Downhole Emulsion Problem, The Causes and Remedy, Ras Budran Field

Abstract

Abstract Ras Budran (R/B) field is located 5Kms. offshore at the eastern coast of the Gulf of Suez and consists of a massive Nubian Sandstone Reservoir compartmentalized by partially major faults. The field is undersaturated and production is maintained by gas lifting while the pressure is supported by a combined water flood and limited aquifer drive. The R/B produced crude oil has an intermediate base with asphaltene content ranging from 10–15% wt and an average API Gravity 25°. With the increase in water production and injected seawater breakthrough a very viscous tough emulsion was formed in some wells, causing production problems. Also, due to scale deposition, calcium carbonate and sulphate, the hydrochloric acid and other scale dissolvers were applied to clean the tubing and the formation. Some of these additives have an adverse effect on the emulsion viscosity and cause asphaltene deposition. The paper presents the study carried out to identify the problem and find a solution for it. The study includes:The rheological properties of the emulsion at different downhole conditions; shear rates, temperatures and water contents at different salinities.The effect of the different chemicals used for scale removal and inhibition on the asphaltene deposition and the produced crude oil emulsion viscosity.The effect of the flow improver products; demulsifier, Asphaltene dispersant, viscosity and drag reducers...etc. on increasing the fluidity and reducing the drop in pressure of the produced crude oil emulsion. The study results showed that the hydrochloric acid causes asphaltene deposition and tough emulsion formation. Also the increase in the water content form a very tough/viscous emulsion at a certain percentage, which is defined as the inversion point, below and above this percentage the emulsion viscosity is reasonable. The injection of the flow improver chemicals through the gas lift valves could reduce the emulsion viscosity. Introduction Suez Oil Co., (SUCO) is one of the biggest oil producing companies in Egypt. Our field of concern Ras Budran (R/B) is operated by SUCO, located 5 Kms offshore at the eastern coast of the Gulf of Suez. The current production of R/B oil field is about 20,000-bbls/day crude oil. Ras Budran crude is asphaltic base crude oil with asphaltene contents ranged from 10–15% by weight and average API gravity of 25°. The company is currently applying water injection strategy to increase the productivity of the wells. Due to the water injection and the nature of R/B crude oil, very viscous tough water-in-oil emulsion is formed in some of the producing wells and causes a significant decrease in the wells productivities. This paper summarized the work done to study the rheological properties of R/B crude oil emulsions formed downhole. The rheological properties were measured at different water/oil ratios, shear rates and at two temperatures. Emulsions inversion points were determined. Effects of the chemicals used for scale removal/inhibition and flow improvers on the emulsions behaviors were also studied. Background Formation of Emulsions An emulsion is a mixture of two mutually immiscible liquids, one of which is dispersed as droplets in the other, and is stabilized by an emulsifying agent. The dispersed droplets are known as the internal phase. The liquid surrounding the dispersed droplets is the external or continous phase. In the oil field, oil and water are encountered as the two phases. They generally form water-in-oil emulsion, although occasionally the reverse or oil-in-water emulsion is formed. The emulsion produced is thermodynamically unstable and this is why pure water and pure oil will never form emulsion no matter how much agitation is applied.