Flowing Material Balance Equation for Coalbed Methane Reservoirs

  • 吳 昇峯

Student thesis: Master's Thesis

Abstract

In this research using the flowing p/z* method to estimate the original gas in place (OGIP) for two-phase-flow coalbed methane (hereafter referred to simply as “CBM”) reservoirs is proposed With flowing bottomhole pressures (FBHP) for wells and production data together with fluid PVT (pressure volume and temperature) properties the OGIP of a CBM reservoir that contains both gas and water can be estimated using a flowing p/z* plot versus a record of cumulative gas production without shutting in the well To use the flowing p/z* method for CBM reservoirs FBHPs for wells are used to calculate average reservoir pressures based on the inflow equation during the pseudo-steady (i e boundary-dominated flow) state With the calculated average reservoir pressures and production data a p/z* plot versus cumulative gas production will yield a straight line with an x-intercept equal to OGIP which can be obtained by extrapolating this straight line to zero p/z* Because of the assumption of boundary-dominated flow the procedure to determine when the pseudo-steady state will start is also presented A numerical Computer Modelling Group (CMG) simulator GEM (a compositional and unconventional reservoir simulator) has been used to generate synthetic pressures (including FBHPs for wells that are not shut in and shut-in average reservoir pressures) and production data The FBHPs for wells that are not shut in are verified by being compared with the analytical solution The comparison shows substantial agreement The proposed flowing p/z* method for CBM reservoirs is then used to analyze the verified synthetic data to determine OGIP In contrast OGIP obtained using the traditional p/z* plot (which uses the shut-in average reservoir pressures and production data) and OGIP determined using volumetric calculation (based on the known reservoir volume which is used to build the numerical model) also show agreement with OGIP calculated using the proposed flowing p/z* method Therefore this proposed flowing p/z* method for CBM reservoirs is useful for calculating OGIP from FBHPs for wells without shutting in the wells and even more accurate than traditional p/z* material balance calculation for OGIP estimates For completeness the procedure for calculating OGIP for single-phase-flow CBM (dry CBM) reservoirs is also included in this research
Date of Award2014 Aug 15
Original languageEnglish
SupervisorBieng-Zih Hsieh (Supervisor)

Cite this

Flowing Material Balance Equation for Coalbed Methane Reservoirs
昇峯, 吳. (Author). 2014 Aug 15

Student thesis: Master's Thesis