贵州省织金区块岩脚向斜煤层气富集高产规律研究

针对南方煤层层数多、单层薄，构造复杂，糜棱煤发育，选区评价难度大等问题，利用织金区块勘探成果及分析化验数据，开展了多煤层煤层气成藏条件研究。结果表明，南方多煤层煤层气具有“沉积控储，保存控气，地应力、煤体结构控产”四元富集高产规律。沉积控制煤层厚度、层数、煤岩煤质等，决定了煤层气资源基础，潮坪沼泽控制下的煤层分布稳定，连续性好，灰分小于20%，镜质组体积分数大于80%。构造、水文地质联合控制煤层含气性，呈现出向斜核部富气特征，珠藏次向斜翼部往核部方向，随着埋深增大，氯根质量浓度及储层压力逐渐增大，含气量由8 m³/t逐渐增大到28 m³/t。构造作用影响煤体结构、地应力大小及现今地应力状态，进而影响压裂改造效果、渗流条件，直接影响煤层气井产能，研究区NE向与NW向构造分属不同形变区，北西向构造珠藏、阿弓、三塘次向斜较北西向构造比德、水公河次向斜形成时间晚，构造作用相对弱，现今地应力小于20 MPa，煤体结构主要为原生结构煤或碎裂煤，且水平应力大于垂向应力，压裂缝以水平缝为主，利于裂缝在煤储层中延伸，煤层气开发条件更有利。通过富集高产规律研究，认为南方多煤层资源基础较好，构造及其对地应力、煤体结构的影响是多煤层选区评价的关键因素，岩脚向斜珠藏–阿弓–三塘次向斜为煤层气开发有利区。区域上，远离威宁—紫云断裂的NE向含煤向斜是南方多煤层煤层气勘探的重点方向。

The enrichment and high yield law of CBM in Yanjiao syncline in Zhijin Block,Guizhou Province

In view of the problems such as the large number of coal seams, the thin single layer, the complex structure, much mylonite coal and hard to evaluate favorable area in southern China, this paper makes use of the exploration achievements and tests data of Zhijin Block to study the reservoir-forming conditions of multiple coal seam CBM. The results show that the enrichment and high yield CBM in south China is characterized by “sedimentation storage-control, preservation gas-control, geostress coal structure control production”. The thickness, number and quality of coal are controlled by sedimentation, which determines the resource base of coal bed methane. The coalbed controlled by tidal flat marsh has stable distribution and good continuity. The ash content is less than 20% and the volume fraction of vitrinite is more than 80%. The structure and hydrogeology jointly control the gas content of coal seam, showing the characteristics of rich gas at the core of syncline and the wing part of Zhuzang sub-syncline develops towards the core. With the increase of burial depth, the mass concentration of chlorine root and the reservoir pressure gradually increase, and the gas content gradually increases from 8 m3/t to 28 m3/t. Tectonization affected coal structure, the magnitude and state of geostress, directly affects the productivity of coalbed methane wells by influencing the effect of fracturing and seepage conditions. NE trending structure and NW trending structure belong to different deformation areas. The Zhuzang, Agong and Santang subsyncline of NW trending structure formed later than Bide and Shuigonghe sub-syncline of NW trending structure, and the tectonic action is relatively weak. The present geostress is less than 20 MPa, and the coal body structure is mainly composed of primary structural coal or fractured coal, and the horizontal stress is bigger than the vertical stress, the fracture is mainly horizontal fracture, which is advantageous to the fracture extension in the coal reservoir, so the CBM development condition is more advantageous. Based on the study of the law of enrichment and high production, it is considered that the implementation of multiple coal seam resource base in south China and the effect of structure on geostress and coal body structure are the key factors for multiple coal seam selection evaluation, and it is clear that the Zhuzang, Agong, Santang sub-syncline in the Yanjiao syncline is a favorable area for CBM development. Regionally, the NE coal-bearing syncline, far from the Weining fault, is the key direction of multiple coal seam CBM exploration in southern China.