Standardization of Gas Well Tests
Authors: Galloway L.D. , Kendrick H.L. 
Published: December 2007

Three types of initial potential tests are presented in this paper with explanations of each and their applications and limitations. These are explained as to when and where each may be used. Also, deliverability testing is covered as applicable to low-permeability reservoirs as encountered in the Rocky Mountain region. Particular emphasis is placed on testing in the San Juan Basin of New Mexico and Colorado. Initial potential testing may, vary from locale to locale, but all testing within a common pool should be conducted in the same manner if the results are to be comparable. Standardization should be made by the engineers within the industry with the object in mind to obtain the best data, at the least cost, to attempt to predict future deliveries from gas wells and gas pools. In heterogeneous reservoirs of low permeability, the actual producing ability of each well cannot be accurately determined from either the initial potential test or from short periods of intermittent flow to the pipeline. Instead, the deliverability test is utilized as the most accurate tool for well evaluation.

Introduction

The natural gas industry supplied approximately 10 trillion cu ft of gas from 91,082 dry gas wells during the year of 1962. The proven gas reserves increased some 85 per cent from 1945 to the end of 1962 to a figure of 273.8 trillion cu ft. This figure of reserves represents approximately a 20-year supply according to the 1962 consumption rate.

To evaluate each of the over 90,000 gas wells in existence today, we must utilize some medium of testing that will yield the necessary information about the well.

For data determined from tests to be of maximum value, all tests within a common reservoir should be done with identical procedures. In fact, if results are to be compared from reservoir to reservoir, or from state to state, tests should be done with standard procedures providing a common basis of evaluation and utilization. This would assure the reliability of data available to the engineer, even though he may not have worked in the area in which the test was taken. A major step in accomplishing standardization in testing has been made through the publication by the Interstate Oil Compact Commission of a "Manual of Back Pressure Testing of Gas Wells", which has recently been prepared and recommended for use throughout the gas industry. The need of such standardization is particularly apparent to those engineers whose work requires them to test wells in different states which utilize various test procedures, or in some instances have no specified procedures.

From the beginning of drilling operations until the final plugging of a gas well, gas well tests should be conducted periodically to obtain information as to the performance of each individual well. Good test results can be used for:

an aid in determining the effectiveness of well completion and stimulation methods: sizing location production equipment: sizing pipeline laterals and trunk lines; the determination of appropriate line pressure for the design of gathering systems; the determination of the number of wells necessary to supply the market demand; and defining suitable withdrawal rates for contractual requirements, ratable takes, or proration allocation purposes.

These same gas well tests can often be used in the determination of reservoir producing characteristics as:

evaluation of reserve estimates and field life; determination of the most desirable well spacing; and determination of the most practical and economical withdrawal rates.

These tests may further be used to define a well as commercial or non-commercial. And last, but possibly not least, a test value may be used to close the pages of the drilling activity of a well and thus, remove it from the scout report and place it among the completed wells. From these requirements have come several types of gas well testing procedures. All of these are predicated on the one basic premise that stabilized rates of flow and pressure can be obtained on a gas well. This is, in turn, a reflection of the permeability of the producing interval of the reservoir.

Types of Tests

The two general types of gas well tests that can be conducted are the open-flow test, with gas being vented to the atmosphere, and the closed-flow test with gas flowing into a pipeline.

JPT

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