Unconventional Scale Inhibition and Acid Stimulation Strategies for Enhanced Oil Recovery in Sandstone Formations: A Case Study from Southern Oman

Abstract

Abstract Field X is an oil field characterized by sandstone formations, discovered in 1984 and put into production in 1987. Waterflooding has been integrated into field development plan since 2007 to enhance oil recovery. One of the main challenges in Field X is the underperformance of the water flood system, which led to a severe oil production decline, 30% below target by the end of 2022. The water injector wells suffer from significant scale deposition over time caused by water incompatibilities and pressure/temperature changes. Even though measures such as applying downstream scale inhibitors and performing acid stimulation have been in practice since 2010 to tackle the problem, the severity of scale deposition remains severe. A comprehensive review on previous scale formation prediction studies has been done, along with taking downhole samples to identify main scale elements in place. Four different lab analysis have been conducted including solubility tests, XRD, XRF, and bulk scale analysis (BSA). Lab analysis from the downhole scale samples showed up to 60% of samples are insoluble in HCL acid, in which two dominant scale types were identified CaCO3 and CaSO4. Assessment of the current field inhibition strategy to survey and quality assure different aspects, such as the applied scale inhibitor type, dosage, and skid locations. Three different scale inhibitors were tested at both surface and downhole conditions to identify the optimum candidate. Testing has shown an increase in dosage from 15-20 ppm to 30 ppm. Due to the presence of HCl insoluble mineral deposits, the old acid treatment recipe was found inadequate and only provided temporary solutions. Based on Laboratory results using mineralogy data from analogous wells, mud acid (9%Hydrochloric acid-1%Hydroflouric acid) was proposed for stimulating poorly performing injectors in field X. Trail camping was done using new acid treatment strategy. As a result of these efforts, Field X's injection has improved by 73% compared to 2022. This has led to an improvement in overall field production by 27%. Additionally, there has been a decrease in total suspended solids (TSS) when compared to previous years. This paper investigates the effectiveness of non-traditional acid and solvent systems in sandstone formations in Southern Oman for healthier waterflood management.