A Calculation Method of Bottomhole Flowing Pressure in Coalbed Methane Wells With Double-Layer Commingled Production in Gas-Water Co-Production Stage

doi:10.7657/XJPG20230415

Abstract

Abstract:

Bottomhole flowing pressure (BHFP) is a key factor determining the rational production system of coalbed methane (CBM) wells for purpose of long-term stable production. The constant mass model (CMM) is not applicable to the wells with double-layer commingled production, since it does not consider the acceleration pressure drop (APD) in the reservoir interval and the mass variation in well sections. Additionally, the BHFP in the lower reservoir is taken as a control parameter for the two intervals, which does not meet the adjustment requirements of the upper reservoirs. In this paper, the APD expression was decomposed and derived, the relationship between APD and the radial flow rate per unit length was established, and the pressure drop formula for the reservoir interval with radial inflow was derived. The reservoir was divided into multiple intervals, and the pressure drop calculation method for each interval was established. Based on the gas/water flow rates in each well section, the corresponding equations for calculating gas/water phase velocities were derived. Combining the above equations, a variable mass model (VMM) was established. The production data were input into the VMM and CMM for comparative verification. The results show that when gas and water are co-produced, the error of the VMM is 2.75%-6.58%, while the error of the CMM is 7.15%-15.18%, indicating that the VMM is more accurate. The BHFP differs significantly in the two reservoir intervals, with the maximum difference of 47.3%. Therefore, it is necessary to adjust the production system depending upon the respective BHFP of the two reservoirs. The VMM can accurately provide BHFP for each commingled interval, so it agrees more with the field conditions. It also avoids the problem of using the same BHFP for both intervals, which hinders precise adjustment of the production system. Thus, the new model provides a technical support for developing optimal production strategies and achieving high and stable production.

Key words: coalbed methane well, double-layer commingled production, BHFP, constant mass model, variable mass model, acceleration pressure drop, variable flow rate formula

CLC Number:

TE37

ZHANG Peng, ZENG Xinghang, ZHENG Lihui, ZHANG Jihui, WANG Xiangchun, PENG Xiaojun. A Calculation Method of Bottomhole Flowing Pressure in Coalbed Methane Wells With Double-Layer Commingled Production in Gas-Water Co-Production Stage[J]. Xinjiang Petroleum Geology, 2023, 44(4): 497-509.

Figures/Tables 9

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