Reservoir Characteristics Of The 8th Memeber Of Lower Shihezi Formation In Su5 Block, Sulige Gas Field

In this paper, the lithology, sedimentary facies and sand body structure characteristics of the 8th memeber of lower Shihezi Formation(H8) of Sulige gas field, Ordos basin, is studied based on detailed core observation, and combined with drilling data, well logging interpretation, comprehensive regional geological knowledge and previous research data. As a result, compiled the He84-He81 sandstone thickness isoline map and sedimentary facies distribution graph based on the above-mentioned characteristics and fine contrast and tracking of small layer sand body. Mainly according to cast thin section, scanning electron microscope, X-ray diffraction, pore permeability and capillary pressure curve analysis results, the rock types, physical property, diagenesis and diagenetic evolution pattern of He8 main reservoir in the study area was studied. The He8 reservoir was predicted and evaluated comprehensively by classifying on the basis of sand body thickness, structure, porosity and other parameters.The lower part of He8 member mainly deposited a set of braided river sand body and low-sinuosity meandering river in the upper part in study area. The river is mainly NW-SE and N-S direction trending. According to single sand body thickness and the combination of sandstone and mudstone relationship,the He8 sand body structure was classfied into continuously stacked, interval superimposed, cross layer and lens isolated these four structure types, of which the continuously stacked structure type is the optimal, and most developed in He84 and He83 layer.He8 reservoir sandstone primitive type is mainly arkose, feldspathic quartz sandstone, lithic feldspathic sandstone, feldspathic lithic sandstone and lithic sandstone, primarily went through the compaction pressure solution, cementation, dissolution and metasomatism, rupture and authigenic mineral filling diagenesis effects, which early chlorite rim cementation, and meteoric water leaching and organic acid hot liquid effect related to the dissolution and rupture effect play a positive role on reservoir protection and transformation.He8 reservoir is controlled at the same time by the original sedimentary environment and late diagenesis effect, sedimentary environment not only determines the distribution of sand body, but also importantly influenced on the properties and structure, main channel and mid-channel bar are mostly continuously stacked, and less content of plastic debris and mud matrix in the clastic particles, thus better primative reservoir characteristics. Under the circumstance, the sandstone is more conducive to the early chlorite cementation and primary intergranular pore preservation, also more conducive to the later dissolution and pore formation of secondary dissolution. Cracking effect can effectively improve the reservoir permeability which also contributed to the dissolution.The reservoir sand body of the He8 is consist of multi period river channel sand body overlapped each other, and the body form is top flat and bottom bumped. Mainly according to the thickness and structure of the sand average porosity, the He8 reservoir is divided into four types in which the reservoir of the lower part of the He8 member which the braided river cause deposition is the most favorable.