emulsion viscosity 60 times more than the crude oil viscosity, and the mixture becomes thinning at high shearing rate; when C_S<0.080% or C_S>0.300%, the oil-water miscible liquid has 2 phases and the emulsion viscosity decreases with the increase of the volume of separated water. Setting R_WO=4/6, when 0.001%≤C_S≤0.500%, oil and water are mixed completely, with the emulsion viscosity of 55-75 mPa·s, and the emulsion becomes thickening at the shearing rate of 3.00-70.00 s^-1. The results show that the aqueous dispersion system of Janus SiO₂/PS nano-particles allows the crude oil to form stable, high-viscosity water-in-oil emulsion at relatively high water cut, and within a certain range of water-oil volume ratio, the higher the water cut, the higher the viscosity of the emulsion. The conclusion can provide a new idea for improving sweep efficiency in heterogeneous reservoirs.

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Architecture Analysis and Remaining Oil Distribution in Mouth Bar: A Case Study of the First Member of Xishanyao Formation in Wellblock Cai-10 and Caican-2, Cainan Oilfield

YIN Senlin, ZHANG Tong, WAN Wensheng, WU Chengmei, LI Chen, FENG Wenjie

2018, 39 (zk(English) ): 124-133.

摘要 ( 60 )

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To study the inner architecture and remaining oil distribution in the mouth bar of meandering river delta, based on the production performance and core data in the Wellblock Cai-10 and Caican-2 of Cainan oilfield, the paper performs detailed analysis on the mouth bar architecture by using the methods of analytical hierarchy process, multi-dimensional interaction and dynamic verification, and establishes mouth bar architecture models for the meandering river delta in the study area. The study shows that there are 2 categories of marks to identify mouth bar boundary, namely vertical superposition of the units of different periods and lateral merging of the units of same periods, among which the latter structure can be classified into 3 types such as main body-main body of the mouth bar, main body-bar margin-main body and main body-between-bar mud. There are 2 mouth bar architecture models such as progradation and accretion. The progradational architecture model mainly refers to the structures in which the sediments of late stage accreted and superposed onto the mouth bars of early stage when the distributary channel was under the circumstance of stable hydrodynamic force, and the lateral accretional architecture model mainly refers to the mouth bars which are developed at the margin of breached distributary channel when the hydrodynamic force became stronger. In the study area, there are 129 single mouth bars and 12-24 mouth bars that are developed in the single layers. The single mouth bars are about 500 m long and 450 m wide. The dip angle of accretional architecture mouth bar is 0.31°-2.40°, which decreases from bottom to top. The remaining oil distribution can be divided into 4 patterns, namely retention, one-way effect, poor water injection effect and planar interference patterns. Various development programs and measures can be adopted to enhance oil recovery.

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Main Controlling Factors on Liquid Productivity Index for Polymer Flooding in Offshore Multi-Layered Heavy Oil Reservoirs

WEI Zhijie, KANG Xiaodong, HE Chunbai, ZHANG Jian, SHENG Han

2018, 39 (zk(English) ): 134-140.

摘要 ( 51 )

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To address the apparent decline of liquid productivity index during polymer flooding in some offshore heavy producers, a sophisticated mathematical model to predict productivity behavior in multilayered reservoirs is established, then the main controlling factors on the variations of liquid productivity index of polymer flooding are studied. The results show that the productivity index after conversion into polymer flooding undergoes 4 phases — rise, decline, stabilization and rise again; the largest drop of the dimensionless liquid productivity index is significantly influenced by polymer viscosity, polymer injection timing and permeability ratio, and the trough timing is highly impacted by crude oil viscosity, permeability ratio, relative thickness of low-permeability zone and absorption capacity. Based on which formulas to calculate the largest drop of dimensionless liquid productivity index and trough timing are proposed. Under the typical polymer flooding conditions in offshore oilfields, the average largest drop of liquid productivity index is 53.1%, and the average cumulative injection pore volume corresponding to the trough timing is 0.250 PV. The research results are of guiding significance for the liquid productivity index prediction, program design and adjustment for polymer flooding.

