EMMENDORFER, ALAN P., Coleman Oil & Gas, Inc., Denver, CO

ABSTRACT: The St. Johns CO2 Field, A Giant That Nearly Escaped Detection Again

Discovered in 1994, the St. Johns CO2 Field covers an area in excess of 400 square miles in the southeast corner of the Holbrook Basin. This high porosity, low pressure reservoir contains an estimated 21 TCFG trapped on structure, within sandstones, siltstones, and dolomites of the Permian Supai Formation. The Ridgeway/Canstar Plateau Cattle Company #1 became the discovery well for the field, despite being drilled near the down dip limits to the accumulation. Casing was ran after inflammable gas flowed to the surface from 2 separate DSTs, as a follow up to very minor mud log shows and limited neutron-density log crossover. The confirmation well, drilled 4 miles to the south and 267' structurally higher, flowed 650 MCFGD natural from 150 feet of perforations, yet no mud log shows were detected while drilling. Several wells were drilled and completed as dry holes near the top of the structure in the late 1950s and 1960s due to a lack of shows. It is thought that a combination of factors, including, fresh drilling mud systems, water flows, zones of lost circulation, high mud weights, and the lack of modern gaseffect logs kept this major field from being discovered 30 years earlier.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico