Summary A true in-situ oil shale retort bed preparation experiment was performed by detonating an explosive slurry that had been displaced from well bores into preformed horizontal hydraulic fractures. The objective was to test this method for producing a distributed fracture network with sufficient void and permeability for retorting in a controlled manner. Numerous diagnostic and evaluation measurements were performed during the course of the experiment for initial site characterization, hydraulic fracture assessment, explosive displacement and detonation performance, and post detonation fracture and permeability assessment. Results show that fractures were induced; the fractures were found to be randomly distributed with no regions of extensive fracturing or shale dislocation. Enhancement of permeability was limited essentially to enlargement of the preformed hydraulic fracture horizons into which the explosive slurry was inserted and detonated. Successful retorting would be contingent on the ability to retort shale layers with random fractures but without significant permeability between the enlarged fractures. Introduction The potential advantages of true in-situ processing techniques, as compared with mining and surface retorting, for extracting hydrocarbons from oil shale have been recognized for many years. With such techniques, the only linkage between the underground shale bed and the surface is through a series of wells. Both the bed preparation and the retort processing phases are conducted from the surface through these wells. Resulting attractive features are that requirements for mining large quantities of raw shale and disposal of the spent shale are eliminated. Other environmental impacts, such as water requirements, may be reduced significantly. In preparing an oil shale bed for in-situ processing, the naturally impermeable oil shale must be rubblized to introduce sufficient void and permeability. This permits process gases to flow from injection wells to the combustion front and permits product liquids and gases to flow from the pyrolysis zone to production wells during retorting. Past experiments1,2 have used variations of two basic methods (well bore springing and hydraulic/explosive fracturing) to fracture the shale bed and attempt to achieve the required void and permeability. The well bore springing method3 involves the detonation of explosive charges contained within the well, while the hydraulic/explosive fracturing method involves the detonation of slurry explosives that have been displaced from wells into preformed horizontal hydraulic fractures (hereafter called hydrofractures or simply cracks).

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Bi-Center Drill Bits and MWD/LWD Tools in a Horizontal Application Prove Effective in Reducing Well Costs and Increasing Liner-Size Capability Rick Parrish,*,** Chevron Niugini Pty. Ltd., and Coy Fielder* and Rod Ishmael,* Diamond Products Intl. Inc. Abstract A horizontal drilling program at the Kutubu Project in Papua New Guinea (PNG) called for the use of bi-center drill bit technology to be applied with MWD/LWD tools in a drill-in fluid system. This was the first time that bi-center polycrystalline-diamond-compact (PDC) bits were utilized in a horizontal drilling application. Bit performance while drilling with MWD/LWD tools was enhanced through the use of a sized-salt biopolymer drill-in fluid system. The fluid system was being enlisted for the first time in PNG. The tool combination was able to drill a larger 9 1/8-in. hole out of the 9 5/8-in.-OD casing, as opposed to the 8 1/2-in. holes in four previous horizontal wells (includes one sidetrack) drilled with conventional PDC bits. The larger hole drilled by the 8 3/8-by-9 1/8-in. bi-center bits allowed a 7-in. production liner to be run, instead of the 5 1/2-in. liners run in the previous horizontal wells. The larger liner permits installation of larger production tubing required to selectively produce the desired 8,000-bopd flowrate, as well as a packer/sliding-sleeve completion system. In addition to the benefit of multizone-completion ability and increased flowrate capability, drilling time in the horizontal section was reduced by 13 days using the bi-center-bit/MWD-LWD combination. This reduction in drilling time alone amounted to more than a $ 1.56 million savings to the operator. Bi-center drill bit applications can now yield predictable results in demanding directional environments. The ability to log-while-steering in a horizontal lateral while providing an enlarged hole diameter, without need for additional trips in and out of the hole, results in an extremely cost-effective drilling system. Project background Oil was discovered at the Kutubu Project in 1986 by the Iagifu 2X exploratory well in a remote location in PNG's Southern Highlands Province about 300 mi northwest of Port Moresby, Fig. 1. The petroleum development license (PDL) was approved in December 1990 and first commercial production began in June 1992. Average Kutubu production for 1996 was 107,000 bopd. Before the PDL could be approved, extensive appraisal drilling was required. Including sidetracks, some 31 delineation wells were drilled in the Iagifu/Hedinia and Agogo fields to determine the extent of the Kutubu oil reserves. A large number of appraisal wells were needed due to the significant structural complexity in each well. Massive karsted limestone beds also covered the surface of much of the license area that made acquisition of useful seismic data virtually impossible. Current Kutubu original oil-in-place (OOIP) estimates are slated at about 515 MMSTB based on information from appraisal and development drilling. This is a combined estimate for seven distinct reservoir blocks in two fields. About 80% of the total OOIP, or 420 MMSTB, is from the Toro formation and about 73% is contained in one fault block, the Main Block Toro in the Iagifu/Hedinia field. P. 551^

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