The Use of Diutan Biopolymer in Coiled Tubing Drilling Mud Systems on the North Slope of Alaska

Abstract

Abstract Diutan biopolymer has recently been introduced for drilling with coiled tubing on the North Slope of Alaska. Diutan biopolymer has replaced a xanthan biopolymer based mud system when drilling new sidetrack laterals from existing wells and also in well servicing with non-rig coiled tubing operations. This change in fluid systems was made by replacing the existing xanthan biopolymer used in the solids free mud system with a diutan biopolymer. The new diutan based solids free mud has shown improvements in several areas thus providing a significant performance advantage. Coiled tubing drilling (CTD) has been conducted in Alaska since 1994 with over 600 sidetrack laterals drilled to date. For the majority of these wells a solids-free mud system was used to drill in either an overbalanced or managed- pressure drilling mode. The solids-free mud used was based on a xanthan biopolymer. In 2009 planning for more difficult well candidates suggested that the existing xanthan drilling fluid systems would be inadequate for drilling certain wells without exceeding acceptable working pressures in the coiled tubing or surface equipment. The higher pump pressures expected, along with acceptable coiled tubing design parameters associated with this higher pressure demonstrated the need to modify the drilling fluid. The standard solids-free mud was modified by replacing the xanthan biopolymer with diutan biopolymer. This new system demonstrated a 20% reduction in pump pressure, better hole cleaning, a higher tolerance to the pH changes related to cementing operations and longer fluid system life. This paper will document the development of the diutan reservoir drilling fluid (RDF) system, including laboratory testing, field testing, a comparison to the xanthan based RDF, and the results of drilling actual wells. This new drilling fluid system has been in use now since July of 2009 and is the preferred drilling fluid used for coiled tubing drilling and well servicing in Alaska.