Fluid-Loss Mechanism for Gels and Suspensions

Abstract

Summary We present a new model of fluid loss with wall building that applies to gelled fracturing and drilling fluids. Our model separates leakoff into two parts: an invasion phase and a wall-building phase. The invasion phase begins with Darcy flow, which carries residue into pore spaces near the rock face. This phase ends when sufficient residue has accumulated to allow the formation of a wall on the rock face. Once the wall has formed, it dominates the fluid-loss mechanism through its extremely low permeability. During the wall-building phase our model predicts a hyperbolic rather than a linear relation between leakoff volume and t. We made laboratory fluid-loss measurements for a variety of fluids and rock materials to test this model. We monitored effluent volume produced by flowing a gel or suspension through a fully saturated core sample. We found that the new model fit these measurements over periods of several hours, whereas the conventional Cw model did not. The Cw method can lead to large errors in fluid-loss estimates for long-term operations, such as massive fracturing and drilling. Our model requires the measurement of three leakoff parameters. We collected enough measurements to determine some general relations between these parameters and fluid and rock properties. These relations are discussed in terms of practical applications.