Lithologic Reservoirs

The Erlian Basin is a group of small Meso-Cenozoic rift basin,which act as an important oil production zone. During its early stage,structural reservoirs were taken as the main objects. With the deepening of exploration, it is more difficult to find them,and the output of oil production declines rapidly. Therefore,it is urgent to search new fields of hydrocarbon exploration for reserve replacement. The hydrocarbon accumulation conditions of the Erlian Basin were understood again. It is characterized by small lake basins,multiple sources,rapid deposition and abrupt change of facies belt,which are favorable for the formation of stratigraphic-lithologic reservoirs. Therefore,a new exploration thought was proposed to change the exploration focus from structural reservoirs to stratigraphic-lithologic reservoirs. Based on exploration practice,the exploration method for the stratigraphic-lithologic reservoirs was developed:“evaluating resource to determine potential,studying structure to figure out the settings,analyzing sedimentation to search for sandbodies,comprehensive research to build the model,rolling evaluation to determine the scale”. By virtue of this method,hydrocarbon exploration is newly broken through in some sags where new oilfield has not been discovered for over 20 years,such as Bayindulan Sag. Meantime,in A'er Sag newly discovered,A'er oilfield with a hundred million reserves was discovered efficiently and quickly by focusing on stratigraphic-lithologic reservoirs according to the successful exploration experience of oil-rich sags. The success of stratigraphic-lithologic reservoirs exploration in the Erlian Basin launches the new hydrocarbon exploration fields in this basin,and can be used as the important reference for the hydrocarbon exploration in similar basins.

Fine sedimentology of Hong 10 block in Honghaoershute Sag,Erlian Basin

ZHU Xiaomin, DONG Yanlei, ZHANG Mingjun, PAN Rong, LIANG Guanzhong, ZHANG Jiuqiang

2017, Vol.29(2): 10–18 Abstract ( 346 ) PDF (28487 KB) ( 202 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.002

In order to demonstrate the distribution of sedimentary sandbodies and guide fine hydrocarbon exploration in key areas in Honghaoershute Sag,Erlian Basin,under the guidance of the theories of sequence stratigraphy and sediemntology,based on the seismic reflection termination,lithology,sedimentary structure and well log facies,the Cretaceous A'ershan Formation was divided into one third-order sequence including lowstand systems tract(LST),transgressive systems tract(TST)and highstand systems tract(HST)in Honghaoershute Sag. The oil producing interval of HST could be divided into three parasequence sets(sand groups)and ten parasequences(sublayers),and nearshore subaqueous fan and braided delta are developed. The nearshore subaqueous fans are characterized by coarse sandy conglomerate with massive and grading beddings,scour,and interbeded with dark mudstone;while the braided deltas developed sandstone with middle-large wedge-shaped cross bedding, scour surface and discontinuous rhythm. The nearshore subaqueous fan and braided delta will prograde toward central lake or retrograde toward parent rock region following the lake level up or down. Large sandbodies are developed in sand group Ⅱ of A'ershan Formation because of sufficient source supply,therefore,sand group Ⅱ can be taken as key strata for further exploration in Hong 10 block of Honghaoershute Sag.

Distribution characteristics and main controlling factors of stratigraphic lithologic reservoirs in Jizhong Depression

JIN Fengming, CUI Zhouqi, WANG Quan, LI Li, REN Chunling, CUI Mingyang, XIAO Wei

2017, Vol.29(2): 19–27 Abstract ( 306 ) PDF (2611 KB) ( 468 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.003

In order to understand the distribution law and controlling factors of stratigraphic-lithologic reservoirs in sags of Jizhong Depression,these sags were divided into three types(inherited type,migratory type and early prevailing type)according to their unique geological structures and sedimentary characteristics. It shows that the prospects of stratigraphic-lithologic reservoirs are the best in inherited sags with the largest exploration area,are medium in migratory sags,and are relatively poor in early prevailing sags with disadvantage hydrocarbon accumulation conditions. Various plays of stratigraphic-lithologic reservoirs formed by virtue of configuration between sedimentary systems and structural settings,and distributed in different zones,such as gentle slope belt, steep slope belt and trough belt. It is indicated that the zones of stratigraphic overlap denudation belt,lithofacies transition belt and lake strandline change belt are favorable for the formation of various lithologic or stratigraphic traps,and the changes of lithology,physical properties and contact relationships of sandstone reservoirs provide the favorable conditions for the development of lithologic-tratigraphic traps. The enrichment of“sweet spot”of stratigraphic-lithologic reservoirs in groups and belts is controlled by favorable lithofacies belts and favorable diagenetic facies belts. The areas near the“five belts”(lake strandline change belt,lithofacies transition belt,stratigraphic overlap denudation belt,favorable lithofacies belt and favorable diagenetic facies belt)are the important targets for deepening the exploration of stratigraphic-lithologic reservoirs.

