Iteration and evaluation of shale oil development technology for continental rift lake basins

By benchmarking with the iteration of drilling technology,fracturing technology and well placement mode for shale oil and gas development in the United States and considering the geological characteristics and development difficulties of shale oil in the Jiyang continental rift lake basin,East China,the development technology system suitable for the geological characteristics of shale oil in continental rift lake basins has been primarily formed through innovation and iteration of the development,drilling and fracturing technologies.The technology system supports the rapid growth of shale oil production and reduces the development investment cost.By comparing it with the shale oil development technology in the United States,the prospect of the shale oil development technology iteration in continental rift lake basins is proposed.It is suggested to continuously strengthen the overall three-dimensional development,improve the precision level of engineering technology,upgrade the engineering technical indicator system,accelerate the intelligent optimization of engineering equipment,explore the application of complex structure wells,form a whole-process integrated quality management system from design to implementation,and constantly innovate the concept and technology of shale oil development,so as to promote the realization of extensive,beneficial and high-quality development of shale oil in continental rift lake basins.

Quantitative Modelling of Multiphase Lithospheric Stretching and Deep Thermal History of Some Tertiary Rift Basins in Eastern China

The stretching process of some Tertiary rift basins in eastern China is characterized by multiphase rifting. A multiple instantaneous uniform stretching model is proposed in this paper to simulate the formation of the basins as the rifting process cannot be accurately described by a simple (one episode) stretching model. The study shows that the multiphase stretching model, combined with the back-stripping technique, can be used to reconstruct the subsidence history and the stretching process of the lithosphere, and to evaluate the depth to the top of the asthenosphere and the deep thermal evolution of the basins. The calculated results obtained by applying the quantitative model to the episodic rifting process of the Tertiary Qiongdongnan and Yinggehai basins in the South China Sea are in agreement with geophysical data and geological observations. This provides a new method for quantitative evaluation of the geodynamic process of multiphase rifting occurring during the Tertiary in eastern China.

Lithologic Hydrocarbon Deposits in Rift Lake Basins in Eastern China

The rift lake basins in the eastern China have abundant hydrocarbon resources of lithologic deposits, which resulted from excellent source rocks and multi-type sandbodies developed during strong rifting. Vertically, the lithologic deposits are mainly distributed in the lowstand, lacustrine invasion and early highstand systems of third-order sequence corresponding to a secondary tectonic episode of strong rifting, and laterally they are closely related to various fans and turbidite sandbodies controlled by syn-sedimentary faults. A variety of lithologic traps have been developed in the rift lake basins, and they generally have favorable conditions of source-reservoir-seal assemblage and hydrocarbon accumulation dynamics, indicating that there is a great exploration potential of lithologic deposits in the rift lake basins. In order to obtain satisfactory effects of lithologic deposit exploration, it is required to combine new theories with advanced technical methods.

Characteristics and genetic mechanism of the Mesoproterozoic rift system,Ordos Basin,China

The Mesoproterozoic rifts are developed in the Ordos Basin located in the western margin of the North China Plate.Based on the latest 3D seismic data and previous research results,this study intends to discuss the zonal differential deformation characteristics and genetic mechanism of the Mesoproterozoic rifts in the Ordos Basin.NE-trending rifts are developed in the Mesoproterozoic in the south-central Ordos Basin,the main part of which are located near the western margin of the North China Plate.NNW-trending rifts are developed in the north of the basin,while NW-NNW rifts in the Mesoproterozoic in Hangjinqi area.The genetic mechanism of the Mesoproterozoic rifts is related to regional extensional stress field,plate boundary conditions and internal preexisting structures.The main extensional stress direction strikes NWW-SSE(120°)in the western margin of the North China Plate,based on the forward rift trend of the northern Mesoproterozoic.In Hangjinqi area,the reactivation of the existing NWtrending Wulansu fault and NW-NW-trending Daolao fault,results in dextral shear stress field.The boundary between the western margin of the North China Plate and its adjacent plates forms a nearly NS-trending preexisting basement tectonic belt,which intersects with the NWW-SSE(120°)extensional stress at an acute angle of 60°.Therefore,the western margin of the North China Plate is formed by oblique normal faults under oblique extension.Due to the long time span of Columbia Supercontinent breakup(1.8e1.6 Ga),the oblique rift in the south-central Ordos Basin is formed under the continuous oblique extension at the western margin of the North China Plate.

