Well Productivity Increase From Drain Holes as Measured by Model Studies

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Published in Petroleum Transactions, AIME, Volume 204, 1955, pages 30–34. Abstract The use of drain holes drilled from a well to improve productivity is becoming increasingly common. This paper presents data on the productivity increase that may be expected. The data were obtained by use of an electrolytic tank model of a reservoir. Parameters varied in the study to show their effect on productivity include the length, number, and arrangement of drain holes, formation thickness, and damage near the wellbore. The most important results are that very large increases in productivity can be expected only in damaged wells. The distance to which drain holes penetrate is of primary importance. Additional length is more effective than increasing the number of drain holes. Introduction In planning the use of drain holes to improve productivity, it is important to be able to estimate the increase in production that can be obtained for a given expenditure. It is also important to know what combination of parameters related to the use of drain holes can be chosen to give the largest production increase. This paper presents data on the productivity increase that may be expected, as obtained by use of an electrolytic tank model of the reservoir. In this study, a number of parameters were varied to show their effect on productivity. These included the length, number, and arrangement of the drain holes. The presence or absence of a damaged zone of low permeability around the wellbore and the thickness of the producing formation were also considered. Definitions and Assumptions The productivity increase that might be expected due to drain holes is presented as the ratio: productivity of a well after drain holes are drilled and completed to the productivity of the same well in an undamaged state without drain holes.

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