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01 January 2019, Volume 36 Issue 4 Previous Issue    Next Issue

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Origin and Occurrence of Highly Matured Oil and Gas in Mahu Sag, Junggar Basin Abulimiti1, CAO Jian2, CHEN Jing1, YANG Haibo1, CHEN Gangqiang1, TAO Keyu2 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150401 Abstract ( 162 )   PDF (300KB) ( 280 )   Save Whether the oil and gas are highly matured and light is critical to hydrocarbon enrichment and high yield in dense reservoirs. This paper investigates the basic characteristics, origin and occurrence rules of highly matured and light oil and gas in Mahu sag, northwestern Junggar basin. Results show that the highly matured and light oil and gas in the study area are characterized by low density, high maturity and coexistence with natural gas, which belong to the products of multi?set source rocks dominated by the Lower Permian Fengcheng high?quality source rock under nearly?high maturation stage. During the hydrocarbon generation, migration and accumulation, the highly matured and light oil and gas reservoir got continuous oil?gas charging and good preservation without or with little biodegradation; the occurrence of them is characterized by source controlling, and they can migrate and accumulate in cross?zone and broad areas vertically by faults and fractures, which might be important conditions for forming Mahu giant petroleum province in Junggar basin Related Articles | Metrics

Prediction of Potential Area of Jiamuhe Formation of Lower Permian in Zhongguai Swell in Junggar Basin XI Cheng1, GAO Jun2a, WEI Liyan2b, LIAO Feng1 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150402 Abstract ( 54 )   PDF (300KB) ( 61 )   Save Zhongguai swell is an important area for petroleum exploration in northwestern margin of Junggar basin, and its Lower Jiamuhe formation is the main target zone. Oil and gas shows occurred in Guai?3, Xinguang?1, Guai?201wells at this formation in southern slope of Zhongguai swell, and also got commercial oil?gas flow up to now. However, the scattering oil?gas yielding points allowed the reservoir to be more complicated. In view of the complexity of Jiamuhe reservoir, many geophysical methods are used to analyze it. It is suggested that the conventional impedance inversion cannot be applied to fine description of such a reservoir, but waveform division and oil?gas containing detection technologies can do it. And the idea of finding“sweet spot”areas in the favorable sedimentary facies well solves the difficulty of lateral heterogeneity in the reservoir, providing theoretical guidance for the next step of exploration and deployment in this area. Key Words Related Articles | Metrics

Effects of SourceReservoir Lithologic Assemblage on Tight Oil Accumulation: A Case Study of Yanchang Chang7Member in Ordos Basin YANG Zhifeng, ZENG Jianhui, FENG Xiao, FENG Sen, ZHANG Yidan, QIAO Juncheng 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150403 Abstract ( 52 )   PDF (300KB) ( 227 )   Save According to comprehensive analysis of data from core lab, logging and well logs,the Chang?7member of Yanchang formation of Upper Triassic in the study area can be dividedinto three types of source?reservoir lithologic assemblages such as source sandwiching reservoir(Type1), source?reservoir interbed (Type2) and reservoir sandwiching source rock (Type3). This Paper indicates that such assemblage types have important effects on expulsion and charging of tight oil, based on studied results of source rock thickness, internal fluid pressure feature,geochemical analysis and effective oil charging space coefficient. The former two types have micro?fracture episodic hydrocarbon expulsion and incomplete expulsion, the third type is one with complete expulsion. For the tight oil enrichment extent, Type1is high, followed by Type2, Type3is relatively poor. Related Articles | Metrics

Development Characteristics of Inverted Structures in Baiyun Sag in Pearl River Mouth Basin XU Ziying1,2, SUN Zhen2, PENG Xuechao1 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150404 Abstract ( 57 )   PDF (300KB) ( 151 )   Save To reveal the intensity and timing of inverted structures in Baiyun sag in Pearl River Mouth basin, the quantitative analysis method for inverted structure, including growth index, displacement-distance curve and reversal rate, is applied to quantitative analysis of Baiyun sag抯 inverted structures. The results show that the tectonic inversion happed twice in Baiyun sag. The early inversion began in the Early Oligocene (34.0?06~32.0?06a), mainly developed in the Late Oligocene (32.0?06~23.8?06a), with strong inversion degree; the late inversion began in early Middle Miocene (15.5?06~13.8?06a), mainly developed in late Middle Miocene (13.8?06~12.5?06a), with mild inversion degree. The early inverted tectonic stress contains the gravitational potential created by the intensive subsiding of Baiyun sag and the sinistral compressive?torsional stress produced by South China Sea spreading, of which the gravitational potential is the main controlling factor. The late tectonic stress is mainly affected by the Dongsha movement, so the inversion stress may come from the eastern part of Pearl River Mouth basin, possibly related with squeezed effect of Philippine plate. The late inverted structural trap could be the more favorable area for hydrocarbon accumulation Related Articles | Metrics

