Structural and Stratigraphic Analysis of the Rex Timber No. 1-9 Well, Southern Ouachita Fold and Thrust Belt, Clark County, Arkansas

Peng Li1,   Ted Godo2,   M. Ed Ratchford3

¹Arkansas Geological Survey ,  ²Shell Exploration Company ,  ³Arkansas Geological Survey

In 1985 Shell Oil drilled the Rex Timber No. 1-9 well along the southern flank of the Ouachita fold and thrust belt in Arkansas. The sandstones of the Mississippian Stanley Formation and the Pennsylvanian Jackfork Formation were the exploration objectives. The lack of significant hydrocarbons in the well appears to be attributed to two main parameters, seal and reservoir quality. Four sandstone cores yielded little to no porosity and well log porosities rarely exceed 2%. Open-hole log porosities rarely exceed more than 2%. Pressure solution and destructive diagenetic processes destroyed most of the primary porosity in the sandstones. Petrographic examination indicates that all existing sandstone porosity is probably related to dissolution of carbonate skeletal grains. Interbedded thin shale sequences (less than 150 ft) encountered in the well appear to be ineffective in blocking vertical hydrocarbon migration in the sandstones.

The upper 1,000 ft of the well contains channel fill characteristics that are best described as upper fan or uppermost mid-fan features. The interval of 1,000-4,000 ft is interpreted as a series of prograding, overlapping suprafans. Lower fan deposits are present from 4,000-5,300 ft. The 5,300-6,300 ft interval is interpreted as the distal portion of the lower fan.

Vitrinite reflectance values range from 2.0% at 217 ft (top of Jackfork Formation) to 3.0% at total depth of 6,765 ft (upper Stanley Shale). Both Jackfork and Stanley shales have qualified source rock intervals, with highest TOC values of 1.96% and 2.96%, respectively.

AAPG Search and Discover Article #90097 © 2009 Tulsa Geological Society, Tulsa, Oklahoma

 

 

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