Source kitchen and organic facies of source rocks in Sahantala Sag, Erlian Basin

ZHAO Zhigang, WANG Feiyu, WANG Hongbo, WANG Mingwei, WANG Hao, LAN Baofeng

2017, Vol.29(2): 28–35 Abstract ( 329 ) PDF (3573 KB) ( 396 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.004

The study of organic facies of source rocks can contribute to characterize the source kitchen in the hydrocarbon exploration and development. In order to assess the prospects of Saihantala Sag,Erlian Basin,the Rock-Eval data were used to classify the organic facies of source rocks and realize the evaluation of source rocks. The parameters of alkanes,biomarker and vitrinite reflectance were used to determine the organic matter maturity of hydrocarbon source rocks,and the quantitative characterization of source kitchen was realized. The results show that the Lower Cretaceous source rocks mainly developed in the A'ershan Formation(K1ba),the first member(K1 bt1)and second member(K1 bt2)of Tenggeer Formation in Saihantala Sag. The source rocks in the K1 ba are mainly organic facies F,and the source rocks in K1 bt1 and K1 bt2 are mainly organic facies D/E,with a little organic facies C. The vertical distribution of source rocks shows the characteristics of organic facies F,D/E and F from bottom to top. The source rocks in the K1 bt1 is the main source rocks,and the hydrocarbon expulsion intensity ranges from 5×106 t/km2 to 35×106 t/km2,followed by K1ba source rocks,and the hydrocarbon expulsion intensity is(2-8)×106 t/km2.

The oil families and their geochemical characteristics in Sanhantala Sag,Erlian Basin

WANG Hao, WANG Feiyu, JIANG Shuanqi, WU Zhong, XING Yawen, LAN Baofeng

2017, Vol.29(2): 36–43 Abstract ( 345 ) PDF (2372 KB) ( 385 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.005

The Saihantala Sag is the one of hydrocarbon rich sags in Erlian Basin. The physical properties and geochemisty data of oil samples were analyzed to identify the feature and generation of oil in Saihantala Sag. The physical property data of oil show that the crude oil samples are in low-moderate maturity stage with low viscosity, low sulfur content and API in a range of 28°-39°. New geochemical data have been gathered from crude oil samples, and denote that the crude oil derived from source rocks with similar depositional environment and expelled hydrocarbon in different mature stages. Several variables including ratios of gammacerane/C30 hopane, C30*/ C29 Ts, Pr/Ph,diasteranes/regular steranes, and sterane isomerization parameters, were selected to carry out cluster analysis,and the crude oil in Sanhantala Sag can be divided into two oil families. Oil-family I mainly distributes in Lower Cretaceous K1 ba, K1 bt1 and expelled from source rocks in the late phase of oil window; Oil-family Ⅱ is mainly from K1 bt2 and derived from source rocks in the early phase of oil window. The data of crude oil suggest that the exploration zone should be aimed at the reservoirs of the K1 ba and K1 bt1.

Structural characteristics of the boundary fault and its control on hydrocarbon accumulation in Saihantala Sag, Erlian Basin

XIAO Yang, ZHANG Shaohua, WEI Yan, YANG Minghui, CHEN Yuting, PAN Juan

2017, Vol.29(2): 44–50 Abstract ( 410 ) PDF (1701 KB) ( 386 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.006

Xilin fault is the boundary fault of Saihantala Sag,which controls origin,evolution and hydrocarbon accumulation of Saihantala Sag. Based on seismic and well data,the structural characteristics of Xilin fault were analyzed, and its control on hydrocarbon accumulation was discussed. The results show that the Xilin fault is a listric fault in profile and it consists of three segments. The southern and northern segments are low dip,while the central segment is steepened. The mean active rate indicates that Xilin fault had a strong activity during the sedimentary period of A'ershan Formation and Tengge'er Formation. The evolution of Xilin fault controls the reservoir accumulation,which can be proven by:(1)Xilin fault played an important role on the formation of hydro carbon generating depression and the accumulation of high-quality source rocks,and it also promoted the maturity of source rocks;(2)the evolution of Xilin fault has a great influence on palaeogeomorphology and the distribution of sand bodies,which dominated the formation of varied traps;(3)faults,sand bodies and unconformity surfaces constituted the hydrocarbon drainage system together. Therefore,the traps controlled by Xilin fault around the source depression are favorable for hydrocarbon accumulation.

