基于等温吸附曲线煤储层评价指标的建立

Establishment of coal reservoir evaluation indexes based on adsorption isotherm curve

云南YW煤层气区块9号煤层平均含气量虽然较高,达9.7 cm^(3)/g,但由于地质构造复杂,经多年勘探评价,仍未取得突破,单井产气量仅50~300 m^(3)/d。基于等温吸附曲线,从煤层气成藏要素-吸附气体、煤储层介质及外部围岩环境的角度,通过数学推导、计算及实验数据的统计分析,筛选并定义了三个煤储层评价指标-含气指数(GBI)、构造煤指数(TDCI)和保存压力(PP)。采用该指标体系对云南YW区块9号煤层进行了评价,结果表明:含气指数较高区域(GBI>0.6)位于区块中部,但该区域主要为碎粒和糜棱结构的煤体结构,容易造成气体运移通道堵塞,导致现有单井产气量不高;仅在北部原生-碎裂结构分界线附近较适宜部署,实际有利区非常有限。因此,该指标体系为构造复杂煤层气区块的储层评价提供了一种新思路。

Although the average gas content of the 9th coal seam in YW CBM block of Yunnan Province is relatively high,reaching 9.7 cm^(3)/g,due to the complex geological structure,after years of exploration and evaluation,no breakthrough has been made,and the gas production per well is only 50~300 m^(3)/d.Based on the adsorption isotherm curve,from the perspective of main coalbed methane accumulation elements-adsorbed gas,coal reservoir media and external surrounding rock environments,through mathematical deduction,calculation and statistical analysis of experimental data,three coal reservoir evaluation indexes were screened and defined,gas bearing index(GBI),tectonically deformed coals(TDCI)and preserval pressure(PP).And this index system was used to evaluate the 9th coal seam of YW block.The results show that an area with a higher gas bearing index(GBI>0.6)is located in the middle of the block,but it is only suitable for deployment near the northern primary-cataclastic structure boundary,and the actual favourable area is very limited due to the coal body structure of granulated and mylonitic textures in this area,which is easy to cause blockage of gas migration channel and lead to low gas production in the existing single well.Therefore,these indexes provide a new idea for the reservoir evaluation of coalbed methane blocks with a complex geological structure.