Neil H. Suneson, Jock A. Campbell
Oklahoma Geological Survey Norman, Okla.
Recent exploration activity in the Ouachita Mountains frontal belt in Oklahoma started in late 1986 with the drilling of the Amoco 1 Jenkins (9-1-13e) in Atoka County. At approximately 10,400 ft, the well encountered high-pressure gas and blew out. Amoco moved the rig and drilled the Amoco 1-A Jenkins, which flowed about 1.1 MMcfd from commingled Wapanucka limestone at 8,926 ft to 9,096 ft and Spiro sandstone at 8,758 ft to 8,822 ft. That well is the discovery well for the W Wesley field, (Fig. 1). Arco followed Amoco's discovery with the 1-19 Ingersoll (19-1-13e) on June 7, 1987, which drilled to 15,080 ft TD, but was dry. Amoco spudded the 2 Jenkins (9-1n-13e) on December 10, 1987, and drilled to 10,930 ft. Results from the well have not been made public to date. Amoco spudded the 1 McEntire (3-1n-13e) on November 3, 1989, drilled to 9,208 ft, and tested 9.5 MMcfd from Spiro-Wapanucka perforations below 7900 ft.
In the middle of 1988, Texaco became active near the W Wesley field, and on May 18, spudded the 1 Lafevers (10-1-13e). The well drilled to 12,850 ft and tested 8.1 MMcfgd from Wapanucka perforations at 12,258 ft to 12,285 ft. Texaco has continued to be active in the area. The 5-1 Chastain (25-2n-13e) spudded on June 29, 1988, was plugged back and whipstocked, drilled to 12,321 ft, and tested 2.8 MMcfd from Wapanucka perforations at 11,062 ft to 11,240 ft. The 2-1 Smith (2-1n-13e) spudded on October 13, 1988, drilled to 13,806 ft, and was plugged and abandoned. The 11-1 Smith B (11-1n-13e) spudded on January 13, 1989, drilled to 13,517 ft, and tested 253 Mcfd from middle Atoka perforations at 6,388 ft to 6,688 ft. The 16-1 Jenkins (operator changed to D-Pex) (16-ln-13e) spudded on January 15, 1989 and drilled to about 13,500 ft. A third operator, Tide West, spudded the 1 Atoka Wildlife (23-1n-13e) on February 17, 1990.
In early 1988, exploration efforts also began to focus on more eastern parts of the Ouachita Mountains frontal belt (SW Haileyville area, Fig. 1). The Exxon Mabry Trust (1 2-4n-17e) spudded on January 8, 1988, and drilled to 13,200 ft. The well tested 225 Mcfd from Spiro perforations at 12,406 ft to 12,465 ft.
About 9 miles southwest of the Exxon well, Amoco spudded the 1 Garrett (2-3n-16e) on January 9, 1988, the 1 Zipperer (32-4n-17e) on March 13, 1988, the 1 Rosso (5-3n-16e) on June 22, 1988, the 1 Patterson (27-4n-17e) on November 26, 1988, the 1-6 Collins (6-3n-16e) on January 6 1989, the 1 Retherford (25-4n-17e) on March 7, 1989, the 1 A Tscappat (3-3n-16e) on March 17, 1989, the 1 Tomlin (29-4n-17e) on October 25, 1989, and the 1 Watts (6-3n-17e), on January 11, 1990. Amoco's success in this part of the Ouachita frontal belt has been firmly established. The 1 Garrett tested 15 MMcfd from the Cromwell and Spiro between 13,196 ft and 13, 910 ft; the 1 Zipperer tested 49 MMcfd from Spiro-Wapanucka at 12,148 ft to 12,286 ft; the 1 Rosso tested 2 MMcfd from Spiro-Wapanucka; the 1 Patterson tested 15 MMcfd from Spiro-Wapanucka at 11,944 ft to 12,124 ft, and the 1A Tschappat tested 5.2 MMcfd from Spiro at 9616 to 9648 ft.
Other operators have followed up on Amoco's success. The Texaco 21-1 Wayne Wallace (21-4n-17e) spudded on December 6, 1988, drilled to 13,694 ft, and tested 11 MMcfd from overthrusted Spiro at 13,258 ft to 13,308 ft. The Exxon 1 H&H Cattle Co. (33-4n-17e) spudded on January 1, 1989, drilled to 14,518 ft, and tested 709 Mcfd from an Atoka sandstone to 5030 ft to 5201 ft. The Exxon 1 Szenasy (1-3n-16e) spudded on April 30, 1989, drilled to 15,000 ft, and tested 1.3 MMcfd from Wapanucka at 14,088 ft to 14,154 ft. Other wells spudded in 1989 and early 1990 include the TXO 1 Dromgold (4-3n-16e) and six operated by Exxon: 1 Davis Elliot (31-4n-17e), 1 Roy Retherford (31-4n-17e), 1 Ellis Rudy (30-4n-17e), 1 Garrett B (34-4n-16e), 1 Garrett A (26-4n-18e), and the 1 Garrett C (33-4n-18e).
Additional drilling has taken place west of Amoco's Zipperer discovery and subsequent follow-up activity. The first wildcat in this area was the Texaco 2-1 Carl Goddard (2-3n-15e), which spudded on August 4, 1989, was plugged back and whipstocked, drilled to 12,140 ft, but was dry. This was followed by the Texaco 1-1 J.A. Goddard (1-3n-15e), which spudded on November 3, 1988, and tested 4.5 MMcfd from Atoka sandstone at 6,080 ft to 6,144 ft and 1.7 MMcfd from Atoka sandstone at 4,339 ft to 4,340 ft. The Texaco 2-2 Goddard (2-3n-15e) spudded on November 5, 1989, drilled to 7,252 ft, and tested 1.1 MMcfd from middle Atoka at 3,394 ft to 3,51 2 ft.
Texaco is also drilling the 7-1 Mabry (7-4n-18e), the 11-1 Norton (11-3n-16e), and the 28-1 Manuel Rudy (28-4n-17e), and the 6-2 Collins (6-3n-16e).
In addition to the well-publicized exploration activity by major operators in the Ouachita Mountains frontal belt, smaller operators have been active elsewhere in the mountains, particularly in Atoka County.
Wellhead Compression drilled the 2 Sumar (28-5n-19e) to 3,200 ft in a Wapanucka wildcat (dry), Abide drilled the 1 Lambert (6-1n-14e) to 3,393 ft and tested the Springer and Cromwell (dry), United Petroleum and Energas drilled the 1-24 Wyrick (24-1n-14e), to 2,128 ft (junked and abandoned), and A&I Properties drilled the 1-A JR (i-1n-15e) to 1,525 ft as a Stanley development well (7 bopd).
While much exploration has focused on Cromwell, Wapanucka, and Spiro objectives in thrust and sub-thrust positions in the frontal belt, a second major exploration play has developed immediately north of the trace of the Choctaw fault in the southern part of the Arkoma basin immediately west of the town of Wilburton. Arco discovered the "Wilburton Deep" field (Fig. 1) in Aurbuckle group carbonates with the 2 Yourman (15-5n-18e), which spudded on February 2, 1987 (about the same time as exploration activities near W Wesley were beginning), drilled to 15,391 ft, and tested 9.3 MMcfd from 14,259 ft to 14,500 ft. Arco's discovery was confirmed with the 2 Fazekas in 16-5n-18e, and field development now includes 8 additional Arco wells. Anadarko also successively completed a deep Arbuckle well with the 3-23 Williams A (23-5n-18e). Stepout wells to the northwest and west of the field include the Arco 1 Sharp (2-5n-17e-dry); the D-Pex 1 Hall (17-5n-16e) - 180 Mcfd from Oil Creek at 13,112 ft to 13,313 ft); and the Nicor 4 Bowman (20-5n-17e-drilling). A step-out well attempting to define the southern limit of the field (Arco 1 Hart in 6-4n-19e) was dry, but Arco is drilling additional Arbuckle objectives over 6 miles south of the trace of the Choctaw fault in the 1 Ulysses (35-4n-18e).
East of the "Wilburton Deep"field, the An-Son 1-21 Cindy (21-5n-20e) and Anadarko 1-15 Alford (15-5n-21e) are also drilling to Arbuckle objectives.
In a separate test nearly 35 miles southwest of the "Wilburton Deep" field, the Texaco 29-1 Burnett (29-2n-14e) is drilling an Arbuckle test near the previously described W WESLEY Spiro-Wapanucka activity.
In summary, there are two major exploration plays in the Ouachita Mountains frontal belt and southern Arkoma Basin at the present time. The limits of production from the Cromwell sandstone, Wapanucka limestone, Spiro sandstone, and Atoka formation sandstones in thrusted and sub-thrust structural positions are currently being tested between the W Wesley field and the Pittsburg field the S Blanco field and the Wilburton field. Major operators include Amoco, Exxon, and Texaco. The second major play is in Arbuckle group carbonates, and several operators are testing structures west, south, east, and far to the southwest of the recently discovered "Wilburton Deep" field. The relation of the structural trap in the "Wilburton Deep" field to Ouachita tectonics is unclear, the extent of the field is unknown, and the location of similar traps to the west or east in the Arkoma basin or to the south beneath the thrust sheets is currently being tested.
FUTURE EXPLORATION PLAYS
The Cromwell-Wapanucka-Spiro-Atoka play is prospective in the frontal belt eastward into Arkansas and consists of open to tight, narrow, thrust-faulted or overturned anticlines associated with blind thrusts above and below the Choctaw fault. The Wapanucka produces from both porous rock matrix and fractures. Outcrop observations suggest that fractures probably contribute significantly to production from this reservoir. The Cromwell, Spiro, and Atoka appear to produce primarily from porous rock matrix but it is unknown to what extent fractures contribute to permeability in these units. Tilford (1990) discusses this play in much greater detail.