Diagenesis and Effect on Physical Property of Lower Jurassic Badaowan Formation in Mobei-Mosuowan Area, Junggar Basin SHAN Xiang1, XU Yang1, TANG Yong2, CHEN Nenggui1, GUO Huajun1, HAN Shouhua1 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150405 Abstract ( 28 )   PDF (300KB) ( 273 )   Save Based on comprehensive analysis of cast thin?section, SEM, X?ray diffraction, petrophysical property data, this paper presents the diagenesis types of compaction, cementation and dissolution existed in the Badaowan reservoir of Lower Jurassic, and points out that its diagenesis stage is now in period A of mid?diagenesis, and the reservoir quality is obviously influenced by the diagenesis. The coal measure strata of Badaowan formation belong to diagenetic environment of acidic fluid. The early dissolution of clastic particles and the high content of the reservoir plastic particles result in stronger diagenesis in it, by which its porosity drops dramatically by averaging28.75%, followed by continuously reducing due to existence of kaolinite, calcite and siliceous cements by3.03%in average. The late dissolution of feldspar grains forms intragranular dissolved pores which improve the reservoir porosity by averaging1.15%. Comprehensive analysis shows that midcoarse sandstone has high content of rigid grains, low content of plastic lithic fragments, and stronger compaction resistance, which is the most favorable reservoir sandbody Related Articles | Metrics

Diagenetic Evolution of Wutonggou Reservoir in Southeastern Margin of Beisantai Swell, Junggar Basin LI Ling1, Delaqiati1, CHEN Chunyong2, TAN Qiang2, FENG Wei1 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150406 Abstract ( 52 )   PDF (300KB) ( 225 )   Save The Permian Wutonggou formation is an important target zone for petroleum exploration in Beisantai swell of Junggar basin, andtypical litho?stratigraphic reservoir has been found in it. Based on the analyses of core and sedimentary facies, combined with cast thin section, SEM, electron micro?probe and X?ray diffraction data, a systematic study of the diagenesis of the Wutonggou formation is presented in this paper. The Wutonggou reservoir underwent compaction, cementation and dissolution, and is in stage between early diagenetic period B and mid?diagenetic period A. The clay minerals in the study area are dominated by authigenic kaolinite and illite/smectite, and the acidic aqueous media and organic matter produce large amount of acid and CO2 during diagenesis, which create favorable conditions for detrital feldspar kaolinization. The rich volcanic debris and low geothermal gradient as well as low speed of smectite illitization are the major reasons for rich illite/smectite in the clay minerals Related Articles | Metrics

Geochemistry and Accumulation Analysis of Gas Reservoir of Leikoupo43 SubMember of Middle Triassic in Longgang Area, Central Sichuan Basin ZHOU Shichao1, WANG Xingzhi1, ZENG Deming1, HE Bing2, ZOU Xiang2 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150407 Abstract ( 54 )   PDF (300KB) ( 78 )   Save The gas reservoir of Leikoupo43 sub?member of the Middle Triassic in Longgang area of central Sichuan basin has no uniform gas?water interface, and its late development is controlled by the complex gas?water relationship. Based on the analysis of the geochemical characteristics, the study on the gas and water distribution regularities reveals that the gas accumulation was controlled by the reservoir heterogeneity, sedimentary facies, tectonic setting, fault and fracture and preservation condition, etc. The comparative analysis of gas composition and isotopic characteristics indicates that the overlying Xujiahe formation is the main gas source layer of Leikoupo gas reservoir; In a certain condition of hydrocarbon generation intensity, the reservoir of grain shoal subfacies has good physical properties, with a high degree of gas charging. The gas layer, gas?water layer, gas?containing water layer are all dominated by isolated structural traps, the tectonic setting is of obvious differentiation effect on the gas and water; the developed faults and fractures in this area provide primary gas conduction system and reservoir space; the bottom mudstone of the Xujiahe formation and the Leikoupo gypsum?salt rocks constitute good conditions for hydrocarbon preservation Related Articles | Metrics

