保德区块煤层气勘探历程与启示

主要根据地质认识转变、技术发展、钻井数量、勘探成果与产气量,将保德区块煤层气勘探历程划分为4个阶段。对外合作勘探评价阶段,水平井型排采8+9#煤层,产水量大、排液降压困难;井组试采评价阶段,丛式井组合层排采4+5#煤层和8+9#煤层,排水采气效果显现;勘探开发一体化先导试验阶段,优选富集区井网面积降压试采,获得高产突破;大规模开发与滚动扩边评价阶段,有利区规模建产及复杂区滚动扩边勘探,实现年产气量5×10⁸ m³。以地质认识进展和勘探成果为依据,总结了保德区块低阶煤层气气源成因、成藏模式与“甜点”评价对于勘探开发的启示,提出低阶煤层气“热成因气为主、生物成因气补充”、“水动力控气、单斜缓坡成藏”理论,建立低阶煤层气富集“甜点”评价指标体系。以期对低阶煤层气勘探工作具有启迪意义。

Exploration History and Enlightenment of Coalbed Methane in Baode Block

Mainly based on the changes in geological knowledge, technological development, number of drilled wells, exploration results and gas production, this paper divides the CBM exploration process of the Baode Block into four stages: (1) Stage of foreign cooperation on exploration and evaluation: 8+9# coal seams were recovered by drainage in horizontal wells, with large water production and difficulties in drainage and pressure reduction; (2) Stage of production test and evaluation of well groups: 4+5# coal seams and 8+9# coal seams were recovered by drainage in cluster wells, with good effect of gas production by drainage; (3) Pilot test stage with integrated exploration and development: the breakthrough in high-yield was achieved through area depressurization of the optimized well pattern in oil-enriched zones; (4) Large-scale development and rolling expansion and evaluation stage: Large-scale productivity construction in favorable areas and rolling expansion exploration in complex areas have been implemented and an annual output of 5×10⁸ m³ have been achieved. Based on the geological understanding and exploration results, this paper summarizes the origin of low-rank coalbed gas, accumulation mode, and “sweet spot” evaluation and the enlightenment to CBM exploration and production in Baode Block. The accumulation theories such as “thermogenic gas as the main source, biogenic gas as the supplement”, “hydrodynamics-controlled gas, monocline and gentle slope” are proposed, and the evaluation index system of “sweet spot” of low-rank coalbed methane enrichment is established. We hope to provide implications to the exploration of low-rank coalbed methane.