Monitoring and Mitigating Asphaltene Issues in a Deepwater Production System

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 27123, “Strategies To Monitor and Mitigate Asphaltene Issues in the Production System of a Gulf of Mexico Deepwater Subsea Development,” by Doris Gonzalez, Fabio Gonzalez, Marney Pietrobon, Mehdi Haghshenas, Megan Shurn, Amber Mees, Carlos Stewart, SPE, and Chinenye Ogugbue, SPE, BP, prepared for the 2016 Offshore Technology Conference, Houston, 2–5 May. The paper has not been peer reviewed. Copyright 2016 Offshore Technology Conference. Reproduced by permission. An asphaltene threat was identified in production wells located in a Gulf of Mexico deepwater field. During reservoir-fluids characterization, asphaltenes were identified as a key risk factor for successful field development. This paper presents an integrated approach to evaluate the key elements of asphaltene risk for deepwater projects, the strategy to manage the issues during production implementation, and aspects to be considered in the mitigation of asphaltene in the field-development plan. Introduction Asphaltene precipitation and deposition can occur at different stages during petroleum production, causing reservoir formation damage and plugging of pipelines and production equipment. Remediation of asphaltene deposits requires solvent-soaking operations, followed by removal through exposure to turbulent flow. These intensive operations require high amounts of chemical solvents with potential effects on health, safety, and environment, along with production deferrals because of operations downtime. The focus of this study is to understand the effects of asphaltene precipitation in a Gulf of Mexico deepwater field. The approach is based on reservoir-fluid characterization and monitoring tools. Being able to predict the presence and type of trouble zones along the production system from downhole to production facilities is becoming progressively more important as water depths increase. Acquisition of Downhole Fluid Samples High-quality pressurized bottomhole samples were collected for asphaltene-onset-pressure (AOP) and wax-appearance-temperature (WAT) measurements in pressure-compensated chambers. Because the samples tend to cool to below reservoir temperatures as they are retrieved from the well, the samples were maintained at pressures above reservoir condition at all times to reduce the possibility of irreversible asphaltene precipitation resulting in non-representative samples. Asphaltene Prescreening The de Boer Plot. The de Boer plot is a method to screen crude oils for their tendency to precipitate asphaltenes. It essentially evaluates the loss of asphaltene solubility as a reservoir-fluid sample is depressurized. This pressure/volume/temperature screen is a crossplot of in-situ density and the degree of undersaturation with respect to gas (the difference between reservoir pressure and saturation pressure). Because this screening assumes that the fluid is saturated with respect to asphaltene at reservoir conditions, it is extremely conservative.