Technology Update: Tool Enables Boost in Brownfield Production

Abstract

Traditional well-construction techniques relying on cementing or mechanical isolation systems for primary zonal isolation can often fail in brownfield developments. Or, they are unable to fulfill requirements for zonal isolation across complex, multilayered formations that may contain depleted, overpressurized fluids or gas/water zones lying ahead of the target oil sand. Swell packers are an enabling technology that is allowing production from wells that otherwise would not have been feasible either technically or economically. Easy Well's packer technology consists of a standard oilfield tubular with an elastomer bonded along its length. The packer uses hydrocarbon to swell the elastomer downhole. The packer has no moving parts and requires no service tools, dropping of balls, hydraulic actuation, or surface/downhole manipulation to set it. Any number of packers are simply made up in the completion or casing string and deployed in a single trip into the well. On contact with hydrocarbons—from the reservoir, oil-based mud (OBM), or a spotted fluid—the bonded rubber swells to form a seal either inside the casing or against the open hole (Fig. 1). The process works by the thermodynamic absorption of hydrocarbon molecules into the molecular structure of the rubber, allowing it to swell and stretch. Zonal Isolation Without Cement The first application of this tool in the U.K. sector of the North Sea was on Shell's North Cormorant asset in 2004 (Fig. 2). The challenge of assuring future production was for the asset's well engineers to find ways of drilling cheaper wells to exploit smaller pockets of reserves. After reviewing the portfolio of work, it was decided that, by introducing a series of technologies over a six-well program, a 25% reduction in drilling costs could be made. The key leading technology was through-tubing rotary drilling over the six-well campaign. Project engineers devised a strategy that first addressed the least challenging wells. New technology was introduced in an orderly manner, allowing opportunity to see the challenges in advance and to tackle the necessary learning curve. Nevertheless, the first well (CN24s2) was unsuccessful. The bottomhole assembly from the coiled-tubing cleanout string became stuck and was not recoverable. Solids debris from the cementing operation coupled with low annular clearances, not normally associated with conventional wells, caused the problem. The second well also ended up at a higher cost than anticipated as a result of cementing issues. At this point, the team rethought its zonal-isolation strategy. Needing to find a technology that would simplify the well construction and dramatically reduce the risk profile, swell-packer technology was considered as a way to avoid the necessity of cementation. Shell already had some experience with the technology in approximately 20 wells around the world, including some wells drilled by Shell Malaysia, but not in the small-diameter, high-pressure conditions being drilled on the North Cormorant. The team decided to try the packers because they showed the potential for better zonal isolation in a small hole size, with a concomitant increase in oil production.