Abstract

TOTAL AUSTRAL operates the Carina and Aries fields, which are located in offshore Tierra del Fuego in the most southern region of Argentina. These fields are prolific gas producers and are being developed with a reduced number of wells with departures of up to 3.5 km at approximately 1000 m TVD.

This paper discusses the issues surrounding the TOTAL AUSTRAL Carina field development project and the innovative processes that were used to address these situations. Through careful planning, the processes selected to facilitate the completions were successful in achieving the project goals of the operator. These goals included not only the production of gas at relatively high rates from the shallow unconsolidated sand-stone reservoir at approximately 1000 m TVD but also minimization of impact to the environment.

To minimize cost and still accomplish the project goals, the wells were drilled from a single platform.

Introduction

Project Challenges. The Carina field contains a considerable amount of oil and gas accumulation and is made up of two to three main sandstone sequences, generally with good reservoir properties, having an average porosity of 35% and an average permeability of ±1 Darcy. The reserves to be produced from the CARINA sands belong to the Springhill formation and are reasonably heterogeneous with eight main defined sand types. While the Carina sands are largely heterogeneous in nature, they are poorly sorted.

Effective sand control in these reservoirs is imperative for project success. As such, and since there is a lack of experience in this geographical area, a horizontal well trajectory was needed to achieve effective field drainage and the required well productivity. Because of the sandface conditions, the horizontal openhole gravel pack method using an Alpha- and Beta-wave placement technique was adopted. Although this type of sand-control completion is used quite extensively world wide and the technology is considered well proven, documented data regarding its application in shallow horizontal gas reservoirs was limited. Nevertheless, this technique was considered the best suited to the prevailing conditions and defined deliverables. Since the service company experience in running long horizontal well completions had been quite extensive in Brazil, operator confidence in attempting this type of completion was increased.[1,2]

Geographics and Logistics

To provide insight for the reader into the extreme remoteness of the area of operation, these fields are located in the very southern tip of South America, in Terra Del Fuego Punta Quilla, Argentina. The shore base for this project is 3,200 km (1,990 miles) south of Buenos Aires and 500 km (310miles), which is an 8-hour drive south of Comodoro, the nearest area supporting any form of ongoing oilfield operations. This, along with maximum tides of more than 12 m (39.5ft) (which limit supply-vessel access to the harbor to once per day in the harbor of Punta Quilla) introduced significant logistical concerns. To further complicate the operational strategies, the extreme tidal-wave conditions also generate very strong currents, and these make equipment loading and offloading to and from the rig very tide dependant.

The environmental conditions also included an average temperature of 7.7 °C (46 °F) and wind speeds up to 70 knots with sustained winds above 40 knots more than 35% of the time. A high-performance jack-up drilling unit suitable for operations in 122 m (400-ft) water depth was being used. The above conditions in conjunction with the extreme environmental restrictions necessitated the need for increased reliance on efficient operational planning to address the constraints.

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