Production Optimization of Tubing Restricted Wells: A Case History
Authors: Gunawan Ronald , Ismanto Bambang S. , Dyer George R. , Napitupulu Edison 
Published: December 2007

Abstract
Wellbore optimization is one of the key factors in field management and development of multilayer deltaic reservoirs having a wide range of reservoir properties and size. This optimization will affect current field deliverability and the number of wells required to be drilled in the future to meet gas demand. Tubing size is one of the factors that can be used for wellbore optimization. This paper presents VICO Indonesia's experience in optimizing tubing restricted wells in Nilam Field.
The results of a VICO Tubing Size Optimization Study showed that larger tubing size does not significantly affect reserve recovery in high kh (permeability-thickness) reservoirs. All wells were evaluated to determine which wells were tubing restricted and candidates for optimization. The optimization work included tubing change-out with a rig and rigless wireline intervention. Nodal Analysis and DEPLAN, a Field Depletion Planning model developed by VICO Indonesia, were used as tools to identify the candidate wells and estimate the benefits of the production optimization.
The 1996 optimization program resulted in 87 MMSCFD gas deliverability increase. This increase will result in the two year deferral of three drilling wells and eliminating two drilling wells for deliverability during the field life. This paper discusses not only the obvious benefits of increasing production, but also the effects on reservoir depletion planning and ultimate recovery.

Introduction
VICO Indonesia, the operator of Sanga-Sanga Block in East Kalimantan - Indonesia (Fig. 1), has four major gas fields that produce an average of 1.5 BSCFD. The gas is transported via pipeline to the Bontang Facility and converted to LNG for distribution and sale in the Asia Pacific Rim. Nilam Field is one of VICO's main gas producers. The field consists of more than 300 unique reservoirs that have permeability ranges from less than 1 md to greater than 1,500 md. Most reservoirs are volumetric depletion drive. A typical well will have as many as 20 reservoirs in each well, distributed over a 5,000 foot interval. Currently, there are 168, wells most of which are completed as dual completions (Fig. 2). They range in depth from 7,000 to 14,000 ft. The Nilam Field has three gathering system pressures, high (950 psig), medium (375 psig), and low (150 psig). A well typically begins producing into the high pressure system, then moves to the medium pressure system and finally to the low pressure system as the reservoir pressure depletes. Once the well has depleted, it is then worked over to different zones and the cycle starts over again.
In such numerous widely separated reservoirs, wellbore optimization is very important. The objective of the wellbore optimization is to optimize production as well as reserve recovery of each well. The optimization work can have significant impact on field deliverability and the required work program to meet the gas demand.
In the Sanga-Sanga Block, the effect of increasing gas production is complex. This is because that increasing gas production does not directly affect the cash flow to the company. The amount of gas that can be sold is restricted by the processing capacities of the liquefying natural gas plant (LNG plant). Under specific gas sales commitments, the demand of the LNG plant is dictated by the long term LNG contracts. Therefore, increasing gas production from production optimization does not directly increase the cash flow to the company. The production optimization can only be justified in such an economic environment by reducing the future expenditures required to meet demand and maximizing reserves recovery from the field.
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