The Application of Drilling Fluid System Based on Salt-Saturated Direct Emulsion in Construction of Wells on Yurubcheno-Tokhomskoye Field

Abstract

Abstract One of main drilling challenges in the Yurubcheno-Tokhomskoye field is fluid losses. In particular, the requirement of a drilling fluid with minimal mud weight to minimize risks associated with fluid losses when drilling overbalanced, enabling drilling through salt intervals. Historically, the technical column interval has been drilled using generic OBM using local crude oil. However, such fluids carried significant health and safety risks associated with low flashpoints. Invert emulsion fluids, based on local crude oil as the continuous phase, are characterized by flashpoints of 6-8 °C, which does not address the safety concerns. Alternatively, a drilling fluid, designed based on a salt-saturated, continuous phase, direct emulsion, with up to 30 % local crude oil (as the internal phase) to achieve a mud weight 1.10 SG is characterized by a flash point higher than 100 °C. A flash point >100 C enables significant minimization of these health and safety risks. As well as improving the fluid flashpoint and avoiding related incidents, direct emulsion fluids can be formulated to present high long-term stability, a stable rheology profile, and superior filtration control. Five 245 mm casing intervals were drilled to date using the direct emulsion and successfully set at targeted TDs. The solutions applied have assisted to achieve following KPIs: 15% less mud volume due to lower volume lost into the formation. 45% less crude oil used due to significantly lower oil content in the fluid. 15% less losses into the formation presumably due to low Pumps on ECD achieved. 50% less time associated with lost circulations. These achievements resulted in a three-day reduction in the time of the interval construction (average of five wells drilled) compared to similar intervals drilled using generic invert emulsions. This paper discusses the development and selection of a new, economical, safe, and efficient drilling fluid, for 245 mm casing intervals in the Yurubcheno-Tokhomskoye field. Supporting laboratory test results, fluid performance achieved, lessons learned and recommendations for further system optimization of the drilling fluid and drilling practices, are presented for consideration. The positive KPIs and superior mud performance achieved enable expanding the use of the direct emulsion on the field and recommend its application to other fields in the area.