Text 6 Well testing

In producing gas and oil, efficient performance of the producing wells has more and more importance. A variety of tests must be made to determine the performance of an oil or gas well. This procedure is called testing. There are a large number of types of well tests and each is needed to obtain certain information about thewell.

Various personnel make the many well tests, some of which are routine and some of which are complicated. Depending upon the type of test to be performed, the standard lease producing equipment may be all that is necessary for the test. In other tests, specially designed apparatus may be necessary. In any event, it is very important that the test be done accurately since well test data presents the true history of a well and the reservoir in which it is completed.

Potential test: The most frequently conducted well test is the potential test, which is a measurement of the largest amount of oil and gas, produced by a well in a 24-hour period under certain fixed conditions. The produced oil is measured in an automatically controlled production and test unit. It also can be measured by wireline measurement in the lease tank. Produced gas is measured at the sametime

with equipment such as an orifice meter or an orifice well tester. The major items of equipment needed for a test of this type are usually available as standard equipment at the lease tank farm.

The potential test is normally made on each newly completed well and often during its production life. The information obtained from this test is required by the state regulatory group, which assigns a producing allowable, which must be followed by the operator of the well. It is necessary to make the tests from time to time and producing allowables are adjusted according to the results of the tests. Very often these tests are performed by the producer to help in establishing proper productionpractices.

Bottom-hole pressure test: This test is a measure of the reservoir pressure of the well at a specific depth or at midpoint of the producing interval. The purpose of this test is to measure the pressure in the zone in which the well is completed. In making of this test, a specially designed pressure gage is lowered into the well by means of a wire line. The pressure at the selected depth is recorded by the gage. After that gas is pulled to the surface and is taken from the well. Regular bottom- hole tests will provide valuable information about the decline or depletion of the zone in which the well has been producing.

Productivity tests. Productivity tests are made on both oil and gas wells, and include both the potential test and the bottom-hole pressure test. The purpose is to determine the effects of different flow rates on the pressure within the producing zone. In this way, it is possible to establish some certain physical characteristics of the reservoir and to calculate maximum potential rate of flow. This test mitigates risk of damaging the well, which might occur if the well were produced at its maximum possible flow rate.

Special tests: Two types of special tests are fluid level determination and bottom hole determination. The first is required for wells, which will not flow and must be made to produce by pumping or artificial lift. The bottom-hole determination is normally made along with the bottom-hole pressure test and is made to determine the temperature of the well at the bottom of the hole. It is necessary to lower a specially designed recording manometer into the well on a wire line. The temperature tests are used by the engineer in solving problems about the nature of oil or gas that the well produces. It is also useful in locating leaks in the pipe above the producing zone. Other special tests are performed with flow rate indicators and radioactive tracers.