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ASSESSMENT OF SCALE INHIBITOR IMPACT IN STEAM ASSISTED GRAVITY DRAINAGE

Irina Guskova, Vadim Sayakhov

Abstract

The paper considers the issue of effective scale inhibitor applied while developing an oilfield using steam assisted gravity drainage technique, and presents a case study of injecting superheated steam of 140-160?C in the Ashalchi oilfield. In such conditions, organophosphorus chelating agents conventionally used to prevent scale formation degraded and proved to be ineffective. The authors analyzed chemical composition of scales deposited on the electric submersible pump pulled from one of the wells in the Ashalchi oilfield using EDX-800HS2 energy dispersive X-ray fluorescence spectrometer for performing X-ray fluorescence analysis . Salt deposits of scales were composed of mixed silicates with complex structure, calcium carbonate, sulfide and iron disulfide. The issues of scale formation and using amine-based surfactants as a promising trend in choosing effective high temperature scale inhibitors are of significant interest for professionals. The mechanism of amines is based on their ability to affect the processes of formation, growth and accumulation of inorganic salt crystals. In addition, amines enter into a reaction with anions forming with them water-soluble or loose insoluble compounds, thereby preventing crystallization. The authors discuss using diethanolamine as a scale inhibitor which currently is a widespread experience. Along with the above mentioned influence on salt nuclei, diethanolamine is traditionally used as a component for amine treatment of gases from hydrogen sulphide. The use of diethanolamine would lead to partial neutralization of hydrogen sulfide. Before physical simulation of oil displacement had been carried out, the authors assessed solubility of diethanolamine in ethyl acetate and ethyl acetate. When diethanolamine and ethyl acetate were mixed, a deposition would form. Ethyl acetate does not mix with diethanolamine, however, adding 10% water allows to obtain a homogeneous solution. Assuming crude oil recovery model to involve water and steam, the influence of diethanolamine on the dynamics of oil recovery was evaluated when it was injected in combination with ethyl acetate. In the experiments diethanolamine was pre-mixed with chemicals, its amount made up 10% of the weight of the chemical. There were two scenarios simulated: steam injection with diethanolamine and steam injection with ethyl acetate and diethanolamine. According to results of physical simulation the cumulative recovery has been assessed. The results of the studies made it possible to draw the following conclusion: diethanolamine as a scale inhibitor does not significantly influence oil recovery rates. Therefore, in order to increase technological and economic efficiency of high viscosity oil and natural bitumen recovery it is expedient to select chemical agents with combined effects to be successfully used for consistent treatment while injecting a heat-carrier to increase both volumetric sweep efficiency and displacement efficiency.

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DOI resolver: doi.org/10.5593/sgem2017/12/s02.014

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