Formation mechanism and drainage control of the bottom hole flowing pressure fluctuation in the coalbed methane wells of the Dahebian Block,Western Guizhou

ZHOU Xiaozhi; ZHU Shiliang; ZHAO Fuping; WANG Shaolei; WEI Yuanlong; ZHOU Peiming; ZHAO Lingyun

doi:10.13247/j.cnki.jcumt.20240372

Abstract：In addressing the engineering issue of frequent fluctuations in bottomhole flowing pressure(BFP)during coalbed methane(CBM)well drainage in the Dahebian Block of the Li-upanshui coalfield in Western Guizhou,a comprehensive study was conducted by integrating data from coal reservoir parameter testing,3D seismic exploration,microseismic monitoring of hydraulic fracturing,and real-time intelligent drainage monitoring.The types and characteris-tics of BFP fluctuations were investigated,and the formation mechanism of these fluctuations,as well as the geological and engineering synergistic control effects on inter-well differential e-volution,were explored.Control measures for suppressing BFP fluctuations during drainage were proposed,which have guiding significance for CBM well drainage in complex structural areas.The study revealed that BFP fluctuations in CBM wells can be categorized into four types:high amplitude and low frequency,medium amplitude and medium frequency,low am-plitude and high frequency,and medium amplitude and high frequency.Prior to casing pres-sure manifestation,there were no BFP fluctuations.As gas production rapidly increased and water production rapidly decreased,both the amplitude and frequency of BFP fluctuations showed an increasing trend.The instability of gas-water two-phase flow in the coal reservoir,the"water locking"of low-conductivity fractures leading to accumulated desorbed gas,and the rapid increase in casing pressure after"gas surging"were identified as the causes of periodic BFP fluctuations.Severe BFP fluctuations are more likely to occur during the development of deeply buried,high-stress,low-permeability,and difficult-to-reform CBM reservoirs.In the early stages of drainage for low-water-producing wells,the daily BFP drop should be reasona-bly controlled,and more fracturing fluid should be drained before gas production rapidly in-creases.During the process of increasing gas production,large BFP fluctuations can be sup-pressed by adjusting drainage intensity and increasing casing pressure.Ensuring the continuity of the CBM well drainage process and avoiding long periods of pumping cessation during rapid production increases and stable production stages is crucial.