An echoing in-situ combustion oil recovery project in a Utah tar sand

U.S. tar sand resources contain an estimated 30 billion bbl (4.7 Gm3) of oil in place in about 550 occurrences in 22 states. Over 90% of the known resources are in six large deposits in Utah, each containing from 1 to 16 billion bbl (0.15 to 2.5 Gm3) of oil. 1 Four major tar sand deposits in Alberta, Canada, contain some 900 billion bbl (143 Gm3) of oil, and deposits in Venezuela and Colombia contain an estimated 1 to 1.8 trillion bbl (0.15 to 0.28 Tm3).3 The first U.S. DOE tar sand field experiment (LERC TS-lC) was conducted in Utah's Northwest Asphalt Ridge deposit in late 1975. LERC TS-lC accomplished its two primary goals: (1) to demonstrate the feasibility of applying a reverse combustion process to a heterogeneous tar sand reservoir with a high average oil saturation and (2) to provide the Laramie Energy Technology Center (LETC) research personnel with valuable experience in application of the combustion process and operation of its related equipment. Results of LERC TS-lC and supporting research are reported in several publications.4-14 LERC TS-lC provided encouragement for a second field experiment (LERC TS-2C) designed to use reverse combustion as a preparatory phase for forward combustion. LERC TS-2C tested the technical feasibility of the application of a combination thermal recovery process -reverse and forward combustion- for the in situ extraction of oil from tar sands. The reverse combustion (preparatory) phase improved the natural reservoir conditions for application of the forward combustion (production) phase. However, the fire front moved through the pattern in a series of reverse and forward combustion phases (echoing combustion) during the experiment. The experiment was ignited in late August, 1977, and completed in February, 1978. More than 25% of the oil in place was produced in 183 days from a 13-ft (4-m) thick test zone at a depth of 350 ft (107 m) within a 40 x 120 ft (12 x 36 m) nine-well drive pattern.