Drilling Fluids Planning and Execution for a World Record Water Depth Well

Abstract

Proper drilling fluids planning and execution play a major role in minimizing the likelihood of drilling difficulties such as those encountered in ultra-deep waters. Deepwater drilling is inherently expensive. Because of this, the proper selection of drilling fluids and other support technologies requires careful evaluation to diminish commonly observed deepwater challenges. These challenges include hydrate suppression, shallow water flows, logistics, lost circulation mitigation, viscosity profiles. Another critical deepwater challenge is properly managing ECD to maintain optimal well site safety and environmental compliance. This paper discusses the planning and execution of a drilling fluids program for a world record ultra-deepwater well. The well was located at a water depth of 10,011 ft. (3,051 m) in the Gulf of Mexico's Alaminos Canyon (Block 951). The well was drilled to TD (22,695 ft. [6,917 m]) using an advanced synthetic-based mud that met all Gulf of Mexico compliance requirements and advanced engineering software and tools. Introduction Since the mid-1990's, operators have been exploring and developing fields in ever-increasing water depths. As a result, the industry has identified techniques and developed new technology allowing them to safely and successfully drill wells at depths greater than 10,000 ft. The learning curve on these wells has been relatively steep and new records are being established at a rapid pace. Due to the presence of young sedimentary deposits many of these wells possess an extremely narrow margin between the pore pressure and reservoir's fracture pressure. Because of the greater the likelihood of drilling success. The use of a riserless drilling technique, known as Dynamic Kill Drilling (DKDSM), has proven instrumental in successfully pushing casing depths in deepwater and ultra-deepwater environments1. This technique played an important role in the success of this challenging deepwater project as the initial upper section was extended to obtain required LOT's at the 22" and 17–7/8" casing shoes. The unmatched combination of technical performance and environmental compliance presented by synthetic-based drilling fluids has made them the fluids of choice for the deepwater drilling in the Gulf of Mexico. Based on an overall analysis of this project the operator selected a proprietary synthetic compliant drilling fluid for the drilling of the well from the 18" × 22" section to TD. This decision was driven primarily by the presence of highly reactive shales in the deepwater formations and the system's prior performance in offset wells. In the deepwater environment several important factors must be considered. Chief among these considerations is the effect of temperature and pressure on the fluid system. As the water depth increases, temperature decreases and pressures at seabed rise. A typical temperature curve (Figure 1) for the Gulf of Mexico indicates an average seabed temperature lower than 40°F at depths greater than 4,000 ft. This cooling, combined with increased pressure, impacts the design of the drilling fluid for use in the well. Due to the chemical composition of the GOM-compliant synthetic-base fluids, the cooling will increase a base fluid's viscosity resulting in an increase in the overall drilling fluid viscosity. Because of this, particular importance must be paid to the fluid's viscosity profile in order to minimize potential problems such as formation fracturing which can result in costly lost circulation and non productive time. A proper viscosity is also critical in ensuring that adequate hole cleaning is maintained throughout the entire wellbore. Although planning for deepwater operations is an extremely complex process involving many technical disciplines, this paper will focus primarily on the planning and execution of this world-record deepwater well's drilling fluid program.