Estimation method for recovery ratio and limit drainage radius of low-permeability gas well

Abstract

The invention discloses an estimation method for a recovery ratio and a limit drainage radius of a low-permeability gas well. The estimation method comprises the following steps: estimating the limit drainage radius, and estimating the recovery ratio, wherein an estimation formula of the limit drainage radius is Re=(Pi-Pw) / [Theta];the step of estimating the recovery ratio comprises the following substeps: S1) calculating the volume (Vp=Pi[a0b0ze+1 / 2(a0+b0)c*Z<2>e+1 / 3C<2>Z<3>e]) of an elliptical table; S2) calculating the volume (V=Pi(a0+Re)(b0+Re)h) of an elliptical cylinder of a drainage area; and S3) calculating the recovery ratio ER=Vp / V. The estimation method has the following beneficial effects that the method is simple and quick, integrates the influences of a startup pressure gradient, a pressure-break length scale and well point abandonment pressure, brings forward a practical method used for estimating the average startup pressure gradient within the gas well drainage range by the early-period spot-measurement static pressure data of production performance, realizes the early evaluation of the limit drainage radius and the recoverable reserve of the gas well, and provides guidance for designing the reasonable well spacing of a low-permeability gas reservoir.

Description

technical field [0001] The invention relates to a method for estimating the recovery factor and the limit producing radius of a low-permeability gas well. Background technique [0002] Low-permeability gas reservoirs have a large amount of resources and are difficult to exploit. The characteristics of low porosity, low permeability and high water saturation lead to the prominent influence of capillary force. In the development practice of low-permeability gas reservoirs such as Sichuan and Changqing, a large number of gas wells reflect the development characteristics of "one well and one reservoir" under the condition of continuous reservoir itself, and infill wells are drilled in the surrounding "empty" well areas But it reflects that the formation pressure has hardly dropped. How to estimate the limit supply radius of low-permeability gas wells, determine the reasonable well spacing, and improve the recovery of gas reservoirs is one of the important aspects of tapping the...

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Problems solved by technology

Central Sichuan Oil and Gas Mine has carried out physical simulation experiments on the depletion of water-bearing gas reservoirs for the Xuer gas reservoir in Hechuan. figure 1 As shown, the experimental results show that: when the gas flow rate drops to zero, there is still residual pressure at each point of the physical model; the farther away from the outlet end, the higher the residual pressure, indicating that the gas cannot be produced when the production pressure difference is small to a certain extent ; With the increase of water saturation, the residual pressure rises and the recovery factor of the gas reservoir decreases

[0004] There are many domestic research documents on the threshold pressure gradient problem, mainly focusing on three aspects: experimental evaluation, productivity impact, and producing radius, but the application in the development of low-permeability gas reservoirs needs to be deepened

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