Orderliness of Hydrocarbon Accumulation Distribution in Rift Basins of Eastern China

The Cenozoic rift basins in eastern China show a clear temporal and spatial zonation and episodic tectonic evolution, which control their episodic hydrocarbon generation and zonal accumulation. In this paper, based on the study of depositional architecture, hydrocarbon migration system and dynamic evolution in the rift basins, combinations of hydrocarbon accumulation elements were analyzed using sequence stratigraphy. Hydrocarbon distribution in system tracts with different sequence orders was further studied. And we summarized stacking patterns and horizontal combination relationships for different types of reservoirs, such as lithological, tectonic-lithological, tectonic and stratigraphical reservoirs which can be observed from depression center to basin margin. The result reveals that various scales of pools exhibit significant distribution and evolution orderliness in different pool-forming units, i.e., depositional systems, plays and depressions. The regular distribution of various scales of pools is closely related to tectonic evolution and depositional filling in the rift basins. The result can be applied to the fine petroleum exploration in rift basins in eastern China. It will promote the scientific prediction and evaluation of reservoir types and their spatial distribution, lead to the active shifts of exploration targets in different zones, and thus support the stable progress of fine exploration in mature exploration areas.

Syn-rift to post-rift tectonic transition and drainage reorganization in continental rifting basins:Detrital zircon analysis from the Songliao Basin,NE China

Tectonic transition from a syn-rift stage to subsequent post-rift stage is an important mechanism in the evolution of extensional basins.The sedimentary infill records the crustal response to this process.We have obtained new detrital zircon U-Pb and Lu-Hf signatures from the Lower Cretaceous stratigraphic successions encompassing the commonly accepted syn-to post-rift transition boundary,the T4 unconformity,in the Songliao Basin,NE China.These constrain the Songliao Basin’s evolution from its center to distal margins,providing insights into the sediment provenance and dispersal pattern over the tectonic transition.Analysis of zircons from the syn-rift(the Shahezi and Yingcheng formations)and immediate post-rift(the Lower and Middle Denglouku Formation)stages reveals Phanerozoic age populations with positiveƐHf(t)values,which were derived from the proximal juvenile mantle-derived melt origin bedrocks of the Songliao Block.In contrast,the overlying samples from the Upper Denglouku Formation deposited in the subsequent post-rift stage contain exotic and ancient zircon populations with ages of 2.5 Ga&1.8 Ga and complex hafnium signatures,characteristic of a mixed origin.These are interpreted to be transported from distant cratonic terranes via larger drainage networks.It is obvious that the sediment dispersal pattern switched from being a local and hydrologically closed“intraregional”pattern to a“transcontinental”pattern during the transition.The time lag between the development of the T4 unconformity and the drainage reorganization also ensures a distinguishable3 Myr(106103 Ma,Late Albian)transition period of regional extent.During this transition stage,syn-rift faulting was replaced by postrift thermal subsidence,exhibiting a uniform sag configuration.Our new findings are important for understanding other continental rift basins during syn-to post-rift transition,which often demonstrates a complex interaction between the linkage and integration of sub-basins,and the reorganization of fluvial drainages and catchment systems.

Modeling for Inter-Basin Groundwater Transfer Identification: The Case of Upper Rift Valley Lakes and Awash River Basins of Ethiopia

Groundwater movement beneath watershed divide is one component of the hydrological cycle that is typically ignored due to difficulty in analysis. Numerical ground-water models, like TAGSAC, have been used extensively for predicting aquifer responses to external stresses. In this paper TAGSAC code was developed to identify the inter-basin groundwater transfer (IBGWT) between upper Awash River basin (UARB) and upper rift valley lakes basin (URVLB) of Ethiopia. For the identification three steady state groundwater models (for UARB, URVLB and for the two combined basins) were first created and calibrated for the 926 inventoried wells. The first two models are conceptualized by considering the watershed divide between the two basins as no-flow. The third model avoids the surface water divide which justifies IBGWT. The calibration of these three models was made by changing the recharge and hydrogeologic parameters of the basins. The goodness of fit indicators (GoFIs) obtained was better for the combined model than the model that describes the URVLB. Furthermore, the hydraulic head distribution obtained from the combined model clearly indicates that there is a groundwater flow that doesn’t respect the surface water divide. The most obvious effect of IBGWT observed in these two basins is that it diminishes surface water discharge from URVLB, and enhances discharge in the UARB. Moreover, the result of this study indicates potential for internal and cross contamination of the two adjacent groundwater.

