Application of fuzzy mathematics in selecting the favorable location of shale gas survey well: Taking northwest Guizhou as an example

Exploration and development of shale gas in China is now in the early-middle stage. Drilling geological survey well is an important mean to obtain data and discover shale gas in the blank area of Lower Paleozoic shale data in south China. However, due to the extremely complex structure and geomorphic conditions in these areas, it is very difficult to optimize the location of wells. Taking northwest Guizhou as an example, based on a large number of field geological survey work, the evaluation criteria of geological and engineering geological conditions for shale gas survey well location are put forward. In the respects of geological conditions, according to shale thickness, predicted depth, dip angle, fracture density, organic matter features, stress field, hydrogeology and other conditions, the alternative well position is divided into 5 levels:excellent, good, medium, medium deviation and poor. In the respects of engineering geological conditions, according to topographic height difference in well site, road distribution, water resources can be used, air barrier, the distance from the building and other conditions, the alternative well position is divided into the same 5 levels. At the same time, the weight of each element in the evaluation is determined. 5 alternative well locations were evaluated and sorted by using fuzzy mathematics. And 2 selected drilling wells have been drilled successfully. This method has reference value for obtaining shale gas data in the blank area, obtaining shale gas quickly and carrying out further evaluation work.