深部(层)煤层气成藏模式与关键技术对策——以鄂尔多斯盆地东缘为例

Deep(layer)coalbed methane reservoir forming modes and key technical countermeasures:Taking the eastern margin of Ordos Basin as an example

我国埋深大于1500 m的深部(层)煤层气资源丰富,但由于地质条件复杂,煤层气富集成藏特征和成藏模式尚不明晰,严重制约了勘探与开发过程中的关键技术选择,一直被公认为是效益勘探与规模开发的禁区,面临许多世界级难题。本文基于鄂尔多斯盆地东缘煤层气生烃、储集、保存条件的系统分析,通过深、浅部(层)煤层气富集成藏条件的精细对比,总结出深部(层)煤层气具有煤层厚度大、煤体结构完整、热演化程度高、煤层含气量高、含气饱和度高、游离气丰富、水动力条件弱等有利成藏条件和基质渗透率低、孔隙连通性差等不利成藏条件,提出“广覆式生烃、自生自储毯式成藏”基本成藏特征;在进一步分析构造、沉积、水文地质成藏条件及开发动态特征基础上,建立深部(层)煤层气微幅褶皱、单斜与水动力耦合、断层与水动力耦合、鼻状构造等4类成藏模式;针对储层精细描述与甜点区识别标准、地质-工程一体化钻井、压裂等理论技术难题,提出地质-工程甜点综合定量评价、工厂化水平井优快钻完井、水平井大规模体积缝网储层改造等关键技术发展方向,助推深部(层)煤层气资源的高效探明和规模效益开发。

China is rich in deep(layer)coalbed methane resources with a buried depth of more than 1500 m,but due to complex geological conditions,the characteristics and modes of coalbed methane enrichment and accumulation are not clear,which seriously restricts the selection of key technologies in the process of exploration and development.It has been recognized as a forbidden area for economic exploration and scale development of CBM,and faces many world-class problems.Based on the systematic analysis of gas generation,reservoir and preservation conditions of coalbed methane in the eastern margin of Ordos Basin,and through the fine comparison of deep and shallow coalbed methane enrichment and accumulation conditions,this paper summarizes that deep(layer)coalbed methane has the characteristics of the favorable reservoir forming conditions such as large coal seam thickness,complete coal body structure,high degree of thermal evolution,high coal seam gas content,high gas saturation,rich free gas,and weak hydrodynamics as well as the unfavorable reservoir forming conditions such as low matrix permeability and poor pore connectivity,therefore puting forward the basic reservoir forming characteristics of“extensive hydrocarbon generation,self generation and self storage blanket type reservoir forming”.On the basis of further analyzing the structural,sedimentary,hydrogeological reservoir forming conditions and development dynamic characteristics,four types of reservoir forming modes,including deep(layer)coalbed methane micro fold,monocline and hydrodynamic coupling,fault and hydrodynamic coupling,and nose structure,are established.In view of the theoretical and technical problems of fine reservoir description and sweet spot identification standards,drilling(fracturing)based on geological engineering integration,this paper puts forward the development direction of key technologies such as comprehensive quantitative evaluation of geological engineering sweet spot,optimal and fast drilling and completion of industrialized horizontal wells,large-scale volume fracture network stimulation of horizontal wells,and promotes the efficient exploration and scale benefit development of deep(formation)coalbed methane resources.