Using MPD To Drill Wells With Narrow Operating Windows: Pressure and Temperature Effects

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 119882, ’Drilling Wells With Narrow Operating Windows Applying the MPD Constant Bottom Hole Pressure Technology - How Much the Temperature and Pressure Affects the Operation's Design,’ by M. Arnone and P. Vieira, SPE, Weatherford International, originally prepared for the 2009 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 17-19 March. The paper has not been peer reviewed. Narrow pore-/fracture-pressure-gradient margins translate to a real drilling-hazard scenario where a slight change in the bottomhole-pressure (BHP) conditions can lead to an increase in the nonproductive time (NPT) because of time spent in solving possible fluid losses or gas kicks. In specific and nonrare cases, deep formations with small gaps between pore and fracture pressure are undrillable with conventional drilling practices. Constant BHP (CBHP), one of a number of variants of managed-pressure drilling (MPD), enables staying in the window between pore- and fracture-pressure gradients. Introduction The International Association of Drilling Contractors (IADC) recently has updated the definition of MPD. MPD is 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 contained safely by use of an appropriate process. The IADC definition for MPD also includes some key technical notes: The MPD process employs a collection of tools and techniques that may mitigate the risks and costs associated with drilling wells that have narrow downhole environmental limits by proactively managing the annular-hydraulic-pressure profile. MPD may include control of backpressure, fluid density, fluid rheology, annular fluid level, circulating friction, and hole geometry, or combinations thereof. MPD may allow faster corrective action to deal with observed pressure variations. The ability to control annular pressures dynamically facilitates drilling of what might otherwise be economically unattainable prospects. At present, there are four recognized variations of MPD. CBHP: Narrow pore- and fracture-pressure-gradient windows present a drilling hazard. When the hole is being drilled or circulated, the additional circulating friction to hydrostatic head can result in formation fracture. When circulation is ceased, the hydrostatic pressure is below the formation pore pressure. A kick/loss situation ensues, and NPT, lost-fluid cost, and health, safety, and environment (HSE) risk escalate. This variation is applicable to avoid changes in equivalent circulating density (ECD) by applying appropriate levels of surface backpressure, a technique that maintains CBHP during the complete drilling operation.