Abstract
It is important to know the produced volumes and to effectively separate the oil and water phases in oil well effluents to the surface during production. While it is known that the effectiveness of separating the phases and hence the accuracy of measurements are often affected by the nature of the fluids, the specific contributions of the physical parameters of the fluids are little known. In this study, the effect of crude oil PH on emulsion resolution was investigated. Crude oil samples from the Niger Delta with known amounts of water present were obtained. After obtaining the pH and interfacial tension, the oil and water phases were separated by centrifuge at different speeds. The results were used to establish a relationship between interfacial tension, pH and the basic sediments and water (BSW). The results show that without the use of de-emulsifiers, separation of between 66 and 90% was achieved in the light crude oil samples, but less than 30% in heavy crudes. Oil pH was found to affect emulsion resolution and has implications on the choice of de-emulsifiers. On the other hand, interfacial tension was independent of the volume of water and hence BSW of the crude oil samples. Key words: Oil production, interfacial tension, basic sediments and water (BSW), Niger Delta, bottle test.
Highlights
Most oil wells produce petroleum with some basic sediments and water
The crude oil samples used varied from light to heavy crudes; with density ranging from 0.82 to 0.93 g/cc
The recovery of samples A, B and C increased with increasing initial percentage basic sediments and water (BSW) giving an average of 70% recovery while samples D and E gave an average recovery of 20%
Summary
Most oil wells produce petroleum with some basic sediments and water. High flow rates and agitation along the production tubings and flow lines could lead to formation of emulsions. Interfacial tension has been defined as the work required creating a unit area of interface at a constant temperature, pressure, and chemical potential (Drelich et al, 2002; Abhijit, 2006). A wide range of methods have been used to measure the BSW of crude oil during production. The installation of water-cut meters which measures oil and water production at time intervals is another widely used method. Obtaining accurate estimates of oil and water produced in simple and cost effective ways over a wide range of operational conditions is a continued challenge to the oil petroleum industry and has led to studies on measurement of BSW based on parameters such as critical electric field and or the interfacial tension of crude oil-water systems. This work investigated the relationship between BSW, pH and interfacial tension of crude oil systems. Combining Equations (11) to (13), dynamic interfacial tension can be determined
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