Oil & Gas Geology ›› 2023, Vol. 44 ›› Issue (6): 1378-1392.doi: 10.11743/ogg20230604

• Petroleum Geology • Previous Articles     Next Articles

Difficulties and countermeasures for fracturing of various shale gas reservoirs in the Sichuan Basin

Guangfu WANG1,2(), Fengxia LI1,2, Haibo WANG1,2, Tong ZHOU1,2, Yaxiong ZHANG1,2, Ruyue WANG1,2, Ning LI1,2, Yuxin CHEN1,2, Xiaofei XIONG1,2   

  1. 1.Petroleum Exploration and Production Research Institute，SINOPEC，Beijing 102206，China
    2.State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development，Beijing 102206，China
  • Received:2023-08-01 Revised:2023-10-09 Online:2023-12-01 Published:2023-12-20

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Abstract:

The Sichuan Basin and its periphery are rich in shale gas resources. However， diverse sedimentary facies and intricate structures result in significant variations in shale gas productivity across shale gas wells during fracturing tests. Consequently， some fracturing techniques that are effective in high-productivity wells may be subjected to limited popularization. Therefore， there is an urgent need to develop specialized fracturing schemes for different types shale gas. To achieve efficient shale gas recovery， we compare the geological and engineering parameters of blocks with proven shale gas reserves within the Sichuan Basin. These parameters， along with the sedimentary facies types， lithofacies assemblages， burial depths， and pressure systems， are used to classify the shale gas into six types： marine overpressured type of medium-shallow burial depth （burial depth less than 3 500 m）， deep overpressured marine type （burial depth more than 3 500 m）， deep normally pressured marine type， new marine type， deep overpressured type of transition from continental to marine sedimentation， and overpressured continental type of medium-shallow burial depth. Our findings， obtained from numerical simulations and experiments， are as follows： （1） Natural fractures and complex in-situ stress distributions cause uneven fracture propagation and merging. Optimizing perforation parameters and employing the temporary plugging technique can effectively control fracture morphologies and enhance stimulated reservoir volume （SRV）； （2） Interlayers and laminae affect vertical fracture height growth， as well as the proppant migration and placement morphology. Increasing the amount of preflush of high viscosity for fracturing and small-particle-size proppant， is conducive to the fracture longitudinal penetration layers and balanced proppant support； （3） Strong hydration of shales with high clay content can lead to the deterioration of shale mechanical properties and exacerbation of proppant embedment， while optimizing the type and dosage of additives in fracturing fluid systems can inhibit shale hydration. We formulate the optimal design principles and techniques for volume fracturing of horizontal wells in various shale gas reservoirs. The methodology has been successfully applied to the development of deep high-pressure shale gas reservoirs with complex tectonic stress field in the Dingshan block， deep normally pressured shale gas reservoirs in the Lintanchang block， the new-type shale gas reservoirs in marine clastic rocks in the Jingyan-Qianwei block， the shale gas reservoirs of the marine-continental transitional facies in the Dalong Formation in Puguang area， and lacustrine shale gas reservoirs in the Qianfoya Formation， resulting in significant improvement in single well productivity. This study provides valuable experience and reference for efficient fracturing and commercial exploitation of various complex shale gas reservoirs.

Key words: fracturing mechanism, in-situ stress, clay mineral, interlayer, natural fracture, shale gas reservoir classification, Sichuan Basin

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