Research on Water Invasion Intensity of Coalbed Methane Wells Based on Material Balance Method

At present, many coalbed methane wells expose the problem of large water production and low depressurization efficiency which seriously affects gas production. External water supply affects adequate depressurization of coal reservoirs, impeding the desorption and output of coalbed methane and significantly reduces the gas production of coalbed methane wells. In order to evaluate the external water recharge, this paper introduces the concept of conventional oil-gas water invasion and establishes a water invasion intensity calculation model for coalbed methane wells based on the calculation of average formation pressure and the principle of material balance using dewatering data. The model quantitatively evaluates the water invasion intensity of coalbed methane well and is verified by the water head elevation and gas production rate, which is also consistent with the development of faults and aquifer. Corresponding technical measures are taken to avoid the impact of water invasion, including selecting retention and weak water invasion area for productivity construction, using area depressurization well pattern and fracturing the intervals free from water invasion. After field application, the production of low-rank and low-gas-content coalbed methane wells has made a breakthrough. The establishment of this model provides a basis for the productivity construction, well pattern design and fracturing layer selection of coalbed methane wells and has a good application prospect and promotion significance.