--> Iron Bridge and South Spur Fields, Dickens County, Texas–the Rest of the Story

Southwest Section AAPG Annual Convention

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Iron Bridge and South Spur Fields, Dickens County, Texas–the Rest of the Story


The Iron Bridge Croton lime / Tannehill sand oil fields are located in southern Dickens County, Texas. These Wolfcampian aged reservoirs trend east to west on a gently dipping eastern shelf of the Midland basin. These reservoirs are stratigraphic in nature and occur from fluvial – deltaic processes. The Iron Bridge Croton production occurs on the western side of the multi complex while the Tannehill “A” production occurs on the eastern side. Both reservoirs are related but are separate reservoirs. This field's discovery was the result of regional subsurface mapping and soil gas surveys collected and analyzed in 2001.

Discovery of these fields was a classic geology-geochemical exploration success. The value of liquid hydrocarbon surface signatures in the area has been discussed previously. Gas petroleum hydrocarbons complete the rest of the story. Integration of subsurface geology, gas hydrocarbon data, and petroleum liquid data is the subject of this presentation.

Gas data play a principal role in geochemical exploration. While petroleum liquids migrate up larger fractures and faults, gas migration is fairly ubiquitous. Petroleum gas migration patterns make these data useful for mapping oil reservoir size, shape, and location.

In the case of the Iron Bridge and South Spur fields, petroleum gas concentration data reasonably outlined the producing Croton Lm reservoirs. Geology, gas geochemistry, and liquid geochemistry were combined into a single interpretation illustrating the power of integrating independent data prior to drilling.

The Iron Bridge field was discovered in Jan 2002 with a combined cumulative production of 1.07 million BO. The South Spur field was discovered in October 2000 and has produced 640 thousand BO.