(241e) Design of Base Fluids for High Pressure/High Temperature Drilling

One of the important factors that influence drilling costs in oil and gas production, is the drilling fluid used. Drilling fluids, also known as drilling muds, are suspensions with many soluble and insoluble additives in a base fluid like water or diesel. These fluids perform many functions and can be effective in optimizing the drilling operations. Although under high pressure/high temperature (HPHT) conditions, oil-based or synthetic fluid-based drilling muds have better performance than water-based fluids, environmental restrictions, and prohibitive costs prevent their use in such wells, particularly in offshore drilling operations. At the same time, increasing demand for oil and gas has lead to exploration of deep reservoirs with extreme temperature and pressure conditions and designing base fluids to withstand such demanding conditions is a challenging task.

Computer-aided molecular design (CAMD) is an effective technique used for product design. CAMD techniques based on group contribution have been successfully applied to problems like refrigerant design, solvent replacement design, and polymer design. The design framework developed by Samudra and Sahinidis [1], based on the GC+ model [2], is efficient, versatile, and allows integration of different property models. Although the original GC+ model includes some environmental metrics, the framework can incorporate other molecular modeling methods to predict properties like LC50. Another advantage of the framework is its modular structure and use of mixed-integer optimization in each module to increase the calculation speed by orders of magnitude compared other enumeration-based methods. This paper presents the use of the CAMD framework to design the base fluid for HPHT drilling. The properties that dominate the choice of drilling fluid are included in the design model. These include boiling and melting points, flash point, viscosity, and surface tension. One of the objectives in this work has been to include reliable property models to predict environmental metrics and use them in the design process. Properties like octanol-water coefficient, aqueous solubility, and LC50 are used to guide the molecular design. The targets for molecular design are formulated after an extensive review of deep well conditions and previously used synthetic fluids. We discuss the results of the design problem and compare them to current synthetic fluids like esters, mineral oils, and polyolefins.

Finally, we report on the use of computer-aided mixture/blend design using known fluids and mixture property models.

Bibliography:

[1] Samudra, A. and N. V. Sahinidis, Design of secondary refrigerants: A combined optimization-enumeration approach, in M. M. El-Halwagi and A. A. Linninger (eds.): Proceedings of the 7th International Conference on the Foundations of Computer-Aided Process Design, CRC Press, pp. 879-886, 2009.

[2] R. Gani, P. M. Harper, and M. Hostrup. Automatic Creation of Missing Groups through Connectivity Index for Pure-Component Property Prediction. Industrial & Engineering Chemistry Research, 44:7262?7269, 2005.