Characteristics of deep sandstone reservoirs and lithologic reservoir exploration of Paleogene in Baxian Sag

CUI Zhouqi, LI Li, WANG Hongxia, WANG Yuanjie, GUO Liuxi, HOU Fengmei

2017, Vol.29(2): 51–58 Abstract ( 375 ) PDF (25964 KB) ( 185 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.007

Baxian Sag is one of the main oil-rich sags in Jizhong Depression. The multi phase Paleogene sandstone of fan delta and braided delta superimposed in succession in deep zones(> 3 500 m). The composition and texture of sandstone are high mature,and the reservoir physical properties are relatively good,which provides better reservoir conditions for deep hydrocarbon accumulation. In order to understand the distribution characteristics of deep reservoirs and their controlling factors,the study was carried out by the conventional evaluation methods, oil occurrence method and porosity-permeability crossplot method,combined with the data of drilling,logging and mud logging. The effective sandstone reservoirs are controlled by five factors,such as parent rock type,sedimentary facies belt,diagenetic facies belt,undercompaction and early hydrocarbon charging. The Paleogene deep reservoirs in Baxian Sag have geological features such as the abundant-feldsparparent rock, the braided/fan delta front,the strong dissolution-weak cementation diagenetic facies belt,the abnormal pressure belt and early hydrocarbon charging. They are favorable for effective reservoirs at least at depth of 5 500 m. The deep exploration of Paleogene lithologic reservoirs is prospective in Baxian Sag.

Depositional system of shallow-water meandering river delta:a case from the first member of Shahejie Formation in Zhaohuangzhuang-Suning area of Raoyang Sag, Jizhong Depression

ZHU Mao, ZHU Xiaomin, ZENG Hongliu, DONG Yanlei, LIU Chang, ZHENG Ronghua

2017, Vol.29(2): 59–67 Abstract ( 360 ) PDF (12413 KB) ( 321 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.008

The first member of Shahejie Formation(Es1)is one of the main oil-bearing series in Raoyang Sag, Jizhong Depression. In order to define the reservoir distribution and exploration prospects,The sedimentary system of Es1 in Zhaohuangzhuang-Suning area of Raoyang Sag were studied based on the data of cores,logging and seismic. The results show that shallow-water meandering river delta is widely developed during the Es1 depositional stage,which is characterized by small lake basin,shallow water,low water energy and frequent migration of lake strandline. Periodic oscillation of lake level resulted in the interbeds of sandstone and mudstone,and the alternation of red and black mudstones. The sheeted net-shaped subaqueous distributary channel is well developed in the shallow-water meandering river delta. The distributary channel sandbodies are widely distributed and vertically superimposed. These features are favorable for reservoir space.

Lithofacies and reservoir space characteristics of the tuffaceoussiliciclastic mixed rocks of the Lower Cretaceous Tenggeer Formation in Anan Sag, Erlian Basin

WEIWei, ZHU Xiaomin, ZHU Shifa, HE Mingwei, WU Jianping, WANG Mingwei

2017, Vol.29(2): 68–76 Abstract ( 337 ) PDF (56460 KB) ( 168 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.009

