Managed-Pressure Drilling - A Solution for Challenging Wells in Vietnam

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 165775, ’Managed-Pressure Drilling - A Solution for Drilling the Challenging and Undrillable Wells in Vietnam and Southeast Asia,’ by Ben Gedge, SPE, Harpreet Kaur Dalgit Singh, Elsofron Refugio, and Bao Ta Quoc, Weatherford Asia Pacific, and Nguyen Viet Bot, PVD Well Services, prepared for the 2013 SPE Asia Pacific Oil and Gas Conference and Exhibition, Jakarta, 22-24 October. The paper has not been peer reviewed. Managed-pressure drilling (MPD) has been used in Vietnam since 2007 to address a number of drilling and reservoir challenges. The main application of MPD has been to overcome the challenges of granite-basement, fractured and vugular carbonate, high-pressure/ high-temperature (HP/HT), and overpressured clastic reservoirs. This paper examines the procedural approaches of MPD, including constant bottomhole pressure (CBHP), equivalent-circulating-density (ECD) management, early kick detection, and pressurized-mud-cap drilling (PMCD). MPD Techniques and Applications The International Association of Drilling Contractors (IADC) defines MPD as “an adaptive drilling process used to 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. MPD is intended to avoid continuous influx of formation fluids to the surface. Any influx incidental to the operation will be safely contained using an appropriate process.” MPD Variants The definition of MPD covers a wide range of variations and applications, but the most commonly used among them are the PMCD and CBHP variations (Fig. 1). PMCD as defined by the IADC as “a variation of MPD that involves drilling with no returns to surface and where an annulus fluid column, assisted by surface pressure [made possible with the use of a rotating control device (RCD)], is maintained above a formation that is capable of accepting fluid and cuttings. A sacrificial fluid with cuttings is accepted by the [lost] circulation zone. This technique is applicable for cases of severe [lost] circulation that preclude the use of conventional wellbore construction techniques.” The PMCD variant of MPD allows conventional drilling operations until losses are experienced and has been used successfully to drill through fractured and vugular carbonate formations where circulation losses can be simultaneously sudden and severe. This allows drilling to target depth despite massive losses being encountered. The CBHP variant of MPD involves the ability to maintain a constant bottomhole pressure (BHP), especially when drillpipe connections are made and the rig mud pumps are turned off. In this instance, the MPD system exerts a backpressure value that corresponds to the frictional pressure loss. This backpressure is slowly relieved once the connection has been completed and the rig mud pumps resume operation. However, given the sophistication of current MPD-control systems, BHP not only can be kept constant but also can vary to ascertain the downhole-pressure-environment limits and allow drilling personnel to manage the annular- hydraulic-pressure profile accordingly, thereby making the drilling operation more effective and more efficient.