准噶尔盆地煤层气勘探开发与地质研究进展

Advance on exploration-development and geological research of coalbed methane in the Junggar Basin

准噶尔盆地煤层气资源极为丰富,已开展近30个煤层气勘查项目,施工煤层气井270余口,建成白杨河、四工河、乌鲁木齐河东煤层气开发先导试验区,正在着力推进煤层气规模化开发利用,多个区块呈现出煤层气单井高产势头,针对多、厚、大倾角煤层顺煤层钻井、储层改造、优化排采技术不断推广应用,带动了新疆煤层气产业起步发展。系统总结准噶尔盆地煤层气成藏特殊地质条件,科学分析前期煤层气勘探开发的现状与趋势,全面梳理煤层气勘探开发所面临的地质难题,以期为新疆地区乃至中国中低煤阶煤层气的高效开发提供借鉴。盆地周缘构造隆升、水力逸散、煤层气风氧化带深延是制约煤层气资源分布和勘探开发潜力的不可忽略的地质因素,盆地腹地包括煤层气在内的深部煤系气资源潜力巨大,开展煤系油气地质综合研究、拓展煤系气勘探开发领域势在必行。盆地边缘多个区块煤层气富含CO_(2)且呈现随煤层埋深增大CO_(2)体积分数增高的异常现象,拟以水动力场和水化学场耦合作用为主线,气体差异构成与禀赋为线索,鉴别多源多阶气体来源、混合度及成藏贡献,揭示CO_(2)异常富集成因,探索流体场主导作用下的煤层气多源多阶多因素耦合成藏机制。盆地西山窑组与八道湾组2套煤系地层厚度巨大,受聚煤环境控制,多层叠置统一、多层叠置独立、多层叠置混合含煤层气系统空间分布有别,基于沉积、构造、水文耦合作用归纳出煤层气富集成藏基本模式,有效厘定流体压力系统,合理选层选段、组合开发,优势成藏地质配置及其区域、局域、层域变化规律有待深入研究。盆地周缘煤储层倾角大多超过35°,急倾斜煤储层在较小空间随深度发生快速变化,储层流体运动方式、储层应力状态等影响制约压降传播和煤层气产出过程,开发过程储层力学性质与物性变化、流体相态与饱和关系转化、气/水产出机制与生产规律需要进一步揭示。

The Junggar Basin is extremely rich in coalbed methane(CBM)resources.Nearly 30 CBM exploration projects have commenced,and more than 270 CBM wells have been drilled.Some pilot test areas for the CBM development in Baiyang river,Sigong river and the eastern Urumqi river have been built,and large-scale CBM development and utilization is being promoted.In the Junggar Basin,many blocks show the momentum of high production in a single CBM well.For multiple,thick and high dip angle coal seams,the technologies including drilling along coal seam,reservoir transformation,and optimized drainage have been continuously promoted and applied,which leads to the development of CBM industry in Xinjiang.This paper systematically summarizes the special geological conditions of CBM accumulation in the Junggar Basin,scientifically analyzes the current status and trends of CBM exploration and development in the early stage,and comprehensively presents the geological problems faced by CBM exploration and development,in order to provide a reference for the efficient development of low-and medium-rank CBM in Xinjiang and even in China.The structural uplift,hydraulic dissipation,and the deep extension of the CBM aeolian oxidation zone in the basin margin are geological factors that restrict the distribution of CBM resources and the potential of CBM exploration and development,and cannot be ignored.The deep coal measure gas resources in the basin center,including CBM,have huge resource potential.It is imperative to carry out comprehensive geology research on coal measure gas and expand the exploration and development field of coal measure gas.The CBM in many blocks at the basin margin is rich in CO_(2)and presents an abnormal phenomenon that the CO_(2)concentration increases with the increase of coal seam depth.Taking the coupling effect of hydrodynamic field and hydrochemical field as the main guide,and the difference of gas composition and occurrence as clues,the source,mixing degree and accumulation contribution of multi-source and multi-stage gas have been identified,and the abnormal CO_(2)enrichment has been revealed.Furthermore,the multi-source,multi-stage and multi-factor coupling accumulation mechanism of CBM under the leading action of fluid field is being explored.The thickness of the two sets of coal measure strata in the Xishanyao Formation and the Badaowan Formation in the basin is huge.Under the control of the coal accumulation environment,it has different spatial distributions between the unified,independent and mixed multilayer overlapping gas-bearing systems.Based on the coupling of sedimentation,structure and hydrology,the basic accumulation model of CBM is summarized.However,many issues need to be studied in depth,including the effective determination of fluid pressure system,reasonable layer selection and combined development,advantageous geological configuration of CBM accumulation and its regional,local and stratigraphic change rules.Most of the dip angles of coal reservoirs at the basin margin exceed 35°,and the steeply inclined coal reservoirs change rapidly with depth in a small space.The fluid movement mode,stress state in the reservoir,etc.affect the pressure drop propagation and CBM production process.As a result,the changes in reservoir mechanical properties and physical property,transformations in fluid phase state and saturation relationship,gas/water output mechanism and law during the CBM development process need to be further investigated.