Reservoir Characteristics Of Mud Shale During The Middle And Upper Permian In Suolun-linxi Area, Inner Mongolia

Late Paleozoic strata are developped in Suolun-Linxi area of Inner Mongolia. Especially Zhesi and Linxi formation strata of the middle and upper Permian series have a wide distribution in the study zone. Comprehensive analysis shows that in the period of Zhesi formation depositing, the research area developed argillo calcareous neritic- argillaceous neritic- fan delta depositional systems; during the period of the Linxi formation of Upper Permian, the study zone earthcrust started to uplift, neritic facies turned into continental facies, moreover, the semi-deep lacustrine facies-fan delta sedimentary system formed.In Suolun-Linxi area, there widely exposed rich organic matter of dark mud shale during the middle and upper Permian series. It is of rich thickness, and contains grey,grey black and black mudstone and shale, silty mudstone. By the total rock test analysis report of XRD, it comes to that the content of brittle mineral of Zhesi and Linxi formation varies between 59.1%-82.7%, especially including quartz and feldspar, implying a high brittleness index. Thus, these features mean that fracture can be easily made, moreover, it is beneficial to improve the migration pathway and reservoir space; Zhesi and linxi formations contain low content of clay mineral in shale, and the average content is 29.8%- 37.1%. The main type of clay mineral is illite, it is good for fracture and alteration latterly.By the report of SEM and reservoir physical property, it comes to that the Zhesi and Linxi formations have good micropore and microcrack in the shale, and they are most of intergranular pores and intraparticle pores. The pore diameter is general 1-3μm, the maximum is 8μm; the average porosity is 1.288%, the maximum is 4.42%,the average matrix permeability is 0.0262×10-3μm2,the maximum is 0.2758 × 10-3μm2. Comparing to other shale gas basins in and outside, the shale in the middle and upper Permian series of the study area has definite potentiality of condition for accumulation, also has the petrologic feature for reservoir construction.By comprehensive evaluation and analysis of the petrologic and geochemistry features, and the type of reservoir space, also referring to reservoir forming conditions at home and abroad, it comes to a conclusion that the shale in Zhesi and Linxi formation strata of the middle and upper Permian series has broad prospects and certain resource potential of shale gas. It can also come to a preliminary predict that the northeastern region of Holingol area, Tuquan basin and Jarvd has the exploration prospect of shale gas of middle and upper Permian series.