Practice and understanding of fracturing in Weirong shale gas field
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摘要: 相比于中浅层,威荣深层页岩气工程地质特征更复杂,具有地应力高、水平应力差高、塑性高、地层压力高的“四高”特征,复杂的工程地质特征带来难以形成复杂缝网、人工裂缝难以支撑与保持及套变异常情况频发三大挑战,具体表现结果就是气井压后单井最终可采储量低。为解决上述难题,经过坚持不懈的探索和实践,压裂工艺在不断发现问题、解决问题过程中持续进步,探索形成了一套基于均衡压裂理念的“精细优化+实时预警+控运行节奏+W型井网”的预防套变及提高压后产量的系列措施。采用该工艺推广应用39井次,压裂效果不断提升,单井平均最终可采储量提高了500×104 m3,套变率从2022年的42.4%降低至目前的16.67%。由于邻井老井生产影响新压裂投产井,导致新井压后产量低于前期,现有400 m(一期)/300 m(二期)井距,压裂规模有下降优化的空间。后续新井应该在剩余储量基础上差异化优化,持续做好压裂技术攻关,实现威荣深层页岩气效益开发。Abstract: Compared to the middle and shallow strata, the engineering geological characteristics of Weirong deep shale gas are more complex, with the four characteristics of high ground stress, high horizontal stress difference, high plasticity, and high formation pressure. The complex engineering geological characteristics bring three major challenges: difficulty in forming complex fracture networks, difficulty in supporting and maintaining artificial fractures, and frequent occurrence of abnormal situations such as casing deformation. The specific performance result is the low single well EUR after gas well fracturing. Through unremitting exploration and practice, the fracturing technology has been continuously improved in the process of discovering and solving problems, and a series of measures of "fine optimization, real-time warning, operating pace control, and W-shaped well network" for preventing casing deformation and increasing post fracturing output has been formed based on the concept of balanced fracturing. The technology has been promoted and applied in 39 wells, and the fracturing effect has been continuously improved, with an average EUR increase of 500×104 m3 per well, and a decrease of casing deformation rate from 42.4% in 2022 to 16.67% at present. Due to the impact of the production of adjacent old wells on the production of newly fractured production wells, the output of new wells after fracturing is lower than the previous stage. With the existing well spacing of 400 m (Phase Ⅰ)/300 m (Phase Ⅱ), there is room for reduction and optimization in fracturing scale. Subsequent new wells should be differentiated and optimized based on remaining reserves, and research on fracturing technology shall be carried out continuously, achieving the beneficial development of Weirong deep shale gas.
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表 1 威荣深层页岩气与邻区浅层页岩气工程地质对比
Table 1. Comparison of engineering geology between deep shale gas in Weirong and shallow shale gas in adjacent areas
对比项目 威荣深层页岩气(中国石化) 威远浅层页岩气(中国石油) 岩石力学特征 埋深/m 3 550~3 880 2 400~3 500 储层厚度/m 27~39 35~50 脆性矿物含量/% 60 57.8~60.1 杨氏模量/GPa 21.6 25~49 泊松比 0.23 0.19~0.24 力学脆性指数/% 0.43 0.45~0.54 应力特征 垂向应力/MPa 92.7 51.9~79 最大水平主应力/MPa 98.6 54.2~89 最小水平主应力/MPa 86~98 48.3~83 水平应力差异系数 0.12~0.2 0.11 水平应力差值/MPa 10~16 5.2 天然裂缝发育程度 相对发育 发育 表 2 威荣深层页岩气不同阶段压裂主要参数对比
Table 2. Comparison of main fracturing parameters in different stages of Weirong deep shale gas
相关参数 探索阶段
(2019年前)提升阶段
(2019—2020年)强化阶段
(2021—2022年6月)均衡压裂阶段
(2022年6月至今)单段段长/m 72 77.2 74.5 40~50 簇间距/m 29.4 12.8 10.6 8.6 加砂强度/(m3/m) 0.78 1.24 2.01 2.0 用液强度/(m3/m) 26.5 27.4 25.4 25~28 综合砂比/% 3.0 4.7 8 6~8 支撑剂粒径 70/140+40/70陶粒 100/200石英砂+70/140陶粒+40/70陶粒 100/200石英砂+70/140石英砂+40/70陶粒 100/200石英砂+70/140石英砂+40/70陶粒 施工排量/(m3/m) 13~15 13~15 16~18 18~20 暂堵工艺 无 缝口暂堵 缝口+缝内暂堵 缝口复合暂堵+缝内暂堵 应用井数/口 6 63 38 39 表 3 威荣深层页岩气不同生产方式生产指标对比
Table 3. Comparison of production indexes of different production modes of Weirong deep shale gas
生产时间 控压生产井 放压生产井 压力/MPa 日产量/104 m3 累产量/104 m3 压力/MPa 日产量/104 m3 累产量/104 m3 半年 20.8 6.8 1 409 10.1 4.3 1 605 一年 6.4 5.7 2 550 3.8 1.8 2 123 一年半 3.5 1.9 3 098 3.5 0.9 2 347 二年 3.5 1.1 3 354 3.5 0.6 2 476 表 4 威荣深层页岩气威荣25平台均衡压裂试验井压裂参数
Table 4. Fracturing parameters of balanced fracturing test wells of Weirong 25 platform for Weirong deep shale gas
井号 改造段长/m 段数 簇数 砂量/m3 加砂强度/(m3/m) 液量/m3 用液强度/(m3/m) 排量/(m3/min) 威页25-1HF 1 372.4 28 157 2 66.7 1.80 39 098.8 28.48 16.5~20.0 威页25-3HF 1 493.0 35 165 2 51.7 1.98 44 873.6 30.05 16.5~19.6 威页25-2HF 1 041.0 11 137 1 10.6 1.36 27 597.0 26.5 13.5~16.5 威页25-4HF 1 334.5 14 168 1 94.0 1.42 37 574.2 25.9 13.5~16.0 表 5 威荣深层页岩气威荣25平台先导试验裂缝监测结果对比
Table 5. Comparison of fracture monitoring results of pilot test of Weirong 25 platform for Weirong deep shale gas
井号 监测段长/m 解释段数 总MSRV/104m3 总ESRV/104m3 威页25-1HF 1 324.4 27 5 600.0 3 773.5 威页25-3HF 1 405.0 33 5 803.5 4 031.2 威页25-2HF 1 041.0 11 3 497.0 2 262.5 威页25-4HF 1 334.5 14 5 250.2 2 619.0 表 6 威荣深层页岩气威荣25平台先导试验压裂效果对比
Table 6. Comparison of fracturing effect of pilot test of Weirong 25 platform for Weirong deep shale gas
井名 初期压力/MPa 初期产量/(104 m3/d) 配产6×104 m3/d,预测EUR/108 m3 威页25-1HF 45 10~13 0.83 威页25-2HF 49 9.5~12 0.78 威页25-3HF 46 10~13 0.81 威页25-4HF 48 9~11 0.76 合计/平均 47 9~13 0.80 -
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