Formation of Natural Bitumen and its Implication for Oil/gas Prospect in Dabashan Foreland

Natural bitumen is the evolutionary residue of hydrocarbon of sedimentary organic matter. Several kinds of bitumen with different occurrences, including bitumen in source rock, migration bitumen filled in fault, oil-bed bitumen and paleo-reservoir bitumen, are distributed widely in the Dabashan foreland. These kinds of bitumen represent the process of oil/gas formation, migration and accumulation in the region. Bitumen in source rock fiUed in fractures and stylolite and experienced deformation simultaneously together with source rock themselves. It indicated that oil/gas generation and expelling from source rock occurred under normal buried thermal conditions during prototype basin evolution stages prior to orogeny. Occurrences of bitumen in source rock indicated that paleo- reservoir formation conditions existed in the Dabashan foreland. Migration bitumen being widespread in the fault revealed that the fault was the main channel for oil/gas migration, which occurred synchronously with Jurassic foreland deformation. Oil-bed bitumen was the kind of pyrolysis bitumen that distributed in solution pores of reservoir rock in the Dabashan foreland depression, the northeastern Sichuan Basin. Geochemistry of oil-bed bitumen indicated that natural gas that accumulated in the Dabashan foreland depression formed from liquid hydrocarbon by pyrolysis process. However, paleo-reservior bitumen in the Dabashan forleland was the kind of degradation bitumen that formed from liquid hydrocarbon within the paleo-reservior by oxidation, alteration and other secondary changes due to paleo-reservior damage during tectonics in the Dabashan foreland. In combination with the tectonic evolution of the Dabashan foreland, it is proposed that the oil/gas generated, migrated and accumulated to form the paleo-reservoir during the Triassic Indosinian tectonic movement. Jurassic collision orogeny, the Yanshan tectonic movement, led to intracontinental orogeny of the Dabashan area accompanied by geofluid expelling and paleo-reservoir damage in the Dabashan foreland. The present work proposed that there is liquid hydrocarbon exploration potential in the Dabashan foreland, while there are prospects for the existence of natural gas in the Dabashan foreland depression.

Migration and accumulation characteristics of natural gas hydrates in the uplifts and their slope zones in the Qiongdongnan Basin,China

Various factors controlling the accumulation of natural gas hydrates(NGHs)form various enrichment and accumulation modes through organic combination.This study mainly analyzes the geological and geophysical characteristics of the NGHs occurrence in the uplifts and their slope zones within the deep-water area in the Qiongdongnan(QDN)Basin(also referred to as the study area).Furthermore,it investigates the dominant governing factors and models of NGHs migration and accumulation in the study area.The results are as follows.(1)The uplifts and their slope zones in the study area lie in the dominant pressure-relief direction of fluids in central hydrocarbon-rich sags in the area,which provide sufficient gas sources for the NGHs accumulation and enrichment through pathways such as gas chimneys and faults.(2)The top and flanks of gas chimneys below the bottom simulating reflectors(BSRs)show high-amplitude seismic reflections and pronounced transverse charging of free gas,indicating the occurrence of a large amount of gas accumulation at the heights of the uplifts.(3)Chimneys,faults,and high-porosity and high-permeability strata,which connect the gas hydrate temperature-pressure stability zones(GHSZs)with thermogenic gas and biogenic gas,form the main hydrate migration system.(4)The reservoir system in the study area comprises sedimentary interlayers consisting of mass transport deposits(MTDs)and turbidites.In addition,the reservoir system has developed fissure-and pore-filling types of hydrates in the pathways.The above well-matched controlling factors of hydrate accumulation enable the uplifts and their slope zones in the study area to become the favorable targets of NGHs exploration.

