Relative Productivity of Perforated Casing - II

Abstract

Abstract The effect of depth of formation penetration by casing perforations has beenstudied by means of an electrolytic model. It is found that the relativeproductivity of perforated casing is profoundly affected by the depth to whichthe formation is penetrated. The first in. of penetration is of especialimportance. A scaling equation which was shown to agree with experimentalresults at zero penetration is used to calculate the relative productivity of ascaled down casing with scaled down perforations. Introduction In an earlier paper the authors showed that the point sink representation ofcasing perforations is inadequate. It was pointed out at that time that whilethe electrolytic model results were a marked improvement over point-sinkcalculations, they still left a great deal to be desired in that theelectrolytic model represented a case not realizable in practice, namely, aclean hole through the casing but undisturbed formation on the other side ofthe casing. Obviously, to be effective, the perforation must penetrate a finitedistance into the producing formation. It was the purpose of the presentinvestigation to find how the relative productivity of perforated casing varieswith depth of penetration. The term "depth of penetration" as used in this paper refers to thedistance which the perforation penetrates the producing formation. The amountof casing and cement penetrated is not taken into account, a fact which isdiscussed more fully later. The "casing radius," therefore, is to beinterpreted as the radius of the boundary between cement and formation wall, incases where the casing is not in contact with the formation wall. Apparatus The electrolytic model experimental setup was identical with that describedin the previous paper except that the platinum electrodes were now allowed toproject from the lucite cylinder by varying amounts. When fewer than eightelectrodes were used, the unused ones were covered with a coat of insulatingmaterial to minimize disturbances to the current flow-lines. T.P. 2933