MODELING AND PREDICTION OF SCALE FORMATION IN PETROLEUM RESERVOIRS DURING WATER INJECTION PROCESS
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Abstract
The formation of mineral scale in petroleum reservoir is one of the most severe oil field problems that inflict water injection process primarily when two incompatible waters are involved. Typical examples are sea water, with high concentration of sulphate ions and formation water, with high concentrations of calcium, barium, and strontium ions. Mixing of these waters, therefore, could cause precipitation of calcium sulphate, barium sulphate and/or strontium sulphate. Different mathematical models currently exist in the literatures that predict the tendency of scale formation during water injection technique but not the amount of scale mineral that would be precipitated. This research work was conducted to develop a mathematical model that will be able to predict the amount of scale minerals that would be formed at different locations few inches from the injection well toward the petroleum reservoir. The relationship that exists among the saturation index, solubility product and concentration of scale precipitated was used as the basic principle in deriving the mathematical model. The results of the research work show that in Siri – C oil field, at saturation index of -3.00, the mass of Gypsum precipitated was 3986.455mg but when the saturation index increased to 0.4, the mass reduced to 3985.001mg. In Siri – D oil field, at saturation index of -1.20, the mass of Gypsum precipitated was 4792.014mg, but when the saturation index increased to 0.1, the mass reduced to 4792.001mg. In Siri – E oil field, at saturation index of -3.50, the mass of Gypsum precipitated was 9184.572mg, but when the saturation index increased to -0.4, the mass also reduced to 9184.000mg. This trend was similar for Barite and Celestite. It was inferred from the analysis that the amount of scale precipitated is dependent on the saturation index of the scale and the ionic composition of the system. v vi TABLE OF CONTENTS TITLE PAGE CERTIFICATION i LETTER OF TRANSMITTAL ii DEDICATION iii ACKNOWLEDGEMENT iv ABSTRACT v LIST OF FIGURES viii LIST OF TABLES ix LIST OF SYMBOLS x CHAPTER ONE 1.0 INTRODUCTION 1 1.1 OBJECTIVE OF THE WORK 3 1.2 SCOPE OF THE WORK 3 1.3 TECHNICAL CHALLENGES 3 1.4 JUSTIFICATION OF THE RESEARCH WORK 3 CHAPTER TWO 2.0 LITERATURE REVIEW 5 2.1 THEORETICAL PRINCIPLES 11 2.1.1 Water Injection Technique 11 2.1.2 Causes of Scale Formation 12 2.1.3 Factors affecting Scale Formation 13 2.1.3.1 Supersaturation 13 2.1.3.2 Reaction Kinetics 14 2.1.3.3 Changes in Temperature and Pressure 14 2.1.3.4 Mixing of Incompatible waters 14 2.1.3.5 Effects of other compounds and impurities 14 2.1.4 Types of Inorganic Scales 15 2.1.5 Nature of common Oil Field Scales 15 2.1.5.1 Calcium sulphate scales 15 2.1.5.2 Calcium Carbonate Scales 17 2.1.6 Mechanisms of Scale Formation 19 2.1.6.1 Attainment of Supersaturation/Induction Period 19
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