The Lower Cretaceous Tenggeer Formation developed a set of lacustrine tight oil tuffaceous-siliciclastic mixed rocks in Anan Sag of Erlian Basin, which has become an important exploration target. Based on the data of core observation, thin section, scanning electron microscope, and X-ray diffraction, the lithologies, lithofacies and reservoir spaces of the mixed rocks were studied. This set of mixed rocks are mainly grey-green to grey tuffaceous rocks, including tuff, tuffite, tuffaceous sandstone and tuffaceous mudstone. The tuffite and tuffaceous mudstone are widely developed. There are six types of lithofacies:massive tuff, massive tuffite, deformed tuffite, massive tuffaceous sandstone, wavy-bedding tuffaceous sandstone, massive tuffaceous mudstone and horizonalbedding tuffaceous mudstone. The massive tuff lithofacies is characterized by middle to low porosity and ultralow permeability reservoir. It is the best reservoir in the mixed rocks,and its main reservoir space is devitrified pores. The deformed tuffite lithofacies is chaterized by extremely low porosity and low to ultra-low permeability reservoir, with good reservoir properties and the main reservoir space of dissolved pores and marix pores. The massive tuffite lithofacies, massive tuffaceous sandstone lithofacies and wavy-bedding tuffaceous sandstone lithofacies are characterized by extremely low porosity and ultra-low permeability reservoir. It is poor reservoir, and its main reservoir spaces are crystal fragments dissolved pores and crystal intergranular pores.

Tight reservoir characteristics and diagenesis of A'ershan Formation in Erennao'er Sag, Erlian Basin

HE Mingwei, ZHU Xiaomin, ZHU Shifa, WEIWei, WU Jianping, WANG Mingwei

2017, Vol.29(2): 77–86 Abstract ( 332 ) PDF (47687 KB) ( 185 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.010

The Lower Cretaceous reservoirs are characterized by tight and complex types of rocks and good oil shows in the sags of Erlian Basin. Based on the data of cores,thin sections,cathodeluminescence,X-ray diffraction and scanning electron microscope,the tight reservoir characteristics and diagenesis of the Lower Cretaceous A'ershan Formation in Erennao'er Sag were studied. The results show that the reservoirs are composed of dolomitic(calcareous)mudstone,dolomitic(calcareous)tuffite,dolomitic(calcareous)siltstone and calcareous sandstone. The reservoir properties are poor,with the average porosity and permeability of 7.44% and 1.11 mD, respectively. The dolomitic(calcareous)mudstone and dolomitic(calcareous)tuffite are mainly developed in semi-deep lacustrine and shore-shallow lacustrine,and the pore types are mainly intercrystal pores and fractures.Dolomitic(calcareous)siltstone and calcareous sandstone are mainly developed in sheet sand and subaqueous distributary channel in fan delta,and the reservoir spaces are mainly intergranular pores,intragranular pores and cracks. The tight reservoir properties are mainly controlled by diagenesis and sedimentation. Although compaction leads to the decrease of original pores,and calcareous and dolomitic cementation make reservoir properties significantly deteriorated,dissolution improves the reservoir properties.

Characteristics of dolomitic reservoirs of A'ershan Formation in Bayindulan Sag,Erlian Basin

SUN Shuyang, ZHU Xiaomin, WEI Wei, ZHU Shifa, HE Mingwei, LIU Wei, WU Jianping

2017, Vol.29(2): 87–98 Abstract ( 318 ) PDF (18315 KB) ( 146 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.011

A set of dolomitic reservoir developed in the Lower cretaceous A'ershan Formation of Bayindulan Sag,Erlian Basin. Based on the data of cores,cast thin sections,petrography,cathodoluminescence,SEM and Xray diffraction,the lithologies,reservoir spaces types,physical properties and diagenesis of the dolomitic reservoirs were studied. The result shows that the dolomitic reservoirs of A'ershan Formation can be divided into two types in lithology:dolomitic sandstone and dolomitic mudstone,and these two types of lithology can be divided into more types according to the occurrence of dolomite or ankerite. The dolomitic mudstone developed dissolved pores,fractures and intracrystalline pores. The porosity of dolomitic mudstone is 4.4%-36.4%,with an average of 16.01%,and the permeability is 0.01-26.30mD,with an average of 1.92 mD. The main reservoir spaces developed in dolomitic sandstone are dissolved pores. The porosity of dolomitic sandstone is 1.1%-33.7%,with an average of 16.07%,and the permeability is 0.01-5 163.00 mD,with an average of 79.72 mD. Replacement and dissolution are the main diagenesis types developed in dolomitic mudstone,and the diagenesis sequence is the formation of dolomite and ankerite→organic acid generation→dolomite dissolution. The main diagenesis types of dolomitic sandstone include dissolution,cementation and replacement, and the diagenesis sequence is:slight compaction→ quartz secondary overgrowth→cementation of dolomite and ankerite→organic acid generation→dissolution of dolomite,ankerite and feldspar.

