Lookback on Performance of 50 Horizontal Wells Targeting Thin Oil Columns, Mahakam Delta, East Kalimantan Part A: Well Performance Data
Authors: Harding T.G. , Smith K.H. , Norris B. 
Published: March 2010

Abstract
Paper A presents a case study to look back on the performance of over 50 horizontal wells drilled in three different fields in the Mahakam Delta, offshore East Kalimantan, Indonesia. The common application of these horizontal wells is to produce thin oil bands sandwiched between a gas cap and a bottom/edge aquifer.
Based on well performance data, the lookback is mainly focused on the reservoir evaluation aspect of these horizontal wells. Reservoir and well performance is analyzed using a variety of techniques, varying from single-well analytical modelling (or decline curves) to more complex reservoir simulation. Based on statistical data resulting from the analysis of these wells, specific relations between reserves and reservoir-well parameters are identified which will be useful for predicting future well performance, especially during early prognosis.

Introduction
The development of thin oil columns has been a challenge that operators have faced over the years(1–4). The key concern is economic and optimal operations, as coning could cut short production and hinder recovery. Many authors have looked at this problem and suggested ways to lengthen well or reservoir life by reducing coning. In the 1990s, more and more horizontal wells were drilled to tackle this class of reservoir problem. Although observations about their success have been mixed, horizontal
FIGURE 1: Rate control to maximize oil recovery from thin oil column. Available in Full Paper.
wells generally have been accepted as a way to improve recovery compared to conventional wells. On individual projects, factors that need to be compared include considerations for stacked pay completion, drilling and completion techniques, future well workover plan, slot availability, and project cost.
This paper presents a lookback of over 50 horizontal wells, targeting thin oil columns with gas cap and water leg, that Unocal Indonesia Company (UIC) has drilled since 1996 in their offshore fields in East Kalimantan, Indonesia. As these wells are intended to minimize coning effects for improving recovery, the objective is to observe actual well performance as related to reservoir well properties to provide a basis for improving future well planning and operations. Practical issues related to well planning, drilling and completion methodology, and operations are also discussed.
First, a general discussion of fluid flow behaviour and parameters affecting thin oil column exploitation is presented. A brief description on the evaluation techniques used in the performance lookback follows. A discussion specific to data from the three particular fields operated by UIC in East Kalimantan is then presented.

Fluid Flow Behaviour in a Thin Oil Column
Oil and gas recovery from a thin oil column under the influence of gas cap and water support is strongly dependent on oil column thickness, formation permeability, gas cap size, aquifer strength,
FIGURE 2: Effects of completion standoff to GOC and gas cap size on recovery (1 Bcf / MMBo = 178.1 m3/m3). Available In Full Paper.
TABLE 1: Summary of field data. Available In Full Paper.
FIGURE 3: Contribution of horizontal wells to the total Attaka oil production. Available In Full Paper.