Particle Invasion Into Porous Medium and Related Injectivity Problems

Abstract

Abstract The invasion of reservoir rock by particles and their subsequent movement through porous media as well as the associated reservoir damage are well recognized as major problems throughout the oil and geothermal industries. Particles contained in the injection water (or brine) can cause serious reservoir damage. However, most of the literature on this subject considers only particles (or fines) having an "equivalent" circular diameter of 2 microns or larger. Particles smaller than 2 microns and specifically submicron suspensions are generally believed, if considered at all, to move away from the wellbore and to reach locations in the reservoir where their impact on fluid flow is practically nil. This assumption is very difficult to ascertain even in the laboratory and has led to numerous misconceptions documented in the published literature. A new attempt is made to study the mechanisms of particle invasions into porous media and the subsequent particle movement. This paper describes the following subjects: A critical survey of the literature indicating that the mechanism of particle invasions and movements is not known in sufficient detail. Earlier studies published in the open literature used assumptions that either cannot be substantiated or are internally inconsistent with the proposed mechanisms. This literature search indicates the obvious misconceptions and lack of knowledge still prevailing in the industry. The pros and cons of existing particle measuring devices are briefly described in the paper. Results from a new laboratory study on particle characterizations are given. Existing particle measuring equipment and procedures are used but are not suited for monitoring of injection water quality aimed at a prevention of particle induced damage in the field. The results of the laboratory studies on the flow of particle suspensions (submicron to 2 micron particles) through porous media (up to 200 md) are discussed. The effects of flow rate and particle concentrations on the degree of damage (i.e., permeability impairment) and depth of core penetration are particularly emphasized. Water quality monitoring based on membrane filter methods (e.g., using Millipore filters) cannot be used to determine particle invasions into porous medium. Any predictions of injection problems based on Millipore filter (or any other membrane filter) measurements are useless and should be discarded. Only cores but not filters can be utilized for determining formation damage due to particle invasion and movement. This paper describes experimental data on flow of particle suspensions (2 microns and smaller) through porous media. Different means of measuring the particle size distributions and associated particle characterization problems were tried. These methods, their pros and cons, are explained. Flow tests using essentially submicron particle suspensions through Berea sandstone cores at different concentrations and flow rates are given. The effects of particle concentrations and fluid flow rates on the degree of damage and on the depth of particle penetration into cores are emphasized in this study.