The complexity of typical completions in Handil and Bekapai fields, i.e. dual completions in deviated wells to produce selectively 2 to 6 productive layers, leads to very delicate and expensive workovers.
In order to increase oil and gas gain, as well as to increase water- injection points without having to pull out the existing completion string, a light workover (LWO) system has been applied in both fields. LWO operations (which include additional perforations, isolation of perforations or communication by cementation, and gravel packing) may involve either slickline, electrical wireline, snubbing, cementing / gravel packing units or any combination of the above, but neither drilling nor work-over unit is involved. LWO's are the last chance to produce a zone having insufficient potential to justify economically a Heavy Work Over by using drilling or workover unit.
Since 1986 up to August 1992 TOTAL Indonesie has performed 103 LWO jobs which have obtained an additional cumulative production of more than 6.4 million barrels oil and 13.8 billion SCF gas and an additional 10 million barrels injected water. The total cost for such jobs was 7.2 million USD or an average of 69 620 USD / LWO. Compared to heavy WO's (pulling out the existing completion string and running in hole a new one) which cost between 0.75 to 2 million USD each, LWO is really the cheapest solution as long as the WO goal is achieved.
TOTAL Indonesie exploits two major oil fields, Bekapai (discovered in 1972) and Handil (discovered in 1974). Since both fields consist of multilayer reservoirs (Bekapai more than 100 reservoirs and Handil more than 330 reservoirs), dual multi-zones completions have been run to allow each zone to produce selectively and to reduce well number - see figure 1.
The typical reservoirs and the dual completions selected have carried classical risks and problems i.e. :
As completions aged, unexpected leaks and communications among the zones were experienced, for which isolation using wireline unit became more and more delicate or impossible.
Workover by replacing the existing completion string with a new one is very delicate and costly, typically 0.75 million USD to 2 million USD depending on WO purpose, and may not be economically justified.
Many wells contain productive zones which were not completed in original completion (due to limitation of number of zones to be completed i.e. 4 – 5 zones / completion). These productive zones have become more and more interesting and significant compared to the originally completed zones which are depleted or non productive due to high GOR or WOR.
LWO, a workover without pulling out or replacing the existing completion string, can be used to modify existing completions or carry out remedial work to render them productive. This method has been applied since 1986 in both fields. Wells which have undergone LWO contribute to additional oil/gas production and water injection gain which otherwise could not be achieved.