Managed Pressure Drilling - Recent Experience, Potential Efficiency Gains and Future Opportunities

Abstract

Abstract Recent development of Managed Pressure Drilling (MPD) Techniques for use from floating drilling rigs began in the late 1990's concurrent with the development of 5th generation offshore drilling vessels(1). During this period a number of industry efforts focused on developing "riserless" or dual gradient drilling systems employing subsea mud return pumping system. One of these efforts (2) culminated with the drilling of a test well in the Gulf of Mexico employing a subsea pump based Dual Gradient drilling method. Additionally, during this period another industry group employed aerated drilling fluid and a closed loop circulating system to drill a pressure depleted well section offshore Brazil from a floating drilling rig (3). While technically successful, these efforts did not result in commercially deployable drilling systems. Much of the initial industry focus has been on developing MPD methods for deepwater applications, many of the techniques are applicable to all offshore drilling operations and a number of recent applications of Constant Bottom Hole Pressure drilling methods have been employed from fixed installation in both the North Sea and US GOM (4, 5, 6). At the same time both Surface BOP and RiserCap™ equipment configurations (Fig 1) have been employed to implement Pressured Mud Cap Drilling from floating drilling rigs offshore South East Asia. Introduction A number of authors have presented studies of drilling non-productive time (NPT) suggesting that some 20 to 30% of total time spent drilling is non productive (7, 8). Further these studies indicate that as much as 50% of this NPT is well bore pressure related. By solving many of the technical challenges related to well bore pressure problems, MPD methods can significantly improve drilling efficiencies by minimizing the time spent monitoring and interpreting well conditions (flow checks, drilling fluid expansion, ballooning, influx and loss detection, etc). Further, having the ability to manage the well bore pressure profile may enable changes in well design minimizing the requirement for close tolerance casing programs, and contingencies such as drilling liners and expandable casing. In other instances these methods may enable wells to be drilled where application of conventional drilling practices would not be technically or economically feasible. As MPD methods gain broader application offshore, opportunities to combine various techniques will emerge enabling further optimization of well design and operations yielding significant improvements in well construction efficiency and reduction in cost (9). Background Most of the drilling practices now referred to as Managed Pressure Drilling have their origins in land based drilling operations. These drilling practices can be categorized as; over balanced or under balanced with respect to pore pressure depending on the pressure regime maintained in the wellbore while employing a particular method. Generally MPD refers to overbalanced or, at balance operations, and is defined (10) as: "... an adaptive drilling process used to more precisely control the annular pressure profile throughout the wellbore. The objectives are to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly"