Geothermal Distribution Characteristics in the Qinshui Basin and Its Significance to the Production of Coalbed Methane

Abstract

Temperature significantly affects the storage and transport of coalbed methane (CBM). Studies of geothermal distribution characteristics are important for the exploration and exploitation of CBM. In this study, more than 150 heat flow temperature data from coalbed methane wells in the Qinshui Basin were analyzed to investigate the geothermal distribution and its controlling factors. The results show that the geothermal gradient of the no. 3 coal seam ranges from 0 to 3.7 °C/hm with an average of 1.6 °C/hm, and the terrestrial heat flow of the no. 3 coal reservoir ranges from 0.9 to 94.6 mW/m2 with an average of 41.5 mW/m2. The reservoir temperature shows high values in the central and northwest parts of the basin, while the east and west edges of the basin show negative geothermal anomalies. It is found that groundwater has significant effects on the geothermal distribution in the Qinshui Basin, and with the increase of the groundwater level, the geothermal gradient decreases linearly. In addition, the geothermal gradient and terrestrial heat flow first increase and then tend to be stable with the increase in value of the total dissolved substances. Besides, with an increase in floor elevation, the geothermal gradient first increases linearly and then decreases linearly, obtaining a maximum value at about 450 m (transition floor elevation). This phenomenon is the result of the balance between heat supplying and heat losing. The geothermal distribution characteristics in the Qinshui Basin determine the reservoir temperature of the coalbed methane, and in turn, the reservoir temperature affects the adsorption, desorption, and diffusion behaviors of coalbed methane in situ.

CBM Desorption Model and Stages Based on a Natural Desorption Experiment

“…The study area, the Panzhuang Block, located in the south of the Qinshui Basin, China ( Figure 1 ), is the first large-scale commercial block of surface CBM development; it has a relatively long developmental history and rich exploration and developmental data. 22 As a result, many desorption tests and associated well production histories can be assembled to evaluate the usefulness of such data to investigate the relationship between CBM desorption characteristics and well productivity. Sixty-four samples from six different CBM wells were selected from a larger database for desorption tests from the depth of 244.68 to 775.15 m in Permian in coal seam No.…”