Unique Crosslinking Pill in Tandem With Fracture Prediction Model Cures Circulation Losses in Deepwater Gulf of Mexico

Abstract

Abstract Even in routine applications, the safety, economic and technical problems associated with lost circulation can severely impact drilling operations. The negative consequences are magnified greatly in the deepwater environment. Dramatic reduction in penetration rate and the downtime spent regaining circulation can further escalate already high operating costs. More importantly, the well control issues surrounding lost circulation pose critical safety concerns. In many of these wells, merely identifying the thief zone or zones is a major technical challenge. Furthermore, once identified, the vugs and fractures in the loss zones are at times too large to be bridged with conventional lost circulation material. This paper describes the development of a uniquely engineered lost circulation pill that when used in tandem with new real-time geomechanical analysis methods and pill formulation software, cured severe losses in the deepwater Gulf of Mexico. The authors will describe the development and laboratory modeling used in producing the specialized and chemically activated cross-linked pills, engineered to stop whole drilling fluid losses. As detailed in the paper, the pill proved to be far superior to conventional lost circulation material. Further, the paper will discuss its application in a well drilled in more than 2,800 ft of water in the Gulf of Mexico, which had encountered losses of up to 2,000 bbl of synthetic-base drilling fluid. The 100-bbl pill was formulated using a specialized software package. This was used in combination with a new process for analyzing the location, and extension pressure of the drilling induced hydraulic fracture using resistivity and annular pressure measurements. Once the pill was placed across the fracture zones, squeezed and later drilled out, normal drilling resumed with pre-fracture parameters resulting in penetration rates in excess of 50 ft/hr with no further losses. In addition to discussing the development and application, the authors will outline the lessons learned on the deepwater project featuring pre-planning issues geared toward ensuring circulation is maintained throughout the wellbore. Introduction The challenge of controlling fluid losses when drilling with synthetic-based drilling fluid systems in deepwater has been well documented1,2,3. The narrow operating window between pore pressure and fracture gradient often results in major fluid losses when drilling, running casing, and cementing. While drilling with synthetic-based mud delivers superior performance, the cost implications of massive losses often have forced operators to solve the problem rather than living with the consequences1. A technical and economic challenge associated with synthetic-based fluids is the fact losses are more difficult to cure, because of the tendency of fractures not to heal once closed. Consequently, the low fracture re-opening pressures allow for continual losses. Many products and techniques have been used in attempts to restore circulation while drilling. These include fibrous, flaky and granular materials2, as well as techniques such as gunk and reverse gunk squeezes, high fluid-loss squeezes and cement squeezes. More recently, a chemically activated cross-linked pill (CACP) has been developed and applied on challenging deepwater wells to cure and limit losses when drilling with synthetic-based fluids.