Abstract

This paper is a ‘case study’ of the techniques developed by Sarawak Shell Berhad (SSB) to successfully overcome problems encountered in primary cementing of shallow-gas bearing intervals. During a recent gas development project, successful isolation from surface of three separate intermediate project, successful isolation from surface of three separate intermediate gas sands above the main reservoir was achieved by improved cement displacement gelation. This was possible by drilling a smaller hole minimizing hole washouts, using fast setting cement, displacing the cement as fast as possible, reducing the length of cement columns by use of dual stage equipment and by applying backpressure above the cement columns immediate after displacement. The approach used can in principle be applied for the design of any cementation. The specific techniques developed will be applied in future gas developments to be undertaken by SSB, and may find applications with other operators facing similar problems.

Introduction

The Ell field was the first dedicated gas fields to be developed under the Central Luconia Gas Development Plan, offshore Sarawak.

Sarawak Shell Berhad (SSB), on behalf of PETRONAS, is developing these fields under a long term gas supply contract with Malaysian Liquified Natural gas (MLNG). Development drilling of 10 gas development wells on the Ell field took place between May 1981 and December 1982 from a 20-slot drilling platform in-stalled in 230 ft of water.

While drilling the first three development wells primary casing cementation problems were encountered. Isolation of intermediate gas sands above the problems were encountered. Isolation of intermediate gas sands above the main carbonate reservoir was not successful. These sands were present in both the 13-3/8" and 9-5/8" casing intervals and significant wellhead annular pressures and the presence of gas were observed outside both casings.

Following unsuccessful attempts to repair leaking primary cementations a shallow pressure observations well was installed immediately below the drilling platform in order to ensure the long term safety of operations. The observation well monitors and if necessary could be used to blow down any significant buildup of pressure seen.

The task of improving cementation results was addressed during the latter half of 1981 leading to development of revised techniques which were successfully applied in the remaining gas development wells.

p. 14–1 p. 14–1

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