New Generation Rotary Steerable System and Pressure While Drilling Tool Extends the Benefits of Managed Pressure Drilling in the Gulf of Mexico

Abstract

As hydrocarbon basins mature, reservoir pressure depletion caused by hydrocarbon production leads to severe pore pressure/fracture gradient anomalies that can reduce an otherwise sufficient mud weight window significantly. At the same time, reentries involving slim-hole sidetracks incur high annular losses that further widen the gap between equivalent static and circulating densities - ESD and ECD. In this situation, it is not possible to drill using normal overbalanced methods. The risk of formation fracturing and fluid losses, fluid influxes, and wellbore collapse would far outweigh the reward of increased production. The effective variation of static and circulating densities must be minimized. A major project in the Gulf of Mexico posed such a problem. Managed pressure drilling (MPD) was adopted as the solution to manage a tight hydraulic window and effectively drill reservoirs which would have been extremely challenging using conventional drilling methods. Traditional directional drilling with a positive displacement motor would normally create more pressure balance complications under a MPD environment due to the continuous fluctuations to the ECD when the motor is in sliding or steering mode. This paper outlines how new generation rotary steerable systems coupled with the interpretation from a downhole real time pressure while drilling sensor was engineered to maximize drilling performance for a directionally drilled well in MPD environment. This paper will also discuss the case histories and lessons learned and thoroughly review the range of opportunities these technologies have created in the maturing areas of the Gulf of Mexico. Introduction Conventional drilling using either steerable systems or rotary steerable systems utilizes drilling fluids which are overbalanced to suspend the drilled cuttings, clean the hole and maintain wellbore stability. The drilling fluid as it is circulated down the hole also cools and provides energy to the bit required to break the rock and drill ahead but most importantly applies overbalance pressures which is a combination of hydrostatic pressure and annular friction pressure to prevent formation fluid influx into the formation. This is illustrated in Figure 1.