Heavy Oil From Kentucky Tar Sands By Using a Wet Combustion Process
Authors: Ward Charles E. , Ward George D. 
Published: December 2007

The size of the heavy oil or tar sands resource base in western Kentucky is currently estimated at 3.4 × 10- bbl [0.54 × 10 m3] of heavy oil or bitumen in place. Westken Petroleum Corp. constructed a 1-acre [4047-m2] inverted seven-spot pattern in the summer and fall of 1981 to produce heavy oil from the Big Clifty formation tar sands on a 19,000-acre [76.9 × 106-m2] lease in Edmonson County, KY, which contains more than 400 × 10 bbl [63.6 × 10 m3] of heavy oil in face (OIP). Through March 1983, 6,005 bbl [955 m ] of 10API [1.0-g/cm3] oil were produced from this pilot, representing 22.5% of the original oil in place (OOIP) on the 1-acre [4047-m2] pattern. Very satisfactory production rates and air/oil ratios (AOR's) were achieved. production rates and air/oil ratios (AOR's) were achieved. Ultimate recovery with this improved wet-combustion technology is estimated at approximately 50% of the OOIP. Heavy-oil production costs, including investment amortization and interest of $12 to $16/bbl [$75.50 to $101/m3], are projected for production of heavy oil from Kentucky tar sands with this approach.

Reservoir characteristics

The heavy oil or tar sands in this area exist in three different clean, well-consolidated sand formations:an uppermost deposit in the Caseyville sandstone, which outcrops in the area,a deposit in the Hardinsburg sandstone at a depth of about 150 ft [45.7 m], anda deposit in the Big Clifty or Jackson sandstone at a depth of 350 to 450 ft [106.7 to 137.2 m].

Table 1 gives a general summary of the characteristics of the reservoirs in the Edmonson County area based on analysis of more than 60 core holes in the area.

Crude-Oil Quality and Processing

The quality of the heavy oil from the Edmonson County deposits is compared with other heavy oils in Table 2 and Fig. 1.

Table 2 shows that although the oil from the Big Clifty tar sands is a heavy crude, it is significantly better than the oil in the Utah tar sands and only somewhat more viscous than the commercially produced California Midway-Sunset crude. Estimated refining yields from the crude based on fluid coking and catalytic cracking processing are listed in Table 3. Economic processing of the crude to high yields of gasoline and middle distillate will require high bottoms conversion refining capacity.

Extraction Processes

Previous work on in-situ extraction processes for these Previous work on in-situ extraction processes for these Kentucky tar sands includes the work of Gulf Oil Co., who carried out a fireflood in the Caseyville formation with a small test pattern in 1959. Gulf reported a 54% recovery of the OIP during a dry fireflood following a hydraulically propped fracture of the formation. In 1969 Sunset Petroleum, with the assistance of Tejas Petroleum Engineers,* initiated a test operation in the Big Petroleum Engineers,* initiated a test operation in the Big Clifty. This test was successful in producing oil but was discontinued before technical results were available.

Pilot Field Test Pilot Field Test For the Big Clifty project, Westken consulted with the Tejas Petroleum Engineers and elected to use a forward wet combustion preceded by a steam preheat to establish good communication with the producing wells. Westken designed, constructed, and operated the 1-acre [4047-m2] inverted seven-spot pilot facility (Fig. 2). The equipment included a 25 × 10 -Btu/hr [26.37-kl/h] oilfield boiler to produce 80% steam and an 800 × 10 -scf/D produce 80% steam and an 800 × 10 -scf/D [22.65 × 10 -std m3/d] electric-driven, reciprocating air compressor. All fluids were produced by flowing the producing wells. Flue gas and the produced liquids were producing wells. Flue gas and the produced liquids were separated at the surface. No downhole pumps were used. The reservoir properties in the 1-acre [4047-m2] pattern are summarized in Table 4.

Steam Preheat Pilot Results

The first step in the pilot operation was a steam preheat operation. High-pressure steam was injected down the injection well to establish a hot path to each of the producing wells, thereby facilitating the movement of the oil and producing wells, thereby facilitating the movement of the oil and flue gas in advance of the flame front on initiation of burn. Because the oil was highly viscous, the initial mobility of the formation was low. However, as the steam-heated area increased, the formation mobility improved markedly. The rate of steam injection is shown in Fig. 3. With steam pressures up to 550 psi [3.792 MPa], steam rates increased until rates exceeding 800 B/D [127.2 m3/d] were achieved.

Based on the pilot data and on computer analysis, a heat input (net of losses) of about 25 % of the theoretical heat required to bring the entire pattern to steam temperature is needed to establish the hot paths with this technique.

JPT

P. 2083