An Evaluation of a Steamflood Experiment in a Utah Tar Sand Deposit

Abstract

Johnson Jr., Lyle A., SPE, Laramie Energy Technology Center, U.S.DOE Fahy, L. John, SPE, Laramie Energy Technology Center, U.S.DOE Romanowski Jr., Leo J., SPE, Laramie Energy Technology Center, U.S.DOE Thomas, Kenneth P., Laramie Energy Technology Center, U.S.DOE Hutchinson, Harold L., SPE, U. of Wyoming Summary The first U.S. DOE Laramie Energy Technology Center (LETC) steamflood experiment in a Utah tar sand, LETC TS-1S was conducted in the Northwest Asphalt Ridge deposit near Vernal, UT. Steam was injected into the center well of two concentric inverted five-spot patterns. The zone chosen for the experiment was a sandstone 45 ft (14 m) thick in the Rimrock member of the Mesaverde formation. The pattern area was 0.25 acres (1012 M2) and contained a 13 degrees API (979 kg/m) bitumen with a viscosity greater than 10 Cp (10 Pa.s) at reservoir conditions. The average oil saturation was 78.9% PV. During 160 days of operation, 65,700 bbl (10.4 × 10 m) of water-equivalent steam were injected at 360 to 530 psig (2.5 to 3.7 MPa) and 180 to 650 B/D (29 to 103 m /d). Total production during the test amounted to 1,150 bbl (183 m) of oil and 6,250 bbl (994 M) of water. Introduction LETC has been working toward development of U.S. tar sands since 1973. To date LETC has conducted several laboratory studies and three field tests of the technical feasibility of in-situ thermal processing of Utah tar sand. The first two field tests, LERC TS-1C and LERC TS-2C, were conducted in 1975 and 1977-78 to test the technical feasibility of the reverse combustion process and a combination reverse/forward combustion process, respectively. Results of these laboratory and field tests have been reported in several publications. The third field test (LETC TS-1S conducted during 1980) tested the technical feasibility of steamflooding a tar sand formation; it is the basis for this paper. LETC TS-1S steamflood began April 23, 1980, and ended Sept 29, 1980. During 160 days of operation, 65,700 bbl (10.4 × 10 m) of water-equivalent steam were injected into the 45-ft (14-m) thick, 500-ft (152-m) deep tar sand zone. During the operational period, 1,150 bbl (183 m) of oil and 6,250 bbl (994 m) of water were produced. Experimental Plan The objectives of LETC's first steam in-situ recovery experiment were (1) to determine the technical and economic feasibility of using a steamflood as an in-situ recovery technique in a Utah tar sand deposit, (2) to evaluate an injection well completion scheme with a high-temperature packer, (3) to evaluate several types of downhole completion schemes for the production wells, and (4) to determine recycle and fuel use possibilities for produced water and oil. Design of LETC TS-1S was based on core analysis, data from a small two-well steam injection test, laboratory studies, a literature survey, and computer modeling. The pattern was two concentric inverted five-spot patterns (Fig. 1). The outer four producers (Wells 3P1 through 3P4) were on the perimeter of 0.25 acres (1012 m), while the inner four producers (Wells 3PS through 3P8) bounded 0.1 acres (405 m2). Monitor Wells 3M1 through 3M4 were spaced at approximately half the spacing of the 0.1-acre (405-m2) pattern. On the basis of preliminary computer modeling results, the 0.25-acre (1012-m2) and 0.1-acre (405-m2) areas represented the best estimates of the maximum and minimum areal sweeps expected during the desired 120-day test period. Test Zone Description The major source of tar sand on Northwest Asphalt Ridge is the Rimrock sandstone member of the Cretaceous Mesaverde formation. The Rimrock is a highly saturated, semiconsolidated, fine-grained sand- stone interrupted by many low-saturated siltstone or shale intervals that vary in thickness from less than 1 in. (2.54 cm) to more than 10 ft (3 m). JPT P. 1119^