Sequence stratigraphic framework and lithologic reservoir potential in Jabung block

TIAN Xin, WANG Xuben, GUO Weihua, LYU Ximin, LI Guobin, WANG Ronghua

2017, Vol.29(2): 99–106 Abstract ( 317 ) PDF (2585 KB) ( 315 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.012

Jabung block is located in South Sumatra Basin,Indonesian,in which structural reservoir exploration has been basically completed,and many lithologic reservoirs have been found,with lack of integral research and understanding. In order to tap the potential and define the next replace exploration area,under the guidance of theories of sequence stratigraphy and reservoir seismic stratigraphy,the geology,logging and seismic data were applied to identify third-order sequence boundary in Jabung block,and the sequence stratigrapgic frameworks of the Paleogene and Neogene were established. According to the theory that sequence stratigraphic framework controls hydrocarbon accumulation and migration,the relationship between sequence stratigraphic characteristics and hydrocarbon accumulation of lithologic reservoirs was studied. The results show that the strata can be classified as SQ1-SQ7 seven third-order sequences,and the sequence evolution controls the pattern of source reservoir cap assemblage and development position of lithologic reservoirs. SQ1 controls the distribution of main source rocks(developed in the rifting period). SQ2 and SQ3(developed in the conversion period from rifting to depression) control the development of nearshore subaqueous fan. SQ4(early depression)developed shallow marine limestone reservoir. SQ5 mostly developed shallow marine sedimentary facies. SQ6 and SQ7 mainly developed river-delta facies. Four favorable exploration areas for lithologic reservoirs were identified,guiding the exploration prospect for further lithologic reservoir exploration in Jabung block.

Source rocks and geochemical characteristics of crude oil of the Yanchang Formation in Xunyi exploration area,Ordos Basin

TANG Jianyun, WANG Zhiwei, YE'ERHANATI Heizhati, ZHU Jianbing, CHEN Yubao

2017, Vol.29(2): 107–116 Abstract ( 354 ) PDF (1708 KB) ( 312 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.013

There is controversy about effective source rocks of Triassic Yanchang Formation and oil source of Triassic Yanchang reservoir in Xunyi area,Ordos Basin. To clarify the problem,organic petrology and geochemical analysis were used to analyze the samples of source rocks and oil-gas samples. The results show that the type of kerogen of Chang 7 source rock is mainly type Ⅰand Ⅱ,followed by type Ⅲ,the maturity of organic matter is medium,so it is good source rock. Based on the characteristics of light hydrocarbon,carbon isotope,saturated hydrocarbon gas chromatography and the characteristics of biomarker,it is considered that the oil of Chang 6 and Chang 8 have the similar sedimentary environment and maturity with Chang 7 source rock,they all are mid-mature oil,with fresh water and weak redox environment,and the parent material is with hybrid source based on algae. The Chang 7 source rock has certain contribution for the formation of Chang 6 and Chang 8 reservoirs in Xunyi exploration area.

Formation mechanism of deep high-quality reservoirs of Yingcheng Formation in Longfengshan area,Songliao Basin

LIU Xixiang, ZHANG Shaonan, YANG Peng, ZHANG Yongmei, HE Hao

2017, Vol.29(2): 117–124 Abstract ( 318 ) PDF (22208 KB) ( 252 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.014

With the new exploration development of Longfengshan area in Changling graben,it is proved that the Yingcheng Formation with burial deeper than 3 000 m has favorable gas exploration potential. Although commercial oil and gas flow was produced in several wells,the formation mechanism and controlling factors for high-quality reservoirs remained undefined. Based on the data of core observation,casting thin sections,computed tomography(CT)scanning,physical properties testing and constant-rate mercury penetration,the formation mechanism and controlling factors for high-quality reservoirs were analyzed. The results show that the reservoir property in the study area is mainly controlled by diagenesis. According to this,the reservoirs were divided into compacted tight sandstone,chlorite-cemented sandstone and laumontite-cemented sandstone. The distribution of cementation and dissolution shows the characteristics of obvious zonation under the control of fresh water filling and lake water. The distribution model of various types of sandstones was established. During the middle diagenetic stage,the laumontite was dissolved by organic acids produced by source rock,and formed high-quality reservoirs in outer skirt of the fan delta front,which is the “sweet point” for the further hydrocarbon exploration.

