A method for determining the initial drainage rate of coalbed methane development based on pressure propagation

Abstract

The invention relates to a pressure propagation-based method for determining the drainage and production speed of coalbed methane at the initial stage of development, which comprises the following steps: 1) according to the relationship between pressure propagation distance and time, the time required for interwell pressure interference under a given well pattern and well spacing condition is determined; 2) According to the time required for interwell pressure interference obtained in step 1), the depressurization rate is determined according to the concept of balanced depressurization; 3) The depressurization rate of the wellbore liquid level is determined according to the depressurization rate obtained in step 2). The invention has a strict theoretical basis and realizes the quantitative determination of the coal bed methane drainage rate at the initial stage of development. The invention can be widely applied to the quantitative determination of the coal bed methane drainage rate at the initial stage of coal bed methane development in different reservoir physical property conditions.

Description

technical field [0001] The invention relates to a method for determining the drainage rate, in particular to a method for determining the drainage rate at the initial stage of coalbed methane development based on pressure propagation. Background technique [0002] At present, coalbed methane is mainly developed through drainage and depressurization for gas recovery. Coal seams are generally saturated with water. In order to desorb and produce adsorbed gas in coal seams, drainage and depressurization are required in the early stage of development. There is a problem of drainage speed. From the perspective of shortening the development cycle, the faster the initial drainage speed is, the faster the gas well will see gas. However, if the drainage speed is too fast, on the one hand, it will cause the coal seam to be excited, so that the pulverized coal will be produced and the seepage channel will be blocked. On the other hand, too fast drainage speed will cause gas-liquid two-p...

AI Technical Summary

Problems solved by technology

There is a problem of drainage speed. From the perspective of shortening the development cycle, the faster the initial drainage speed is, the faster the gas well will see gas. However, if the drainage speed is too fast, on the one hand, it will cause the coal seam to be excited, so that the pulverized coal will be produced and the seepage channel will be blocked. On the other hand, too fast drainage speed will cause gas-liquid two-phase flow to appear prematurely in CBM wells, resulting in small pressure drop funnel and small gas leakage area

At present, the determination of the coalbed methane drainage system mainly considers the control of pulverized coal output and the reduction of stress sensitivity effects. The drainage speed is based on the accumulation of field experience, lacks a theoretical basis, and has poor applicability in different coalbed methane fields.

In terms of the influence of phase change on pressure drop funnel and interwell pressure interference in the process of coalbed methane development, there is still a qualitative understanding, and there is a lack of quantitative determination methods

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