浅谈煤层气与游离气共同开发新思路

A Discussion on New Ideas in CBM and Free Gas Joint Exploitation

游离气是由煤系地层生成的烃类气体,游离于储层储集空间之中而形成天然气气藏,与煤层中的吸附气呈共生关系。根据游离气储集层的岩性及空间组合特征,可将其分为3种类型:煤岩顶板砂岩型、煤岩顶板灰岩型、不整合面灰岩型。测井中子密度重叠法是判别煤系地层游离气层主要的方法之一,拉梅常数、剪切模量及密度预测法可有效识别砂岩中的气饱和层。AVO高异常可准确解释煤层气的富集部位,等温曲线法及补偿中子变化量法能够有效计算煤层气的含气量。游离气与煤层气的成藏特点使得煤层气与游离气共同开发成为可能。以山西沁水盆地为例,介绍了在查明煤层气和游离气富集高产部位后,利用高密度勘探开发井网,有望实现煤层气与煤系地层浅层游离气的联合开发。

The free gas is a kind of hydrocarbon gases generated in coal measures strata,dissociated in reservoir space and forming natural gas deposit and presents coexisting with adsorbed gas in coal seams.According to free gas reservoir lithology and spatial combination features,free gas deposit can be divided into 3 kinds： coal rock roof sandstone,coal rock roof limestone and unconformity surface limestone types.The neutron-density overlapping logging is one of major methods to discriminate free gas layer in coal measures strata,while the Lame＇s constant,shear modulus and density prediction can identify gas saturated layer in sandstone effectively.The AVO high anomaly can interpret CBM enrichment position accurately;isothermal curve method and compensated neutron variation method can estimate CBM content effectively.The reservoiring characteristics of free gas and CBM make the joint exploitation possible.Taking the Qinshui Basin as an example,introduced after the identification of CBM and free gas enrichment and high yield positions,using high density exploration and exploitation well network,the joint exploitation of CBM and coal measures strata shallow free gas is expected to be realized.