Fracability Evaluation of Tight Sandstone Oil Reservoirs Based on Combination Weight Method
摘要
The reservoir fracbility evaluation is an essential prerequisite for the selection of fracturing sweet spots and the productivity evaluation after hydraulic fracturing. In this work, in the geological setting of the Chang 7 tight sandstone formation in the Ordos Basin, China, based on the combination weight method combining the analytic hierarchy process, CRITIC method and entropy weight method, a fracability evaluation model of tight reservoirs was established. And a two-level fuzzy comprehensive fracability evaluation method in combination with combination weight is presented. A field pilot confirms the effectiveness of both evaluation methods. Field application cases indicate that the two methods obtained basically consistent evaluation results. The results show that the horizontal stress difference coefficient has the largest impact on the reservoir fracability, followed by the brittleness index, and Poisson’s ratio ranks third. Reservoirs with a fracability index higher than 50% are fit for large-scale volumetric fracturing; reservoirs with a fracability index ranging from 30% to 50% are suitable for conventional fracturing; and reservoirs with a fracability index lower than 30% are generally considered unsuitable for hydraulic fracturing operations. The findings in this study can provide a guide for the selection of favorable areas for volume fracturing and the optimal design of hydraulic fracturing.