Extensional Tectonics, Rifting, Formation of Sedimentary Basins, Cretaceous Volcanism, Emplacement of Dyke Swarms and Development of Hydrocarbon Pools: Case Studies from Peninsular India and Indian Ocean Region

Prolonged extensional regime in peninsular India resulted in formation of rift and grabens,elongated basins and Gondwana sedimentation along them.Downward progression of rift related faults caused decompression

Formation mechanisms of good-quality clastic reservoirs in deep formations in rifted basins:A case study of Raoyang sag in Bohai Bay Basin,East China

In order to reveal the development mechanism of high-quality clastic rock reservoir, the basic characteristics of Sha-3 Member of the Shahejie Formation in the Raoyang sag, Bohai Bay Basin, are analyzed based on cores observation, thin-sections and SEM images, and petrophysical properties measurements as well. It is found that high-mature composition and texture, early oil charging, and dissolution are the main factors controlling the formation and preservation of pores in deep reservoirs. Compaction is the major factor destructing pores, whereas formation overpressure is conducive to the preservation of original pores, high compositional and medium textural maturity can enhance the resistance capacity to compaction and protect primary pores. Early oil charging could lead to temporary cessation of diagenesis and thus inhibit the cementation. When organic acids entered reservoir formations, considerable amounts of secondary pores were formed, leading to the local improvement of petrophysical properties. When predicting good quality belt in exploration of deep basin, it is recommended that the superimposing effects of the multiple factors(overpressure, early oil charging, compositional and textural maturity, diagenesis) be taken into consideration.

Oil Pool Forming Model in Small Rift Basins—Multiple Hydrocarbon Accumulation in Fault Troughs

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Occurrence of Laminated Dolomitic Exhalative Rocks in Continental Rift Basins of Northwest China

Objective Researchers have recently discovered that sublacustrine sedimentary exhalative mechanism associated with volcanism,is the principle way to form lacustrine exhalative rocks.These rocks differentiate themselves from normal sedimentary rocks in their specificpetrofabric and material composition.

Research advances on transfer zones in rift basins and their influence on hydrocarbon accumulation

Transfer zones are structural areas of faults interactions where fault motion or displacement can be transferred from one fault to another, regional strain maintains laterally constant. Transfer zones are widely developed in rift basins and have significance on hydrocarbon accumulation. In this review article, we attempt to summarize recent advances on the types, distance-displacement curves, evolutionary stages and controlling factors of transfer zones in rift basins and their effects on sedimentary systems, reservoir properties, trap formation and hydrocarbon migration. The formation of transfer zones is genetically related to the segmented growth of normal faults. Depending on the degree of interaction between these normal faults, transfer zones in rift basins could be divided into two types: soft-linked and hard-linked, which are further subdivided into transfer slope, oblique anticline, horst and transfer fault based on the combination patterns of normal faults. In general, the development of transfer zones experiences several stages including isolated normal faulting, transfer slope forming, complicating and breaking. During the interaction and growth of segmented normal faults, stress-strain and spatial array of faults, pre-existing basement structures, and mechanical conditions of rocks have a great influence on the location and development processes of transfer zones. A transfer zone is commonly considered as a pathway for conveying sediments from provenance to basin, and it hence exerts an essential control on the distribution of sandbodies. In addition, transfer zone is the area where stresses are concentrated, which facilitates the formation of various types of structural traps, and it is also a favorable conduit for hydrocarbon migration. Consequently, there exists great hydrocarbon potentials in transfer zones to which more attention should be given.

