GEOTHERMAL TEST HINTS AT OIL POTENTIAL IN EASTERN ARIZONA VOLCANIC FIELD

Steven L. Rauzi
Arizona Geological Survey
Tucson

A recently drilled geothermal well, funded by the U.S. Department of Energy and the Arizona Department of Commerce, has provided information about the geology of east central Arizona and west central New Mexico.

Tonto Drilling Services in cooperation with New Mexico State University completed the well, the 1 Alpine-Federal, at a total depth of 4,505 ft on Aug. 29, 1993. The well is located among volcanic rocks in the Apache Sitgreaves National Forest about 6 miles north of the town of Alpine and 6.2 miles west of the Arizona-New Mexico line in 23 6n-30e, Apache County (Fig, 1).

Ground elevation at the wellsite is 8,556 ft.

The well was drilled to determine the hot dry rock geothermal potential of Precambrian rocks. The operator expected to penetrate Precambrian at about 4,200 ft, but the hole was still in Permian rocks at that depth and was in a mafic dike that intruded the Permian rocks at the total depth of 4,505 ft.

Thus the well did not provide any information about the depth and nature of the Precambrian rocks or the presence, thickness, and hydrocarbon potential of Pennsylvanian, Mississippian, or Devonian rocks.

The hole did, however, show that Cretaceous and Permian strata contain potentially important source rocks for oil and gas that are apparently unaffected by nearby volcanism. These potential oil source rocks are the focus of this article.

STRATIGRAPHY

The 1 Alpine Federal, cored from 500 ft to total depth, penetrated Tertiary, Cretaceous, and Permian rocks (Fig. 2). The Permian rocks were cut by three mafic dikes.

The operator reported the Tertiary Datil formation at the surface, Eocene Baca formation at 1,093 ft, early Tertiary redbeds at 3,139 ft, Cretaceous rocks at 3,260 ft, Permian San Andres limestone at 3,369 ft, Permian Glorieta sandstone at 3,436 ft, and Permian Yeso (Supai) formation at 3,751 ft.

H. Wesley Peirce, in an initial inspection of the core with the author, identified the Fort Apache member of the Yeso formation from 4,224 4,414 ft. The Fort Apache member is cut by a mafic dike from 4,260 4,360 ft. The dike apparently did not alter these sediments to any appreciable extent, the widest baked zone being less than 3 in.

TERTIARY STRATA

The Tertiary strata in the 1 Alpine Federal consist of tuffaceous clastic rocks ranging from dense mudstone and well indurated siltstone and sandstone to boulder conglomerate. The operator reported paleosols with root casts and thin bedded crevasse splay deposits in the finer grained material. The top of the Baca formation was picked at the first occurrence of red granite clasts in conglomerate.

CRETACEOUS ROCKS

The Cretaceous rocks, which resemble the Dakota sandstone, consist of white to light gray coarse grained quartzose sandstone and dense dark gray to black mudstone. Thin coaly seams between 3 and 4 in. thick and dark gray to black laminations are common in the sandstone.

The laminations dip at an angle of about 30' and in some instances are disrupted. The sandstone has a salt and pepper texture in places. The dark mudstone gets progressively lighter and more calcareous uphole. The operator described the Cretaceous sequence as being organic rich and an oil source rock and reported what looked like dead oil a the top of the Cretaceous.

Woodward and Grant identified the Dakota sand stone as containing both potential reservoir and source beds in west central New Mexico.

PERMIAN OIL SHOWS

The San Andres limestone in the 1 Alpine Federal is a medium dark gray micritic limestone. The limestone is dark, laminated, and interbedded with thin, dark gray to black shales.

Stylolites filled with a black, earthy organic material are common in the limestone. The organic material can be scraped off with the fingers.

The base of the San Andres includes a 2 ft thick zone of solution or collapse breccia. The breccia consists of light colored clasts of limestone that have an even, golden colored fluorescence surrounded by non fluorescing, dark gray to black micritic mudstone. The operator reported organic debris in the collapse zone.

The strongest shows of oil in the 1 Alpine Federal are in the Yeso formation, which consists of classic seamargin sabkha deposits. Solution brecciated blue gray to light brown dolomite is interbedded with white to brown anhydrite and red to dark brown siltstone and mudstone. The anhydrite has a chickenwire pattern in places.

