ABSTRACT: Heluma and King Mountain Fields, Back-Thrusted Structures, Upton County, Texas

TURMELLE, JOHN M., Columbia Gas Development Corporation, Houston, TX

Heluma field was discovered and initially developed in 1956 as a four-well Ellenburger pool with some marginal Devonian reserves up-hole. For fifteen years it was reasonable to map the field as a tilted fault block at the Ellenburger level. In 1971, a field extension well proved that the supposed bounding high-angle normal fault was instead a low-angle backthrust, which overrides and does not cut the Ellenburger. The Devonian came in 500 ft structurally high to the older wells and has since produced nearly 4 million bbl of oil.

Eighteen additional Ellenburger locations were also drilled beneath the backthrust. The present spacing shows that some structurally low Ellenburger tops were due to drilling into Ordovician sinkholes.

King Mountain field is a long narrow anticline that has produced 5.5 million bbl of oil from the Ellenburger. This field was more completely developed than Heluma during the late 1950s and the same style of backthrust so prolific at Heluma is also present here, yet with a lesser throw.

During the 1950s, all faults easily may have been interpreted as very high-angle normal faults. Similarly, we easily can conclude they are flower structures created by wrench tectonics. These oil fields lie

in an ancillary direction to the Big Lake fault. The key to the backthrusts, however, is the compression of the intervening asymmetric synclines. The thick section of Devonian limestone and chert could not be tightly folded so it rode up the flank of the syncline until the limb was higher than the adjacent anticline.

AAPG Search and Discovery Article #91018©1992 AAPG Southwest Section Meeting, Midland, Texas, April 21-24, 1992 (2009)