Managed-Pressure Drilling With Solids-Free Fluid for Subsea Development Wells
Authors: Carpenter Chris 
Published: February 2015

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 164573, ’Managed-Pressure Drilling With Solids-Free Drilling Fluid Provides Cost-Efficient Drilling Solution for Subsea Carbonate-Gas-Development Wells,’ by Trigunadi Budi Setiawan, Mohammad Mizuar Bin Omar, Mohammad Zarkashi Bin Sulaiman, Mohammad Zarir Bin Musa, Muffaz Fadzli, and Thanavathy Patma Nesan, Petronas Carigali, and Chad H. Wuest, Julmar Shaun S. Toralde, and Prem Ananthan Sridharan, Weatherford, prepared for the 2013 IADC/SPE Managed Pressure Drilling and Underbalanced Operations Conference and Exhibition, San Antonio, TX, USA, 17-18 April. The paper has not been peer reviewed.

The development of the Kanowit field offshore Sarawak, Malaysia, requires the drilling of two subsea development wells with a semisubmersible rig. Previous experience identified the need for solids-free drilling fluid to ensure maximum reservoir productivity and that the quality of the produced gas remains within required specifications. A cost-effective option was to use a less-dense solids-free drilling fluid and use managed-pressure drilling (MPD) to compensate for the difference in density with backpressure.

Introduction

The Kanowit development has a water depth of approximately 78 m and is the first subsea gasfield-development program in Malaysia. The purpose of the program is to extract gas from a carbonate reservoir in an area prone to severe circulation losses. The Kanowit initiative also calls for the drilling and completion of two subsea development wells, Kanowit-SS1 and Kanowit-SS2, by use of a semisubmersible drilling rig.

Offset wells in the area have identified the need for the use of solids-free drilling fluids to ensure that impurities from the drilling process are not passed on to the gas-processing facilities once the wells are put on production. The high reservoir pressure of the Kanowit field, which required an equivalent mud weight of more than 15 lbm/gal (1.8 specific gravity), required the use of high-density solids- free drilling fluids such as cesium formate. However, the costs associated with the use of such a drilling fluid, as well as the high probability of losing a large volume of fluid when the fractured-carbonate reservoir is drilled, made this option economically impractical.

A more cost-effective option was to use a less-expensive, less-dense solids-free drilling fluid such as sodium/potassium formate, and to use MPD technologies to compensate for the difference in density by the exertion of backpressure in a closed-loop-circulation drilling system throughout the drilling operation. The use of the MPD system mitigates the expected circulation-loss risk by using the constant-bottomhole-pressure (CBHP) drilling technique to keep the level of overbalance to a minimum while drilling through the carbonate reservoir. The early- kick-and-loss-detection capabilities of the MPD system, in conjunction with the underbalanced drilling fluid, allow for the collection of critical geopressure-environment data. Furthermore, the MPD system would enable the rig to shift immediately to pressurized mud-cap drilling (PMCD) should the level of circulation losses become severe.