Abstract

Kuwait Oil Company (KOC) is planning to adopt thermal method for the recovery of heavy oil in its north Kuwait heavy oil reservoir. However there are growing concern of salts precipitation and scaling deposits, especially magnesium hydroxide (Mg(OH)2) in the targeted reservoirs due to the potential reaction of alkaline steam water mixture with the reservoir waters which contain significant concentration of magnesium, barium and other components. A comprehensive compatibility study was carried out using laboratory test and computer scaling predictions of scaling tendencies of the fluids as follows:

  • Alkaline steam boiler feed water (SBFW) with the Lower Fars (LF) formation water

  • Heavy oil Produced water (formation + condensed water) from the thermal wells) with the Tayarat formation water

This paper presents the results of computer scaling study performed using ScaleChem simulation software and laboratory examination of water compatibility using the Jar test analysis for mixing alkaline steam boiler water (SBFW) with the Lower Fars formation water (LFW).

The main objectives of this study were as follows:

  • To analyze and characterize the SBFW and LFW

  • To perform computer scale compatibility study to predict type and masses of scale that could be generated as a result of mixing pH adjusted steam water with the LF water.

  • To predict scaling tendency of individual waters at defined temperature and pressure conditions

  • To check compatibility of these waters using laboratory Jar tests

The type of scale and the location in which it is predicted to occur are important factors when considering the risk of scale formation. Scales such as calcium carbonate (CaCO3) can be removed relatively easily with the appropriate chemical treatment. Alternatively, scales such as barium sulphate (BaSO4) are much more resistant to chemical treatments and can require more specialized products. These chemical treatments present significant health and environmental risks, and considerable additional expense. Results indicated that both calcium sulphate (CaSO4) and Mg(OH)2 are predicted to form in the boiler and the amounts of solid phase is computed to exceed 3,000 mg/l, depending on the inlet pH. At lower pH, in the mixing calculation for the reservoir, BaSO4 is dominant scale. At higher pH, several scales are computed to exist.

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