Abstract

Since 1967, TOTALFINAELF has been actively involved in deep water drilling operations but the saga really began in 1976 with the building of the PELERIN drill ship which broke a first water depth world record by drilling a well in 925 m of water offshore Algeria. This was followed by another outstanding performance in 1982 when TFE drilled the first well in a water depth greater than 1500 m (1714 m, in the Mediterranean sea). Following these campaigns, there was a lull in deepwater drilling that lasted about ten years.

However, in 1994 the exploration Offshore Angola on the bloc 17 re-activated the group drilling activity in deep waters. Since this time, 62 wells have been drilled in water depth ranging from 500m to 2851 m in Angola, Congo, Gabon, Equatorial Guinea, Nigeria, Brazil and in the GOM. The majority of those wells are challenging exploration or appraisal wells, for which core have been cut in non-consolidated sands, sand control completion have been run and DST have been performed. Twelve wells are development wells, which have involved installation of subsea completions. All types of rigs have been used from moored semi-submersible, old DP drill ships, to new built semi-submersible and drill ships including two types of dual derrick units.

Those drilling performances leaded to the production start up of the Girassol field by 1400m of water on the 04th of December 2001 with some wells producing over 30,000 BOPD. It will shortly (summer 2002) lead to the start up of the Aconcagua gas field, which is the deepest field ever completed (2200 m of water).

This huge amount of deep water well operations brought a lot of data and experience, the purpose of this paper is to show what type of drilling and completion performance one can expect according to the type of well to be drilled. The paper will compare drilling operations durations achieved for dry hole wells with appraisal wells, including heavy data acquisition program. The type of rig will be analysed with in particular the gain one can expect by using dual derricks drilling rigs. Alternative solutions to conventional Subsea drilling such as surface BOP stack, slender wells will also be discussed.

Introduction

The well construction process performance is clearly related to the type of wells to be drilled. An exploration vertical well cannot be compared with a horizontal producer drilled with a wavy profile. Therefore this paper will be divided in two parts, the first part of the document will consider exploration and delineation wells, while the second part will present the main performance related lessons learned from the main TFE deep water development, GIRASSOL. The paper will focus on the rig and operations sequence related performance drivers, although drilling programme features will also be discussed.

Exploration wells

For this kind of application, TFE extensively used conventional DP, moored semi-submersible, dual activity rig and dual derrick drilling rig. Some programs were drilled in a batch setting mode, other in a more conventional manner, which leads to varying drilling performances. Various drilling and data acquisition strategies have also been used which ended up with different progression curves. This part of the paper will summarise the key drivers identified according to the water depth and the rig type.

This content is only available via PDF.
You can access this article if you purchase or spend a download.