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

Abstract
The objective of the study is to provide lessons learned from the actual well performance data, which is provided in Part A of this paper(1), which will improve future well planning as horizontal wells continue to be used in the fields offshore East Kalimantan, Indonesia. Practical issues related to well planning, such as selection of well location, well length, well path, and standoffs to fluid contacts, are presented. The paper also discusses specific operational strategies used in drilling, completing, and producing these horizontal wells.
Results from the well performance data provide guidelines and refinements for continued implementation of horizontal wells to optimize thin oil column development in these fields.

Introduction
The development of thin oil columns has been a challenge that operators have faced over the years(2–5). In the 1990s, more and more horizontal wells were drilled to tackle this class of reservoir problem. Part A of this paper(1) presented a lookback of over 50 horizontal wells, targeting thin oil columns that Unocal Indonesia
FIGURE 1: A preferable simple horizontal well path. Available in Full Paper.
Company has drilled since 1996 in their offshore fields in East Kalimantan, Indonesia.
This paper presents a discussion related to the data from actual well performance as related to reservoir aspects of those horizontal wells. Common lessons learned and practical considerations used in planning and operating these horizontal wells are summarized. Then, a discussion on continued refinements for these practices for future use is provided.

Lessons Learned
The authors present a summary of common observations and lessons learned from drilling and exploiting the thin oil reservoirs discussed in Part A of this paper(1). Best practices based on performance lookback are drawn and presented.
Pre-Well Planning
Organization plays an important role in the operations of these reservoirs when dealing with horizontal drilling. Cross-functional teams have been focused on exploitation of these reservoirs to
FIGURE 2: An undulated well path to search for WOC before completion. Available in Full Paper.
FIGURE 3: Oil recovery increasing with decreasing cumulative GOR. Available in Full Paper.
optimize asset values since horizontal pre-well work typically requires much more effort compared to that of a conventional well. Specialty support groups, such as reservoir modelling and analysis and cross-disciplined chiefs, play a key role in assisting asset teams in well planning, projects QA/QCs, and lookback. The batch drilling of wells to maximize rig time efficiency requires a careful well-by-well plan and a contingency plan ahead of time since urgent decisions concerning setting landing points, selecting well courses, and completion techniques often arise due to unexpected events or surprises while drilling.
Geological risk remains a key factor in well planning, even when the target reservoirs are thought to have sufficient well control. The key challenge is to assess the current fluid contacts and thus the oil column thickness in the target area. Running saturation logs (e.g., RST) and reservoir modelling could help assess and confirm current fluid contacts. Awareness of uncertainty in logging tool depth (+/-1.5 m) helps to plan for selecting prudent landing points.