The Use of Multi-lateral Well Technology in an Infill Development Project
Authors: Wong Sau-Wai , Boon Wee Si , Chia Richard , Chong Adrian 
Published: December 2007

Abstract
Multi-lateral well technology has been employed in a recent infill development project in the South Furious field, offshore the state of Sabah in Malaysia.
The main motivation for considering multi-lateral well technology is to increase the drainage area, i.e., to connect more reservoir compartments, for a fixed number of available well slots. The successful application of this emerging technology opens up a whole new approach of further developing oil reserves in South Furious and other fields.
The multi-lateral well with a cased and cemented junction is the first in Malaysia and perhaps, the Asia-Pacific Region. It was successfully drilled, completed and opened for production. In this paper, the logic and philosophy in employing this technology for South Furious infill development are presented. We highlight the key design concerns, risks and costs. The paper describes only the essential aspects of the drilling and completion operations. We discuss the lessons learnt, the production experience to-date, and offer some recommendations for future implementation.

Introduction
The South Furious Field is located offshore the state of Sabah, Malaysia (Fig. 1). It is a geologically complex oil field, with reservoirs consisting of sand-shale sequences, and compartmentalised by antithetic faults. The existing 2D seismic data quality is poor. Therefore, the structural configuration is uncertain and a satisfactory static model is lacking. The field is broadly divided into the "Eastern Area" and "Central Area". The first development drilling was in 1979, with 11 wells drilled from a 15-slot platform, SFDP-A in the Eastern Area; and 4 wells from a 4-slot jacket, SFJT-B in the Central Area. In 1989, two more wells were drilled from SFDP-A.
Since then, further insights into various aspects of geology, reservoir and production behaviours had confirmed the viability of a second drilling revisit to SFDP-A. The project scope comprised two re-completion workovers and 4 new drainage targets, to be reached either by sidetracking existing wells or drilling new infill wells from the 2 available slots on SFDP-A.
We were immediately constrained by the limited number of well slots and the lack of sidetrack candidates. Therefore, a survey of technical options was conducted, with the aim to improve the attractiveness of development opportunities, not only for the proposed drilling revisit project but also for the overall future development of South Furious field, especially in the relatively undrained Central Area. As a result of the survey, the multi-lateral well technology was deemed to be the most suitable. Other options considered were the use of a strapped-on conductor, side-track existing wells, and 'splitter' well head technology.
During the infill drilling project (April, 96 to August, 96), SF-27 multi-lateral well was drilled and completed. It has a primary (mother) wellbore, with a lateral (child) well branching from it. The targeted reservoirs have sand permeabilities ranging from 20mD to 100mD, and they lie approximately between 2000 ftss to 3800 ftss. Fig. 2 shows the well trajectories and casing scheme of SF-27 multilateral well.

Motivations
There were two main motivations for considering multilateral technology:
Improved Project Economics. The technology is capable of increasing the drainage area by connecting more reservoir compartments for a fixed number of well slots. This overcame the limitation of only 2 spare slots on SFDP-A and eliminated the need to sidetrack existing wells. Therefore, existing wells are permitted to produce down to their economic limit. In short, a lower UTC (unit technical cost) can be achieved through attractive cost savings with increased production. P. 115