Scour marks and rip up clasts of dolomite and anhydrite are present at the tops and bottoms of the siltstone and mudstone layers. Bioturbation, soft sediment deformation, and nodular anhydrite surrounded with mudstone are common. Calcareous zones may represent disrupted algal mats.

The upper part of the Yeso formation in the 1 Alpine-Federal contained several zones of petroliferous limestone, the most notable of which occurs between 4,028-4,140 ft, 200 to 85 ft above the Fort Apache member (Fig. 2).

This zone is a yellowish gray to yellowish brown with pinpoint porosity and thin dark laminations throughout. Stylolites and small anhydrite nodules are common near the center of the zone. The zone yielded brown bubbles and a strong petroliferous odor when acid was applied.

Samples have a very faint straw yellow cut and a pale-yellow cut fluorescence in 1,1,1 trichloroethane. A 2 ft interval at 4,028 ft contains fossil hash and has distinct oil staining along vertical fractures. These stains have a brown to yellowish brown fluorescence and a bright yellow cut fluorescence.

The Fort Apache member is a rhythmically banded medium to dark gray fossiliferous limestone with thin dark laminations and numerous zones of yellowish-brown limestone. Porosity is pinpoint to very vuggy and vertical, calcite filled fractures are present.

Dead oil stains some of the fractures and most of the pinpoint porosity. Most of the Fort Apache member has a faint petroliferous odor and yielded brown bubbles and a strong petroliferous odor when acid was applied. When the acid dried, distinct brown rims were evident on the rock.

The presence of petroliferous rock in the upper part of the Yeso was not unexpected. Heavy oil, oil staining, and dead to asphaltic oil were reported in the upper part of the Supai (Yeso) formation in several wells both north and west of the 1 Alpine Federal.2

The petroliferous zone above the Fort Apache may correlate with a petroliferous zone reported above the Fort Apache in the Eastern Petroleum 1A Coyote Creek well, about 23 miles north of the 1 Alpine Federal.

The 1 Alpine Federal penetrated only 604 ft of the Permian Yeso formation. Isopach mapping based on the few wells to the west, north, and east suggests that as much as 1,500 ft of these rocks are present at this location, which leaves as much as 1,000 ft of Yeso beds yet to be penetrated at this locality. The presence of dikes may increase the depth necessary to fully penetrate the Yeso formation.

PRE PERMIAN ROCKS

The 1 Alpine Federal well was not drilled deeply enough to encounter Pennsylvanian rocks.

Mapping by Wrucke,3 however, suggests that Pennsylvanian rocks may be present beneath the Yeso formation at the 1 Alpine-Federal location. Wrucke reported two large blocks of probable Pennsylvanian Naco limestone at elevations of 8,600 ft and 8,700 ft on the northeast flank of Escudilla Mountain, about 6.5 miles northeast of the 1 Alpine-Federal well. He surmised that volcanism had carried these large blocks of Naco limestone to the surface from their more extensive presence at depth.

The Pennsylvanian rocks are absent in two wells drilled north of Escudilla Mountain. The Eastern Petroleum 1A Coyote Creek in SW NE 27 10n 30e, about 23 miles north of the 1 Alpine-Federal, penetrated Permian rocks over granite at an elevation of + 4,628 ft. The Mae Belcher 1 State in SW NE 20-9n 31e, about 18 miles north of the 1 Alpine Federal, penetrated Permian rocks over granite at an elevation of about + 4,366 ft.4

Thus Wrucke's recognition of the Naco limestone on Escudilla Mountain suggests that an edgeline of Pennsylvanian rocks exists between the I Alpine Federal and the Mae Belcher and Eastern Petroleum wells. These rocks may be as much as 750 ft thick at the 1 Alpine Federal location.5 6 7

Regional isopach mapping suggests that as much as 165 ft of Mississippian rocks8 and 150 ft of Devonian rocks9 could be present at the 1 Alpine Federal location. The Precambrian at the 1 Alpine Federal location may be as deep as 6,570 ft, or rather, at an elevation of + 1,985 ft, about 2,400 ft structurally lower than the Precambrian surface at the Mae Belcher well.

OIL, GAS POSSIBILITIES

Woodward and Grant1 reported that Devonian rocks in west central New Mexico contained ideal source beds and noted the presence of potential source and reservoir rocks in the Pennsylvanian formations.

