How Oil Wells Are Completed in the Paradox Basin

Abstract

Abstract This paper covers the common completion practices for oil wells in the Paradox Basin fields near the Four Corners. The nature of the producing formations is described and the pertinent drilling problems are discussed. Since the pay consists of carbonate rocks, stimulation by acidizing is the principal ingredient of completions. These methods of acidizing which have been tailored to the reservoir characteristics are described. Introduction As in any other geologic province, the Paradox Basin requires its own combination of the myriad of drilling and completion techniques if optimum productivity is to be obtained at minimum cost. With the boom in development activity since the oil pipelines from this basin were constructed the process of making an oil well has undergone considerable refinement so that today better wells are being completed for less money. This treatise describes how this is done. To facilitate an understanding of the problems peculiar to this area and the reasons for the methods used to cope with them, a complete but generalized description of the reservoirs is presented. Pertinent Drilling Information The proved commercial productive horizons in the Paradox Basin are, for all practical purposes, the porous carbonates of the Pennsylvanian Hermosa formation and those of the Paradox member. In the area of greatest exploration and development, this formation is generally between 5,000 and 6,000 ft deep. Drilling times in the Aneth and Ratherford fields are approximately 25 days, and generally somewhat more in wildcats and outlying fields. Most operators drill 9-in. hole and set 7-in. production casing or drill 7 ⅞-in. hole and set 5 ½-in. production casing. Reservoir pressure of the productive zone is less than hydrostatic, and mud weights of 9.2–10.4 lb/gal have been found to be satisfactory after setting surface casing. The mud weight depends on the weight that is necessary to control the water flow from the De Chelly, which lies some 2,000 ft below the surface. For development wells it is frequent practice to emulsify some oil into the mud before reaching the objective zone which improves drilling characteristics, reduces mud costs, and probably reduces contamination of the pay section.