There are numerous technical papers and supporters of both cased-hole frac pack (CHFP) and open-hole gravel pack (OHGP) completions. There are even supporters for cased- hole gravel packs (CHGP) of certain situations. Arguments in favor of one completion strategy versus another can be defended for various reasons, and as such debate regarding the preferred method has continued for many years. The correct completion strategy is the one that provides the most value for the asset(s), usually measured in terms of NPV or DPI. These factors are a function of capital investment.
Early work completed to support CHFP wells for Duri concluded that, among other things, such completions would yield:
the same or better production when compared with OHGP;
a 28% savings in operating costs; and
improved zonal conformance resulting in 2–5% better recovery1.
This paper reviews in brief the history of completions in Duri. It documents the performance results and compares them with the predicted results. Furthermore it explores whether the assumptions made to support CHFP (as noted above) remain true and applicable for development of new areas within the Duri steamflood area. The following objectives have been developed:
Compare cased-hole and open-hole completions for application in Duri;
Revisits results from previous tests performed in Duri;
Determine whether the decision drivers for recommending CHFP completions (for Areas 9, 10*, 11 and 12) were accurate and, more importantly, are still applicable; and
Provide a recommendation and establish "best practices" for completing new area wells in Duri.
This paper focuses on initial completions in new areas where steam has not yet broken through, rather than recompletions, supported by actual performance data where prudent (available at the time of writing). This paper is not intended to review application of completion techniques nor optimization of same although some discussion is included.
The Duri steamflood project, located in central Sumatra, Indonesia is reported to be the largest thermal enhanced oil recovery project in the world2. More than 5000 wells were producing in excess of 280,000 BOPD in March 2000. In the coming years new development areas (Area 10 13, inclusive) will add to the well count as will development of the shallower sands in existing areas. Furthermore, an aggressive infill drilling campaign is also underway.
The principal oil-bearing formations are the Pertama and Kedua sands, both of Miocene Age. Combined pay thickness averages 140 ft. and range in depth 430 to 680 ft. The fine- grain sands are highly unconsolidated with permeability of up to 2 darcies and oil viscosity of 120 cp (at 100°F) to 6cp (at 300°F)3.
Open & Cased Completions
In the early days of Duri development, the completion strategy for Duri wells was CHGP or OHGP. The latter becoming the completion of choice since experiments were concluded in Areas 1, 2 and 3 during the late-1970s and early-1980s.
Because the Duri sands are largely unconsolidated, sand control has yielded many challenges (in terms of design and operations) throughout the life of the field. Various trials were performed in an effort to address the sand control issues and improve operability. Such trials included the use of slotted liners, torch-cut liners, bullet or jet perforations, slotted inner liners, CHGP, and OHGP3.