Fine Evaluation of Es3Source Kitchen in Raoyang Sag, Bohai Bay Basin WANG Hao1a, WANG Feiyu1a,1b, ZHOU Renzhi1a, JIN Fengming2, MA Xuefeng2, ZHAO Xianzheng2 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150408 Abstract ( 69 )   PDF (300KB) ( 145 )   Save Raoyang sag is one of hydrocarbon-rich sags in Bohai Bay basin, its major source rock is Es3 lacustrine dark mudstone with strong heterogeneity. Analysis of32exploration wells by source rock logging evaluation technique converts the discrete measured TOC data into continuous data. According to the correlation between TOC and HI, the grading evaluation of heterogeneity of the source rock is presented, obtaining the thickness distribution models in terms of C and D/E organic facies. The bottom hole temperature and paleo?temperature scale parameters are applied to calibrate distribution of geotemperature field and maturity of source rocks in Raoyang sag. Trinity3D petroleum system is used to evaluate the hydrocarbon expulsion intensity of the source kitchen, which shows that the oil expulsion intensity ranges from 1.0×106 to 5.4×106 t/km2, while the gas expulsion intensity is 0.5×108~22.0×108 m3/km2 Related Articles | Metrics

Characteristics of Dense Tuff Reservoir of Haerjiawu Formation in Malang Sag in Santanghu Basin LI Sichen1, MA Qiang2, BAI Guojuan2, LI Xinning2, YAN Ligang2, HUANG Zhilong3 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150409 Abstract ( 78 )   PDF (300KB) ( 175 )   Save The Haerjiawu formation in Malang sag in Santanghu basin is of variety of lithologies. Using logging crossplots can well identify its three types of lithologies such as vitric tuff, crystal?vitric tuff and lithic?vitric tuff. In plane, the sedimentary center of Haerjiawu formation is dominated by vitric tuff and crystal tuff, and toward sedimentary edge, the lithic content is increased and then transitional to volcanic rock. The reservoir space mainly includes primary pores, secondary pores and fractures, among which the intercrystalline pore in primary pores and dissolution pore in secondary pores are the main reservoir spaces, and micro?fracture can effectively improve the local reservoir’s percolation. The study shows that the vitric and crystal?vitric tuffs contain good physical property, but the vitric tuff is in limited distribution, and the lithic?vitric tuff is poor. The formation of Haerjiawu dense tuff reservoir is mostly controlled by mature source rock and favorable tuff reservoir distributions. The interbedded tuff in M2-M15well block has a good relationship of source?reservoir coexistence and could be the most favorable zone for petroleum exploration Related Articles | Metrics

Division and Evaluation of FracturedVuggy ReservoirsFractureVug Units of HA601 Wellblock in Halahatang Oilfield, Tarim Basin LIAO Tao1, HOU Jiagen1, CHEN Lixin2, MA Ke1, YANG Wenming2, DONG Yue1 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150410 Abstract ( 68 )   PDF (300KB) ( 255 )   Save Taking HA601wellblock in Halahatang oilfield as an example, based on the reservoir prediction, guided by the Ordovician outcrop in Tabei area (northern Tarim basin), this paper presents three genetic types of fractured?vuggy reservoir formed in the karstification, including tubulose underground river caves, caves controlled by faults and rivers, caves controlled by faults; considering the difficulties in fracture?vug unit division, it provides two divisive methods of static reservoir prediction and numerical well test to confirm the boundary of fracture?vug units. The study indicates that the key factors for controlling fracture?vug units in carbonate interstratum area is river systems in Lianglitage formation and faults. Based on the scale of reservoir body, geological reserves, energy index, genetic type and pressure level, it establishes the evaluation criterion for fracture?vug units in carbonate interstratum area, and applies it to all the well?controlled and nonwell?controlled units, which provide a reference for well deployment and development adjustment of Halahatang oilfield in the future Related Articles | Metrics