A new approach to the characterization of shale pore structure

SUN Wenfeng, LIWei, DONG Zhiyi, YAN Tie, LI Yue, LI Shichang

2017, Vol.29(2): 125–130 Abstract ( 337 ) PDF (1740 KB) ( 774 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.015

The pore structure is the core content of shale reservoir evaluation,which has important influence on the reservoir performance,seepage capacity and shale gas productivity. In order to show the spatial characteristics of pore structure in shale reservoir comprehensively and visually,MATLAB programming was used to identify scanning electronic microscope(SEM)binary image of samples from Longmaxi shale in southern Sichuan Basin,by which different pore area and corresponding plane porosity were obtained,and the plane porosity function was fitted. Then,the conversion model between the 2D porosity function and the porosity function was established by applying the integral geometry theory. The function relationship between the porosity and the pore size was calculated and the shale pore structure of the Longmaxi Formation was analyzed quantitatively. The results show that the pore size ranges from 1 to 50 nm,13 nm corresponds to the MAX porosity,the volume fraction of mesopores is the most(93.7%). Compared with the results of high pressure mercury intrusion and low temperature nitrogen adsorption experiments,the result obtained by SEM image method is reliable,which verifies the feasibility of this method. The method is applicable for shale and tight reservoirs.

Logging identification and evaluation of tight sandstone gas in the southern Yanchuan block

CHU Cuijin, XIA Zhilin, YANG Zhiqiang

2017, Vol.29(2): 131–138 Abstract ( 293 ) PDF (2748 KB) ( 430 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.016

The tight sandstone gas reservoir has the characteristics of low porosity and low permeability,complex pore structure and strong heterogeneity,which makes the reservoir evaluation difficult. The conventional methods based on volume model in medium-high porosity and permeability reservoir is not suitable for this kind of reservoir due to much more contribution of sandstone framework to logging. Two methods of gas-bearing identification were optimized based on conventional loggings: apparent elastic modulus coefficient method and three porosity ratio method. The combination of the two methods can effectively identify gas layers. According to reservoir characteristics and relationship analysis of rock electricity and response, the porosity,permeability and saturation of tight sandstone reservoir were calculated by using neutron-density weighted average,median grain size linear regression and parameter variable Archie's equation methods,completing the high precision quantitative evaluation of tight sandstone gas reservoir in the southern Yanchuan block. These methods are also applicable to evaluate tight sandstone gas reservoir in other area.

Quantitative identification of coal structure based on coal rock brittleness index by logging data

AI Lin, ZHOU Mingshun, ZHANG Jie, LIANG Xiao, QIAN Bowen, LIU Diren

2017, Vol.29(2): 139–144 Abstract ( 320 ) PDF (3227 KB) ( 601 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.017

An accurate identification of coal structure is one of key issues in coalbed methane(CBM)exploration and development. Different coal structure have different influences on the migration and enrichment of coalbed methane. According to the coal broken degree,the coal structure of No.3 coal bed was divided into primary structure, transition structure and cataclastic structure in F block of Qinshui Basin,and the characteristics of their logging response were analyzed. The results show that the logging curve is usually characterized with lower density and resistivity,and higher borehole diameter and acoustic time as the coal broken degree increases. Based on the qualitative identifying of coal structure by logging data,array acoustic logging data was used to calculate the coal rock brittleness index(BI)quantitatively. The application results show that it is feasible to identify coal structure quantitatively by the coal rock brittleness index,the identification result is consistent with the actual drilling coring data,and it can greatly reduce the error of the qualitative identification.

Mechanism of gas production rate outburst in coalbed methane wells

LI Chuanliang, ZHU Suyang, PENG Chaoyang, WANG Fenglan, DU Qinglong, YOU Chunmei

2017, Vol.29(2): 145–149 Abstract ( 428 ) PDF (2646 KB) ( 746 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.018

