Discovery and inspiration of large-and medium-sized glutenite-rich oil and gas fields in the eastern South China Sea:An example from Paleogene Enping Formation in Huizhou 26 subsag,Pearl River Mouth Basin

Based on the practice of oil and gas exploration in the Huizhou Sag of the Pearl River Mouth Basin,the geochemical indexes of source rocks were measured,the reservoir development morphology was restored,the rocks and minerals were characterized microscopically,the measured trap sealing indexes were compared,the biomarker compounds of crude oil were extracted,the genesis of condensate gas was identified,and the reservoir-forming conditions were examined.On this basis,the Paleogene Enping Formation in the Huizhou 26 subsag was systematically analyzed for the potential of oil and gas resources,the development characteristics of large-scale high-quality conglomerate reservoirs,the trapping effectiveness of faults,the hydrocarbon migration and accumulation model,and the formation conditions and exploration targets of large-and medium-sized glutenite-rich oil and gas fields.The research results were obtained in four aspects.First,the Paleogene Wenchang Formation in the Huizhou 26 subsag develops extensive and thick high-quality source rocks of semi-deep to deep lacustrine subfacies,which have typical hydrocarbon expulsion characteristics of"great oil generation in the early stage and huge gas expulsion in the late stage",providing a sufficient material basis for hydrocarbon accumulation in the Enping Formation.Second,under the joint control of the steep slope zone and transition zone of the fault within the sag,the large-scale near-source glutenite reservoirs are highly heterogeneous,with the development scale dominated hierarchically by three factors(favorable facies zone,particle component,and microfracture).The(subaqueous)distributary channels near the fault system,with equal grains,a low mud content(<5%),and a high content of feldspar composition,are conducive to the development of sweet spot reservoirs.Third,the strike-slip pressurization trap covered by stable lake flooding mudstone is a necessary condition for oil and gas preservation,and the NE and nearly EW faults obliquely to the principal stress have the best control on traps.Fourth,the spatiotemporal configuration of high-quality source rocks,fault transport/sealing,and glutenite reservoirs controls the degree of hydrocarbon enrichment.From top to bottom,three hydrocarbon accumulation units,i.e.low-fill zone,transition zone,and high-fill zone,are recognized.The main area of the channel in the nearly pressurized source-connecting fault zone is favorable for large-scale hydrocarbon enrichment.The research results suggest a new direction for the exploration of large-scale glutenite-rich reservoirs in the Enping Formation of the Pearl River Mouth Basin,and present a major breakthrough in oil and gas exploration.

Effect of gravel on rock failure in glutenite reservoirs under different confining pressures

Due to the existence of gravel,glutenite is heterogeneous and different from fine-grained rocks such as sandstone and shale in structure.To fully understand the effect of gravel on failure mode in glutenite,we performed triaxial compression tests on different glutenites.The results indicate that failure modes of glutenite are complex due to the existence of gravel.Under different confining pressures,three failure modes were observed.The first failure mode,a tensile failure under uniaxial compression,produces multiple tortuous longitudinal cracks.In this failure mode,the interaction between gravels provides the lateral tensile stress for rock splitting.The second failure mode occurs under low and medium confining pressure and produces a crack band composed of micro-cracks around gravels.This failure mode conforms to the Mohr-Coulomb criterion and is generated by shear failure.In this failure mode,shear dilatancy and shear compaction may occur under different confining pressures to produce different crack band types.In the second failure mode,gravel-induced stress concentration produces masses of initial micro-cracks for shear cracking,and gravels deflect the fracture surfaces.As a result,the fracture is characterized by crack bands that are far broader than in fine-grained rocks.The third failure mode requires high confining pressure and produces disconnected cracks around gravels without apparent crack bands.In this failure mode,the gravel rarely breaks,indicating that the formation of these fractures is related to the deformation of the matrix.The third failure mode requires lower confining pressure in glutenite with weak cement and matrix support.Generally,unlike fine-grained rocks,the failure mode of glutenite is not only controlled by confining pressure but also by the gravel.The failure of glutenite is characterized by producing cracks around gravels.These cracks are produced by different mechanisms and distributed in different manners under different confining pressures to form different fracture patterns.Therefore,understanding the rock microstructure and formation stress state is essential in guiding glutenite reservoir development.

