煤层气“甜点区”地震预测技术及其应用

Seismic prediction technologies of CBM sweet spots and their application

煤层气"甜点区"系指煤层埋藏深度适中、厚度较大、热演化程度合适、含气量相对较高、孔渗性相对较好、单井产量高且稳产的煤层气富集区带。寻找和优选煤层气富集的"甜点"区带,对于煤层气开发井位的部署和优化、提高煤层气井产量、促进煤层气藏的有效开发都具有现实的经济价值。以往的研究成果表明,影响煤层气富集的7项关键地质要素为煤层厚度、煤层埋深、热演化程度、煤层含气量、断裂及裂缝、圈闭条件、煤层脆性。在试验分析的基础上,提出了一种利用地震资料来预测煤层气富集区的地球物理方法,即多种属性相结合的精细构造解释、AVO反演预测裂缝发育特征、多种反演方法相结合预测煤层厚度特征、叠前反演技术预测煤层含气性和脆性特征,然后进行综合评价,优选各要素均为有利的区域确定其为"甜点区"。应用这一技术思路预测出了HC地区煤层气的分布范围,"甜点区"面积达到21.64km2,在区内部署的2口开发井目前排采效果良好,产气量远高于"甜点区"外的井,预测结果与实钻结果相吻合,为类似"甜点区"的地震预测提供了技术参考。

CBM sweet spots are characterized by moderate burial depth of coal seams, relatively large thickness, appropriate thermal evolution degree, relatively high gas content, good porosity and permeability, high and stable single well production. The identifica tion of CBM sweet spots is of great economic significance to the deployment and optimization of CBM well locations, enhancement of CBM well production, and the improvement of effective development of CBM reservoirs. Previous studies reveal that there are seven major parameters that influence the enrichment of CBM, including coal-seam thickness, burial depth, thermal evolution, gas con tent, fault and fracture, trapping condition, and brittleness. Based on the analysis of experiment results, we proposed a geophysical method that can directly predict CBM sweet spots with seismic data, i.e. comprehensive identification of sweet spots based on fine structural interpretation with multiple seismic attributes, fracture mapping via AVO inversion, thickness estimation through the in tegration of multiple inversions, as well as gas storage and brittleness prediction of coal seams by pre stack inversion. These technol ogles were successfully applied to the prediction of CBM sweet spots in the HC area. The two wells emplaced in the predicted sweet spot with an area of 21.64 km2 have a better production performance than those outside the sweet spot.