Provenance Analysis and Sedimentary System Characteristics of the4th Member of Xujiahe Formation in Northeastern Sichuan Basin ZHOU Xia1, WANG Wei1, DU Hongquan1, WANG Tao2 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150411 Abstract ( 49 )   PDF (300KB) ( 102 )   Save This paper analyzed the provenance directions of the4th member of Xujiahe formationinnortheastern Sichuan basin using paleocurrent, rock?mineral analysis and heavy mineral methods, and presented the parent rock types in the each provenance area. The study of the provenance directions, sandstone type, debris type and content variation, heavy mineral combination and ZTRindex indicate that the different provenance directions are as follows: in western Yuanba area the sediments are mainly from Longmenshan orogenic belt, the parent rock types are dominated by carbonate rock, followed by siliceous rock and a few low?grade metamorphic rocks; in Tongnanba area the sediments come from Micang-North Dabashan orogenic belt, the parent rock types are dominated by sedimentary rocks, followed by volcanic rock and a few low and mid?high grade metamorphic rocks; in eastern Yuanba area the sediments possibly come from eastern margin of Dabashan area, the parent rock types are mainly sedimentary rocks, secondarily low?grade etamorphic rocks, and characterized by rich feldspars; the middle part of Yuanba area is characterized by mixed provenance. According to the analyses of provenance directions, sedimentary environment, field outcrops, core observation, well logging and seismic data, the northeastern Sichuan basin of the4th member of Xujiahe formation can be divided into three braided?river delta depositional Systems where the microfacies are dominated by braided channels in delta plain and underwater distributary channels in delta front, and the channel sandbody is distributed in the whole area Related Articles | Metrics

Lost Circulation Law in Fractured Strata with Stress Sensitivity WANG Yue 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150412 Abstract ( 67 )   PDF (300KB) ( 203 )   Save The lost circulation problem often brings about great challenges to petroleum engineering sector, especially in the case of encountering fractured strata with stress?sensitivity while drilling deep wells. By means of core soaking experiment and conventional rock mechanics experiment under simulated formation conditions, this paper tests the rock mechanics parameters of fractured carbonate rocks after soaked by plugging slurry, and analyzes the samples’mechanics strength weakening effect and plugging mechanism. Considering the stress?sensitivity differences caused by the fracture and pore structure characteristics, this paper quantitatively analyzes and discusses the lost circulation law of such a formation, providing a theoretical basis for the plugging mechanism study of stress?sensitivity fractured strata Related Articles | Metrics

Mechanism of Hydraulic Fracture Propagation Considering Fractal Crack Length and Bending Effects LI Xiaogang1, YI Liangping1, YANG Zhaozhong1, ZHOU Nayun2 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150413 Abstract ( 62 )   PDF (300KB) ( 125 )   Save To well understand the impact of fractal cracks propagation on hydraulic fracturing, the fracture toughness expressions considering the fractal crack length and bending effects were re?derived based on traditional linear fracture expansion model, establishing a new equation for hydraulic fracture width and the model for crack internal net pressure as required by hydraulic fracture propagation. Theoretical analysis indicates that the fractal dimension increases with crack propagation bending angle. Compared with the linear fracture expansion model, the crack internal net pressure is increasing after considering the fractal crack length and bending effects, and the fracture width given by this linear model is decreasing in the first80%part of a fracture, that is, the fracture width near the fracture end could be increasing, which means that the fracture width computed by the linear fracture expansion model will be bigger than that in actual condition. Subsequently, the proppants available for fracture propagation in the linear model may possibly form bridge plugging in practice Related Articles | Metrics

Polymer Displacement Mechanism with Different Viscoelasticities by Alternating Injection Process ZHANG Dong, WU Wenxiang 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150414 Abstract ( 44 )   PDF (300KB) ( 188 )   Save This paper compares the effect of continuous injection and alternating injection of polymers with different viscoelasticities on stress and deformation of residual oil droplets, explores the hydrodynamic displacement mechanism of them on residual oil, including the stress and deformation calculation of residual oil droplets under the actions of the different fluids, and analyzes the alternating injection mechanism from two aspects of the elasticity and pressure gradient. The results show that the difference between normal deviator and horizontal stress of residual oil droplets by the effect of polymer solution is increasing with the elasticity rise of the polymers in the case of the same pressure gradient. Comparing with continuous injection process, the alternating injection process of polymer solutions can improve the phenomenon of fluid overload in the large pores and the fluid deficiency in the small pores, making the polymer of low concentration and low molecular weight enter into the low permeability layers with more residual oil displacement and stress, hence the swept volume can be expanded and the oil displacement efficiency can be improved Related Articles | Metrics