Coalbed methane(CBM)wells must drain water from coalbeds before producing gas. The gas production rate increases suddenly rather than slowly at breakthrough of gas at wells,which is a strange phenomenon so far people do not know its mechanism. In order to understand production characteristics of CBM,the mechanism of production rate outburst of CBM wells was analyzed. It is recognized that coal rocks are dual porosity media in microscope,consisting of cleats(fractures)and matrix blocks. Cleats and matrix pores of coals are saturated with formation water. CBM exists in the matrix with the form of adsorption,which can be exploited only after desorption from matrix under pressure drawdown through draining formation water. A little of desorbed gas cannot flow due to obstacle of capillary pressure,which are dispersed in water with a small saturation. As desorbed gas is increased and accumulated into continuous phase with a high saturation,the gas pressure and the flowing ability are also increased simultaneously. Coal matrix pores are quite small with high capillary pressure,which can trap massive desorbed gas in coal matrix. When increasing gas pressure breaks the capillary pressure,the massive desorbed gas flows suddenly into cleats of coal rocks,which results in the outburst of gas production rate in CBM wells. The production pressure of CBM is lower than its desorption pressure. The desorption pressure of CBM is actually the saturation or bubble pressure of formation water. Abrupt increase of production rate may damage coalbed or production tubes,so it is necessary to take a possible control of production rate in practice.

The mechanism of reservoir transition through waterflooding of Donghe sandstone in Hadeson Oilfield

LIU Qiang, YU Yichang, JIANG Tongwen, XU Huaimin, CHANG Lunjie, WANG Chao

2017, Vol.29(2): 150–159 Abstract ( 396 ) PDF (14799 KB) ( 151 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.019

In order to block the dominate pathway after waterflooding in Donghe sandstone reservoir of Hadeson Oilfield efficiently,the data of reservoir physical properties,mercury injection,cast thin sections,clay mineral Xray diffraction,scanning electronic microscope and waterflooding interpretation conclusions,were used to study the petrologic features,pore throat structure,reservoir transition rule and mechanism after waterflooding in Donghe sandstone reservoir. The results show that the absolute content of clay mineral Donghe sandstone reservoir is low, and most clay minerals are kaolinite and illite with velocity sensitivity,and range from 1 to 2 μm in grain size.Donghe sandstone reservoir can be divided into three types:thin-micro throat and low permeability reservoir with throat radius less than 2 μm,thin throat and middle permeability reservoir with throat radius of 2-5 μm,and middlethin throat and high permeability reservoir with throat radius larger than 5 μm. Clay mineral block and migration after waterflooding are the reasons for the change of reservoir physical properties. The matching of clay mineral grain size and throat radius controls the reservoir transition rule after waterflooding. There are three kinds of mechanism:the porosity and permeability of thin-micro throat and low permeability reservoir decrease after waterflooding,and they decrease from original to low waterflooding,then slightly increase till middle waterflooding, and decrease again in high waterflooding. The porosity and permeability of thin throat and middle permeability reservoir firstly increase,then increase higher and decrease in high waterflooding. The porosity and permeability of middle-thin throat and high permeability reservoir increase with the increase of waterflooding degree, and this type of reservoir is favorable for advantageous pathway development. There are a large number of residual oil after waterflooding,therefore in the study area,so it is of significance to conduct reservoir transition rule and mechanism research after waterflooding.

Laboratory study on surfactant flooding system based on clean fracturing flowback fluid

ZHOU Wensheng, WANG Kai, LIU Chen, PAN Yue, SHEN Jian, LIU Yifei

2017, Vol.29(2): 160–166 Abstract ( 302 ) PDF (1411 KB) ( 464 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.02.020

Aiming at the large volumes,great treatment difficulties,high treatment cost of fracturing flowback fluid,and its harmfulness for environmental safety,the effective mass fraction,adsorption behavior,interfacial tension behavior,wettability alteration,incremental oil recovery ability and the mechanism of surfactant flooding were studied in laboratory,and a method was established to realize the reutilization of clean fracturing flowback fluid in surfactant flooding. The results show that the effective mass fraction of clean fracturing flowback fluid is 0.3%. The oi/water interfacial tension could be lowered to 10-4 mN/m to 10-3 mN/m with the effective mass fraction ranging from 0.05% to 0.30%. The clean fracturing flowback fluid system has excellent wettability performance and could easily change oil-wet quartz to water-wet. Meanwhile,the dynamic adsorption is about 9.53 mg/g and the dynamic retention amount is about 25%-33% of the dynamic adsorption. The physical model experiments show that the oil recovery value can be enhanced 12.5% under optimal injection project,which confirms its excellent performances on further enhanced oil recovery for the target area after fracturing treatment.