Stratigraphic traps may be present in these units where the Pennsylvanian, Mississippian, and Devonian rocks onlap the southward sloping Precambrian basement in the vicinity of the 1 Alpine-Federal. The oil and gas for these stratigraphic traps could have formed in place or migrated from Paleozoic source rocks in the deep Pedregosa basin to the south. Hydrocarbons may also have migrated from organic rich sediments deposited in ancient seas to the west and east of the 1 Alpine Federal.

Stratigraphic traps in the Permian rocks may involve mafic dikes or sills. Igneous rock does not seem compatible with the accumulation of oil and gas, but in Northeast Arizona at Dineh bi Keyah field igneous rock of Tertiary age has produced more than 17 million bbl of a high gravity crude oil.

The igneous reservoir rock at Dineh bi Keyah field intruded white to light tan carbonates and black shales of the Pennsylvanian Hermosa formation and has yielded the largest amount of oil of any reservoir rock in Arizona.

The oil identified in the Permian rocks in the 1 Alpine Federal could very well have accumulated in stratigraphic traps consisting of Permian aged lenticular sands and fractured carbonates, or even in post Permian igneous reservoir rocks.

CONCLUSIONS

The 1 Alpine Federal penetrated three potentially important oil source rocks in east central Arizona and west central New Mexico and showed that the Precambrian surface slopes more steeply to the south than was anticipated at this location.

Regional studies suggest that oil and gas may be trapped in pre-Permian formations yet to be penetrated at this locality.

The oil source rocks in the 1 Alpine Federal include Cretaceous rocks, the Permian San Andres limestone, and most notably the Yeso formation. The Cretaceous contains organic material and possibly dead oil at the contact with the overlying Tertiary rocks.

The San Andres limestone was eroded to a thickness of 67 ft but contained an apparent collapse zone filled with angular to subrounded clasts of limestone cemented in dark gray to black mudstone with organic debris.

The best oil source rocks encountered in the hole were the petroliferous limestones of the Fort Apache member of the Yeso formation and limestone units above the Fort Apache member.

This region offers opportunities for exploration companies bold enough to explore for oil and gas beneath the extensive cover of volcanic rock in east central Arizona and west central New Mexico. Given that the oil source rocks in the 1 Alpine-Federal are unaffected by this volcanism, this region deserves further evaluation for oil and gas.

REFERENCES

Woodward, L.A., and Grant, P.R., Central western New Mexico An exploration frontier for oil and gas, New Mexico Geological Society Guidebook, 37th Field Conference, Truth or Consequences, 1986, pp. 307 314.
Peirce, H. Wesley, Keith, Stanton B., and Wilt, Jan Carol., Coal, oil, natural gas, helium, and uranium in Arizona, Arizona Bureau of Mines Bull. 1823, 1970, 289 p.
Wrucke, Chester T., Paleozoic and Cenozoic rocks in the Alpine Nutrioso area, Apache County, Ariz., U.S. Geological Survey Bull. 1121 H, 1961, 26 p.
Foster, Roy W., Stratigraphy and petroleum possibilities of Catron County, N.M., New Mexico Bureau of Mines & Mineral Resources Bull. 85, 1964, 55 p.
Kottlowski, Frank E., Pennsylvanian rocks on the northeast edge of the Datil plateau, in Weir, J.E., and Baltz, E.H., eds., Guidebook of west central New Mexico: New Mexico Geological Society 10th Field Conference, 1959, pp. 57 62.
Kottlowski, Frank E., and Havenor, Kay C., Pennsylvanian rocks of the Mogollon rim area, Arizona, in Weber, R.H., and Peirce, H.W., eds., Guidebook of the Mogollon rim region, New Mexico Geological Society 13th Field Conference, 1962, pp. 77 83.
Kottlowski, Frank E., Sedimentary basins of south central and southwestern New Mexico, AAPG Bull., Vol. 49, No. 11 (November), 1965, pp. 2,120 39.
Armstrong, A.K., Mamet, B.L., and Repetski, J.E,, The Mississippian system of New Mexico and southern Arizona, in Fouch, T.D., and Magathan, E.R., eds., Paleozoic paleogeography of the west central U.S., Rocky Mountain Section SEPM, 1980, pp. 82 99.
Beus, Stanley S., Late Devonian (Frasnian) paleogeography and paleoenvironments in northern Arizona, in Fouch, T.D., and Magathan, E.R., eds., Paleozoic paleogeography of the west central U.S., Rocky Mountain Section SEPM, 1980, pp. 55 69