Improved Estimation of Gas Well Deliverability From Single-Point Tests
Authors: Chase R.W. 
Published: March 2010

Chase and Alkandari developed dimensionless inflow performance (IPR) curves for predicting the stabilized deliverability of hydraulically fractured gas wells using just a single-point test, namely a pressure build-up or draw-down test. Unfractured wells can also be analysed by converting the apparent skin factor to an equivalent ratio of Xe/Xf. Results obtained from the dimensionless IPR curve model can be used to generate values of n and C for the equation of stabilized deliverability. This research describes the process used to evaluate the effectiveness of the single-point model using data from 25 Canadian well tests and nine simulated well tests. The tests were analysed using fourpoint test methods, the dimensionless IPR curve method, and by assuming that the exponent of the stabilized deliverability equation was equal to one. The mean absolute value of error between the AOF predicted using multi-point deliverability test analysis methods and the dimensionless IPR curve method for the 25 Canadian wells was 9.2%, with a standard deviation of 8.7%. The mean absolute value of error between the AOF predicted using multi-point deliverability test analysis methods and the dimensionless IPR curve method for the nine simulated wells was 5.6% with a standard deviation of 4.3%. The mean absolute value of error between the AOF predicted using multi-point test methods and by assuming that the exponent of the stabilized deliverability equation was equal to one for the 25 Canadian wells was 30.5% with a standard deviation of 25.2%. The dimensionless IPR curve model appears to offer a conservative, easonably accurate, and economical method for predicting current and future gas well inflow performance from a single-point transient pressure test.

Introduction

The deliverability or inflow performance of a gas well is usually predicted by utilizing one of three well testing methods: the conventional backpressure test(1); the isochronal test(2); or the modified isochronal test(3). All three methods normally require that four flow tests be performed on a well, including one to stabilization, to accurately predict stabilized deliverability. Industry practice sometimes shortcuts these methods utilizing just three, two and sometimes just one flow test. In the latter case, the exponent, n, of the stabilized deliverability equation, given by Equation (1) is frequently assumed to be equal to one in order to estimate deliverability.

Equation (1) Available In Full Paper.

Chase and Alkandari(4) developed a single-point test method that uses dimensionless IPR curves for predicting the inflow performance of fractured gas wells producing under stabilized or pseudosteady state flow conditions. The model was developed in an attempt to better estimate gas well deliverability when just a one-point test, namely a drawdown or build-up test, is conducted. The model was based on concepts proposed by Vogel(5) and Standing(6) for oil wells, and Mishra and Caudle(7) for unfractured gas wells.

The following equation serves as the basis for the single-point dimensionless IPR curve method.

Equation (2) Available In Full Paper.

The SPE paper by Chase and Alkandari describes how a Monte Carlo simulation was used to develop the model and generate values for the coefficient M and exponent N as a function of Xe/Xf.