Mound-shoal reservoirs characteristics and genesis mechanism in the fourth Member of the Dengying Formation of PS8 well area in Sichuan basin
The fourth Member of the Sinian Dengying Formation(Deng 4 Member)in Sichuan basin is a key petroleum exploration stratum recently.High gas yield was obtained in the well PS8 during the gas test in the Deng 4 Member,indicating a promising gas exploration potential.Based on drilling cores,cuttings,thin sections,analysis tests,and logging data,the characteristics and genesis mechanism of mound-shoal reservoirs of the Deng 4 Member in the PS8 well area were conducted.Results show that,①The Deng 4 Member in the PS8 well area has a tendency to thicken from aulacogen to platform.The lithology of the reservoir is mainly algal clot dolomite,algal stromatolite dolomite,and granular dolomite.Reservoir space is given priority to with solution pores and cracks,reservoir space is given priority to with solution pores and cracks.The porosity of plunger samples ranges from 0.86％～6.59％(average:3.58％);the permeability is 0.000 85～14.75 mD(average:1.71 mD).The porosity of full diameter cores is 1.15％～8.42％(average:3.84％);the permeability is 0.003～16.8 mD(average:2.16 mD).The reservoir is mainly dissolution pores and fractures,and belongs to the low porosity and permeability reservoir.②The platform margin microbial mound sedimentation is the basis for the development of high-quality reservoirs in the Deng 4 Member in the PS8 well area.Supergene regolith karst and buried hydrothermal dissolution are the key factors controlling the development of dissolution pores of the reservoir.This study evaluated the mound-shoal reservoir characteristics defined the genesis mechanism of the Deng 4 Member.It provides a theoretical basis for the reservoir development and distribution prediction,as well as geological evidence for the designation of evaluation schemes.
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