Development practice and challenges of deep shale gas in southern Sichuan Basin
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摘要: 深层页岩气资源量丰富,开发潜力巨大,但工程地质条件相对略差,效益开发难度较大。为支撑深层页岩气的效益开发,以四川盆地南部地区威荣和永川气田的开发实践为例,针对深层页岩气构造复杂、断缝发育、优质储层薄、产量递减快、最终可采储量低等难点,以“布好井、打好井、管好井”为目标,在气藏精细描述、渗流实验等研究基础上,采用地球物理—地质建模—压裂模拟—数值模拟一体化方法,形成了以地质甜点评价与预测技术、复杂构造区井网优化设计技术、“四位一体”钻井跟踪保障技术和全生命周期生产精细管控技术为核心的开发关键技术体系。同时,根据开发中暴露出的问题,梳理总结了在“构造—断裂—应力场”耦合机理、小—微尺度裂缝精细刻画、开发技术政策优化等方面的难点,提出了持续攻关的方向。研究认为:①深层页岩孔隙度、含气量等地质参数与中深层基本相当,但工程参数更复杂,具有地应力高、水平应力差高和破裂压力高的特征,改造难度大;②深层页岩气已在甜点评价与预测、建模—数模一体化技术和精细生产管理等方面形成了关键配套技术,取得了较好的开发效果;③目前深层页岩气主要面临套变、压窜、最终可采储量不达标等方面的难题,需要持续深化地质精细评价、流体运移规律和建模—数模一体化等技术攻关。Abstract: There is great potential for developing deep shale gas resources, but the engineering geological conditions are relatively poorer, making it difficult for benefit development. In order to support the benefit development of deep shale gas, taking the development practices of Weirong and Yongchuan gas fields in the southern region of Sichuan Basin as an example, focusing on the difficulties of complex deep shale gas structures, developed fractures, thin high-quality reservoirs, rapid production decline, and low EUR, with the goal of "good well placement, good well drilling, and good well management", a key development technology system is formed by use of the integrated method of geophysics, geological modeling, fracturing simulation, and numerical simulation based on the research on precise gas reservoir description and seepage experiments, which is characterized by geological sweet spot evaluation and prediction technology, well network optimization design technology in complex tectonic areas, "four in one" drilling tracking guarantee technology, and full life cycle production control technology. At the same time, based on the problems exposed during development process, the difficulties and challenges in the coupling mechanism of "structure-fault-stress field", characterization of small-scale and microscale fractures, optimization of development technology strategies were summarized, and the problems that need to be continuously studied were proposed. The conclusion is that: ① The geological parameters such as porosity and gas content of deep shale are basically equivalent to those of medium-deep strata, but the engineering parameters are more complex, characterized by high in-situ stress, high horizontal stress difference, and high fracture pressure, making it difficult to transform; ② Key supporting technologies in dessert evaluation and prediction, modeling-numerical simulation integration technology, and fine production management has been formed in deep shale gas, with good development results; ③ At present, deep shale gas is mainly faced with challenges such as casing deformation, pressure channeling, and EUR non-compliance. It is necessary to further advance technical research in geological fine evaluation, fluid migration patterns, and modeling-numerical simulation integration.
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表 1 川南威荣、永川深层页岩气与涪陵中深层页岩气地质工程参数对比
Table 1. Comparison of geological engineering parameters between Weirong, Yongchuan deep shale gas reservoirs and Fuling medium-deep shale gas reservoir, southern Sichuan
地质工程参数 中深层 深层 对比情况 涪陵气田 威荣气田 永川气田 埋深/m 2 400~3 500 3 550~3 880 3 800~4 200 深500~1 500 TOC大于3%页岩厚度/m 30.5 17.5 20.5 薄10~13 孔隙度/% 5~7 4.6~6.5 5~6 相当 含气量/(m3/t) 6~10 5~8 5~9 相当 沉积微相 硅质深水陆棚 内灰质深水陆棚 外灰质深水陆棚 相带略差 硅质含量/% 55 38 42 低13~17 钙质含量/% 10 22 13 高3~12 黏土含量/% 35 40 45 高5~10 地压系数 1.35~1.55 1.9~2.0 1.6~2.1 高0.3~0.6 杨氏模量/GPa 38.4 21.6 26.8 低10~15 泊松比 0.19 0.23 0.25 高0.04~0.06 力学脆性指数 0.62 0.43 0.46 低0.16~0.20 最小水平应力/MPa 48.3~58.4 86~98 90~100 高30~40 水平应力差/MPa 7.5~8.2 10~16 10~20 高3~12 破裂压力/MPa 55~70 95~113 91.4~114 高30~40 表 2 川南威荣、永川深层页岩气与涪陵中深层页岩气主要生产动态指标对比
Table 2. Comparison of main production performance indicators of Weirong and Yongchuan deep shale gas reservoirs and Fuling medium-deep shale gas reservoir, southern Sichuan
不同阶段生产动态指标 威荣气田 永川气田 涪陵气田 排液阶段 初期井口压力/MPa 47.3 52.8 26.5 最高日排液量/m3 650 420 35 阶段返排率/% 39 17 4.3 定产降压 初期产量/(104 m3/d) 7.5 5.5 8 稳产期/d 120 260 680 单位压降产气量/(104 m3/MPa) 58.6 51.8 272.4 稳产期累产气量/(104 m3) 1 983 1 942 6 785 定压降产 首年递减率/% 64 58 45.2 返排率/% 85~90 55~60 10~15 表 3 川南威荣、永川深层页岩气排液阶段“五段式”闷排制度
Table 3. "Five stage" shut-in drainage system for Weirong and Yongchuan deep shale gas during drainage stage, southern Sichuan
序号 阶段 时间/d 目的 制度/mm 1 闷井 5~9 达到渗吸平衡 2 纯排液 9~15 降低应力敏感性、防支撑剂回流 2~5 3 见气初期 10~20 降低应力敏感、防裂缝快闭合 5~7 4 气相突破 12~18 降低地层能量损失 7~9 5 稳定测试 5~7 获取稳定测试产量及压力 6~8 表 4 川南威荣、永川深层页岩气定产降压阶段生产管控标准
Table 4. Rate control standards for Weirong and Yongchuan deep shale gas fields in southern Sichuan
压力区间/MPa 生产制度/(104 m3/d) 压降速度/(MPa/d) 稳产期/d 单位压降产气量/(104 m3/MPa) 35~45 6~8 ≤0.12 80 ≥45 25~35 5~7 ≤0.1 100 ≥50 20~25 4~6 ≤0.08 60 ≥60 10~20 4~6 ≤0.05 200 ≥80 3.5~10 3~5 ≤0.03 220 ≥100 注:当井口压力下降至20 MPa时,开展下油管作业,以提升气井的携液生产能力。 -
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