(51c) Design of High Pressure/High Temperature Drilling Fluids

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. We have developed a molecular design framework that is efficient, versatile, and allows integration of different property models. In addition to property estimation based on the GC+ model, our framework incorporates molecular modeling methods to predict environmental 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 components of the drilling fluid for HPHT drilling. We primarily present the efforts to design the base fluid in the drilling mud. 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 present the formulation of design targets for various additives in the drilling muds and preliminary results from the design problem.