Hashim, H., Sarawak Shell Bhd. (Malaysia)

Abstract

A five well trial with Environmentally Acceptable Invert Oil Emulsion Mud (EA-IOEM) has been carried out in the Balingian area offshore Sarawak during 1985 and 1986. The trial was initiated after an unsatisfactory outcome of a field test programme with KCl/polymer muds.

Two appraisal and three development wells with planned deviation angles ranging from 45 to 58 deg. were selected. The trial was carried out in the 12 1/4" and 8 1/2" hole sections.

The objections of the trial were to eliminate drilling, evaluation and production problems caused by poor hole conditions which were experienced in high angle wells drilled with simple water based mud (WBM).

A suitable base-oil for the trial was selected to meet the following three criteria: a high flash point, a low kinematic viscosity and a low toxicity.

The experience gained in the field trial has been successfully applied to the Erb West infill drilling programme to solve the zonal isolation and drilling problems experienced in this area with WBM.

The paper addresses the operational, petrophysical and geological aspects of the trial and includes recommendations on cost and consumption estimating.

Introduction

The Balingian Province consists of a number of fields (including Temana and D18) which are located off the coast of Sarawak in the South China Sea (Figure 1). Sarawak Shell Berhad (SSB) is the operator for these fields under a Production Sharing Contract with the Malaysian National Oil Company, Petrolian Nasional Berhad (PETRONAS).

Poor hole conditions (severe washouts and erosion of the bore hole wall) cause a number of drilling, evaluation and production problems in the Balingham Province. These include:

  • inadequate hole cleaning caused by irregular hole shape and local washouts, leading to low rate of penetration (ROP), tight hole and tripping problems;

  • difficulties in getting logging tools to bottom;

  • poor quality logs resulting in a reduction in the standard of log evaluation;

  • difficulty in assessing cementation volumes resulting in excessive bottom hole pressures (due to long cement columns) and higher or lower than planned top of cement (TOC);

  • poor mud displacement efficiency during cementing due to oversize hole, either locally or over the whole open hole resulting in channeling and consequent poor zonal isolation;

  • later production problems such as early water/gas breakthrough due to flow behind casing.

REASONS FOR EA-IOEM TRIAL

Many of the wells drilled with conventional water based mud in SSB operations reach their objectives and are logged and completed without serious operational problems. Where problems relating to poor hole conditions occur these are usually, although not exclusively, in higher angle wells (generally above 50 deg. inclination). The first step in attempting to resolve such difficulties is to provide a better quality, near gauge hole.

P. 58^

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