Influence of Propping Sand Wettability on Productivity of Hydraulically Fractured Oil Wells

Abstract

Published in Petroleum Transactions, AIME, Volume 216, 1959, pages 324–329. Abstract Of the many factors which affect the productivity of hydraulically fractured wells, the wettability of the propping sand has received little attention in the past. This paper shows that the wettability of the propping sand is an important factor which should not be overlooked. An analysis of relative permeability data shows that fractures packed with water-wet sand should be more permeable to oil than are fractures packed with oil-wet sand. Laboratory results verify this conclusion. Calculations show that higher permeability to oil in the fracture should provide higher well productivity. A method is presented which ensures that the propping sand in an induced fracture is water-wet even though oil is used as the fracturing fluid. The method has been used in more than 150 field jobs; the field results are discussed briefly. The fluidized nature oil water-wet sand in oil has given unexpected benefits. This characteristic of water-wet sand and how it has been used advantageously in field operations are discussed. Introduction Hydraulic fracturing of subsurface strata to increase the productivity of oil and gas wells has been practiced for about 10 years. Today, fracturing is used more often than any other method of well stimulation. Basically, the process consists of breaking down (fracturing) a subsurface formation with pressure applied by means of a carrier fluid, usually oil or water, and propping the induced fractures apart by means of an agent, usually sand, suspended in the carrier fluid. Currently about 68 per cent of all fracturing is done with a simple mixture of refined oil or lease crude oil and sand. The research of other investigators has suggested that dry sand is rendered oil-wet when it is contracted with certain types of crude or refined oils. Hence, it may be expected that some fracturing operations employing an oil as the carrier for sand leave fractures packed with oil-wet sand. Conversely, those operations which employ water as the carrier for the sand probably leave the fractures packed with water-wet sand. Since the permeability of a sand-packed fracture to a mixture of oil and water is dependent upon the wettability of the fracturing (frac) sand, research was undertaken to determine to what extent the wettability condition (water-wet or oil-wet) controls fracture permeability which, in turn, affects well productivity. Additional research was directed toward the development of a method for obtaining the desired fracture wettability.