Carlson, E.S. (The University of Alabama) | Venkataraman, M. (The University of Alabama) | Clark, P.E. (The University of Alabama) | Sifferman, T.R. (Kelco, A Unit of Monsanto Company) | Coffey, M.D. (Kelco, A Unit of Monsanto Company) | Seheult, J.M. (Kelco, A Unit of Monsanto Company)
SPE 35227 Predicting the Fluid Loss of Drilling, Workover, and Fracturing Fluids into a Formation With and Without Filter Cake E.S. Carlson, SPE, M. Venkataraman, P.E. Clark, SPE, The University of Alabama, T.R. Sifferman, SPE, M.D. Coffey, SPE, J.M. Seheult, Kelco, A Unit of Monsanto Company Copyright 1996, Society of Petroleum Engineers, Inc.
An evaluation of the tests described in the American Petroleum Institute's Recommended Practice "Standard Procedure for Testing Drilling Fluids" would probably lead to the conclusion that the control of fluid loss during drilling or completion operations requires the use of a wall-building fluid. As we will show in this paper, this is not a valid conclusion because power-law fluids can be very effective for invasion control. The lack of a standard test for the invasion characteristics of a power-law fluid is understandable, because the invasion behavior for these fluids depends on both fluid and formation properties.
In this paper, we describe the theory of non-Newtonian fluid invasion from a wellbore to a formation, and discuss a computer model that we developed which is based on this theory. We present computational results which validate the model against analytical and experimental results. Using average parameters that were determined from experiments, we show that formation invasion can be effectively controlled using power-law fluids. We also show that the power-law fluid characteristics which lead to good invasion control do not necessarily lead to long-term restrictions to well productivity. Theory We have searched exhaustively to find invasion models which are comparable to the those presented in the following sections. Many models exist which describe invasion characteristics of wall-building fluids. There are papers which discuss the flow of power-law fluids through linear cores, and other papers which discuss transient pressure behavior of power-law fluids in a reservoir. However, we have not found any which rigorously evaluate the invasion behaviors of power-law fluids. Flow of Non-Newtonian Fluids in Porous Media Unlike Newtonian fluids, which exhibit a constant apparent viscosity, general non-Newtonian fluids have an apparent viscosity which depends on the shear rate, and the shear rate depends on the fluid velocity. For power-law fluids, the apparent viscosity can be given by
(1) where app is the apparent viscosity in cp, n is the flow behavior index, K is the consistency index in dyne.sn/cm2, and is the shear rate in s-1. For a given power-law fluid, it is a routine matter to measure n and K. When a rotational viscometer is used, shear stress is measured as a function of rotational speed. The shear rate is directly proportional to the rotational speed, and the apparent viscosity is the ratio of shear stress to the corresponding shear rate.