Multiwell Ojo Alamo development advancing in San Juan basin

East Blanco Field, Ojo Alamo Project [97,338 bytes] Commercial production from a new formation is rare in a basin as mature as the San Juan. Such a development can be economically attractive because with so many existing wellbores, behind pipe formations can be placed on production quickly and inexpensively. That is happening on the east side of the San Juan, where what appears to be the first significant commercial gas production from Tertiary Ojo Alamo sandstone started last year.

April 27, 1998

3 min read

East Blanco Field, Ojo Alamo Project [97,338 bytes]

Commercial production from a new formation is rare in a basin as mature as the San Juan. Such a development can be economically attractive because with so many existing wellbores, behind pipe formations can be placed on production quickly and inexpensively.

That is happening on the east side of the San Juan, where what appears to be the first significant commercial gas production from Tertiary Ojo Alamo sandstone started last year.

Even more gas

Mallon Resources Corp., Denver, has recompleted 23 wells in Ojo Alamo since last September, when it started up a gas sweetening plant (OGJ, Sept. 29, 1997, p. 106). At that time the first two wells were producing a combined 1.5 MMcfd of gas.

The company estimated reserves of 2.1 bcfe/well for its Ojo Alamo project. Pictured Cliffs wells in the area ultimately recover 750 MMcf. Ojo Alamo is an aquifer in many parts of the basin and holds no gas on Mallon's other San Juan properties, said Kevin Fitzgerald, president.

Mallon's leases have eight potential pay zones, including Paleocene Nacimiento, Ojo Alamo, and the deeper Cretaceous stack. With recent emphasis on Pictured Cliffs, Fruitland, and Ojo Alamo, the company hiked its San Juan basin production fivefold to 742 b/d of oil equivalent in fourth quarter 1997 from the 1996 average.

The first two Ojo Alamo wells on production last fall are in 17 and 18-30n-3w, Rio Arriba County, on the 17,800 acre East Blanco Unit.

Mallon said it has 98 drilling locations and 35 recompletion opportunities on the unit. It holds interests in 35,400 acres in the basin.

Eyeing Ojo Alamo

Ojo Alamo is 40-120 ft thick at a vertical depth of about 3,150 ft on the East Blanco Unit. Mallon perforated 98 ft and 36 ft in the first two recompletions.

The formation is a fluvial deposit and a high energy, braided stream environment, notes James Fassett, U.S. Geological Survey, Denver.

It is the basal Tertiary rock unit throughout most of the basin. It overlies the Cretaceous Kirtland shale and Fruitland formations. There is a large hiatus at the K-T boundary in the San Juan basin representing around 8 million years of missing time.

Ojo Alamo is 350-400 ft above the top of the Pictured Cliffs sandstone in that area. Pictured Cliffs is a regressive marine shoreface sandstone that overlies the marine Lewis shale.

The Lewis would be the most likely source rock for the Ojo Alamo gas. Fruitland formation coal beds are quite thin in this area and probably would not be the source of much gas.

How the gas got from the source rocks into the Ojo Alamo is a mystery, but there are numerous vertical dikes at the surface in Mallon's area that may have contributed to communication.

Records show an old Ojo Alamo gas field on a feature called the Schmitz anticline in 24n-1w. Total cumulative production was 1.2 bcf during 1957-70.

In that area the Ojo Alamo is about 200 ft above Pictured Cliffs and again, the gas must have come up from the Lewis shale source rocks, possibly through fractures related to the formation of the Schmitz anticline, Fassett reasoned.

Fassett, James E., Oil and gas resources of the San Juan basin, New Mexico and Colorado, The Geology of North America,: Vol. P-2, Economic Geology, U.S., Geological Society of America, 1991, pp. 357-372.