Challenges of Drilling and Completion Operations of Deep Wells in Ultradeepwater Zones in the Gulf of Mexico
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 125111, ’Challenges of Drilling and Completion Operations of Deep Wells in Ultradeepwater Zones in the Gulf of Mexico,’ by J.C. Cunha, SPE, and O. Moreira, Petrobras America, and G.H. Azevedo, SPE, B.C.M. Pereira, and L.A.S. Rocha, Petrobras S.A, prepared for the 2009 SPE Annual Technical Conference and Exhibition, New Orleans, 4-7 October.

Challenging wells are being drilled in deepwater zones in the US Gulf of Mexico (GOM). Many are in water depths of 8,000 ft or more, with several target reservoirs at 30,000 ft and deeper. Completion challenges include completing multiple zones while trying to minimize future expensive workover operations. Practical experiences dealing with these problems and suggestions to make them manageable are presented.

Introduction

Exploration, appraisal, and production in areas such as Mississippi Canyon, Atwater Valley, Walker Ridge, Keathley Canyon, and others present inherent difficulties associated with deepwater drilling along with new difficulties in very deep zones that demand careful planning to be reached without compromising safety, well integrity, formation evaluation, and estimated budget. Challenges include difficult-to-find seafloor locations to place the production wells or drilling center.

The complex directional drilling requires planning, follow-up, and feedback that must be fine tuned to reduce nonproductive time (NPT) and improve well-construction performance. A “Plan/Do/Check/Act” (PDCA) routine should be implemented.

The completion design may include stimulating deep, high-pressured, tight reservoirs. Completing the Lower Tertiary section of deep wells in the GOM proves to be as challenging as the drilling. With few analogous wells drilled and no production history to date, validation of any completion design and the corresponding engineering solution is affected by uncertainties.

Weather-related events are a major source of NPT. Ocean currents associated with the Loop Current and Eddies may cause massive losses of time. Moreover, the always unpredictable hurricane season has caused such large losses that many operators will delay an operation rather than try to drill during hurricane season.

Weather—Be Prepared To Be Surprised

The GOM Loop Current, a stream of warm ocean water that flows northward from the Yucatan Peninsula, loops clockwise and eventually exits through the Florida Straits. The Eddy, or Loop Current ring, occurs when a stream of water “breaks” (shears) and separates from the main stream. The Eddy can be up to 250-km diameter and more than 1000 m deep. Once formed, it travels west across the GOM as it rotates clockwise, completing a rotation once every 10 days. It may take from 2 months to 1 year for an Eddy to dissipate.

In a recent operation in the Walker Ridge quadrant, an anchored rig in the presence of strong Loop Current lost significant time while trying to perform mooring operations. A total of 224.5 hours in 13 days of operations (72%) was lost waiting on weather. This type of delay can postpone rig operations and delay development and production. It is recommended that a rigorous monitoring and forecasting service be used to enable accurate predictions of the possible effects of Loop Current and Eddies on planned offshore operations.