Understanding and practice of fracturing in normal-pressure shale gas,Dingshan block,Sichuan Basin
Normal-pressure gas reservoirs in Dingshan block along the margin of Sichuan Basin are confronted with techni-cal challenges,i.e.,low fracture-induced complexity giving rise to shortage of fracture-conditioned reserves,inconvenient post-fracturing drainage creating slow productivity release,and small recoverable reserves and difficult benefit develop-ment.With three objectives of addressing these challenges,such as the adequate reserve control in stimulation areas,and the reduction of both drainage load and stimulation cost,an efficient stimulation process with low cost,which the extreme limited-entry perforation to promote equilibrium and the integrated fracturing and drainage for composite load reduction are conducted as the dominant measures,and the simple formula of"drag reducer+cleanup additive"is used for cost re-duction,has been developed for the normal-pressure shale gas in this block.Results show that(i)the extreme perforation can ensure the uniform initiation of fracture clusters,enhance the coverage rate from 75%to 90%in single-stage fractur-ing,and make the stimulated reservoir volume(SRV)by 15%higher than before;(ⅱ)the drainage load is released through the composite load reduction,and the intensity of both fracturing fluid and proppant is optimized to be 15-20 m3/m and 1.5-2.0 m3/m,respectively.The rapid startup and drainage after fracturing without shut-in,running tubing during the ini-tial fracturing,and gas lift cleanup can release the productivity while SRV assurance;and(ⅲ)the fracturing-fluid system with low damage and cost can cut down the cost under such stimulation.Practice has proven that,after the application of this new low-cost fracturing technology to normal-pressure gas reservoirs by 6 well times from 2022 to 2023,the stimula-tion effect is improved by 60.2%and the fracturing cost reduced by 15.3%,respectively,which may provide successful ex-perience for the subsequent large-scale benefit development in the low-grade reservoirs with normal pressure.
Margin of Sichuan BasinNormal-pressure shale gas reservoir in Dingshan blockLower Silurian Longmaxi FormationLow-cost efficient fracturingLimited-entry perforationIntegrated fracturing and drainageCost reduction
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