Abstract:

Enrichment mechanism and geological evaluation method of coalbed methane (CBM) enrichment and high production areas is crucial for CBM successful exploration. Previous studies have mostly focused on the formation and forecast of CBM resource enrichment areas. However,CBM production practice in a few decades shows that the source enrichment area is not necessarily a high production area. Therefore, a facing challenge in CBM exploration is how to confirm a CBM high production zone in a resource enrichment area. In this paper, considering the geological characteristics of the middle to high rank coal bearing basins in China, three different middle to high coal rank CBM production fields including the south of Qinshui Basin, the east of Ordos Basin and Lianghuai coal mines were chosen as the study fields. Combining the analysis of geological factors statistics, and the experimental and production data, the results indicate that the coupling of gas content and permeability of coal reservoir determine the formation of enrichment and high production area. Three formation models of CBM enrichment and high production area were proposed. Geological evaluation indicator including seven geological parameters of CBM enrichment and high production area were established by analytic hierarchy process and principal component analysis. CBM production capacity based evaluation method for CBM enrichment and high production area was developed. The above understandings will play an important guiding role in optimizing beneficial CBM exploration target.

Key words: coalbed methane, middle to high coal rank, enrichment and high production area, formation mechanism, evaluation method