Abstract

"The first place to start in the hunt for oil, is the library."—A. I. Levorsen

In fact, that is where Enigma field was first conceptualized. John Pedry (1975) published a field study on North Cottonwood Tensleep Field (discovered 1972). This small thrust fault trap, with an estimated ultimate recovery of about 2,000,000 BO, provided an ideal model for the search for similar accumulations, but 15 years passed before nearby Enigma Field was discovered. Enigma field is almost surrounded by old dry holes, only seven miles to the northwest of North Cottonwood Field. How could this happen during a period of intensive domestic exploration? What prevented someone from finding additional small Tensleep fault traps during this period? After all, common wisdom amongst some old oil finders is, "Where there is one field, there has to be another."

The Enigma discovery drill site, drilled by Fossil and CNG in 1987, was defined and refined by detailed seismic analysis. Much of the seismic was already available through commercial purchase. In addition, the actual fault trace was identified in the RMAG seismic publication on Rocky Mountain seismic profiles. Since the Enigma discovery, Fossil has drilled three (3) similar seismic prospects, unsuccessfully.

What is different about Enigma and these three prospects? What information was available to convince management to commit to the Enigma wildcat? Who made the difficult decisions to proceed? What exploration philosophy was involved? What possible conclusions can be drawn that may lead to additional Tensleep reserves being discovered around the margins of the Bighorn Basin?

Enigma Field covers approximately 300 acres, has a 500 foot oil column, against a thrust fault with about 300 foot displacement. Reservoir studies indicate 13,000,000 BO in place. Cumulative production as of 01-01-96 was 2,054,000 BO. Recently an infill drilling program for water flooding was completed. Daily production increased from 400 BOPD to over 1,200 BOPD. The field is projected to produce for at least another 25 years.

The Enigma Field discovery was not the result of some new high-tech, gee-whiz, computer age exploration tool. Rather, it was the result of using industry's most underutilized data base - the geologic literature. The literature generated the idea, the idea was then coupled with an exploration philosophy, oil field experience and working with partners who could make decisions and commitments based on what was known at the time.