Geochemical Characteristics and Migration Pathways of Ordovician Carbonate Oil Reservoirs in the Tuoputai Area,Tarim Basin,Northwestern China

Exploration potential is huge and the oil resources are rich in the Ordovician reservoirs of the Tarim Basin.However,the mechanism of hydrocarbon accumulation is complex and not yet fully understood.In the Tuoputai area,the hydrocarbon migration pathways and characteristics of deep hydrocarbon accumulation are revealed through analyses of the physical data of rich oil and gas,the geochemical parameters of oil,and fluid inclusions.The results show that the Ordovician oils in the Tuoputai area have the same geochemical characteristics as the mixed oil from the Lower Cambrian source rock and the Middle–Upper Ordovician source rock.The Ordovician reservoirs have been charged three times:in the late Caledonian,late Hercynian,and Himalayan stages.Oil charging occurred in the Hercynian stage,in particular,as it is the main filling period of hydrocarbon.The north-northeast(NNE)-trending TP12 CX major fault,active in in these times and is dominant migration channel of hydrocarbon,but there is segmentation affected by the difference of activities.Oil maturity is higher in the south than in the north and is abnormally high near the major fault.Parameters related to migration indicate that oil migrated northeastward along the NNE-trending TP12 CX major fault and adjusted laterally along the secondary faults and weathering crust,forming the present characteristics of oil and gas distribution.

Fluid Potential Distribution and Oil & Gas Accumulation in Tertiary of Western Qaidam Basin

With the development of oil and gas exploration industry, researchers and engineers have realized that the key element controlling the migration of underground oil and gas and other fluid is not the pressure of stratum, but the underground fluid potential. Therefore, it is very crucial to study the distribution rule of fluid potential in order to correctly determine the exploration target areas. This paper studies the fluid potential distribution in Tertiary of west Qaidam Basin, puts forward the model of underground oil and gas migration and predicts the areas for further exploration.

Features of the fault system and its relationship with migration and accumulation of hydrocarbon in Liaodong Bay

The fault system of Liaodong Bay developed extensively under the control of the Tanlu Fault. The fault system can be grouped into strike-slip faults of grade Ⅰ, trunk faults of grade Ⅱand branch faults （induced faults） of grade Ⅲ respectively based on its developmental scale. The faults of grade Ⅰ and Ⅱwere deep, early and large while the faults of grade Ⅲwere shallow, late and small. The formation, evolution and distribution features played a significant role in controlling the migration of oil and gas in both horizontal and vertical directions. The fluid transfer in the fault system occurred in the process of faulting. The strike-slip and trunk faults moved actively forming predominant pathways for oil and gas migration. The branch faults, with weak activity, generally controlled the development of traps and were beneficial for the accumulation and preservation of oil and gas. The faults of grade Ⅰ and Ⅱ formed the major migration pathways for oil and gas, but their fault activity rates appeared to vary along their strikes. The zones with a relatively low fault activity rate might be favorable for oil and gas accumulation. When the activities of strike-slip, trunk, and branch faults came to a halt, the fault seal behavior had a vitally important effect on the accumulation of oil and gas. The controlling role of the fault over fluid distribution was further analyzed by calculating the fault activity quantitatively.

Mesh model building and migration and accumulation simulation of 3D hydrocarbon carrier system

Migration and accumulation simulation of oil and gas in carrier systems has always been a difficult subject in the quantitative study of petroleum geology. In view of the fact that the traditional geological modeling technology can not establish the interrelation of carriers in three dimensional space, we have proposed a hybrid-dimensional mesh modeling technology consisting of body(stratum), surfaces(faults and unconformities), lines and points, which provides an important research method for the description of geometry of sand bodies, faults and unconformities, the 3 D geological modeling of complex tectonic areas, and the simulation of hydrocarbon migration and accumulation. Furthermore, we have advanced a 3 D hydrocarbon migration pathway tracking method based on the hybrid-dimensional mesh of the carrier system. The application of this technology in western Luliang Uplift of Junggar Basin shows that the technology can effectively characterize the transport effect of fault planes, unconformities and sand bodies, indicate the hydrocarbon migration pathways, simulate the process of oil accumulation, reservoir adjustment and secondary reservoir formation, predict the hydrocarbon distribution. It is found through the simulation that the areas around the paleo-oil reservoir and covered by migration pathways are favorable sites for oil and gas distribution.

