Development Conditions And Distribution Characteristics Of Dolomite Reservoirs Of Lower Ordovician Penglaiba Formation In Tahe Area

The Ordovician strata in the Tahe area of the Tarim Basin is an important carbonate reservoir development zone in China.Its large-scale buried hill karst reservoir dominated by the middle and upper Ordovician in the region is a distinctive feature and has formed a mature set.Exploration and development theory.However,the exploration of the Lower Ordovician Penglaiba Formation is relatively low.There are only 4 wells in the Tahe area encountering the Penglaiba Formation.The characteristics,development patterns,control factors,and distribution laws of the reservoirs need to be further clarified.The thesis analyzes the predecessors'research by consulting a large number of documents,and based on the existing drilling cores,logging,earthquakes,and sample testing data in the study area,it compares with the field outcrop data in the Keping area.Combining with related theories of sedimentary petrology,reservoir geology,geophysics,and geochemistry,the reservoir of the Penglaiba Formation in the Tahe area was carefully studied.The Penglaiba formation in the Tahe area mainly develops two sequences,namely the Psq1 corresponding section of the lower section of the Penglaiba Formation and the Psq2 corresponding section of the upper section of the Penglaiba Formation.There are three sequence interfaces related to it,the third-grade sequence interface T₇⁸(the Yingshan Formation and the Penglaiba Formation boundary),the third-grade sequence interface T₈⁰(the boundary between the Penglaiba Formation and the Cambrian),and the fourth-grade sequence interface T₇^8-1(Bound between Pengliaba Section 1 and Penglaiba Section 2).The sedimentary facies of the Penglaiba Formation in the study area mainly consisted of restricted platform.The depositional environment was dominated by tidal flats.The intertidal zone and the subtidal zone were mainly developed.The microfacies such as barrier shoals,low energy beach shoals and lagoon were observed.From Penglaiba Section 1 to Penglaiba Section 2,the overall process of a sea level rise,the water becomes deeper,the circulation of the water becomes better,and gradually changes to the open platform.The reservoirs of the Penglaiba Formation in the Tahe area are mainly dolomite,followed by limestone.The dolomite in the area is divided into mud-powder subhedral-anhedral shaped dolomite,fine-grain subhedral-enhedral shaped dolomite,fine-grain subhedral-anhedral shaped dolomite,and medium-coarse-crystal subhedral-anhedral shaped dolomite.Limestone is mainly composed of bioclastic limestone,bright crystal sandstone limestone,algae-bound limestone and mudstone limestone.Among them,cementation,pressure dissolution and compaction,filling,dissolution,fracture,and dolomitization are all important diagenesis types in the region.The reservoir mainly develops three types of reservoir space:porosity,dissolved pores and cracks.The study found that among the many factors affecting reservoirs,the most important are the unconformity exposed karst controlled by the T78 interface,the quasi-constant karst controlled by the high-energy facies in the sedimentary environment,and the deep hydrothermal erosion controlled by the fracture in the study area.Through the superposition treatment of the three major controlling factors,the three-level favorable zone of the dolomite reservoir in the Penglaiba Formation was determined.This determines the plane distribution characteristics of the reservoir.