Abstract

Performing coiled tubing and wireline well interventions outside of the short string in dual completions has become an acceptable part of well intervention activities in the Offshore West Java field over the last 2 years. Previously, most well intervention activities below the end of the short string tubing were avoided due to the perceived high risk of problems such as getting stuck by wrapping tools around the long string or wedged between the long string and the casing wall.

West Java is a mature field with almost all the wells penetrating multi-layer reservoirs. Reservoir management issues have resulted in a large number of dual completions. In order for wells to maintain production at their potential rates and for the shut-in wells to be reactivated, well intervention activities need to be performed regularly in both strings. To date, 14 coiled tubing interventions outside of short string have been completed. Coiled tubing intervention consists of 8 fill clean outs, 2 cementing jobs, 1 fishing job, 1 polymer water shut-off and 2 stimulation jobs. Perforation jobs were done after performing coiled tubing cementing and water shut off jobs. All these jobs have been done with a high degree of success under a varity of well conditions (high angle, etc).

This paper will explain several problems that were encountered while working outside of short string, especially during coiled tubing interventions. Several ideas have been applied and lessons learned to overcome these problems. If we look back at the results in the Offshore West Java field over the last two years, working outside of short string has become a common practice in sustaining or even increasing production and in re-activating shut in wells.

Background

The Offshore West Java Production Sharing Contract (West Java PSC) area is located off the North Coast of Java Island in Indonesia (see Figure 1). The contract area is about 18,000 sq-km. The area first production was in 1971. The West Java PSC is divided into four main areas: Ardjuna, Arimbi, Bima and North West Corner. It consists of about 50 fields, most of them oil, distributed across three productive formations: Parigi, Upper and Lower Cibulakan. Throughout its 30 years of production history, 13 flow stations, 150 production platforms, 700 wells with 1013 production strings and more than 1,000 miles of sub-sea pipeline have been built in an average sea depth of 40 meters. Gas lift is the primary artificial lift method in this area.

Peak West Java Production was achieved in 1984 with a production rate of 180,000 BOPD but now it has declined to around 50,000 BOPD. The continuous decline in production is a challenge to the company goal of being a low cost offshore operator.

Currently, approximately fifty-five percent (55%) of the strings are currently shut-in either because they have reached their economic limits, have mechanical problems or have watered out. Evaluations of the shut-in wells identified unrecovered reserves in the wellbores that could potentially be recovered through well intervention. Identified problems were wellbore fill, formation damage, and watered out zones in a multi-layered reservoir. Economic evaluation eliminated rig workovers as an option in most cases. In others the long string was still producing and a rig workover to restore short string production was considered an unacceptable risk to the long string production. These conditions have challenged the well intervention team to look for alternative techniques and challenge the perceived risk of working with coiled tubing and wireline outside the end of tubing on the short string side of a dual completion.

This re-evaluation has resulted in working outside of short string becoming an accepted practice in maintaining short string production. Prior to this re-evaluation, this practice was avoided. To date, 14 coiled tubing jobs (8 fill clean outs, 2 cementing jobs, 1 fishing job, 1 polymer water shut-off and 2 stimulation jobs) have been done with various degrees of success. Coiled tubing cementing and water shut off were continued with perforating job by using Electric line.

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