Another major play is in faulted Ordovician Arbuckle group carbonates. Examination of cores indicates that the Arbuckle reservoir consists largely of vugs and solution-enlarged fractures in clean dolostone. However, most of the reservoir permeability is the result of younger fractures and microfaults (Hook, 1989). Gas shows have been reported by some operators in the Viola and Hunton Groups, suggesting that they may also prove to be reservoirs.
The relation of the structural trap in the "Wilburton Deep" field to Ouachita tectonics is unclear. Jacobeen and Kanes (1975) and Nicholas and Rozendal (1975) showed that thrust faults ramp over basement block faults. If this structural style characterizes the Oklahoma Ouachitas, then the Windingstair fault may be the "trailing" thrust of a zone of complex imbrication (frontal belt) that marks block-faulted basement. This interpretation would suggest that there are significantly fewer and/or smaller basement faults south of the trace of the Windingstair fault. If the Sohio 1-22 Weyerhaeuser did, in fact, penetrate Arbuckle, then it is possible that Arbuckle group carbonates extend southward beneath the entire exposed width of the Oklahoma Ouachita Mountains. However, good seismic resolution is difficult to achieve because of multiple low-angle faults and the thick sedimentary section. Magnetic surveys may be helpful in determining basement character and the optimum position and azimuth for seismic profiles.
South of the frontal belt, exploration plays above the Arbuckle take on a different character because of differences in structure and stratigraphy. Jackfork group sandstones constitute the shallowest major conventional reservoir in the central Ouachitas. The Jackfork contains most of the sandstone in the Carboniferous flysch sequence in the Oklahoma Ouachita Mountains (Evoy, 1990). Locally, (as in northeastern Atoka County) the Jackfork consists of as much as 1,100 ft of amalgamated sandstone beds with no interbedded shale.
Potential Jackfork traps are both structural and stratigraphic. Pinch-outs of sandstone bends may form stratigraphic traps on the flanks of the broad synclines that typify the central belt, (Fig. 3). This trap type was explored in a test by Sohio (Legg and others, 1990). Structural traps consist of relatively narrow anticlines and faulted folds (Fig. 3). The Jackfork overlies the thick Stanley group and is therefore in an advantageous position above gas-prone shales of that unit. Furthermore, recent field work by the Survey has identified solid hydrocarbons in sandstones of the Jackfork group.
The Stanley group is not emphasized in this play, because the sandstones are generally thin and/or discontinuous and commonly have poor reservoir properties. However, the numerous discoveries and/or significant hydrocarbon shows in the Stanley are relevant to the Jackfork play. Marginal to subcommercial gas has been found in Stanley Group sandstones at the S Jumbo (1958), SW Moyers (1960), and SE Daisy (1983) fields. Perhaps more significantly, six small fields produce, or have produced, 32 to 41 API gravity oil from shallow sandstones in the Stanley. These fields are Redden (1914), S Bald (1932), Potapo Creek (1932), Bald (1933), and W Daisy (1953). All produce (d) from less than 500 ft. The sixth field is unnamed, although we have chosen to call it "Star" for the adjacent abandoned townsite. It was discovered in 1982, and two wells continue to produce from about 1,200 ft. Two other occurrences are also significant. A few barrels of oil were recovered at "Minnett" in 1958 from probable Stanley at 230 ft. A well drilled for water near Talihina recovered an unknown amount of oil (no water) from Stanley at about 160 ft in 1985. These occurrences, mostly in the McGee Creek Valley, occur south of the trace of the Windingstair fault in an arc from T. 14 E. to T. 21 E., and help define the central oil belt (Fig. 1). Oils from three of these fields have been correlated with Ordovician-Silurian petroleum source rocks, indicating substantial vertical migration. These small accumulations in minor reservoirs may also be leaks from deeper traps parallel to the trace of the Windingstair fault.
Another play in the central belt consists of objectives in fractured cherts. The Bigfork chert and Arkansas Novaculite have been shown to have commercial potential where fractures coincide with structural highs and the trap is adequately sealed. Gas was produced from the Bigfork chert in the Potato Hills field for many years, and there was a gas discovery in the same reservoir in the S Jumbo field in 1978. Gas was also discovered in the Arkansas Novaculite in the W Daisy field in 1958. Oil was recovered in subcommercial quantities from the Arkansas Novaculite at the southeast Atoka Townsite field (Table IB). Thrusted novaculite has produced over four million barrels of oil at the Isom Springs field since its discovery in 1977. Although this field does not underlie the exposed Ouachita Mountains, it is part of the same structural trend (Morrison, 1980). Other pre-Carboniferous reservoirs that are potential exploration objectives in the Ouachitas are the Crystal Mountain sandstone, the Blakely sandstone, and the Blaylock sandstone.
In summary, hydrocarbon exploration in much of the Ouachita Mountains is in its very early stages. South of the trace of the Windingstair fault, the drilling density of wells greater than 10,000 ft deep is 1 well per 265 square miles. Clearly, exploration targets will be selected based on imaginative analysis of seismic data, drilling expertise through steeply dipping rocks, and careful integration of surface and subsurface structure and stratigraphy.
END PART 2 of 2
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