An Experimental Model to Predict and Control Oilfield Emulsion Tightness: A Novel Approach
ABSTRACT
Formation of water-in-oil emulsions are among the major challenges encountered by production and surface facilities engineers during the recovery of crude oil, especially in a large multi-wells system in both onshore and offshore oilfields.
The development of systematic approaches to handle emulsion problem has been very slow. Several important aspects of emulsion that have not being studied extensively to date include mechanism, kinetics and energy levels associated with emulsion formation.
Such information is needed to understand the emulsification process, model it and hence solve lots of operational and economical emulsion issues.
This study presents a novel experimental approach to model the process of water-in-oil emulsion formation and also study the shearing energy levels associated with its formation.
Oilfield emulsions were simulated using agitator rated between 0 to 1000 RPM. Mixture of crude oil, formation water, asphaltene, inorganic solid, scale precipitates and reservoir fines were agitated at various revolutions to form the emulsion. The emulsions that result were stabilized using re-solubilized asphaltene precipitated out of the crude oil.
A demulsifier chemical sample was used to properly treat over 300 bottle samples, and the rate of separation of their emulsified water was used to determine their tightness.
INTRODUCTION
Overview
Crude oil is seldom produced alone from reservoirs. It is always produced as a complex mixture of hydrocarbons and formation water.1
These mixtures undergo extreme agitation under high shear rate and turbulence as they flow from the reservoir pores through perforated casing into the wellbore, to the tubing and finally through the surface production facilities.
This occurrence causes the water phase to be dispersed and stabilized as fine droplets in the bulk oil phase and hence forms emulsion.
Emulsion is among the many problems encountered in the production, transport, and refining of crude oil and dealing with this complex structural arrangements account for much of the expenses incurred by oil companies in their daily operations.2
Their control and resolution is among the major challenges encountered both onshore and offshore by production engineers, production chemists and facilities engineers during production, especially in a complex multi-wells system. Emulsion problems are usually more problematic in fields where heavy crude oils are produced.3
Emulsions are stabilised by rigid interfacial films that forms a ‘’skin’’ on the water droplets and prevents them from coalescing.4
The stability of these interfacial films, and hence the tightness of the emulsions, depend on a number factors, including the heavy materials present in the crude oil (e.g. asphaltenes, resins, waxes), inorganic solids (e.g. clays, scales and corrosion products), temperature, droplet size and droplet size distribution, pH and brine composition.5
As the producing field depletes, the nature of petroleum emulsion changes continuously due to changes in some of these factors and production methods.5
References
Kokal, S. ‘’Crude Oil Emulsions: A state-of-the-art Review,’’SPE paper 77497 presented at the SPE Annual Technical Conference and Exhibition, San Antonio, 29 September – 2 October
Becker, J.R., Crude Oil Waxes, Emulsions, and Asphaltenes. 4th edition; Pennwell publishing company: Oklahoma,
Opawale, A.O., ‘’Optimising the Demulsification of Heavy Crude Oil: A means of Improving its Flow through Flowlines, Manifolds and Processing Facilities’’, Proceedings of the 11th Offshore West Africa Conference and Exhibition, Abuja,
Schramm, L.L., “Emulsion: Fundamentals and Applications in the Petroleum Industry, Advances in Chemistry Series-231, Washington DC, 1992
Kokal, S.L. ’’Crude-Oil Emulsions,’’ Petroleum Engineering Handbook, SPE, Richardson, Texas,
Gary, W.S., Moshen. Z. ‘’ The practised art of Emulsion Resolution in Electrostatic Processes’’ presented at Spring Meeting, Houston,
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