As important unconventional oil and gas resources, tight gas occupies an important position in oil and gas exploration in China. China has about more than 2×105 t tight gas reservoirs, accounting for up to 47% of the total... [ view full abstract ]
As important unconventional oil and gas resources, tight gas occupies an important position in oil and gas exploration in China. China has about more than 2×105 t tight gas reservoirs, accounting for up to 47% of the total proved reserves. Sulige gas field is China's current monolithic natural gas field, with the exploration about 40000 km2, and the proved reserves is 1.27 km3. Shan 1 section of Shanxi Formation and He 8 section of Shihezi Formation are the brunt reservoir of tight gas reservoir exploitation in Sulige gas field Upper Paleozoic reservoir. But because of its complex geological conditions, serious reservoir heterogeneity, low porosity, low permeability, small-scale reservoir sand body, low development efforts led to the current study is still at a preliminary stage. The research has applied multidisciplinary theories, such as Sedimentology, reservoir sedimentology, Petroleum Geology, combined with cores, logging, well logging, seismics, analysis assay data and the microscopic data, studied the sedimentary facies types, reservoir physical properties and pore structure characteristics, and analyzed the causes.
The sedimentary environment of He 8 and Shan 1 section in Sulige gas field is relatively complex. The upper part of He 8 section and Shan 1 section developed meandering river deposition, and the lower part of He 8 section is breaded river deposition. High-quality reservoir development mainly in meandering channel, breaded channel and batture microfacies. The reservoir rocks are mainly quartz sandstone, lithic quartz sandstone and lithic sandstone. Pore types are mainly debris dissolution pore, intracrystalline pore, followed by intergranular pore, intergranular dissolution pore and microcrack. Throat types are mainly bending flake throat and flake throat. Diagenesis are mainly compaction, cementation and dissolution. Heterogeneity of reservoir pore throat structure is relatively strong, with features that "small pore throat, poor sorting ,high displacement pressure and small main contribution throat ". Poor physical properties, the overall performance are low porosity and low permeability, porosity is mainly distributed in the range of 4% to 10%, and permeability is mainly 0.1 ~ 0.5mD.
The formation of tight sandstone reservoirs in Sulige gas field is not only related to sedimentation ,but also closely related to diagenesis, from which diagenesis is the dominant factor of the formation of low permeability reservoir in He 8 and Shan 1 section. And the strong compaction and cementation are the key factors of low porosity and permeability, and dissolution make relatively high porosity and permeability zone in tight reservoirs.
