Model Characterizes Formation Damage Caused by Fines Breakage and Migration

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 208810, “Formation Damage Caused by Fines Breakage and Migration,” by Abolfazi Hashemi, Sara Borazjani, and Bryant Dang-Le, SPE, University of Adelaide, et al. The paper has not been peer reviewed. _ Fines migration is a major cause of formation damage; the detached clays migrate and impair well productivity. Two types of damaging clays are encountered in petroleum reservoirs: authigenic clays that grew on the grain surfaces during geological times, and detrital clays that have been broken off the grains because of local stresses. The aim of the work described in the complete paper was the development of a laboratory procedure to estimate formation damage by authigenic clays and the derivation of a mathematical model for core scale. Background Detrital particles are attached to a substrate by an electrostatic force and can be modeled using the DLVO theory. Most core samples, however, have some authigenic clay content (i.e., clay particles bonded to rock). To study formation damage caused by the detachment of authigenic clay, a new formulation should be presented. The formulation should be based on failure or breakage criteria of the contact bond between the particle and a substrate. To the best of the authors’ knowledge, the theory for detachment of a single authigenic particle is not available. The purpose of this study was the development of a laboratory-based mathematical model to estimate formation damage by authigenic clays. In the complete paper, the authors assumed that the bond between the authigenic clay and rock acts as a cantilever beam. The cohesive beam model (CBM) was applied to formulate the detachment of the particle because of the applied drag force. The stress state at the bond was governed by the Timoshenko beam theory. These equations are applicable for the elastic limit of both brittle (elastic) and ductile (elastic/plastic) materials, and only different failure criteria were applied. Kaolinite in porous media was assumed to be elastic/perfectly plastic. For defining failure for this type of material, yield criteria were applied. The von Mises yield criterion was used to define failure. For detachment of every particle, a specific drag force or a fluid velocity must be applied. Because a large number of particles with different random properties exist in porous media, by considering a distribution for each property, a distribution for detachment velocity can be obtained. By taking an integral from this distribution bounding to experimental velocities, the amount of detachment between two fluid velocities can be obtained. The same procedure can be followed for detrital particles and authigenic particles. Total detachment concentration is the sum of authigenic and detrital particles. The total detachment is matched with laboratory data. Having obtained the matching parameters, a maximum retention function curve can be plotted. This new maximum retention function takes into account the detachment of both authigenic and detrital particles. In the complete paper, the authors initially presented the assumptions of their models, then governing equations for detrital particle detachment and detachment of authigenic particles; finally, the formation damage formulation and solutions were provided, which are applicable for both detrital and authigenic particles.