Candidate well selection model of shale gas wells for refracturing based on geological and engineering conditions and stimulation performance of primary fracturing

It is difficult to select candidate wells for shale gas refracturing. In this regard, an evaluation model for shale gas refracturing candidate well selection was built with five evaluation indexes depending upon the geological conditions, treatment parameters and stimulation effects of primary fracturing. The indexes are the horizontal stress difference coefficient, shale gas reservoir evaluation index, single-well liquid injection index, single-well proppant injection index and primary SRV (stimulated reservoir volume) ratio. First, the geological conditions of candidate wells during primary fracturing were evaluated as per the horizontal stress difference coefficient and shale gas reservoir evaluation index. Second, the primary fracturing treatments of candidate wells with better reservoir geological conditions were evaluated according to the single-well liquid and proppant injection indexes. Finally, the target wells for refracturing were optimized in accordance with the geological and engineering conditions and the SRV ratios of primary fracturing. The model was validated via applications to shale gas wells in the southern Sichuan Basin to optimize the target wells for refracturing. The results show that the model is helpful to the optimization of refracturing candidates of shale gas horizontal wells in South Sichuan, and is of great significance to refracturing of shale gas wells.