煤层气井两层合采气水同产井底流压计算方法

doi:10.7657/XJPG20230415

摘要/Abstract

摘要：

井底流压是确定煤层气井合理工作制度，进而实现长期稳产的关键影响因素。针对定质量模型不考虑储集层段加速度压降和不同井段质量变化导致不符合两层合采特性，以及采用下部储集层井底流压作为2个储集层井底流压来调节生产制度导致不符合上部储集层调节需求的问题，对加速度压降表达式进行了分解和推导，建立了其与单位长度径向流量的关系式，推导了含径向流入的储集层段压降公式;将储集层分成多个微元段，建立了每个微元段的压降计算方法;根据各井段气水流量，推导了相应的气相和水相速度计算方程;将上述方程结合，建立了变质量模型。将生产数据分别代入变质量模型和定质量模型，气水同产时，变质量模型的误差为2.96%~6.67%，定质量模型的误差为7.33%~15.10%，变质量模型更加准确。2个储集层的井底流压相差较大，最大相差47.3%，因此需要根据各自的井底流压调节生产制度。变质量模型能够准确给出合采各层的井底流压，更符合现场实际，同时也避免了采用相同井底流压导致无法精准调节2个储集层生产制度的问题，从而为制定最优化排采制度、实现高产稳产提供技术支撑。

关键词: 煤层气井, 两层合采, 井底流压, 定质量模型, 变质量模型, 加速度压降, 变流量速度公式

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

中图分类号:

TE37

张鹏, 曾星航, 郑力会, 张吉辉, 王相春, 彭小军. 煤层气井两层合采气水同产井底流压计算方法[J]. 新疆石油地质, 2023, 44(4): 497-509.

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.

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