Abstract: Brooks Field, Southeast Midland Basin, Irion County, Texas

Elton Rodgers

The Brooks field, in southeastern Irion County, Texas, is in the Midland basin adjacent to the Eastern shelf. Regional maps of the area, contoured on the Ellenburger and the Strawn limestone, show a broad west-plunging nose at Brooks field. The pre-Canyon beds have had sample shows and have tested tight or waterbearing with occasional slight shows of oil or gas. Continuity requires structure for trapping in either the Strawn limestone or Ellenburger. The probability of a structural trap at Brooks appears remote.

Originally the Canyon sands were considered fondothems of cycloform deposition similar to production in Coke, Nolan, and Stonewall counties. Cross-section work does not demonstrate any of the characteristics of cycloform deposition in the Canyon beds.

All of the Canyon sands appear to be neritic nearshore bars and are basin equivalents to a time hiatus in Tom Green County on the east. Cores show good examples locally of graded bedding with poor sorting, large mud balls, and wood fragments in most of the section. In log cross sections the Canyon sands and enclosing shale envelopes abut against Strawn carbonate masses in Tom Green County. There are rocks of Canyon age on the Eastern Shelf area, but in most cases they are bedded carbonate deposits and locally a continuous-growth phase of Strawn reefing. No paleontologic control is available to confirm the regional-correlation age relations.

Within the Pennsylvanian beds the upper unit, or Cisco by our correlations, seems to follow the cycloform pattern.

Transgressive San Angelo sandstones of Guadalupian age are present as beach deposits. Reworking of the sands has made unique trap geometry unrelated to the geometry of the total sand body. The result is significant oil recovery and economics.

Depositional genesis is critical in determining where the sands will pay. Where they will be deposited is easy to predict but hydrocarbon traps are very elusive. Modeling is one method necessary for forecasting the traps.

AAPG Search and Discovery Article #90970©1977 AAPG Southwest Section Meeting, Abilene, Texas