ABSTRACT

The use of Potassium Carbonate as a non-corrosive, chloride free completion fluid has gained acceptance by several operators in the Middle East and North Sea. These brines can be formulated to reach a specific gravity of 1.52 (12.5 lbm/gal).The formulated brines possess physico-chemical properties such as high solubility, low crystallization temperature, low intrinsic viscosity, low corrosivity, etc., which make them candidates for utility as completion and/or packer fluids. Theoretically, these properties should provide a brine completion fluid which is operationally functional, corrosion resistant (high pH) and which eliminate the potential for chloride stress cracking of corrosion resistant alloys. However, the significance of these benefits is unpublished and other obvious potential incompatibilities were apparently not evaluated.

This paper presents results from an extensive laboratory evaluation as to the suitability of potassium carbonate brines as completion fluids. Data from average weight loss and stress cracking corrosion (SCC) tests confirm both low general corrosion rates and little or no tendency toward stress corrosion. However, this low corrosion potential is not significantly lower than other chloride free brine alternatives such as sodium bromide.

At test temperatures as high as 300°F, no evidence of 13 Chrome Stainless Steel stress cracking was identified in any of the completion brine systems tested, including chloride and bromide based fluids. Furthermore, fluid-fluid and fluid-rock compatibility test results indicate that carbonate based brines produce precipitation reaction products when intermixed with a range of synthetic and natural formation waters. Single-phase, brine flow tests on Berea cores showed an almost total loss of permeability after exposure to potassium carbonate brines.

Guidelines are presented to assist the completion engineer in thoroughly evaluating completion fluid brine chemistries as to functionality and formation compatibility.

INTRODUCTION

The potential for premature workovers caused by materials failure in corrosive environments has challenged the Oil and Gas Industry for many years.

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