Numerical Simulation of Two-Phase Flow in Glutenite Reservoirs for Optimized Deployment in Horizontal Wells

It is known that the pore media characteristics of glutenite reservoirs are different from those of conventional sandstone reservoirs.Low reservoir permeability and naturally developed microfractures make water injection in this kind of reservoir very difficult.In this study,new exploitation methods are explored.Using a real glutenite reservoir as a basis,a three-dimensional fine geological model is elaborated.Then,combining the model with reservoir performance information,and through a historical fitting analysis,the saturation abundance distribution of remaining oil in the reservoir is determined.It is shown that,using this information,predictions can be made about whether the considered reservoir is suitable for horizontal well fracturing or not.The direction,well length,well spacing and productivity of horizontal well are also obtained.

The Features of Sedimentary Facies and Copper Enrichment Metallogenic Regularities of Kuzigongsu Group in Sareke Glutenite Type Copper Deposits,Wuqia,Xinjiang

1 Introduction Sareke glutenite-type copper deposit is the large size copper deposit discovered in recent years,and it is located Sarekebayi intracontinental pull-apart basin in the western margin of the Tarim basin.Conglomerate of

Hydrocarbon Reservoir Model of Glutenite in the Fourth Member of Shahejie Formation in Northern Dongying Depression

The glutenite in the fourth member of Shahejie Formation(Es^4) in northern Dongying depression straightforwardly penetrated into the muddy bathyal -abyss facies.The conditions of reservoir is very superior:(1) the high quality thick bedded oil source rock is developed very well in the Lijin sag and Minfeng sag of the study area,and it has the higher capability of generating hydrocarbon;(2) the

Formation of X-shaped hydraulic fractures in deep thick glutenite reservoirs:A case study in Bohai Bay Basin,East China

Tight glutenite reservoirs are widely developed in Bohai Bay Basin,East China.They are mostly huge thick and rely on hydraulic fracturing treatment for commercial exploitation.To investigate the propagation behavior of hydraulic fractures in these glutenite reservoirs,the geological feature of reservoirs in Bohai Bay Basin is studied firstly,including the reservoir vertical distribution feature and the heterogeneous lithology.Then,hydraulic fracturing treatments in block Yan 222 are carried out and the fracturing processes are monitored by the microseismic system.Results show the hydraulic fractures generated in the reservoirs are mostly in X shape.The cause of X-shaped hydraulic fractures in this study is mainly ascribed to(I)the reservoir heterogeneity and(II)the stress shadow effect of two close hydraulic fractures propagating in the same orientation,which is confirmed by the following numerical simulation and related research in detail.This study can provide a reference for the research on the fracturing behavior of the deep thick glutenite reservoirs.

Genetic Mechanism of the Dolomite in Dolomitic Glutenite of the Shahejie Formation—A Case Study of QHD 29-2 Oilfield in Bohai Bay Basin, China

The dolomite in dolomitic glutenite of the shahejie formation in the eastern steep slope of the Shijiutuo bulge in Bohai is a high-quality reservoir, and the content of dolomite is positively correlated with reservoir physical properties. In this paper, by using thin section, core, wall core, geochemical data and analyzing petrology and mineralogy characteristic, we systematically analyzed the paleogeographic environment and genetic mechanism of this kind of dolomite and established the genetic models. The dolomite in the glutenite body has many characteristics of development, which is formed by three kinds of genesis: quasi-synergy dolomitization, buried dolomitization and hydrothermal dolomitization. The dolomite in glutenite is produced in the form of matrix, grain (sandstone, oolith), biological skeleton (conch, ostracod), clastic shell and dolomite cement. The minor elements, carbon and oxygen isotopes, trace minerals and paleontological combinations reveal that the paleogeographic environment was closed continental salt-brackish water bay, the climate was arid and hot, and the evaporation was strong. It provides favorable conditions for the production of the dolomite in dolomitic glutenite. There are three genetic models of dolomite. The first model is penecontemporaneous dolomitization. The climate was arid and hot, the aragonite and high-magnesium calcite deposited with sand and gravel. Due to the effect of evaporation, dolomitization occurred. The second model is buried dolomitization. The water from dehydration of clay minerals causes the Mg2+ in the high-magnesium formation migrating into the rock, leading to the occurrence of dolomitization. The third model is hydrothermal dolomitization. Deep faults can bring geothermal fluids into the overlying reservoir and form the hydrothermal dolomite.

