Determination of the Orientation of a Vertical Fracture by Interference Tests

Abstract

An analytic solution for the pressure distribution around a fractured well in a homogeneous, infinite reservoir is presented in terms of tabulated functions. This solution can be used to determine fracture orientation from interference tests. Introduction The advent of costly tertiary recovery programs has resulted in the need to determine flow patterns created by fractures intersecting wellbores. This requires a knowledge of the compass orientation and length of fractures. Several papers have discussed determination of fracture length by pressure analysis. However, methods for determining the compass orientation using pressure data have not received much attention. This paper pressure data have not received much attention. This paper discusses a method for determining the compass orientation using pressure data obtained at shut-in observation wells due to pressure data obtained at shut-in observation wells due to production or injection at the fractured well. production or injection at the fractured well. In 1960 Elkins and Skov reported a method for determining the orientation of natural fractures. They assumed the system of natural fractures to behave like an anisotropic system and used the classical line-source solution to analyze, pressure behavior. More recently, Pierce et al. demonstrated the use of pulse testing for calculating fracture length and orientation. Other studies on the determination of fracture orientation include (1) use of acoustic signals; (2) measurement of pressure response at observation wells during fracture initiation and propagation; and (3) use of inflation impression packers and television cameras.Even though the problem has been recognized for quite some time, no general method exists for determining pressure distribution in the area drained by a vertically fractured well. The objective of this paper is to present an analytic expression, in terms of simple tabulated functions, for the pressure distribution in a uniform, homogeneous, infinite reservoir drained by a vertically fractured well. This solution may be used to analyze pressure data in adjacent observation wells to determine fracture orientation in a manner analogous to standard interference tests. It also may be used to analyze test data obtained by pulsing a vertically fractured well. pulsing a vertically fractured well. Theory The mathematical model considered in this study is identical to the uniform-flux fracture examined by Gringarten et al. We assume that a single vertical fracture intersects a wellbore located in an infinite, homogeneous, porous medium (Fig. 1). The surface production rate is assumed to be constant and all the production is obtained by means of the fracture. Fluid enters production is obtained by means of the fracture. Fluid enters the fracture at the same rate per unit area of the fracture (uniform-flux fracture). JPT P. 73