Abstract:

The effective prediction of high production areas of CBM is of great significance to improve the production and the development benefits of single wells. In order to the evaluate the production capacity of CBM formation quantitatively, based on the development mechanism of CBM, the data of CBM in southern Qinshui Basin was used to define the absorption efficiency index and the gas production capacity index through the theory and statistical analysis. And the reliability of gas production capacity was quantitatively evaluated from 3 aspects of gas content ability, desorption efficiency and output capacity of the reservoir. The results showed that, in the evaluation of gas content, to remove gas saturation and increase the differential pressure of formation pressure and desorption pressure—which represented the macroscopic desorption efficiency—in the desorption efficiency index can greatly improve the correlation between daily gas production and gas content, desorption efficiency index respectively. The daily gas production increased with the increasing of gas bearing index, desorption efficiency index and the production capacity index. When the gas content, the desorption efficiency index and the permeability were respectively higher than 15 m ³/t, 0.11 （MPa·d） ^-1 and 0.03×10 ^-3μm ², the daily gas production could be more than 800 m ³. When the gas content, desorption efficiency index and production capacity index were defined as the gas production capacity index of CBM, high production areas of CBM could be effectively predicted. When the gas production capacity index was great than 0.05×10 ^-3μm ²·m ³·（t·d·MPa） ^-1, the daily gas production was more than 800 m ³, while the index was greater than 1×10 ^-3μm ²·m ³·（t·d·MPa） ^-1, the daily gas production was more than 1 500 m ³.

Key words: Qinshui Basin, high coal rank, coalbed methane（CBM）, formation evaluation, quantitative evaluation, gas production capacity index