Girassol: Drilling and Completion Experience gained through first 12 wells
Authors: Dessus Jean Lassus , Abreu Jorge 
Published: October 2008

The Girassol development, offshore Angola, will have 39 subsea wells. Development drilling and completion are being conducted from two dynamically positioned newbuild drillships. Twelve wells weren completed when this paper was completed.

The paper's focus is on deepwater drilling and completion activities, eg top hole and conductor jetting, directional drilling, sand control, completion equipment, well productivity, etc. The paper also presents well construction performance, in terms of well durations and Non Productive Time, and offers insights into the success of the first year's activity.

Introduction

The Girassol field was discovered in May 1996 by the GIR-1 well and appraised in 1997 by 2 additional wells. The field is located offshore Angola, 210km northwest of Luanda, in water from 1,250-1,400m (Fig. 1). It is part of Block 17, awarded by Sonangol under a Production Sharing Agreement to the Contractor Group.

An integrated project team was set up early 1997 for this fast track project which had a very ambitious target for first oil, given the extent of the existing technological challenges.

The development scheme selected for Girassol is a full subsea development tied back to a spread moored Floating Production Storage and Offloading (FPSO) unit. The field facilities were split into four packages for project management and contractual strategy considerations : the FPSO, the Umbilical and Flowlines (UFL), the Subsea Production System (SPS) and the Wells Package.

Drilling and completion (D&C) resources were mobilised in the first half of 1997. The scope of work given to the D&C team covers the full life-cycle of the Wells Package:Carry out conceptual engineering as an input for fielddevelopment scheme selection, including costs estimates and relevant data for project scheduling;Provide assistance to the SPS project team for detailed engineering and preparation of subsea completion equipment;Carry out detailed well engineering, together with specifications for procurement of well equipment and tendering of services;Award rig contracts and follow up rig construction;Award service contracts for well equipment and all services contracts required for the well construction phase;Develop project documentation including manuals and procedures; andConduct operations from Luanda, Angola during the well construction phase.

Reservoir Description

The upper Oligocene Girassol reservoir corresponds to distal turbidites deposited in channels extending over an area approximately 18km long and 10km wide. Reservoirs are shallow, the top of the reservoir being approximately 2,450m below sea level, or 1,100m below the mudline.

The Girassol B System (Ref. 1) is made of three different turbiditic complexes - B1, B2, B3. Eeach channel complex is typically 50-100m thick, a few kilometers wide and many kilometers long. There are also additional thin reservoirs with large extension called Sheets complexes (Fig. 2). Each turbiditic complex is separated from the others by regional seals which are correlated at a large scale over Girassol area. All these turbiditic complexes are normally pressured and were found to be oil bearing (32°API) within a regional structural closure with common oil/water contact.