The characteristics and main controlling factors of high quality tight sandstone reservoir in the 3th member of Xujiahe Formation in West Sichuan Depression

This paper is the result of oil and gas exploration engineering.

Objective The development characteristics and controlling factors of high quality tight sandstone reservoirs have become important and difficult issues in the cooperative exploration of conventional and unconventional oil and gas in the integration of source and reservoir in western Sichuan Depression, the relationship between tight sandstone reservoir characteristics and tight gas accumulation is discussed.

Methods Geochemical, geophysical and sedimentological analysis methods were used to study the development characteristics of tight reservoir in the 3th member of Xujiahe Formation.

Results Analysis of test data revealed the porosity of the reservoir in the third member of the Xujiahe Formation is distributed between 1.11%-5.70% and the permeability is distributed between (0.0017-0.45)×10^-3 μm², which belongs to the category of tight reservoir.Based on the grain size of sandstone, three types of high quality reservoirs are identified in tight reservoir of the third Member of Xujiahe Formation in western Sichuan Depression, namely quartz sandstone and lithic quartz sandstone mainly coarse sandstone, the medium and fine sandstone are mainly lithic sandstone, lithic quartz sandstone and feldspar lithic sandstone.Coarse sandstone is less developed in the study area, and medium and fine sandstone with large thickness are relatively developed in the middle of delta front facies of the central and upper sub-member, and in the late stage and early stage of the high and low system tracts.It is a tight reservoir with low porosity and low permeability, ultra-low porosity and ultra-low permeability, and the reservoir space is dominated by secondary pores, micro-pores and micro-fractures.

Conclusions The development of high quality tight sandstone reservoir is mainly controlled by lithology, sedimentation, stratigraphic sequence and diagenesis.Lithology controls the development type of high-quality reservoir, sedimentation and stratigraphic sequence control the development location of high-quality reservoir, and diagenesis control the formation of high-quality reservoir, tight gas accumulation is restricted by tight sandstone reservoir distribution.