Hydrocarbon Migration and Accumulation in Dongying Basin

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Discovery of “Enveloping Surface of Oil and Gas Overpressure Migration” in the Songliao Basin and its bearings on hydrocarbon migration and accumulation mechanisms

The Fuyang oil layer of the Songliao Basin is a tight and low-permeability sandstone pay zone formed in the fluvial-shallow water delta environment.In the formation are mainly lithologic reservoir and tight reservoir.The lacustrine-mudstone of K2qn1 is a good source rock and also acts as a good regional cap rock.The Fuyang oil layer is a typical upper-source and lower-reservoir pattern distributed in a large area.Based on a large number of exploration and development data, a macroscopic enveloping surface is found developed in the Fuyang oil layer, which is below K2qn1.The effective reservoirs within the enveloping surface are commonly saturated with oil, and below the enveloping surface are mainly water layers.The distance from the enveloping surface to the bottom of the source rock is usually 100-350 m and at most 550 m.Through the research of the distribution patterns and the physical properties of the sandbodies above or beneath the source rock, it is concluded that: 1) the enveloping surface is the boundary of the overpressure hydrocarbon migration; 2) the spacial distribution of the pressure release beds controls the direction and the distance of the overpressure hydrocarbon migration; 3) tight oil reservoirs and lenticular oil reservoirs are mainly formed inside the envelope surface, whereas, conventional reservoirs are formed outside the envelope surface as a result of the buoyancy hydrocarbon migration.The discovery of the "overpressure hydrocarbon migration enveloping surface" and the concepts of overpressure hydrocarbon migration and buoyancy hydrocarbon migration not only challenge the old notion that "hydrocarbon migrates along the faults and is distributed along fault belts" in the Fuyang oil layer of the Songliao Basin, give a new explanation to the long-distance-oil-downwards migration (hundreds of meters) and expand the exploration potential of the Fuyang oil layer, and provide a rational guidance to the exploration of syncline plays, but also better categorize tight oil/gas and conventional reservoirs in all of the key elements related to hydrocarbon migration, accumulation, reservoir characteristics and oil and gas spatial distribution.

Oil/Gas Migration and Aggregation in Intra-Continental Orogen Based on Numerical Simulation: A Case Study from the Dabashan Orocline, Central China

Geofluid, driven by tectonic stress, can migrate and aggregate in geological body. Thus, numerical simulation has been widely used to rebuild paleo-tectonic stress field and probe oil/gas （one type of geofluid） migration and aggregation. Based on geological mapping, structural data, and mechanical parameters of rocks, we reconstruct the traces for gas/oil migration and aggregation in Dabashan intra-continental orogen using numerical simulation. The study shows that gas/oil, obviously dominated by late Middle Jurassic-Early Cretaceous paleo-tectonic stress field that is characterized by NE-SW shortening in the Dabashan thrust belt and SW-emanating shortening in its foreland belt, massively migrate from the Dabashan thrust belt to its foreland belt, that is, NE to SW, resulting in the formation of some probable favorable areas for oil/gas mainly along the Tiexi -Wuxi fault, in some superposed structure （e.g., Zhenba , Wanyuan , Huangjinkou , and Tongnanba areas）, and in the Zigui Basin. Thus, our study shows that numerical simulation can be effectively applied to study oil/gas migration and aggregation in intra-continental orogen and provided some significant evidences for oil/gas exploration.

TECTONIC MIGRATION OF OIL AND GAS BASINS IN EASTERN CHINA

This paper deals with the tectonic migration of various types of basins and the regu-larity of time-space distribution of oil and gas in the eastern China basins from the availa-ble geological, geophysical and drill data, and then a preliminary discussion is made onthe relationship between tectonic migration and oil and gas formation.

