The results of an experimental research program which investigated the influence of temperature, effective stress, and non-Darcy flow on the fracture flow capacity of propped fractures are presented. Experiments were conducted using 12/20, 20/40, and 30/60 mesh proppants of varying strengths over a temperature range of 75°F (24°C) to 200°F (93°C) and an effective stress range of 2000 psi (13.8 MPa) to 20,000 psi (138 MPa). From the experiments it was observed that fines generation and lack of edge effects due to proppant embedment significantly reduces the fracture flow capacity of the fracture in comparison to published data.
Naturally occurring fractures or artificially created fractures by hydraulic means are important considerations from a rock mechanics and fluid flow standpoint for hydrocarbon recovery from below ground reservoirs. Long-term performance predictions for producing wells which penetrate such reservoir rocks at great depths are a very difficult task. Low permeability reservoirs or reservoirs which have been hydraulically impaired in the drilling and completion process are routinely hydraulically fractured to enhance productivity. The ability of the propped fracture to conduct fluids is a function of proppant size, proppant strength, effective stress, temperature, and the flow regime which exists in the fracture. Embedment and proppant crushing which can occur at high effective stresses also influences the ability of the fracture to conduct fluids. The purpose of this research was to investigate the influence of temperature, effective stress, and non-Darcy flow on the fracture flow capacity of propped fractures.
At low fluid velocities horizontal flow through porous materials is governed by Darcy's Law, As the fluid velocity increases equation (2.1) no longer predicts the correct pressure drop and hence is normally replaced by the Forchheimer equation, In equations 2.1 and 2.2, μ, ρ and Pare the viscosity, density, and pressure of the fluid, k is the permeability of the rock, V is the fluid velocity and β is referred to as the inertial resistance coefficient. Equation 2.2 can be rewritten in a form similar to equation 2.1 by defining a non-Darcy number as follows (Holditch and Morse, 1976): Historically, the inertial coefficient β was assumed to be solely a property of the porous media. However, more recently it has been clearly demonstrated that β is a function of both the porous rock and the fluid contained in the rock (Evans et al., 1987; Avila and Evans, 1986; Tiss, 1987). In equations (2.5) and (2.6) W is the fracture width, kf and k are the respective permeabilities of the fracture and the reservoir, Lf is the fracture half-length, and Fnd is the non-Darcy flow number as defined previously. In an attempt to identify realistic values of fracture conductivity, several researchers (Maloney et al., 1987; Pursell et al., 1988; McDaniels, 1986, 1987; Penny, 1987) have included many variables which affects this flow parameter. The recent work by McDaniel (1987) measured proppant conductivity over long periods of time to identify realistic fracture conductivity data.
