Abstract

This paper illustrates the procedure for running closed-chamber drillstem tests. The tests, like conventional drillstem tests, provide information on pressures and fluid data that is the basis for a complete well evaluation. Unlike conventional drillstem tests, the closed-chamber method provides for optimization of the test design from initial observations of pressure and fluid influx. It also minimizes hazards to both man and the environment. Because of the advantages of the closed-chamber test procedure, it is recommended that, whenever possible, the initial flow period of all multi flow drillstem tests be conducted under closed-chamber conditions. The information gathered during this period not only guides the design of subsequent stages of the test but, for future reference, provides better documentation of test procedures and formation response.

Introduction

Drillstem tests are time-consuming, specialized and expensive, but they are never monotonous and seldom routine. In the arctic, for example, they pose many problems, the principal one being how to test safely in times of almost total darkness and subzero temperatures.

Testing is carried out to obtain information on pressure, reservoir fluid and well potential. Accurate pressure data are required for hydrodynamic studies during the exploration phase, and as a starting point for reservoir studies. Knowledge of reservoir fluids, if hydrocarbons, is needed for reservoir description and production facility design; if water, enough must be produced to establish its true registivity for log analysis. An estimate of the well potential is required to determine the number of wells and spacing to develop the reservoir in the most economic manner.

This paper describes how drillstem tests can be conducted in conditions such as experienced in the arctic with minimum hazard to both man and the environment, while still providing required pressure and fluid data along with an estimated well productivity.

Nature Of Closed-Chamber Test

A closed-chamber test is similar in many ways to a conventional drillstem test. The difference is that the well is closed in at the surface when producing, and open at the surface only when shut in at the formation. The closed-chamber test is instrumented so that the fluid influx can be monitored during the test. and flow rates can be determined when the test is completed. Such a system provides greater safety and better control of produced fluids than does the conventional drillstem test, and allows the operator to optimize the test program on site. A Further advantage is that reservoir samples are collected at a much higher pressure than with the conventionaltest. In fact, it the surface pressure does not exceed a predetermined safe working level, a sample of oil or water can usually be obtained at reservoir conditions, and a sample of gas at near reservoirconditions. The minor disadvantage of the c1osed-chamber test in that, in the case of a high-permeability zone, is does not provide as great a depth of investigation as the conventional test. This is because the Flow periods of a closed-chamber test are much shorter. With lowpermeabity reservoirs, the results are usually the same for both types of test, as the flow periods in these cases are essentially the same.

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