Abstract

This paper describes a case history of a "Small Outer Diameter -Big BorePermanent Straddle System" installed in a well offshore in the North SeaDecember 2002.

The purpose of the platform well as an injector was WAG injection in thelower zones. To obtain this, the upper zones had to be isolated due tocorrosion in the tubing. This was successfully achieved with Weatherford SealBore Packer system, leaving access to the lower zones with 2 3/8" CTthrough the Straddle.

Economically it is cheaper to use a solution like this instead of changingthe whole tubing with a full workover of the well.

Introduction

Well P-45 is a deviated well located in the Norwegian sector of the NorthSea. The well penetrates the Lunde formation in reservoir zones L06-L12, and isprimarily a WAG (Water Alternating Gas) injector, which is to inject intoreservoir zones L10-L12. The well was being back produced from L06 L09 (Seepicture 1.).

An intervention to close upper SSD, open Middle SSD and clean up reservoirzones L07-L09 was performed in July 2001. After several attempts to close upperSSD and open Middle SSD, the production tubing below Middle SSD wasperforated.

In December 2001 an intervention to perforate the well was performed. PLTand caliper results indicated holes in tubing at 6560m, 6580m and 6710m MD RKB(main rig). When attempting to run perforating guns using a deployment systemsome problems were experienced and the job was cancelled.

The objectives with this intervention that took place December 2002 was tokill the well, perforate reservoir zones L10-L12, isolate holes/perforations intubing and clean up reservoir zones L10-L12.

Purpose of the well was WAG injection in the lower zones L10-L12. To achievethis, the lower zones had to be perforated, and the upper zones isolated.However, the earlier production resulted in sand influx, which locked thesliding sleeves and corroded the tubing. Based on this, the decision was toisolate this 355m long interval with a 3-Packer Straddle system.

This paper refers to the zonal isolation part of the job. Prior to this job,a 2 3/8" CT perforation operation was carried out to obtain injection tothe lower zones (7027–7177 m MDRKB).

The result confirmed the success of the Straddle operation, as the waterinjection rate of 4800 Sm3/d was slightly higher than expected.Smallest ID in the well was only reduced by 1" to 2,688", leavingaccess for optional interventions with 2 3/8" CT through the Straddle (SeePicture 2).

Although there were four different service companies dependant on eachother's co-operation for pumping, CT, Straddle Packer and depth correlation, the complexity of the operation was successfully and safely executed.

Challenges and Solutions

The Weatherford project was to install a permanent Straddle inside a 41/2" tubing by use of a 2 3/8" OD Coiled tubing work string. There werea number of challenges to be addressed regarding the well P-45:

  • Corroded tubing

  • Long deviated well, 7200md 80°

  • 4 1/2" Tubing with 3,960"ID

  • Had to pass through 3 ea Sliding Sleeves with 3,688" ID SSD at 6513 D78° SSD at 6638 MD 72° SSD at 6782 MD 63°.

  • A long interval to be isolated

  • Long BHA to be run

  • To stabilise the well, unknown pore pressure in the lower zone

  • Depth control

In order to meet the challenges, a 3,65" OD Permanent Straddle PackerSystem with High Pressure Overshots and 2,688" Big Bore was chosen. TheBottom, Middle and Top Packer Straddles can be stacked and installed in 3 runs, giving option for later zone control. A wireless CCL was used for depthcorrelation.

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