Lost Circulation Minimization Strategy Applied While Drilling Challenging Profile Well on Salym Group of Oil Fields
Authors: Kharitonov Andrey , Pogorelova Svetlana , Bakici Ali , Antonov Alexander , Khomutov Anton 
Published: October 2015

Abstract
Drilling practices for regular design wells for Salym oil fields have been optimized with continuous success for many years. However, new and innovative work practices had to be developed and applied to address the challenging task of drilling with higher than usual mud weight through the permeable Cherkashin formation at a high angle with oil-based mud (OBM) to minimize loss circulation and cost. The mud weight increase was essential to maintain the stability of the Achimov shale, as shown by borehole stability simulation and previous experiences. Typically, wells drilled to date were relatively simple in design as S- and J-shaped wells. Applied past practices enabled fast and trouble-free drilling for many years; in 2014, however, Salym Petroleum Development (SPD) decided to drill wells beyond the production interval at a high angle using non-aqueous based fluid with higher mud weight. Areas of great concern under these conditions were avoiding lost circulation while drilling through the highly permeable Cherkashin formation with an inclination of more than 40 degrees and the development of reliable lost circulation minimization strategy should the lost circulation occur.
Before considering any solutions, all previous experiences acquired while drilling similar profile wells in the area were analyzed, which included well profiles, drilling fluid types and parameters, lost circulation strategies applied and their efficiencies, lost circulation material (LCM) and/or sealants, and concentrations used. At the same time, the lithological information and geological description of the intervals to be drilled through were studied for compatibility. This enabled the identification of potential candidate strategies, materials, and optimal drilling fluid parameters to avoid possible lost circulation events while drilling the planned section using proprietary company software. The final solution was validated in the laboratory and agreed upon with the client team.
The developed strategy was then successfully applied while drilling the intermediate casing interval. Static and dynamic downhole losses observed while drilling were in the range of 0 to 1 m3/hour with their maximum for immediate rate at 4 m3/hour. The lost circulation rate of less than 1.5 m3/hour was considered to be acceptable for continued drilling. When rates exceeded 1.5 m3/hour, specially designed LCM pills were used. The LCM portfolio for this well included a broad spectrum of different types and shapes of inert materials, such as sized marble, resilient graphite, and fiber LCM. This strategy enabled minimal losses while drilling the interval.
This paper shares the experience of with working and applying the technical strategy used to ensure the smooth drilling of the troublesome interval, as well as the lost circulations minimization strategy used while drilling the challenging profile well through the highly permeable Cherkashin formation. This approach may be effectively expanded to other fields where similar challenges need to be resolved.