Development and Field Results of a Unique Drilling Fluid Designed for Heavy Oil Sands Drilling

Abstract

Abstract Drilling Heavy Oil Sands are traditionally fraught with many technical challenges. Stability of the wellbore, accretion of the tar on drill string and solids control equipment, torque-drag considerations, extreme temperature conditions, as well as the handling of oily solids are just some of the challenges that need to be met. This paper describes the development and testing of a new drilling fluid designed to meet these challenges. The water-based fluid is based upon two guiding principles, the ability to incorporate the bitumen into the mud itself, and the capability of the system to later break the bitumen from the mud system. Incorporation of the bitumen into the mud is via a direct emulsification and results in zero accretion, virtually oil-free sand from the solids control equipment, fast drilling rates and good hole stability. The post drilling breaker allows for the oil/bitumen/tar to be skimmed from the surface of the drilling fluid allowing for conventional disposal of the liquid fraction. Data from a six well horizontal heavy oil program in Northeastern Alberta shows the robustness and effectiveness of the system. The new oil in water direct emulsion system drilled 1100 meter average horizontal wells 35% faster, when compared to conventional inhibition salt technology based drilling fluids. Highlights include sand from centrifuging operation containing <0.5% oil, elimination of accretion and common foaming problems, fluid reuse from well-to-well, as well as simple land disposal of liquid mud wastes. Total well costs, drilling fluids costs and disposal costs were significantly less than those wells drilled with conventionally inhibited drilling fluid systems. Introduction As conventional oil reserves are gradually being depleted, the oil industry focuses more and more on other types of hydrocarbon reserves such as coal bead methane, gas hydrates and tar sands. The rise of the oil price has allowed new production technologies to be successfully developed and economically applied to heavy oil and bitumen bearing sands in Northeastern Alberta, Canada. These tar sands contain more reserves than Saudi Arabia, however only 10% of those can be conventionally surface mined. To extract higher amounts of oil, techniques such as SAGD (steam assisted gravitational drainage), horizontal wells and SR (soak radials) horizontal wells are practiced.1 There are a number of challenges that operators face when drilling into the poorly consolidated McMurray tar sands.2 This 1–5 Darcy formation is composed of loose, well-sorted white sand and a bitumen matrix (up to 23% v/v). While drilling these types of wells, the friction generated through the drilling process creates higher downhole temperatures which partially melts the bitumen. Three results are noted:If mud temperature is not controlled, borehole stability becomes an issue as the tar sand formation bitumen matrix melts away. Such problems are typically alleviated by using mud coolers that maintain drilling fluid temperatures below the formation collapse temperature.Even with lower fluid temperatures, the number one challenge is tar sand accretion. Ribbons of tar sands adhere to the surface and subsurface equipment, thereby greatly reducing the performance of this equipment. Elevated torque and drag encountered while drilling and RIH with casing/liner, MWD and mud motors coated in sticky tar, shaker screens blinding, centrifuge's performance reduced due to tar plugging, drilling rig and mud tanks coated in tar sands are only a few problems generated by tar sands accretion.Accretion also leads to large volumes of drilling fluid being used. This in turn creates an environmental issue as seen in excessive disposal and clean-up costs.