Evaluation of Recovery Effect in Hongqian1Wellblock by InSitu Combustion Process in Xinjiang Oilfield ZHANG Xialin1, GUAN Wenlong1, DIAO Changjun2, XI Changfeng1 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150415 Abstract ( 90 )   PDF (300KB) ( 231 )   Save Taking the in?situ combustion pilot test in Wellblock Hongqian?1in Xinjiang oilfield as an example, the recovery effect by in?situ combustion process converted from steam injection process including steam stimulation and steam drive is evaluated using generalized production decline and numerical simulation methods. The results show that the steam injection followed by in?situ combustion process applied in this pilot test area has obtained ultimate recovery efficiency of59.9%, of which in?situ combustion stage can get at least30%of the EOR. Also, the comparison of these two methods indicates that the generalized production decline method is actually feasible for evaluation of in?situ combustion recovery effect, less data are needed than numerical simulation method, and more simple to use Related Articles | Metrics

Influence Factors of Immiscible Gas Flooding Recovery in FracturedVuggy Carbonate Reservoirs HU Rongrong, YAO Jun, WANG Chenchen, SUN Zhixue 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150416 Abstract ( 58 )   PDF (300KB) ( 108 )   Save In order to study the influence factors of immiscible gas flooding oil recovery in fractured?vuggy reservoirs, the mechanism models of fractured?vuggy media are developed to analyze the influence of injection and production wells’reservoir type, vug distribution between injection well and production well, injection and production sites and gas injection rate on the EOR. The results show that the main mechanism of immiscible gas flooding is gravity drive due to the density differences between oil and gas, oil expansion and oil viscosity reduction to improve the flow ability. A better process could be gas injecting in fractured reservoir and high site, and oil producing in vuggy reservoir and low site. The existence of vugs could reduce the risk of gas channeling. The closer the vug to the top of reservoir and production well is, the higher the oil recovery will be. The oil recovery of gas flooding will increase and then decrease with the increase of gas flooding rate. The simulation results show that the oil recovery of gas flooding is mainly influenced by gravity, reservoir types, the distribution of vug between injection well and production well and gas injection parameters Related Articles | Metrics

Identification of Abandoned Channels in Meander River and Impact on Horizontal Well Landing Design in Low Oil Column Reservoir: A Case Study of Lm943Sand of Caofeidian Oilfield in Bohai Bay Area MENG Peng, SU Yanchun, FENG Xin, GUO Jingmin, WANG Wei, ZHU Yuguo 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150417 Abstract ( 42 )   PDF (300KB) ( 97 )   Save Caofeidian oilfield is a fluvial facies and low oil column reservoir with edge water in Bohai Bay area. It has been developed by horizontal wells for10years, and now its edge water has become secondary bottom water in it, which puts forward higher requirement for late?stage development by horizontal well in terms of water?avoidance height. This paper identifies the abandoned channels in area with a few wells by using the data of directional wells and horizontal wells, predicts them by means of flattening the sand top height in area with no well, and presents the depiction of the internal sand bodies in single channel and draws the plan of sedimentary microfacies. Based on the abandoned channel outcrop in meandering river, the impact of layer position encountered by horizontal well on its water?avoidance height is analyzed for the purpose of guiding the accurate landing design of adjustment wells and providing the basis for comprehensive adjustment plan’s implementation of horizontal wells in Caofeidian oilfield in the future Related Articles | Metrics

Identification of Abandoned Channels in Meander River and Impact on Horizontal Well Landing Design in Low Oil Column Reservoir: A Case Study of Lm943Sand of Caofeidian Oilfield in Bohai Bay Area HU Shuyong1, LI Yongkai1, MA Chao1,2, YIN Zhaoyun3, CHEN Li4 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150418 Abstract ( 47 )   PDF (300KB) ( 130 )   Save The producer?injector spacing corresponding to the minimum displacement pressure gradient overcoming the start?up pressure gradient in low permeability reservoir is the limit well spacing for establishing effective displacement pressure system between producer and injector. According to producer?injector model of aniso?production one?source and one?convergence point, a new formula for displacement pressure gradient in main stream line between producer?injector is deduced and applied to Fuyang reservoir in Xinmin oilfield which belongs to a typical low porosity and low permeability reservoir. This paper takes account of the real status of the reservoir development and determines the limit well spacing for it by this new method. Comparing common calculation methods available, the result shows it can be well applied in practice Related Articles | Metrics

