An oil sample, collected from the wellhead of a shallow sand of a Malaysian reservoir, was identified as a very stable crude oil emulsion. This micro-emulsion type crude could not been separated in field separation facilities by gravity settling alone. The emulsion was very stable that it required either a high speed centrifuge (40,000 ppm) or high doses of emulsion breaker to be demulsified. Hence, from the perspective of field operational cost, it is critical to further investigate the factors that have potentially contributed to the stability of the crude oil emulsions.
The field of interest has been producing for over 30 years and its reservoir pressure has dropped to a level very close to the original bubble point pressure. All the wells in the field are gas lifted to enhance well productivity. Due to the unconsolidated nature of the reservoir rock, fines migration was one of contributing factor to formation damage. The reservoir crude was identified as biodegraded with missing of intermediate components from the reservoir fluid composition. As such, a structured bottom-hole sampling program was developed and bottom-hole samples were collected below gas lift mandrels while the gas lift was shut-in to thoroughly investigate the contributing factors to the formation of the crude emulsions and to identify the in-situ status of the crude.
Potential factors which could contribute to the formation of stable crude oil emulsions include 1) mixing of two or more incompatible crudes; 2) emulsifying agents including surface active materials (asphaltenes and resins, organic acids and bases, injected surfactants or oilfield chemicals) and finely divided solids (clay particles, sands, asphaltenes, wax, scale etc.). This study has investigated several potential contributing factors related to formation of the stable crude emulsions. It was concluded that naturally occurring fines could be the major contributing factor for the formation of the observed stable crude emulsion from the reservoir under study. Effect of gas lift on formation of the crude emulsion was found very minimal since the crude was at emulsion state even at reservoir depth.