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Application of NMR Technology in Evaluation of Low-Permeability Conglomerate Reservoirs: A Case Study from the Lower Triassic Baikouquan Formation in Mahu Sag

MAO Rui, XU Lin, FANG Tao, WANG Zhenlin

2018, 39 (zk(English) ): 141-145.

摘要 ( 52 )

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The low-permeability conglomerate reservoir in the Lower Triassic Baikouquan formation of Mahu sag, Junggar Basin is characterized by complex reservoir lithology, complicated clay minerals and serious heterogeneity, so it is difficult to accurately characterize the effective porosity of the conglomerate reservoir with current logging methods. Considering that the clay mineral content is the controlling factor of reservoir physical properties, the paper uses the difference between CNL logging porosity and NMR logging porosity and clay mineral content obtained from core analysis to establish a clay mineral content characterization model; then uses clay bound water porosity and clay mineral content obtained from core analysis to establish a clay bound water porosity characterization model, based on which the effective porosity can be obtained by NMR logging porosity minus clay bound water porosity. The actual application of the method in 19 exploration wells in the study area shows that the relative error of effective porosity is only 6.8%, indicating that good effect has been gained by using the method, which could provide a new technological means for effective porosity evaluation with NMR logging data.

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Analytic Model of Oil-Based Drilling Fluid Density and Wellbore Liquid Column Pressure in Deep Wells

YANG Hu

2018, 39 (zk(English) ): 146-150.

摘要 ( 51 )

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During the drilling and completion in high-temperature and high-pressure deep wells, there are differences between the measured drilling fluid density on the ground and actual drilling fluid density in wellbore because the drilling fluid is affected by both temperature and pressure, which will lead to the difficulties in accurate calculation of the drilling fluid pressure in the wellbore. Based on the investigation on the prediction models of oil-based drilling fluid density at home and abroad, it is considered that all the previous models are not general and the calculation accuracy can’t meet the demands of deep wells, especially ultra-deep wells because they are empirical models using a few experimental data under the condition of specific formulas. Therefore, the paper uses a mathematical analytical method to establish a precise model to predict drilling fluid density and drilling liquid column pressure. Compared with the empirical models of many scholars, it is concluded that most empirical models are the simplified forms of the newly-established analytical model which can reflect the influences of temperature and pressure on drilling fluid density more fully and accurately. In the actual application, regarding the oil-based drilling fluid as the mixture of base oil, salt water and solid material, the prediction for oil-based drilling fluid density and wellbore liquid column pressure with different formula and oil-water ratio can be performed.

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Tectonic Setting and Environment of Alkaline Lacustrine Source Rocks in the Lower Permian Fengcheng Formation of Mahu Sag

ZHANG Yuanyuan, LI Wei, TANG Wenbin

2018, 39 (zk(English) ): 151-156.

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Mahu sag is one of the most prolific oil-gas sags in the Junggar Basin. The high-quality lacustrine source rocks in the Lower Permian Fengcheng formation are considered as the oldest alkaline lacustrine deposits in China, which provides the resource foundation for the formation of hundred-mile oil province in northwestern margin of Junggar Basin. Based on the investigations of regional geology, sedimentology, mineralogy and petrology, Fengcheng formation is inferred to be developed in the post-orogenic extensional fault depression which is found on the Paleozoic basement in the western Junggar Basin. The formation is overall a set of fan delta-lacustrine deposits with the depocenter in the center of Mahu sag. Abundant alkaline minerals are observed in the Fengcheng formation, including reedmergnerite, northupite, shortite, searlesite, eitelite, wegscheiderite and nahcolite etc., which indicates a representative alkaline lacustrine facies with high salinity, distinct from other common saline-lacustrine deposits. The presence of shortite, wegscheiderite, reedmergnerite and searlesite confirms that the alkaline lacustrine source rocks of the Fengcheng formation were deposited in a closed and high-salinity lacustrine environment highly effected by deep hydrothermal fluids, not due to evaporation, which is also strongly associated with volcanic activities under the extensional fault depression setting.

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