威荣区块深层页岩气井体积压裂技术

Volume fracturing technology of deep shale gas well in Weirong block

威荣区块页岩气储层埋藏深(3550~3880 m),地应力高(垂直地应力86.0~97.7 MPa),水平地应力差大(7~17 MPa),岩石脆性指数低(小于0.50),天然裂缝不发育,压裂面临施工压力高、压力窗口窄、敏感砂比低、加砂难度大的难题。大型物理模拟实验表明,威荣区块深层页岩气井压裂裂缝形态以主缝+分支缝为主,裂缝复杂程度较低。根据地质、工程因素优化分段分簇位置,以最大改造体积为目标优化分段分簇数量,实现了对地层的密切割;采用密切割及复合暂堵压裂技术,提高了水平段裂缝的横向覆盖率;通过研究支撑剂输送规律,优化了3级粒径支撑剂的铺置方式,提高了加砂强度;采取缝内暂堵、二次压裂、增加压裂液黏度和施工排量等措施,提高了缝内净压力及裂缝复杂程度。采用以上技术,最终提高了压裂有效改造体积和最终可采储量。研究成果在威荣区块页岩气井得到了成功应用,平均单井加砂强度提高到2.00 m^(3)/m,平均单井无阻流量为48.2×10^(4) m^(3)/d,平均单井最终可采储量为1.10×10^(8) m^(3),改造效果较前期显著提高。压后评估表明,最终可采储量与加砂强度呈正相关关系。提高深层页岩气加砂强度、控制用液强度,是经济有效压裂的关键。

Due to the large buried depth(3550-3880 m),high in-situ stress(vertical stress 86.0-97.7 MPa),high horizontal in-situ stress difference(7 to 17 MPa),low rock brittleness index(less than 0.50),and the undeveloped natural fracture,the hydraulic fracturing in Weirong block faces the problem of high operation pressure,narrower pressure window,low sensitive sand concentration,high difficulty to pumping sand.Large-scale physical model experiments show that the morphology of shale fracturing fracture in Weirong block is composed of main fracture and branch fracture,the complexity of fracture is lower.The location of stages and clusters was optimized according to the geological and engineering factors,and the number of segment clusters was optimized by maximizing SRV(stimulated reservoir volume)to realize the dense cutting of the reservoir.The transverse fracture coverage rate in horizontal section was improved by dense cutting and the combined temporary plugging and fracturing technology.Through the study of proppant transport law,the placement mode of three-stage particle size proppant were optimized,and the sand adding intensity was improved.By temporary plugging within the fracture,secondary fracturing,optimizing the flow rate and fracturing fluid viscosity,the net pressure within the fracture and the complexity of the fracture are improved,so as to increase the SRV and EUR(estimated ultimate recovery).The research results have been successfully applied in the Weirong block shale gas field.The sand intensity per well has been increased to 2.00 m^(3)/m,the average open flow per well is 48.2×10^(4) m^(3)/d,and the EUR per well is 1.10×10^(8) m^(3)/d.The performance of fracturing is significantly improved.Post-fracturing evaluation shows that the fracturing effect is positively correlated with sand intensity.So how to improve sand intensity and control fluid intensity is the key to economic and effective fracturing for deep shale gas.