Petroleum Resources of the Great American Carbonate Bank (GACB)-Lessons from Heterogeneous Ellenburger, Arbuckle, Knox, Prairie du Chien and Beekmantown Reservoirs, Diverse Traps, Unconformity Thinking
New maps, graphs, and charts of hydrocarbon trends enable insights at the field, basin and regional scale of the prolific Lower Ordovician to Upper Cambrian GACB petroleum system. Approximately 3,650 fields have produced oil and gas in about 30 producing regions concentrated mainly in the US states of Texas, Oklahoma, Kansas, Nebraska, New Mexico, Michigan, Ohio, and Kentucky. More than 28,000 oil wells and 3,000 gas wells have produced 4.13 billion BO and 21.18 TCF gas cum. Most (57%) of the combined 7.66 billion BOE hydrocarbons are oil. Under current market conditions it is timely to review GACB reservoirs. Of note, 50 oil and gas fields with reserves of > 1MMBOE have been found since 1987, indicating discoveries in these fabled reservoirs are still occurring.
There are two giant fields greater than 500 MMBOE: Gomez (5.3 TCF) and Puckett (3.8 TCF) gas fields in Pecos County, Texas; and seven oil fields greater than 100 MMBO in Texas and Kansas. One might ask how do significant outlier discoveries like Wilburton field (400 BCF) or Maben Field (51 BCF) occur? Maben was more than 100 miles away from age equivalent production at time of its discovery. We will discuss possible methodologies to assess frontier areas that may yield future surprises.
Depositional settings include: 1) mid shelf, 2) deep shelf and 3) inner detrital belt. Most production comes from the mid shelf setting from dolomite reservoirs with 3-15% matrix porosity; limestone reservoirs are relatively rare. The deep shelf and inner detrital belt also produce significant hydrocarbons. Paleokarst diagenesis overprints all depositional settings and can result in highly variable well performance. Field examples will be discussed.
GACB fields produce from diverse trap types. Reservoirs juxtapose with source rock and seals in many configurations. Trap analysis can prioritize an exploration program in fault bounded structures by comparing fault throws with thickness of sealing and non sealing strata. Most oil field pay occurs beneath the uppermost unconformity at or near the top of GACB reservoirs. Settings and conditions where notable exceptions occur will be discussed.
The speaker will share insights from personal exploration experiences. It is hoped that insights from historical production, analog fields, and new tools will lead to more reserves in both old and new areas.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013