A dynamic prediction model of reservoir pressure considering stress sensitivity and variable production

Abstract

In the early stage of coalbed methane (CBM) development, a reasonable depressurization rate is beneficial for CBM wells to achieve high and stable production. The daily water production or the bottom-hole pressure (BHP) in current prediction models of reservoir pressure needs to be kept constant, while the production system is constantly changing. To explore the refined drainage strategy, a dynamic prediction model of reservoir pressure considering stress sensitivity and variable production was established. Based on actual production data, the model could achieve real-time monitoring of reservoir pressure, absolute permeability, and pressure propagation distance. Furtherly, the pressure dynamic variation law in the single-phase water flow stage of CBM reservoir development in the Baode area was quantitatively characterized and the dewatering rate was optimized. The study found that in the early stage of CBM well development, the dewatering rate mainly affects the reservoir pressure in near-wellbore areas. The effective stress of the reservoir within 20 m from the wellbore has a great influence, and the key to controlling the influence of stress sensitivity is to monitor the reservoir pressure and adjust the dewatering rate. Reducing the dewatering rate can restore pressure and reduce the effect of stress sensitivity near the wellbore during continuous drainage. Shut-in for 1–2 days during the drainage process to achieve the best effect of pressure recovery. Based on the effective verification of 20 wells, the four-stage drainage scheme (A: slow increase; B: rapid increase; C: pressure recovery; D: continuous depressurization) is formulated, and the depressurization effect of the four well groups is increased by 3.65%, 5.47%, 6%, and 3.74%, respectively.