Porosity calculation method of complex lithological fractured-porous reservoir

The Xiagou Formation reservoir rocks in Liugouzhuang -Qionglongshan structure in Qingnan Seg of Qingxi Depression in Jiuquan Bain are mainly comprised of the low porosity and low permeability glutenites and shaly dolostones, and the reservoir is regarded as the typical complex lithological fractured-porous one because of. complicated rock mineral composition, high shale content, enriched pyrites and complicated fracture type and combination shape. In such kind of complex lithological fractured-porous reservoir, the shale content in formation couldn't be well indicated by natural gamma-ray log and so on, it was difficult to identify accurately the rock mineral composition by conventional log data, and the associability between single log and core porosity was low, so that there existed evident shortcomings in the calculation methods of adopting the conventional porosity logs and the porosity calculation accuracy was far from meeting the needs of reservoir evaluation and reserve estimation. The porosity calculation model of the glutenites and shaly dolostones was set up through learning and training by use of 3-layer BP neural networks. The average error of the porosities calculated by the model was less than 1.5% as compared . with the core analysis porosities, which can meet the need's of reserve estimation. The porosity calculation accuracy was greatly raised because of applying this model.