Factors Controlling Fracture Orientation In Sandstone

Abstract

This paper was prepared for the 48th Annual Fall Meeting of the Society of Petroleum Engineers of AIME to be held in Las Vegas, Nev., Sept. 30-Oct. 3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract Laboratory-scaled hydraulic fracture tests were conducted on directionally oriented sandstone material, along with measurements of directional rock properties such as tensile strength, permeability, sonic velocity, and dynamic elastic constants. In these tests, fracture orientation was determined as a function of various combinations of stress, rock saturation, rate of borehole pressurization, and direction of minimum tensile strength relative to minimum horizontal compressive stress. The objective of the experiment was to investigate whether horizontal stresses always controlled the orientation of induced vertical hydraulic fractures, or if, under conditions of small differences in stress and/or slow borehole pressurization rates, the induced fracture direction was influenced by directional properties of the rock matrix. properties of the rock matrix. This study shows that the expected influence of horizontal earth stress on the orientation of an induced hydraulic fracture becomes negligible whenever the magnitude of the difference between the compressive stresses is 200 psi or less. When this occurs, fracture orientation is controlled by the directional properties of the rock—primarily permeability and tensile strength. permeability and tensile strength Introduction The primary objective of hydraulic fracturing is to create a fracture in a specific formation to improve the drainage from a natural reservoir and therefore increase the productivity of an oil or gas well. Field results, however, have been erratic geographically, excellent in some regions, mediocre in others, and in some places outright failures—either to fracture places outright failures—either to fracture at all, or to increase well productivity. Since the conception of hydraulic fracturing, little attention has been given to the orientation of induced fractures or whether it was consistent throughout the oilfield, although the question was investigated as early as 1955. Now with the ever increasing demand for energy, the recovery of oil by waterflooding has attracted considerable interest and, with it, the importance of utilizing induced fractures has evolved. In particular, along with optimizing well placement and numbers, operators should be able to control the number, size, and orientation of induced fractures in order to take maximum advantage of in situ fractures and planes of weakness.