Evaluation And Analysis Of Carboniferous Tight Sandstone Gas In Wuwei Basin, North Qilian

Wuwei Basin of the Northern Qilian Mountains is located in the east of Hexi Corridor area, mainly including Wuwei Basin, Minle Basin and Jiuquan Basin. Because there are good petroleum geology conditions to generate tight sandstone gas in Wuwei Basin and it also has favorable value of prospecting. So it is the fatal research in this paper. This paper guides with stratigraphy, sedimentology, structural geology, petroleum geology and other multi-disciplinary theories. It also combines previous research results, regional geological data,14profile data, test data of rock samples, then it sorts out Wuwei Basin geologic structure, carboniferous strata and sedimentary features. Through source rocks, reservoir and cap rocks to analyze the conditions of tight sandstone gas reservoirs.Wuwei Basin’s tectonic position is in the convergence zone between the Northern Qilian Caledonian fold belt and the Alashan block, which is mainly located in the Alashan block, it has a transitional nature from fold belt to block. According to gravity and magnetic data, Wuwei Basin can be divided into five first-order tectonic units and twenty two-order tectonic units. According to the classic sequence stratigraphy, Carboniferous strata can be divided into two systems, the lower Carboniferous includes Qianheishan Formation, Chouniugou Formation and Jingyuan Formation, the upper Carboniferous includes Yanghugou Formation and Taiyuan Formation. According to the lithologic features, sedimentary structure and paleontology logo, Carboniferous System has a sedimentary environment which has marine facies and marine-continental transitional facies, the littoral sedimentary system, shallow sea sedimentary system and delta sedimentary system play a vital role in the sedimentary systems. It develops gray, black mudstone, shale, carbonaceous gray, coal and limestone and is the main source rocks and exploration target.Evaluating the Carboniferous source rocks in three aspects, including the abundance of organic matter, types of organic matter and maturity of organic matter, the source rocks in the upper Carboniferous are better than the lower Carboniferous, especially in Taiyuan Formation and Yanghugou Formation, which supply adequate gas source. Evaluating tight sandstone reservoir by petrography, pore type, reservoir characteristics and diagenesis, Yanghugou Formation which has better reservoir performance in the upper Carboniferous than other Formations can be used as beneficial tight sandstone reservoir. Source rocks and reservoir appeared in each other, the dark mudstone, shale and limestone which are source rocks could also be used as cap rocks, so the self-generating, self-storing and self-sealing system is the main combination type.By the comprehensive analysis, the upper Carboniferous is better than the lower Carboniferous in reservoir forming conditions, especially Yanghugou Formation can be the important rich gas horizon in tight sandstone gas reservoirs.