Abstract
The company had an issue with the Electrical Submersible Pump (ESP), which have a short run life because of scale formation. The scale formation in the production wells is derived from some main reservoirs where Upper Burgan (sandstone) is experiencing sulfate scale while Maudud and Lower Burgan reservoir is experiencing carbonate scale. The scale formation in the downhole is unpredictable; therefore, the scale inhibitor is required to prevent loss production of the well due to pump trip and cleaning.
The encapsulated scale inhibitor was trialed at a selected production well, which was experiencing deposited scale and no scale inhibitor treatment. The well has a production rate of 2755 BLPD and 58% water cut with wellhead pressure of 182 psi. The rat-hole capacity of the well is 533 gallon, which is sufficient to store 165 gallons of encapsulated inhibitor for batch chemical treatment. The inhibitor consists of a microencapsulated liquid scale inhibitor, which was weighted with brine to ensure settling in the rat-hole. The injection of inhibitor into the down-hole used a bull heading through the casing annulus with pressure 150 psi.
After the six-month pilot trial of the inhibitor, there was no blockage in the well tubing, pump trip or a change in ampere of the ESP due to scale deposition. In addition, the inhibitor was still active with Phosphate Residual Concentration (PRC) in the produced water of 0.7 mg/liter higher than the 0.5 mg/liter minimum threshold of the project success criteria. From mass balance analysis of the effluent water, the scale tendency slightly reduced after injecting the encapsulated scale inhibitor in the selected well.
This paper explains the value added to the company by deploying the encapsulated inhibitor for batch treatment with return on investment of 445% and pay out time of 2.2 months. Further study is required to estimate the life expectancy for the chemical deployment since it depends on rate-hole dimension, water quantity, temperature, salinity and pH of the reservoir fluids.
