The present techniques of using the drill-stem test as a formation evaluation tool are discussed. The basic drill-stem test operation is divided for discussion into three phases: planning the test, performing the test, and interpretation, both qualitative and quantitative. The use of small bottom choices and large top choices is suggested in order to permit quantitative interpretation for gas-oil ratio, productivity, and permeability. The importance of measuring chloride content on a suite of samples taken from a recovered column of salt water is illustrated.
A drill-stem test is a temporary completion of the well. Drill-stem tests are usually made for one or both of the following reasons:
to determine the producible fluid content of a formation, and
to determine the ability of a formation to produce.
The drill-stem test, or temporary completion, can be made either in open hole or inside casing through perforations. A drill-stem testing program can be planned for a well so that the tests will be made in accordance with one of three general methods:
Test possibly productive intervals in open hole as the zones are penetrated; normally, this method is used in conjunction with coring and ether cuts may be used to detect hydrocarbon shows.
Test possibly productive intervals in open hole after drilling deeper or reaching total depth; normally, this method requires that a cement plug be set for each test, unless straddle packer testing is employed. Sidewall cores and logs are commonly used to detect the shows.
Test possibly productive intervals through perforations after casing has been set; log and core data may be used in selecting the intervals.
Drill-stem testing is widely used to confirm or prove the presence and/or the producibility of oil and gas that is detected by the other services. The testing program in a well can follow any one of the methods of drill-stem testing outlined in the preceding section; however, the method of testing cored shows as the prospective pays are penetrated is probably most widely used at present.