Process and mechanism for oil and gas accumulation, adjustment and reconstruction in Puguang Gas Field, Northeast Sichuan Basin, China

With the discoveries of a series of large gas fields in the northeast of Sichuan Basin, such as Puguang and Longgang gas fields, the formation mechanism of the gas reservoir containing high H2S in the ancient marine carbonate formation in superposition-basin becomes a hot topic in the field of petroleum geology. Based on the structure inversion, numerical simulation, and geochemical research, we show at least two intervals of fluid transfer in Puguang paleo-oil reservoir, one in the forepart of late Indo-Chinese epoch to early Yanshan epoch and the other in the metaphase of early Yanshan epoch. Oil and gas accumulation occurred at Puguang structure through Puguang-Dongyuezhai faults and dolomite beds in reef and shoal facies in Changxing Formation (P2ch) - Feixianguan Formation (T1f) in the northwest and southwest directions along three main migration pathways, to form Puguang paleo-oil reservoir. Since crude oil is pyrolysised in the early stage of middle Yanshan epoch, Puguang gas reservoir has experienced fluid adjusting process controlled by tectonic movement and geochemical reconstruction process controlled by thermochemical sulfate reduction (TSR). Middle Yan-shan epoch is the main period during which the Puguang gas reservoir experienced the geochemical reaction of TSR. On one hand, TSR can recreate the fluid in gas reservoir, which makes the gas drying index larger and carbon isotope heavier. On the other hand, the reciprocity between fluid regarding TSR (hydrocarbon, H2S, and water) and reservoir rock induces erosion of the reservoir rocks and anhydrite alteration, which improves reservoir petrophysical properties. Superimposed by later tectonic movement, the fluid in Puguang reservoir has twice experienced adjustment, one in the late Yanshan epoch to the early Himalayan epoch and the other time in late Himalayan epoch, after which Puguang gas reservoir is finally developed.

Reservoir forming conditions and key exploration technologies of Lingshui 17-2 giant gas field in deepwater area of Qiongdongnan Basin

On September 15,2014,China National Offshore Oil Co.,Ltd announced that a high production of oil and gas flow of 1.6
106 m3/d was obtained in Well LS17-2-1 in deepwater area in northern South China Sea,which is the first great oil and gas discovery for self-run deepwater exploration in China sea areas,and a strategic breakthrough was made in natural gas exploration in deepwater area of Lingshui sag in Qiongdongnan Basin.Under the combined action of climax of international deepwater exploration,high oil prices,national demands of China,practical needs of exploration,breakthroughs in seismic exploration and testing technologies,innovations in geological cognition and breakthroughs in deepwater operation equipment,Lingshui 17-2 gas field is discovered.Among these factors,the innovation in reservoir forming geological cognition directly promotes the discovery.The quality of seismic data in the early time is poor,so key reservoir forming conditions such as effective source rocks,high quality reservoirs and oil-gas migration pathways are unable to be ascertained;with support of new seismic acquisition and processing technology,some researches show that Lingshui sag is a successive large and deep sag with an area of 5000 km2 and the maximum thickness of Cenozoic stratum of 13 km.In the Early Oligocene,the Lingshui sag was a semi-closed delta-estuarine environment,where the coalmeasure and marine mudstones in Lower Oligocene Yacheng Formation were developed.The Lingshui sag is a sag with high temperature,and the bottom temperature of source rocks in Yacheng Formation can exceed 250C,but the simulation experiment of hydrocarbon generation at high temperature indicates that the main part of this set of source rock is still in the gas-generation window,with resources of nearly 1 trillion cubic meters,so the Lingshui sag is a hydrocarbon-rich generation sag.In the Neogene,the axial canyon channel from the Thu Bon River in Vietnam passed through the Lingshui sag,and five stages of secondary channels were developed in the axial canyon channel,where four types of reservoirs with excellent physical properties including the axial sand,lateral accretion sand,natural levee sand as well as erosion residual sand were developed,and lithologic traps or structural-lithologic traps were formed.The diapiric zone in the southern Lingshui sag connects deep source rocks in Yacheng Formation and shallow sandstones in the channels,and the migration pattern of natural gas is a T-type migration pattern,in other words,the natural gas generated from Yacheng Formation migrates vertically to the interior of the channel sandbody,and then migrates laterally in the channel reservoirs and forms the reservoirs.Innovations of geophysical exploration technologies for complicated geological conditions of deepwater areas are made,such as the detuning comprehensive quantitative amplitude hydrocarbon detection technology,which greatly improves the success rate of deepwater exploration;key technologies of deepwater safety exploratory well testing represented by the platform-dragged riser displacement technology are developed,which greatly reduces the drilling test cost.The above key exploration technologies provide a strong guarantee for the efficient exploration and development of Lingshui gas field.

