New Technique Provides Open-Hole Production Test of Wildcat Formations

Abstract

Introduction It is becoming increasingly difficult to find proved oil reserves within the boundaries of the United States. In general, companies must drill much deeper in their search for oil. The depth of present-day wildcat wells and the complex completion procedures used on such wells have brought about a large increase in the cost to put oil back in the tank battery. This skyrocketing of costs has stimulated a constant search for new or improved methods in every phase of drilling for oil. A new testing technique which has helped to a great extent the struggle to cut the cost of finding oil reserves provides conclusive evaluation of questionable wildcat formations without the expense of running casing. The technique and tools used were made available to the petroleum industry in the latter part of 1956. To date, conclusive information has been obtained on more than 200 wildcat formations located in Arizona, Utah, New Mexico, Colorado, Wyoming, Kansas, Oklahoma, Illinois, the Texas Panhandle, North Central Texas, the Permian Basin of West Texas, and Southwest Texas. Successful open-hole production tests have been performed in porous lime, consolidated lime, fractured lime, vugular lime, conglomerate, consolidated sand, coarse sand, shaly sand and red shale. Need of Supplement For Conventional Testing The conventional drill-stem test is the most widely used method to obtain information for the evaluation of the potential production of a formation. When pressures and fluid are obtained in sufficient amounts, the drill-stem test gives exact and conclusive in formation on formation potential. However, quite often a drill-stem test is either void or obtains very little yield of fluid or pressure. This would lead to the normal conclusion of poor production potential. When electric logs indicate possible fluid and a void drill-stem test results, it is possible that the formation has been blocked or plugged by the drilling mud. This blocking action can be of varying degrees. A partial block may occur to give only a slight show of formation pressures and fluid and, thus, indicate poor potential. Therefore, when test results are poor but logs give indication of production, the test is inconclusive. It then becomes necessary or desirable to more thoroughly test the zone, or zones. In order to obtain more conclusive in formation under such conditions, an acid treatment may be required to break down the suspected mud block. When the mud block has extended well into a permeable zone, a substantial treatment is often necessary. Very high pressures normally occur while breaking through these blocked permeable zones.