Sedimentary Basins in the Western White Nile, Sudan, as Indicated by a Gravity Survey

An academic geophysical research as a regional gravity survey was made during1994 in the Western White Nile to infer the shallow crustal structures in the area. The result ofthe survey was compiled as a Bouguer anomaly map with a contour interval of 2 X 10^(-5)m/s^2. It isfound that the negative residual anomalies are related to the Upper Cretaceous sediments (NubianSandstone Formation) filling all depressions in the Basement complex surface while the positiveresidual anomalies are attributed to the relatively shallow or outcropping Basement rocks and thesteep gravity gradients are resulting from the sharp contacts between the sedimentary infill and theBasement rocks. To define the geological structures in the area, 9 profiles were studied. For eachof the profiles, measured and computed Bouguer gravity anomalies, crustal density model, subsurfacegeology evaluation were performed. A G-model computer program was applied in the gravity modeling,which is based on the line-integral method of gravity computation. A geological/structural map wasproposed showing inferred sedimentary basins, faulting troughs and uplifted Basement block andtectonic trends. The basins are believed to be fault-controlled which developed by extensionaltectonics (pull-apart mechanism). As for the mechanism and cause of faulting, the area is consideredas a part of the Central Sudan rift system which had been subjected to several tectonic eventssince Early Cambrian to Tertiary times which resulted in the formation of several fracture systemsassociated with block subsidence, rifting and basin formation.

Structural Architecture for Development of Marginal Extensional Sub-Basins in the Red Sea Active Rift Zone

This paper presents a robust kinematic model that describes northern Red Sea and Gulf of Suez rifting and the development of marginal extensional half-graben sub-basins (ESB). A combination of Landsat Enhanced Thematic Mapper Plus (ETM+) and structural data was used to provide model constraints on the development of rift segments and ESB in the active rift zones. Structural analysis shows rotation and change in strike of rift-bounding faults. The model describes the northern Red Sea region as a poly-phase rift system initiated by late Oligocene (30 - 24 Ma) orthogonal rifting and the development of marginal ESB (now inland ESB), followed by oblique rifting and flank uplift during the early Miocene (24 - 18 Ma). The oblique rifting fragmented the rift depression into segments separated by oblique-slip accommodation within reactivated Pan-African (ca. 600 Ma) fracture zones, resulting in the development of antithetic faults and an en-echelon distribution of inland ESB. The current phase of rifting was instigated by the development of the Dead Sea Transform in response to increased northeasterly extension during the middle Miocene (ca. 18 Ma). The model explains the widening of the Red Sea rift during the last phase more than the Gulf of Suez rift by developing more antithetic faults and formation of offshore ESB, and deepening the rift depression.

Lithospheric Stretching,Subsidence and Thermal History Modeling: Application to Yinggehai,Qiongdongnan and Songliao Basins in East China

he lithosphere stretching, subsidence and basement thermal history of the Songliao, Yinggehai and Qiongdongnan basins in East China have been investigated by using backstripping technique and stretching models. The subsidence curve of the Songliao basin characterizes a rift basin history evolving from synrift rapid subsidence to postrift thermal subsidence. The calculated stretching factor of the basin is about 1.8 to 2.0 and the horizontal extension is about 55-60 km. The reconstructed subsidence curves of the Qiongdongnan and Yinggehai basins show that the basins underwent several rapid subsidence episodes, which has been interpreted as the result of a multiple stretching of the lithosphere. The total mean stretching factors of the Qiongdongnan and Yinggehai basins, calculated by using a multiple instantaneous stretching model, are about 1.7-1.9 and 2.5-3.0 respectively. The stretching factors of these basins, estimated from subsidence, are consistent with those determined from crustal thinning. The reconstructed thermal histories of these basins are in agreement with the geological observation.

Mechanism of diagenetic trap formation in nearshore subaqueous fans on steep rift lacustrine basin slopes—A case study from the Shahejie Formation on the north slope of the Minfeng Subsag, Bohai Basin, China

