Pressure-propagation-based method for determining discharge and recovery speed at initial stage of coalbed methane exploitation

Abstract

The invention relates to a pressure-propagation-based method for determining the discharge and recovery speed at the initial stage of coalbed methane exploitation. The method comprises the following steps: (1) according to the pressure propagation distance and time relationship, determining time required for inter-well pressure interference under the conditions of given well patterns and spacing; (2) determining the pressure reduction rate by virtue of the balanced step-down concept according to the inter-well pressure interference required time obtained in the step (1); (3) determining the liquid level descending rate of a shaft according to the pressure reduction rate obtained in the step (2). The pressure-propagation-based method has a strict theoretical basis, realizes quantitative determination of the discharge and recovery speed at the initial stage of coalbed methane exploitation, and can be widely applied to quantitative determination of the discharge and recovery speed at the initial stage of coalbed methane exploitation of coalbed gas fields under different reservoir physical 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

Images