四川盆地南部威荣、永川地区深层页岩气勘探开发进展、挑战与思考

Deep shale gas exploration and development in the Weirong and Yongchuan areas,South Sichuan Basin: Progress, challenges and prospect

中国3 500 m以浅的页岩气已实现了效益开发,并形成了较完善的地质理论和一系列勘探开发技术。对于3 500 m以深的深层页岩气,虽然地质参数整体优良,但工程地质条件变差,有效开发难度大。为了进一步提高深层页岩气勘探开发效益,以四川盆地南部威荣、永川地区深层页岩气为例,在对比中深层页岩气地质—工程参数特征的基础上,归纳总结了该区深层页岩气在地质、钻完井、压裂、采输等方面的技术进展,剖析了深层页岩气勘探开发面临的问题与挑战,并预测了未来发展方向。研究结果表明:(1)深层页岩在地球化学指标、脆性矿物含量、孔隙度及含气性等基础地质特征方面与中深层页岩相似,但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;(2)深层页岩裂缝总体欠发育,地应力复杂,有效改造体积偏小,以致气井初期产能低、递减快、最终可采气量低、返排液高,制约了深层页岩气效益开发;(3)深层页岩气勘探开发已在甜点评价与预测、建模—压模—数模一体化、优快钻完井、体积压裂、“三精”生产管理、集约化采气等方面形成了关键配套技术;(4)目前深层页岩气勘探开发主要面临套变、压窜以及改造效果不理想等方面的难题,需持续做好地质评价、建模—数模、钻井、压裂以及采输等技术攻关。结论认为,已形成的深层页岩气勘探开发关键技术对提升中国页岩气保障能力具有重大意义,但深层页岩气勘探开发面临的理论认识与工程工艺技术创新是一个长期的过程,需长期投入、循序渐进攻关,才能实现深层页岩气的规模效益开发。

Benefit development of shale gas has been achieved in areas above 3 500 m in depth in China, and relatively thorough geological theories and exploration & development technologies have been formed. Although the deep shale gas at such depth is of good geological parameters, it is difficult to develop effectively due to worse engineering and geological conditions. In order to improve the exploration and development benefit of deep shale gas, based on comparison of geological–engineering parameters between deep and medium shale gas, taking the deep shale gas in the Rongwei and Yongchuan areas as an example, this paper summarizes the technical progresses in geology, drilling, completion, fracturing, production, and transportation, analyzes the involved problems and challenges,and predicts the future development direction. The following results were achieved.(1) The basic geological characteristics of deep shale,such as geochemical indicators, content of brittle minerals, porosity and gas-bearing property, are similar to those of medium–deep shale,but the engineering and geologic features are more complex, with the characteristics of high geostress, high horizontal stress difference,high plasticity and high formation pressure.(2) Due to the less developed fractures within the deep shale and complex geostress of the study area, the effective fracturing volume is small, leading to a low initial productivity, rapid production decline, low EUR and high fracturing fluid backflow rate, which have restrained the benefit development of deep shale gas.(3) A complete set of key matching techniques have been established for the exploration and development of deep shale gas, such as evaluation and prediction of sweet spots,integration of geological modeling–fracturing simulation–numerical simulation, excellent and fast drilling and completion, volume fracturing,production management with "three-precises" and intensive gas production.(4) Currently, the exploration and development of deep shale gas are facing several key problems(such as casing deformation, fracturing pressure channeling and poorly reservoir reconstruction effect), so technological research on geological evaluation, geological modeling–numerical simulation, drilling, fracturing, production–transportation should be carried out constantly. In conclusion, to form key technologies for deep shale gas exploration and development is of great significance to improving China’s shale gas supportability. However, the theoretical understanding and engineering technology innovation during exploration and development of deep shale gas is a long-term process, which needs long-term investment and progressive breakthrough to realize large-scale and benefit development of deep shale gas.