Selection of High Temperature Scale Inhibitor for Squeeze Application in Indian Offshore Carbonate Reservoir

Abstract

Abstract The paper aims to elucidate the process undertaken to identify suitable inhibiting chemical to prevent down hole deposition of scale in ONGC western offshore wells by means of a squeeze job. Detailed description of methodology adopted for chemical selection has been elaborated in the paper. Most fields in ONGC's Western Offshore region are brown/matured fields with depleted reservoirs pressures. Seawater injection is one of the primary techniques used to combat depleting reservoir pressure. This has led to rampant escalation in scaling issues in offshore limestone reservoirs and subsequently, the frequency of scale removal jobs has also increased exponentially over the past two decades. Scale prevention is a superior and economical alternative to scale removal due to lesser consumption of chemicals and prolonged life. As part of this study, the feasibility of carrying out Scale Inhibitor Squeeze Jobs in ONGC offshore wells was examined and subsequently, extensive laboratory experiments were performed to identify suitable chemicals. The experiments included inhibition efficiency tests, thermal stability tests and extended core flow studies (adsorption and desorption methods) to verify chemical compatibility with core sample of a number of generic and vendor based chemicals under simulated reservoir conditions. After a comprehensive literature review and market scouting, six Scale Inhibitors were shortlisted and evaluated for their inhibition efficiency, thermal stability and compatibility with the rock formation through laboratory experiments. After extensive testing, Chemical X was identified as being most suitable for scale squeeze job in carbonate formations having temperatures up to 110° Celsius (230° F) and was also compatible with the formation. The adsorption and desorption isotherms respectively demonstrated sufficient chemical retention in the core and slow elution in the discharge. The measured Scale Inhibitor concentration was found to be greater than the Minimum Inhibitor Concentration (MIC) required for scale prevention. This indicated that any potential squeeze job would likely have a reasonable expected life. The study explores the possibility of carrying out a first ever scale squeeze job in ONGC Western Offshore reservoirs particularly with high temperature application. Core flow experiments were performed using scale inhibitor chemical to derive adsorption and desorption isotherms used to prepare customized job plans.