Identification and Cost Effective Mitigation of Calcium Carbonate Scaling in Gas Field - A Typical Case Study in Niger Delta

Abstract

Beta Integrated Oil and Gas plant is the major supplier of domestic gas to the Lima power plant which provides 16% of the available power to the Nigerian national grid. Efforts are made to ensure that down times in the plant are reduced because of the huge impact to domestic gas supply in the country. Between 2014 and 2015, multiple tripping had been observed on the transfer pump at the Beta gas plant. Laboratory analysis of the recovered solid deposits in addition to scale simulations of the hydrocarbon fluid confirmed the presence of calcium carbonate scale (85.2%wt). Although the culprit well was identified, a cost-effective surface chemical solution was immediately deployed upstream of the facility which significantly reduced the export pump downtime due to scaling and clogging. The overall treatment option adequately mitigated the calcium carbonate scale observed and also led to significant savings in pump maintenance of about a million dollars. This paper will be discussing the problem and underlying restrictions faced by the multidisciplinary team, problem solving approaches considered as well as the solution employed by deploying Phosphate Ester based chemical scale inhibitor. The scale inhibitor is specially formulated to prevent the formation of calcium carbonate, calcium sulphate, barium sulphate and strontium sulphate scales in producing wells, water injection systems and saltwater disposal systems. One major consideration in the choice and use of the product is the cost effectiveness of the product, its potency and suitability at effectively mitigating the calcium carbonate scaling in the gas plant. It was successfully qualified in the lab for use with MIC of 10-20ppm and has been previously deployed in our deep water facility. Laboratory tests indicate it is effective in produced water with iron and high bicarbonate content as is the case for Beta gas plant. In addition, laboratory tests indicate it does not encourage deposition of naphthenates in produced water as is observed with some phosphate based scale inhibitors. The product is also readily available in-country hence no long delivery lead time challenges, besides there is significant cost and logistics value to be realized from its deployment in Beta oil and gas plant.