EOR Technologies of SAGD Development in Zhong37Wellblock, Fengcheng Oilfield, Junggar Basin HE Wanjun1aMuhetaer1aDONG Hong1aZHU Yunfei1bMENG Xiangbing1aQinaerHushan2 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150419 Abstract ( 71 )   PDF (300KB) ( 116 )   Save The study of the relationship between the production performance and the steam chamber development by steam assisted gravity drainage (SAGD) process，the SAGD development effectiveness of Zhong?37wellblock in Fengcheng oilfield is influenced by reservoir heterogeneity，injection?production pipe string structure，production process and key operation parameters of injection and production wells. Based on the typical well group heterogeneous model in Zhong?37SAGD pilot test area，using numerical simulation method，the technical countermeasures for improving development effectiveness are proposed such as secondary huff and puff，infilled well steam injection assisted SAGD，nitrogen gas injection assisted SAGD，and solvent injection assisted SAGD. The research provides ideas for improving the horizontal section’s producing degree，promoting the balanced development of SAGD steam chamber，and enhanced oil recovery (EOR) Related Articles | Metrics

Log Identification of Chert in Ordovician Carbonate Rocks in Tahe Oilfield,Tarim Basin: Method and Application XIE Fang1, LIU Jianhua2, LIU Ruilin1 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150420 Abstract ( 73 )   PDF (300KB) ( 244 )   Save Nodular and banded chert distribute extensively over the4th interval and underlying strata of the Ordovician Yingshan formation in Tahe oilfield in northern Tarim basin. Researching the logging response characteristics of chert and distinguishing the chert?developed formation are of significance to the evaluation of effective reservoir, formation zonation, and stratigraphic correlation. This paper discusses the basic principle of identifying chert by using imaging well logging, chemical element logging and litho?density logging data, and establishes the method for chert logging identification by means of these data and photoelectric absorption cross?section index curve. Taking the chert intensive development section near the bottom margin of Yingshan 4th lithologic interval as marker bed, it makes the stratigraphic correlation of partial strata and resolves the problem of the Middle-Upper Ordovician denudation estimation in Tahe oilfield Related Articles | Metrics

Application of Multiscale Waveform Tomography Inversion in HighAccuracy Velocity Modeling MA Yiming1, SUN Zandong1, TANG Zhiyuan2, YU Liwen1 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150421 Abstract ( 67 )   PDF (300KB) ( 303 )   Save The information of seismic amplitude and phase for reconstruction wave field can be used in waveform tomography inversion method to get a velocity model with higher accuracy and resolution theoretically. However, because of its serious nonlinearity and high dependence on initial velocity model, it often results in unsatisfactory inversion results in field application. This paper presents an improved strategy of multiscale inversion to establish higher?accuracy depth migration velocity field as an initial input model of waveform tomography, so that decrease the serious nonlinearity. This strategy is successfully applied to Marmousi model and case study, in which the updated velocity is used to make Kirchhoff pre?stack depth migration. The final result shows that the waveform tomography can retrieve much more high?frequency details and highly improve the accuracy and resolution of the seismic migration imaging Related Articles | Metrics

Genetic Identification of25Norhopanes ZOU Xianli1, CHEN Shijia1,2, LU Jungang1,2, XU Yaohui3, ZHANG Huanxu1, WANG Li1, PANG Jianchun3, HUANG Youlin1 2015, 36 (4):  1-1.  doi: 10.7657/XJPG20150422 Abstract ( 153 )   PDF (300KB) ( 393 )   Save 25?norhopanes in hopane series compounds exist widely in severely biodegraded oils and are generally considered to be formed due to effect of natural biodegradation on the compounds, which has a special geochemical significance. The analysis of extracts from source rocks in different thermal evolution stages indicates that25?norhopanes are not contained in such extracts in low thermal evolution stage rather than high thermal evolution stage in which there exists high abundance of25?norhopanes in them. This paper suggests that this result is related to the thermal evolution degree, not just resulted from biodegradation. In Sichuan basin, the extracts from bitumen formed by high temperature pyrolysis all contain25?norhopanes, and the distribution features of them are very similar to the saturated hydrocarbon GC?MS diagrams for source rocks in high thermal evolution stage, and reach equilibrium state. Also, the hopane ratio parameter ranges in the same region, it can be deduced that the 25?norhopanes existed in the bitumen are effected by thermal evolution degrees. In order to make clear the differences between25?norhopanes occurrence related with the thermal evolution degree and resulted from degradation, the 25?norhopanes from biodegraded crude oil are compared with that from thermal evolution in distribution, it is verified that there exist large differences in GC?MS and hopane ratio parameter Related Articles | Metrics