M. Bergsma, 1983. "Upthrown Fault Closure, Calhoun County, Texas", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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This seismic line is located in Calhoun County, Texas. The geologic setting is the Texas Gulf Coast Tertiary basin with the exploration objective in the Oligocene Frio. The Frio is characterized by a thick progradational sequence of sandstones and shales. Locally, the Frio was deposited within the Greta/Carancahua barrier/strand-plain system (Galloway et al, 1982). The dominant structural control is growth faulting with a number of fields producing from rollover anticlines. in Calhoun County, there occurs some counter-regional, up-to-the-coast, down-to-the-northwest faulting. This seismic line illustrates one of these faults.
This seismic line illustrates an upthrown fault closure trap, with the producing zone in the middle Frio, Nonion struma sands. Locally, two of the main productive sandstones are known as the G-1 and the K-2 sands. The correlations on the interpreted seismic line are marked with stipling on the reflectors and the faults are marked with a dark line. The trap shown on this seismic line is an upthrown fault closure on a down-to-the-northwest fault. Production from this field is from the G-1 sand, the trapping fault is at shot point 124 with the G-1 sand at approximately 1.910 secs on the seismic line. The throw on this fault is large, about 300 msec, or 366 m (1,200 ft). This throw is great enough to juxtapose the productive sandstone on the upthrown side of the fault with the younger shale zone on the downthrown side. There is some difficulty in correlating the upthrown side with the downthrown side of the large fault, so the correlation marked is an interpretation. The other smaller faults on the seismic line apparently are not important to the production of the field. There is K-2 sand production in the area, but so far none has been found in this trap.
The data quality on this seismic line is good. Since this is a good area for seismic data, careful acquisition and processing is enough to get good data. It is not necessary to do any special technique.