Abstract

Clay minerals in hydrocarbon reservoirs often cause formation damage. The wellknown examples are fines migration, clay swelling, and hydrothermal mineralreactions. In the last few decades, numerous clay stabilizers have beendeveloped to control formation damage related to clay minerals. Claystabilizers have wide applications in acidizing, fracturing, sand control, workovers, and enhanced oil recovery. Field applications of clay stabilizershave been proven 10 be economic.

Hydroxylaluminum (OH-Al) polymers are one of the first group of claystabilizers developed in the late sixties. Due to their high charge, polynuclear OH-AI cations are favoured by negatively charged clay surfaces andthus provide a strong stabilization effect for clay minerals. The adsorption isirreversible and OH-AI polymers can stabilize clayspermanently. However, OH-AIpolymers are stable only in a narrow pH range (3.5 - 6.0); they are notcompatible with basic solutions and their applications are limited to near wellregions. In recent years cationic organic polymers (COP) have been widely usedas clay stabilizers. They are complete soluble in water and compatible withacids and bases. They also provide permanent stabilization to clays. Some COPsave good thermal stabilities up to 250"C However, COPs with high molecularweights may cause damage in low permeability reservoirs. In thermal recovery, ammonium based salts have been used to buffer the pH of the steam condensateand residual liquids. These steam additives are effective in controllingmineral reactions,- but they are ineffective in ontrolling clay swelling orfines migration unless a high concentration of NH4+ismaintained in the flooding solutions good understanding the interactionsbetween clay minerals and clay stabilizers is essential to their successfulapplication.

Introduction

It has been widely recognized that the clay minerals can cause significantformation damage to hydrocarbon reservoirs. Well known examples are finesmigration and smectite swelting which can reduce reservoir permeability by orethan 90%. This formation damage often leads 10 poor productivity and thus cansignificantly raise the cost of oil recovery. In the past thirty years, thepetroleum industry has made a great effort to control/minimize the formationdamage related to clay minerals. The result of this effort is he development ofnumerous chemicals often called clay stabilizers in the industry. From itsconception, clay stabilizer has evolved from simple inorganiccompound2–5 in the 60's to inorganic polymers in the 70's6–9, and to complex organic polymers in the 80's and90's10–15. Many of them have been used in drilling, completion, acidizing, fracturing, sand control. Workover, water flooding, steam injection, etc.. The economic success in applying clay stabilizers depends on an engineerunderstands of the formation damage and his choice of clay stabilizer(s). Toefficiently use clay stabilizers, it is important to evaluate the applicabilityand limitation of each and every clay stabilizer available.

In this paper, we will first summarize clay-related formation damage and major mechanisms of clay stabilization. A comprehensivereview is made on clay stabilizers published in referred and patent literature.Some laboratory results and field cases will be presented to illustrate theapplicability and efficiency of three classes of clay stabilizers: inorganicpolymers, organic polymers, and steam additives.

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