Diagenetic traps in conglomerate in nearshore subaqueous fans in the steep slope zones of rift basins have been important exploration targets for subtle reservoirs in eastern China. However, the mechanism of how those traps were formed is not clear, which inhibits further exploration for this type of reservoir. In order to solve the problem, we take as an example nearshore subaqueous fans in the upper part of the fourth member of the Shahejie Formation （Es4s） on the north slope of the Minfeng Subsag in the Dongying Sag. Combining different research methods, such as core observation, thin section examination, scanning electron microscope （SEM） observation, fluid-inclusion analysis, carbon and oxygen isotope analysis of carbonate cements, and analysis of core properties, we studied the genetic mechanisms of diagenetic traps on the basis of diagenetic environment evolution and diagenetic evolution sequence in different sub/micro-facies. Conglomerate in Es4s in the north Minfeng Subsag experienced several periods of transition between alkaline and acidic environments as ＂alkaline-acidic-alkaline-acidic-weak alkaline＂. As a result, dissolution and cementation are also very complex, and the sequence is ＂early pyrite cementation / siderite cementation / gypsum cementation / calcite and dolomite cementation- feldspar dissolution / quartz overgrowth quartz dissolution / ferroan calcite cementation / ankerite cementation / lime-mud matrix recrystallization / feldspar overgrowth carbonate dissolution / feldspar dissolution / quartz overgrowth / pyrite cementation＂. The difference in sedimentary characteristics between different sub/micro-facies of nearshore subaqueous fans controls diagenetic characteristics. Inner fan conglomerates mainly experienced compaction and lime-mud matrix recrystallization, with weak dissolution, which led to a reduction in the porosity and permeability crucial to reservoir formation. Lime-mud matrix recrystallization results in a rapid decrease in porosity and permeability in inner fan conglomerates in middle-to-deep layers. Because acid dissolution reworks reservoirs and hydrocarbon filling inhibits cementation, reservoirs far from mudstone layers in middle fan braided channels develop a great number of primary pores and secondary pores, and are good enough to be effective reservoirs of hydrocarbon. With the increase of burial depth, both the decrease of porosity and permeability of inner fan conglomerates and the increase of the physical property difference between inner fans and middle fans enhance the quality of seals in middle-to-deep layers. As a result, inner fan conglomerates can be sealing layers in middle-to-deep buried layers. Reservoirs adjacent to mudstones in middle fan braided channels and reservoirs in middle fan interdistributaries experienced extensive cementation, and tight cemented crusts formed at both the top and bottom of conglomerates, which can then act as cap rocks. In conclusion, diagenetic traps in conglomerates of nearshore subaqueous fans could be developed with inner fan conglomerates as lateral or vertical sealing layers, tight carbonate crusts near mudstone layers in middle fan braided channels as well as lacustrine mudstones as cap rocks, and conglomerates far from mudstone layers in middle fan braided channels as reservoirs. Lime-mud matrix recrystallization of inner fan conglomerates and carbonate cementation of conglomerates adjacent to mudstone layers in middle fan braided channels took place from 32 Ma B.R to 24.6 Ma B.P., thus the formation of diagenetic traps was from 32 Ma B.R to 24.6 Ma B.R and diagenetic traps have a better hydrocarbon sealing ability from 24 Ma B.P.. The sealing ability of inner fans gradually increases with the increase of burial depth and diagenetic traps buried more than 3,200 m have better seals.

Mantle heterogeneity,plume-lithosphere interaction at rift controlled ocean-continent transition zone:Evidence from trace-PGE geochemistry of Vempalle flows,Cuddapah Basin,India

This study reports major, trace, rare earth and platinum group element compositions of lava flows from the Vempalle Formation of Cuddapah Basin through an integrated petrological and geochemical approach to address mantle conditions, magma generation processes and tectonic regimes involved in their formation. Six flows have been identified on the basis of morphological features and systematic three-tier arrangement of vesicular-entablature-colonnade zones. Petrographically, the studied flows are porphyritic basalts with plagioclase and clinopyroxene representing dominant phenocrystal phases.Major and trace element characteristics reflect moderate magmatic differentiation and fractional crystallization of tholeiitic magmas. Chondrite-normalized REE patterns corroborate pronounced LREE/HREE fractionation with LREE enrichment over MREE and HREE. Primitive mantle normalized trace element abundances are marked by LILE-LREE enrichment with relative HFSE depletion collectively conforming to intraplate magmatism with contributions from sub-continental lithospheric mantle(SCLM) and extensive melt-crust interaction. PGE compositions of Vempalle lavas attest to early sulphur-saturated nature of magmas with pronounced sulphide fractionation, while PPGE enrichment over IPGE and higher Pd/Ir ratios accord to the role of a metasomatized lithospheric mantle in the genesis of the lava flows. HFSEREE-PGE systematics invoke heterogeneous mantle sources comprising depleted asthenospheric MORB type components combined with plume type melts. HFSE-REE variations account for polybaric melting at variable depths ranging from garnet to spinel lherzolite compositional domains of mantle. Intraplate tectonic setting for the Vempalle flows with P-MORB affinity is further substantiated by(i) their origin from a rising mantle plume trapping depleted asthenospheric MORB mantle during ascent,(ii) interaction between plume-derived melts and SCLM,(iii) their rift-controlled intrabasinal emplacement through Archeane Proterozoic cratonic blocks in a subduction-unrelated ocean-continent transition zone(OCTZ). The present study is significant in light of the evolution of Cuddapah basin in the global tectonic framework in terms of its association with Antarctica, plume incubation, lithospheric melting and thinning, asthenospheric infiltration collectively affecting the rifted margin of eastern Dharwar Craton and serving as precursors to supercontinent disintegration.

