G. Alan Petzet
Exploration Editor
Discovery of Clarksville field in Red River County, Tex., almost 5 years ago created a flurry of seismic surveys, leasing, and drilling as operators tried to duplicate the field along trend.
The activity led to more questions than answers, but interest remains high. Observers don't agree whether the producing formation in Clarksville field is Jurassic Cotton Valley, as in nearby Bogata field, or an updip facies of Jurassic Smackover.
Other questions are who is working the play and from which office. The area is on the fringes of district office responsibilities in Houston, Lafayette, and Dallas, says Gene Cantwell, president, Geotrak Corp., Houston. Geotrak has shot extensive seismic in the region.
The play is being made in Hunt, Lamar, Red River, and Bowie counties, Tex., by most companies. Other companies concentrate efforts in South Arkansas.
Heavy rain since fall has stalled drilling. Operators have several locations ready to be drilled.
H.L. Brown Jr., Midland, will drill 1 Routt in Hunt County about 55 miles west of Clarksville field on a look alike feature to Clarksville field.
This 7,000 ft Paleozoic wildcat is in the "elbow area" where the Mexia-Talco fault trend turns south.
Wagner & Brown, Midland, Santa Fe Energy Co., Houston, and others will test their ideas in and around Bogata field, a lower Cotton Valley and Smackover accumulation about 6 miles southwest of Clarksville field.
Bowie County has seen most of the recent exploration.
Several wells are planned there this summer.
CLARKSVILLE FIELD
Clarksville field was discovered in January 1986 at the Santa Fe Minerals Inc., Dallas, 1 Willis about 5 miles south of Clarksville, Tex. SFM pumped the well for 229 b/d of oil with no water.
The SFM group and others have drilled 30 wells in the field area, and SFM operates most of the field's 17 producing wells. Working interest owners are evaluating the economics of a potential waterflood, said William H. Sydow, production manager, King Ranch Oil & Gas Co., Houston. Original oil in place approaches 20 million bbl, of which 1.25 million bbl is expected to be produced under primary recovery.
GEOLOGY
Several major oil companies first explored the area, testing the updip pinchout of the Smackover.
This rich oil generating source rock, capable of being its own reservoir, is an exploration target from Florida to South Texas. It seems clear that the majors did not look far enough north, because Clarksville field is slightly updip of the Smackover pinchout in East Texas basin. Oil at Clarksville has a fingerprint similar to oil sourced from Smackover and produced along the Mexia-Talco fault system to the south.
The conglomerate interval in the field was deposited on a smoothed Triassic Eagle Mills formation surface that pinched out on the high dipping Pennsylvanian basement surface, said William A. Silk Jr., King Ranch onshore exploration manager.
The reservoir, of Ouachita provenance, was deposited as an alluvial fan sequence of continental origin. Seismic data show that the accumulation is on the edge of an overall low, with structural highs absent in the producing formation.
The productive conglomerate interval at Clarksville field has been identified by a seismic response to the porosity development-preservation within the conglomerate.
The porosity is a sheltered type and occurs in the void spaces between the boulders, cobbles, and pebbles of the matrix. The conglomerate's gross thickness averages 240 ft across the field with an average porosity of 11.7% and a water saturation of 43% in the pay.
An understanding of the timing is critical. The timing of deposition, porosity development, migration, and trapping have to be right, Silk said.
It appears that an initial hydrocarbon migration passed through the Smackover during Cretaceous time and was never adequately trapped. Something changed in a second migration to trap Clarksville field.
Even though the most recent wildcats have been drilled to test the updip prospects, other potential exists. The "knob" play for Smackover production, similar to that in Alabama, could get a second look in Northeast Texas-South Arkansas.
Mike Rogers Drilling Co., Magnolia, Ark., and Murphy Oil Corp., El Dorado, Ark., have been successful in the Texarkana area of Bowie County with Smackover discoveries that may be similar to the Alabama play.
A few in the industry have written off this area, but the Smackover oil production is proof that hydrocarbons have migrated updip of the Mexia-Talco fault system.
Copyright 1990 Oil & Gas Journal. All Rights Reserved.
