3D seismic in the Uinta

March 21, 2005
The valleys, plateaus, cliffs, and weather of the southern Uinta basin make 3D seismic data acquisition, well, interesting.

The valleys, plateaus, cliffs, and weather of the southern Uinta basin make 3D seismic data acquisition, well, interesting.

Hardly a paved road exists in this 4,500-sq-mile area south of Vernal, Utah, says Marc Eckels, lead author of OGJ’s New Views of the Subsurface special article starting on p. 32. Eckels is vice-president and chief operating officer of private Wind River Resources Corp., Roosevelt, Utah.

Wind River is involved in two 3D seismic projects that are 5 miles apart as the crow flies but 52 miles by road. Closest electricity: 40 miles.

Eckels said, “It is always a pretty remote area, but this winter we had very early heavy snow followed by mild temperatures and a lot of rain, even at 7,500 ft. It has been a muddy mess.”

Uinta’s heyday saw the discovery of famous oil and gas fields such as Altamont-Bluebell, Monument Butte, Red Wash, and Natural Buttes. Today independent companies focused mostly on gas are making 3D seismic surveys work in the southern part of the basin.

Survey time

Acquisition time depends greatly on topography and weather, Eckels said.

Surveying and drilling for the 28-sq-mile North Hill Creek 3D survey began on Sept. 26, 2000 (see Fig. 2, p. 34).

Total time was 73 days, or 2.6 days/sq mile. Acquisition alone took 41 days, or 1.5 days/sq mile. The survey involved no heliportable drilling, and no day was lost to weather.

The Rock Spring 3D survey involved 40 sq miles of sources plus a large area of tails (receivers only). The survey included some heliportable drilling, and terrible weather caused problems. The surveyors and archaeologists started in mid-June 2004, and drillers joined them in August.

Bad weather sapped 28 of the 85 acquisition days, giving work rates of 1.4 days/sq mile excluding weather and 2.1 days/sq mile including weather.

Both North Hill Creek and Rock Spring were mixed-source surveys, and the acquisition phase of a dynamite survey goes faster than that of a Vibroseis survey, especially if weather is an issue, Eckels noted.

Each crew had 60-70 people. The topography in several parts of the Rock Spring area is so rough that even some of the planned receiver locations had to be abandoned.

Processing factors

Data processing time depends greatly on survey size and the number of source and receiver points.

“Typically,” Eckels said, “the data are delivered from the field to the processor on a daily basis during acquisition. WesternGeco had all of the data from North Hill Creek on Dec. 7, 2000. We got a first look in early February 2001, and the final processed volume was delivered on Mar. 1.”

Gross interpretation of structure and other large features took several days, and detailed interpretation took about 2 months. Eckels and his team are still working the North Hill Creek data in 2005.

The Rock Spring survey data were in the processors’ hands in the second week in December 2004.

“We got a preliminary look in mid-January and have had the final processed data volume since about mid-February,” Eckels said.

Seeing the data

Usually it is possible to view seismic records in the field to check for data quality, but this was not the case at North Hill Creek, Eckels said.

“We shot the entire survey without ever seeing anything in the field but a black page because a very “ringy” (highly reflective) sandstone layer was at or near the surface nearly everywhere.”

This, he said, was one main reason many geophysicists thought that 3D would not be particularly helpful in the southern Uinta.

“It turned out that sufficient processing horsepower overcame the problem,” Eckels said.

Shallow resolution dictated the design for most of the southern Uinta surveys, Eckels said.

“Our surveys have been more tightly spaced with respect to both sources and receivers than some others. This makes them more expensive but has allowed us to do detailed work in the Wasatch at 3,500 ft.

“It is not yet clear that the wider-spaced surveys will provide comparable resolution at shallow depth. Presumably, everyone has good data at greater depths.”