Hydrocarbon Accumulation in Lacustrine Turbidite in the Rift Basin, Bohai Bay

Three types of turbidites are identified in the studied area, including proximal turbidite along the northern steep slope （alluvial fans, fan delta, and subaqueous fans via short-distance transportation）, distal turbidites along the southern gentle slope （stacked sliding of delta and fan delta front）, and fluxoturbidite in the central depression. Detailed studies of several case histories and the relationship between sedimentary facies and faults suggest a significant role of tectonic setting and faults in the development of turbidite, which created source areas, effected slope topography, controlled the climate and paleo-environment, and formed enough slope angle and slope break for sedimentary instabilities and massive block movement to form turbidite. According to statistics, 0.86%, with an average value of 40.3%, of the trap volumes in the 69 identified Tertiary lacustrine turbidites in the Jiyang Superdepression in the Bohai Bay Basin are filled with oil. The porosity and permeability of turbidite sands vary widely. The productive reservoirs are generally those from the braided channels of both distal and proximal turbidite, and from the main channel of proximal turbidite, with a low carbonate content and the porosity and permeability higher than 12% and 1 mD respectively. Most of the lithologic oil pools in the Jiyang Superdepression are enveloped by the effective source rocks, and the percentage of the trap volume generally increases with the hydrocarbon expulsion intensity of source rocks. This is in contrast with structural-lithologic traps （i.e. proximal turbidite along the steep slope and distal turbidite along the gentle slope）, in which, graben-boundary faults play an important role in oil migration, as the turbidites are not in direct contact with effective hydrocarbon source rocks.

Tectonics and Petroleum Potential of the East China Sea Shelf Rift Basin

There are two Cenozoic sedimentary basins in the East China Sea. They are the East China Sea shelf basin and the Okinawa Trough basin. The former can be divided into a western and an eastern rift region. The development of the shelf basin underwent continental-margin fault depression, post-rift and then tectonic inversion stages. Available exploration results show that the distribution of source rocks is controlled by the basin architecture and its tectonic evolution. In the Xihu depression, mudstones and coals are the main source rocks. The eastern rift region has good geological conditions for the formation of large oil and gas fields.

Key factors controlling shale oil enrichment in saline lacustrine rift basin:implications from two shale oil wells in Dongpu Depression,Bohai Bay Basin

Comparative analyses of petroleum generation potential,reservoir volume,frackability,and oil mobility were conducted on 102 shale cores from the Dongpu Depression.Results show the shale has high organic matter contents composed of oil-prone type I and type II kerogens within the oil window.Various types of pores and fractures exist in the shale,with a porosity of up to 14.9%.The shale has high brittle mineral contents,extensive fractures,and high potential for oil mobility due to high seepage capacity and overpressure.Although the petroleum generation potential of the shale at Well PS18-8 is relatively greater than that at Well PS18-1,oil content of the latter is greater due to the greater TOC.The porosity and fracture density observed in Well PS18-1 are greater and more conducive to shale oil enrichment.Although the shales in Wells PS18-1 and PS18-8 have similar brittle mineral contents,the former is more favorable for anthropogenic fracturing due to a higher preexisting fracture density.Besides,the shale at Well PS18-1 has a higher seepage capacity and overpressure and therefore a higher oil mobility.The fracture density and overpressure play key roles in shale oil enrichment.