Effect of Unsymmetrical Vertical Fractures on Production Capacity

Abstract

Published in Petroleum Transactions, AIME, Volume 204, 1955, pages 251–254. Abstract Electrical model studies have been made of the effect of unsymmetrical vertical fractures on production capacity. The study was restricted to the case of two vertical fractures originating at the well and extending out into the reservoir for various distances and orientations. The ratio of the short fracture length to the long fracture length was varied from 0.1 to 1.0 in successive studies. The angle separating the two fractures was varied from 0 to 180 degrees. The most effective fractured patterns were obtained when the fractures were oriented 180 degrees. It was found that when the total fracture length was equal to 0.2 of the drainage radius, the increase in production capacity may vary from approximately 1.55 to 1.95, depending upon the ratio of the short fracture length to the long fracture length and the angle separating the two fractures. If the total fracture length were 0.5 of the drainage radius, production capacity increases varying 1.95 to 2.65 were observed, depending on the angle between the fractures and the ratio of the short fracture length to the long fracture length. The fractured well production capacity decreased approximately 1 to 10 per cent as the angle separating the fractures was varied from 180 to 90 degrees. It was dependent on the particular fracture. Introduction The commercial application of reservoir fracturing techniques has caused an interest to be expressed in the effect of vertical and horizontal fractures on production capacities. Some data have indicated that substantially vertical fractures may be created in some reservoirs. It is believed that the fractures are possibly unsymmetrical, that is, one fracture may extend due north 100 ft and a second fracture on the opposite side of the well may extend south or southeast only 50 ft. The total fracture length, ratios of the lengths and angles of separation may vary considerably. For this reason variations in these factors were considered. The study was restricted to the case of two vertical fractures originating at the well and extending out into the reservoir. It is not known that such will occur in a reservoir, but the results may be of value in interpreting or studying fracturing applications.