Abstract

The Fahud water flood project is a major brownfield re-development project and a key component to PDO's future production plan. Key value drivers for the successful project delivery are selecting the right recovery mechanisms for the target reservoirs and achieving low-cost well delivery through standardization and technological innovations.

The pilot program, which consists of drilling 39 vertical wells in PDO's Fahud field, commenced in April 2004 to gather data on four Natih target reservoirs. The data will be used to identify applicable recovery mechanisms for future field development. The recovery methods under review include the following:

  • Water flood

  • Gas-oil gravity drainage (GOGD)

  • Combination GOGD and water flood

  • Combination GOGD and depletion

  • Combination GOGD and gas flood

Natih is a stacked layered reservoir. Natih A and C were developed by water floods in 1972–1980. These wells were unsuccessful due to early water breakthrough through fractures and karst parts of the reservoir. From 1984 to 1998 certain reservoir sections were developed by GOGD with 200+ development wells drilled. Since 1997, water flooding has been used to produce different zones in the Natih reservoir. Most of the drilling during this time consisted of horizontal wells with single or dual laterals.

Although horizontal wells, in particular dual-lateral wells, provide excellent area data coverage, they also

  • Provide ambiguous production data from single zones.

  • Do not allow observation of reservoir behaviour in over- and underlying zones.

  • Are costly to enter (hoist/coiled tubing).

  • Present a challenge to manage flow profiles.

These issues led to the consideration of implementing alternative well designs.

This paper will discuss the well planning, wellbore preparation and successful application of solid expandable tubular technology. These systems, combined with swelling elastomers, slim the well design and provide reliable isolation of the Natih sub-units to allow independent testing of the zones. The paper also presents the completion design planned for the test program and long term production.

Introduction

The Fahud water flood pilot project objective consists of gathering static (logging and coring) and dynamic data (production data such as PLT and EMI) on the feasibility and effectiveness of water flood in the Fahud Natih reservoirs. The pilot study is part of an on-going re-assessment of the development strategy for the Fahud field culminating in a field development plan to be issued in 2006

Each drilling location consists of seven wells drilled from a seven-cellar pad comprised of

  • Four oil producing wells

  • Two observation wells

  • One water injector well

The wells are arranged such that the oil producing wells enclose a square study area with the injector located centrally in this pattern. The observation wells are offset from the centre at a distance of 30m and 60m (Figure 1). All wells from this pad will be sub-vertical and are planned with s-shaped trajectories. This type of trajectory allows for the required step-out from the surface location and yet allows the wellbore to return to vertical through the reservoir section (Figure 2).

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