海上高温高盐油藏自聚集调驱体系研发与应用

印尼某海上油田油藏条件复杂,属于高温高盐油藏,长期衰竭式开采导致渗透率极差大、含水率高、采出程度高。为了解决该区块开采问题,研发了一种新型调驱剂YC-1,与普通调驱体系相比,在实现深部调驱的基础上,能够通过电性作用自组装获得较普通微球粒径更大、封堵强度更高、稳定性更强的聚集体。通过马尔文激光粒度仪、SEM、金相显微镜等对其进行性能测定,测定结果显示,YC-1在98℃、矿化度70 000 mg·L^(-1)的高温高盐条件下60天保持结构稳定,且注入性和封堵性能良好。同时,通过探究YC-1在多孔介质中的封堵运移规律,包括注入浓度优化、注入速度优选、运移能力及封堵能力验证等,形成了一套针对目标油田的注入工艺方案,对现场施工具有一定指导意义。

Discovery and geologic significance of organic-biogenic secondary freshwater calcite in the Upper Triassic of Shaan-Gan-Ning Basin

1 Discovery of secondary freshwater calciteFROM well ZJ-23, around 22 m of condensed limestone has been found in member Chang-3 ofthe Upper Triassic Yanchang Formation. Electric log reflects high resistivity, higher densityof rock and lower values of natural gama, with calcite content of 40%—80%. Observation da-ta of 11 core wafers from 883. 05—887.20 m of the well demonstrate that high-angle struc-tural fracture (2 mm wide) and micro-fracture are relatively developed and fully or half

东营凹陷沙一段断层封闭性研究

东营凹陷位于济阳坳陷的东南部,区内断层平面组合特征复杂,剖面组合类型多样,导致了该凹陷内断层体系的复杂性和构造类型的多样性。通过对东营凹陷沙一段断层封闭性研究的总结,概述了该区断层封闭性的主要原理和机理以及影响因素,从定量和定性的角度分析了评价断层封闭性的方法,讨论了泥岩涂抹、挤压和地球化学作用对断层封闭性的影响。

Kinetics of hydrocarbon generation for Well Yingnan 2 gas reservoir,Tarim Basin,CHina

Well Yingnan 2,an important exploratory well in the east of Tarim Basin,yields high commercial oil and gas flow in Jurassic.Natural gas components and carbon isotopic composition indicate that it belongs to sapropel type gas.Because this region presents many suits of hydrocarbon source rocks,there are some controversies that natural gases were generated from kerogen gas or crude oil cracking gas at present.By using the kinetics of hydrocarbon generation and carbon isotope,natural gas of Well Yingnan 2 is composed mainly of crude oil cracking gas,about 72%,it is generated from secondary kerogen gas of Cambrian-Lower Ordovician source rock and crude oil cracking gas of Mid-Upper Ordovician oil reservoir.The main oil and gas filling time is 65 Ma later in the Jurassic gas reservoir of Well Yingnan 2,so the gas reservoir belongs to late accumulation and continuous filling type.