Abstract

Petroleum Development Oman (PDO) is planning a major brown-field re-development project. For that reason a waterflood appraisal drilling campaign has been executed. Drilling through fractured reservoir sections causes drilling losses that have to be cured prior to liner cementation. Liner cementation in wells with severe or heavy drilling losses has had limited success despite novel loss curing materials.

Expandable tubulars with swelling elastomer seals have been applied in 8 wells as an alternative to cemented liners with the objective to

  • Provide zonal isolation, to

  • Attempt time savings by eliminating loss curing and liner cementation and to

  • Slim down the well design.

The reservoir sections of 2 vertical water injector wells and 6 vertical oil producer wells were drilled with losses and lined with expandable casing. Elastomer seals isolate the multiple reservoirs from each other. Expandable casing enables a slim oil producer design still using a 2 7/8" gaslift string. 4 slim wells were drilled. Zonal isolation has been created without cement. This novel approach to drill fractured carbonate reservoirs has proven technically feasible in terms of installation operations, zonal isolation and slimming down well designs. The paper describes the experience with expandable tubular technology for waterflood well delivery.

Introduction

A waterflood pilot has commenced in PDO in April 2004. Re-appraisal of a large oil field is being undertaken to select the right recovery mechanisms for future development. The reservoir is provided by fractured chalky carbonates of the formation which is subdivided into seven major reservoir units, A to G (Figure 1). The average water cut of the field is 50 pct. To date, almost 400 wells have been drilled in this field. Different recovery mechanisms have been tried for different layered reservoirs. This development history of the field has been described in Ref. [1] and [2].In the upper 2 reservoirs water flood trials have been carried out in the seventies. This had limited success due to early water breakthrough via fractures and karstified parts of the reservoir. The majority of the development was by gas-oil-gravity drainage (GOGD) with 200+ development wells drilled. Since 1997 water flooding has been re-introduced to produce certain layers in the reservoir which are considered less fractured. Most of the drilling during this time consisted of horizontal wells with single or dual laterals. Most of the wells were completed barefoot.

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