Inflatable packers have been used in the oil field for many years. The primaryadvantages are that they do not require weight to expand and that they are morefunctional in larger, washed out holes than conventional weight operatedpackers. Their use in drill stem testing requires the application of a downhole pump since surface pump pressure cannot be utilized with an empty orpartially empty drill pipe.
A new inflation type testing packer system has recently been introduced withexcellent success and customer acceptance. The purpose of this paper is todiscuss the developmental efforts and more specifically to describe the fieldexperience gained since introducing the system in August 1978.
Drill stem testing has long been recognized as an effective method of formationevaluation and has progressed significantly since its introduction in 1926. Anumber of important characteristics of a prospective producing well can bedetermined by proper interpretation of data obtained from a drill stem test(DST).
In open hole a DST is sometimes called a temporary completion because theformation is allowed to flow into the drill pipe in order to gatherinformation. Economy is a principal advantage of the DST since this procedureprovides information about a well's potential before the well iscompleted.
Curves of pressure versus time and other data obtained during the various flowand shut-in periods of a DST, can be used to determine the static reservoirpressure, production rate, transmissibility, indicated flow capacity, averageeffective permeability, damage ratio, approximate radius of investigation andpotentiometric surface. This information plays a very important role indetermining the economics of completing a well. In addition, when a decision ismade to complete a well, the interpretation of a DST can often be of assistancein designing the completion and possible stimulation treatments used in puttingthat well into production.1
In some oil and gas producing areas, including areas in the province of Alberta, hydrocarbon bearing formations are rather shallow and soft. Welldrilled in these formations tend to be washed out or over-sized. Conventionaldrill stem testing techniques might require relatively large amounts of pipeweight to obtain a good packer seat. Weight required will vary with the number, durometer and Size of the packer elements used, temperature, and other factors. In addition, the expansion of conventional testing packer elements is limited. These aspects of conventional drill stem testing pose particular problems intesting the shallow, washed out formations described earlier. In areas wherethese formations are present, DSTs can often be performed with inflatablestraddle packers. Such packers are inflated with the drilling fluid in the wellto be tested and this requires a special down hole pump. Pipe movement operatesthe pump which inflates and sets tile packers. Inflatable packers do notrequire pipe weight for setting and can expand much more than conventionalpackers. Thus, they are ideally suited for use in testing shallow, softformations.