In plans to explore the shallow gas potential of the Nagar prospect offshore the southern coast of Myanmar, PETRONAS had to contend with a number of potentially high risk issues. The shallow nature of the hazardous prospect made kick detection speed and pressure control accuracy essential to avoid losing returns. Concerns about a weak casing shoe, a narrow drilling margin, the inability to control bottom hole pressure (BHP) while circulating out gas, and the short response time needed, demanded a solution before the shallow gas-bearing sands could be drilled safely from the available moored drill ship with its conventional subsea equipment.From flow modeling it was estimated that within 3 minutes the system and procedures would have to detect and shut-in a gas influx, then commence circulating it out, all while controlling the BHP of a flowing, multiphase fluid within extremely narrow safe limits. It was concluded that the Nagar well could only be safely drilled with a pressure management system that could maintain BHP within +/-15 psi while drilling and +/-45 psi during connections and well control.In an industry search, PETRONAS learned that no system existed with the functionality needed, but by electing to combine new and existing technologies from three separate providers they were the first to develop one that did.This industry-first solution involved integrating elements of the technology developed for automated pressure control, pressure while drilling (PWD), and high speed, drill string telemetry. Modifications had to be made to a number of elements, including the pressure control and PWD systems, to obtain the necessary functionality. Given the safety critical nature of the drilling hazards, the modifications and system integration were first tested during simulated kicks with downhole nitrogen injection, before drilling out the casing shoe. During testing on the rig and subsequent drilling operations, the integrated system proved its ability to maintain a near constant BHP, with the accuracy and speed needed to safely and successfully drill the Nagar prospect.

The requirements for the early detection and the control of kicks, losses and other anomalous conditions while drilling are becoming increasingly important as the industry drills in more challenging environments both onshore and offshore due to greater challenges with respect to equipment stresses and pressure regimes. This paper will present the design and testing of a high fidelity and high certainty system for the early identification of anomalous conditions while drilling such as kicks, losses, washouts, drill string plugging and hole bridging without the need for traditional delta flow equipment and interpretation methods. An explanation of how the system minimizes false alarms and how visual and audible methods inform the operator of the different anomalies as they are detected will be included. Installation of the equipment on the rig will also be presented and compared to current delta flow methods both for managed pressure drilling operations and conventional drilling operations. Maintenance and reliability issues will also be discussed. Full scale testing and tests using collected field data will be presented to demonstrate the system operation. Further development and field testing will also be discussed.

Within the context of broad industry recognition of two drilling technologies, Underbalanced Drilling predates Managed Pressure Drilling (MPD) by at least a decade. While there are some similarities in some of the equipment and possibly in some of the techniques, the applications are different in their intent. This paper will discuss methodologies comparing Conventional, Underbalanced, and Managed Pressure Drilling Operations with respect to objectives, planning, drilling equipment and operations, and well control. The application of Managed Pressure Drilling was specifically created to give it an identity apart from Conventional Drilling and apart from Underbalanced Drilling. There appears to be some confusion with respect to methodology for Managed Pressure Drilling. What constitutes a Managed Pressure Drilling Operation? What constitutes an Underbalanced Drilling Operation? Are they actually the same? Does it matter? Figure 1 illustrates the general domains of Conventional Drilling Operations, Managed Pressure Drilling Operations, and Underbalanced Drilling Operations. Conventional Drilling Operations Conventional drilling by most accounts had its beginnings at Spindletop, near Beaumont Texas in 1900. Three key technologies contributed to the success of the well and later the drilling industry. They were rotary drive, roller cone bits, and drilling mud. There have been some improvements over the years. Today, the conventional drilling circulation flow path begins in the mud pit, drilling fluid (mud) is pumped downhole through the drill string, through the drill bit, up the annulus, exits the top of the wellbore open to the atmosphere via a bell nipple, then through a flowline to mud-gas separation and solids control equipment, then back to the mud pit. All this is done in an open vessel (wellbore and mud pit) that is open to the atmosphere. Drilling in an open vessel presents a number of difficulties that frustrate every drilling engineer. Conventional wells are most often drilled overbalanced. We can define overbalanced as the condition where the pressure exerted in the wellbore is greater than the pore pressure in any part of the exposed formations. Annular pressure management is primarily controlled by mud density and mud pump flowrates. In the static condition, bottomhole pressure (PBH) is a function of the hydrostatic column's pressure (PHyd) (Figure 2), where… PHyd = PBH In the dynamic condition, when the mud pumps are circulating the hole, PBH is a function of PHyd and annular friction pressure (PAF) (Figure 2), where… PBH = PHyd + PAF In an open-vessel environment, drilling operations are often subjected to kick-stuck-kick-stuck scenarios that significantly contribute to Non-Productive Time (NPT), adding expense for many drilling AFEs. Because the vessel is open, increased flow, not pressure, from the wellbore is often an indicator of an imminent well control incident. Often, the inner bushings are pulled to check for flow. In that short span of time, a tiny influx has the potential to grow into a large volume kick. Pressures cannot be adequately monitored until the well is shut-in and becomes a closed vessel.

Accurate control over bottomhole pressure during drilling is essential as the industry meets increasingly challenging drilling environments such narrow drilling margin formations, HPHT wells and fractured formations. To increase the accuracy of the control over bottom hole pressures during drilling, a fully automated prototype system consisting of a hydraulics simulator, a computer controlled choke manifold and a pump as part of the mud return system has been developed and tested. Rather than mud density alone, the system uses a reduced density mud in combination with a variable back-pressure at the annulus exit to achieve the required downhole pressure. The system is able to substantially compensate downhole pressure variations induced by the drilling operation by varying the surface back-pressure. A number of possible advantages are associated with the use of the system:Reduction of formation impairmentReduction of mud lossesReduction of formation fluid influxIncreased ROPNo flat time during weight-up/downPotential to reduce number of casing stringsAutomatic kick circulation A successful experimental program has been conducted on a real size test well in preparation of a field test sequence. The system was easily retrofitted to the existing test rig and normal drilling procedures were minimally impacted. Introduction Accurate control over bottomhole pressure during drilling is essential as the industry operates in increasingly challenging drilling environments, some of which are:Narrow margin between pore and fracture pressure where static and dynamic equivalent circulating density or surge and swab effects can result insignificant mud losses 1 or well control events.HPHT wells where formation pore and fracture pressure determination byadjusting the mud weight in small increments is time consuming.Fractured or highly permeable reservoirs where equivalent circulating density is above pore pressure and LCM is not effective resulting in early termination of the well due to losses or in the requirement to drill with a mudcap 2 or underbalanced.Transients during under balanced drilling (UBD) exceeding pore pressure resulting in lost benefits of UBD.Mechanical hole stability where weighting-up can result in significant flattime. These difficult drilling conditions are now managed by incorporating bottomhole pressure control procedures primarily using mud density control and to a lesser extent control over pump rate. Manual back-pressure control methods using surface pressure and chokes have also been used3, however automation is essential in these more demanding environments to maintain a constant bottomhole pressure with a high degree of accuracy and dependability. This paper will discuss the novel design and full scale testing of a fully automated system to maintain an essentially constant bottomhole pressure during drilling operations. The system consists of a computer controlled choke manifold and pump as part of the surface mud return system. The downhole pressure is then controlled by automatic adjustment of the choke manifold and pump based on various inputs and the calculation results of a hydraulics simulator. Possible operational methods and considerations are also discussed.

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