Characteristics And Controlling Factors Of Mid-deep Reservoir In Langgu Depression

Using core, logging and analysis of laboratory data on Langgu depression, sedimentarycharacteristics, reservoir characteristics, digenetic characteristics, the formation pressurecharacteristics as well as controlling factors of an effective Es3、Es4reservoir in the depth ofgreater than2500m have been comprehensively and systematicly researched. Deep reservoirin Langgu depression develops braided river delta, Sublacustrine fan and nearshoresubaqueous fan sand body. The mainly diagenesis are compaction, cementation, dissolution,replacement, matrix recrystallization etc. Diagenetic period can be divided into earlydiagenetic stage B, middle diagenetic A1, A2sub-period and the diagenetic stage B. Indifferent tectonic belts, diagenetic sequence can be summarized as follows: compaction�'matrix recrystallization/carbonate cementation in JiuZhou-GuAn tectonic belt; compaction�'feldspar dissolution/quartz overgrowth�'quartz dissolution/carbonate cementation�'pyritecementation in LiuQuan-CaoJiawu tectonic belt; compaction/early pyrite cementation�'feldspar dissolution/quartz overgrowth/authigenic kaolinite�'carbonate cementation/anhydrite cementation�'dissolution of carbonate/pyrite cementation in the north ofHeXiwu tectonic zone; compaction/quartz overgrowth/early pyrite cementation�'feldspardissolution/quartz overgrowth/authigenic kaolinite�'carbonate cementation/anhydritecementation/dissolution of quartz�'dissolution of carbonate/pyrite cementation in thesouth of HeXiwu tectonic zone. The key reservoir space are primary porosity, secondaryaperture and mixed pore; Es3mainly develops low permeability and especially-lowpermeability reservoirs with middle porosity, while especially-low permeability, super-lowpermeability reservoirs with low-middle porosity are commonly found in Es4. Overall,Es3-Es4is in a strong super-pressure environment, multiple overpressure zones are developedvertically, pressure coefficient decreased from the edge to the depression center. Depositionmacro controls the formation of deep high-quality reservoirs, overpressure played a importantrole in protecting the effective reservoir and in different tectonic belt, the impact of diagenesisto the formation of effective reservoir varies from degrees. Lithology with gravelly sandstone,sandstone, thickness, sedimentary facies shunt for the the lakebed fan and underwater distributary channel of braided river delta, diagenetic stage for the early diagenetic stage Band diagenetic stage A, middle-strong overpressure and other conditions are favorable factorsfor development of high-quality effective reservoirs; sedimentation is the main controllingfactor of effective reservoirs in mid-deep strata, then formation pressure, diagenesis play atransformed role in reservoir later.