Stabilizing Clays With Potassium Hydroxide
Authors: Sydansk Robert D. 
Published: December 2007

A newly developed potassium-hydroxide (KOH) treatment, when properly designed and applied to clay sensitive sandstone formations, will effectively and permanently stabilize clays and will prevent reduced oil permanently stabilize clays and will prevent reduced oil production caused by changes in salt compositions of production caused by changes in salt compositions of oilfield brines. The KOH treatment for stabilizing clays is applicable to a wide range of formation temperatures and mineralogies. The treatment consists of slow injection of a single aqueous solution containing KOH, along with soft-water pre- and postflushes. During laboratory flooding experiments in clay-sensitive sandstone, the treatment effectively stabilized clays and greatly diminished the tendency of fresh water to reduce permeability. Also, during laboratory floods. the treatment generated little. and often no treatment-induced permeability damage. Treatment fluids are clear, nonviscous, aqueous solutions. KOH is a reactive, relatively inexpensive, readily available, inorganic chemical. Treatment effectiveness depends on KOH concentration, formation temperature, and treatment-fluid/sandstone contact time. For a studied clay-sensitive sand-static at its 185 degrees F [85 degrees C] formation temperature, optimal conditions were determined to be about 15 wt% KOH and about 16 hours of contact time. KOH clay stabilization results from caustic interacting irreversibly with clays in the presence of potassium ions. KOH "permanently" alters the silicate chemistry of clays and renders them insensitive to fresh water for a period well beyond the commercial life of the reservoir. period well beyond the commercial life of the reservoir. KOH treatments, having, operational and safety considerations similar to those of acid-stimulation treatments, are compatible with most oilfield and platform operation. platform operation. Our concepts and procedures for evaluating clay-stabilization treatments by means of laboratory flooding experiments are discussed.

Introduction

A number of clay-stabilization treatments are discussed in the literature. Our field experience indicated that none of the leading commercial clay stabilizers available just prior to development of the KOH treatment was satisfactory when applied to an Oligocene-Age water-sensitive reservoir of interest to our company. Field experience, along with a laboratory study of the leading commercial clay stabilizers, indicated that, under reservoir conditions, the commercial stabilizerswere not its effective as desired and/orcaused significant treatment-induced permeability damage.

The Oligocene reservoir has a 185 degrees F [85 degrees C] formation temperature and formation water with 28,000 ppm total dissolved solids (TDS) (3,500 ppm divalentcations). Because of the poor field performances mentioned previously and because of discouraging laboratory previously and because of discouraging laboratory evaluations of the studied commercial stabilizers under Oligocene reservoir conditions, we were asked to develop a permanent clay stabilizer that would be effective at elevated temperatures and salinities. The KOH treatment resulted. Although specifically developed for the elevated-temperature and saline Oligocene reservoir, it quickly became apparent that the treatment is applicable to a wide range of water-sensitive reservoirs and conditions. Although the KOH treatment has been field tested and appears to have stabilized clays under field conditions, this paper is limited to the laboratory evaluation of the treatment's effectiveness. The laboratory evaluation exclusively involved flooding experiments, many of which closely simulated field conditions. The term "clay stabilization" refers to treating an oil-bearing sandstone formation so as to prevent permeability damage and reduced fluid tow caused by changes in salt composition of injected and produced waters. Such permeability damage often results when brines become permeability damage often results when brines become progressively fresher (reduced salt concentrations). The progressively fresher (reduced salt concentrations). The term "freshwater permeability damage" often is used to describe freshwater-induced reduced fluid flow and oil production from water-sensitive reservoirs. Reduced production from water-sensitive reservoirs. Reduced flow results from damaging interactions between fresh brines and fine particles-especially clays. Fine particles involved in freshwater permeability damage are not limited to clays but include all swelling and potentially mobile fine particles within the sandstone pore bodies. Muecke defines fine particles as those pore bodies. Muecke defines fine particles as those with diameters of less than 37 microns [37 mu m]. Clay particles have diameters of less than 2 microns [2 mu m]. particles have diameters of less than 2 microns [2 mu m]. Fine particles that can contribute to permeability damage include clay minerals. large-surface-area silica (SiO2) minerals, feldspars, mica, and barite.

Fresh water can induce clay-mineral permeability damage through two mechanisms. Swelling clays, such as montmorillonite, swell in the presence of fresh water and impede fluid flow. Poorly cemented clay particles, such as kaolinite and illite, can become detached particles, such as kaolinite and illite, can become detached during aqueous flow, especially when flowing brines become relatively fresher. The resulting newly mobile clay particles eventually become trapped in restricted pore-throat openings, where they reduce permeability pore-throat openings, where they reduce permeability and fluid flow. This type of permeability reduction is called "clay-particle-migration permeability damage." Swelling clays can also migrate when contacted by fresh water.

JPT

P. 1366