Testing the Compatibility of Hydrochloric Acid and Scale Inhibitor Solutions With Lake Maracaibo Crude Oils and Gasoil
Authors: Teeuw D. , Manzano O. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
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Abstract
In matrix-acidizing and scale clean-out/ inhibitor squeeze treatments it is of major importance that the fluids injected are compatible, both mutually and with the reservoir fluids. An exploratory investigation has been made on the compatibility behaviour of various fluid systems using simple compatibility tests.
Results show that the compatibility of crude oils with hydrochloric acid or scale inhibitor solutions is very problematic if no additives are used. Suitable additives improve the rheology of the emulsions but are not always effective in separating the oil and water phases. Alcoholic acid shows much better compatibility than the common (15%) acid.
Gasoil is in general not compatible with hydrochloric acid or scale inhibitor solutions in which additives are incorporated. In most cases a small amount of demulsifier is sufficient to solve the incompatibility problem.

Introduction
In the course of years several methods and techniques have been developed to stimulate oil wells which show poor production performance. Low productivity may be the result of skin damage, productivity may be the result of skin damage, caused e. g. by mud- and cement particles which have penetrated the immediate vicinity of the bore hole during drilling or workover operations. It is also possible that the production decreases when tubing and perforations become plugged by precipitation of scale after water has broken through, precipitation of scale after water has broken through, in which case the production curve will show a sharp drop. These kinds of well and skin damage can be remedied by injection of hydrochloric acid or mud acid, while wells which suffer from scale can be treated preventively by scale inhibitor squeeze.
In CSV wells in Lake Maracaibo matrix acidisation and scale clean-out/inhibitor squeeze have been applied on a wide scale with varying success. With the majority of the treatments satisfactory results have been obtained with respect to stimulation and scale prevention. However, for a number of wells the production rate could not be increased to the expected level or be restored to the level before treatment. This relative decrease indicates that side-effects can occur which offset, at least partly, the result of cleaning and inhibition. On scrutinizing the techniques and procedures one may think of several factors which adversely affect the treatments. The difficulty in real jobs is that the individual contributions of these factors cannot be assessed. The effect of certain parameters can be investigated in laboratory core-flow experiments, but in general such tests are laborious, even in their simplest form, and the results are of limited value due to insufficient representativeness of the core material.