Quality evaluation of glutenite reservoirs of intergranular-secondary dissolution pore type using a quantitative method

Glutenite(coarse-grained clastic)reservoirs of intergranularesecondary dissolution pore type are dominated by residual intergranular pores and secondary dissolution pores,and characterized by low porosity,low permeability,strong heterogeneity,and highly variable physical properties.It is difficult to conduct a quantitative quality assessment of these reservoirs while their primary control factors remain unclear.In this paper,experimental core data and drilling,logging and seismic data are used to assess the effect of sedimentary facies on reservoir quality.Favorable sedimentary facies zones are identified by analyzing the characteristics of glutenite reservoirs,which includes investigating rock components and their effects on reservoir quality.Argillaceous matrix content and rigid particle content are identified as the primary control factors for these reservoirs.Logging curves sensitive to reservoir quality are selected and examined to continuously characterize the physical parameters of the reservoirs.It establishes a calculation model of reservoir assessment parameters through multivariate regression and determines the quantitative assessment parameter Fr.The quality of the glutenite reservoirs is defined using conventional logging curves.This study also predicts the plane distribution of high-quality reservoirs through geostatistical inversion of the reservoir assessment parameters based on conventional wave impedance inversion,thus providing insight and guidance for quantitative assessment and quality prediction of glutenite reservoirs of the intergranular-secondary dissolution pore type.The application of this method to well deployment based on qualitative evaluation of the glutenite reservoirs in oilfields yielded favorable results.

Distribution prediction of the glutenite in Member 3 of Triassic Xujiahe Formation in Yuanba area,northern Sichuan Basin

Although the Triassic Xujiahe Formation in Yuanba area of northern Sichuan has a large amount of resources,the proportion of proved reserves to the amount of resources is low.Production of most of the pilot production wells is high at the initial stage,but it declines rapidly,mainly due to tight rock properties and strong heterogeneity of Xujiahe Formation.Thus,it is important to investigate the distribution of high-quality reservoirs.The Member 3 of Xujiahe Formation develops sandstone interbedded with mudstone,and its lateral thickness of different sandstone groups varies greatly,so it is a challenge to identify appropriate time windows for seismic attribute analysis,thus,so the prediction effect of the glutenite in the Member 3 of Xujiahe Formation.In this study,through analysis of core data and logging facies,single-well sedimentary microfacies subdivision is carried out.Single-well lithological interpretation is also studied with application of lithological identification technique.Then,lithological associations and its seismic responses at the top and bottom interfaces of each sandstone group in the Member 3 of Xujiahe Formation are well investigated,The lithological association with the glutenite above and the mudstone below the stratigraphic interface respectively,corresponds to a trough in seismic profiles;in this case,when extracting the seismic attributes of sandstone groups above the stratigraphic interface,only the difference of between drilling horizons and seismic horizons needs to be considered.The lithological association with the mudstone above and glutenite below the stratigraphic interface respectively,corresponds to a peak in seismic profiles;in this case,when extracting the seismic attributes of sandstone groups above the stratigraphic interface,influence of which should be eliminated;thus,a method of time window determination for seismic attribute extraction is established.Among amplitude,frequency,and phase attributes,the total peak energy has the good correlation with thickness of the glutenite at well sites and it also can reflect the distribution of distributary channels well.The results show that belt-like glutenite in each sandstone group in the Member 3 of Xujiahe Formation extends in a NW-SE direction and thins out toward the southeast,and the distribution of glutenite has certain inheritance in the longitudinal direction,the glutenite in the third sandstone group in the Member 3 of Xujiahe Formation(TX33)and the first sandstone group in the Member 3 of Xujiahe Formation(TX31)are both developed.