Abstract

The potential for formation damage caused by the use of high density brines has only recently begun to be studied. Unfavorable fluid/rock interaction has been shown to produce mobile fines and swelling clays produce mobile fines and swelling clays with the added potential for the precipitation of brine insoluble salts. Some precipitation of brine insoluble salts. Some operators have started lowering the pH of CaCl2 and/or CaBr2 brines by requiring a minimum of 8% ZnBr2. The hope was to prevent the precipitation of acid soluble prevent the precipitation of acid soluble salts. This approach has significant practical and economic limitations. This practical and economic limitations. This study evaluates alternatives to use of ZnBr2 as a primary component of standard CaCl2 and/or CaBr2 brines. Laboratory core flow tests were conducted to evaluate surfactant systems potential for preventing this formation damage. preventing this formation damage.

Introduction

The trend to solids-free completion fluids has now become a global standard. Three of four wells scheduled for completion in 1991 will utilize high density clear fluids. Almost all of the completions where solids laden fluids are planned will be outside of the domestic operations. This movement in oil and gas completions is being driven by two factors. First, Houchin indicated that formation damage, in most cases, is never completely removable. Therefore, prevention is the only viable alternative. Second, quality management programs no longer focus exclusively on small improvements, but on zero defects or absolute prevention.

Morgenthaler demonstrated that damage from high density brines was most likely with brines formulated with CaBr2 and CaCl2 >14.2 lbm/gal (1702 kg/m3]). He postulated that these brines should postulated that these brines should contain a minimum of 8% ZnBr2 to lower the pH and prevent the precipitation of acid pH and prevent the precipitation of acid soluble calcium salts.

Although this approach is consistent with established theories, it has several practical disadvantages. Many operators practical disadvantages. Many operators perceive this brine system as one that is perceive this brine system as one that is contaminated with low levels of zinc. Reclamation and storage of this system has resulted in five-fold increases in cost.

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