Structural Styles of Eocene Jackson and Oligocene Vicksburg Formations within the Rio Grande and Houston Embayments near the San Marcos Arch, Refugio and Calhoun Counties, South Texas Gulf Coast Osareni C. Ogiesoba and Angela K. Eluwa Bureau of Economic Geology, University of Texas at Austin, 10100 Burnet Rd., Austin Texas 78759 GCAGS Explore & Discover Article #00374 * http://www.gcags.org/exploreanddiscover/2018/00374_ogiesoba_and_eluwa.pdf Posted September 29, 2018. * Article based on a full paper published in the GCAGS Transactions (see footnote reference below), which is available as part of the entire 2018 GCAGS Transactions volume via the GCAGS Bookstore at the Bureau of Economic Geology (www.beg.utexas.edu) or as an individual document via AAPG Datapages, Inc. (www.datapages.com), and delivered as an oral presentation at the 68th Annual GCAGS Convention and 65th Annual GCSSEPM Meeting in Shreveport, Louisiana, September 30 October 2, 2018. ABSTRACT This paper presents structural styles associated with Eocene Jackson and Oligocene Vicksburg formations in the vicinity of the San Marcos Arch within the Rio Grande and Houston embayments of the South Texas Gulf Coast. Previous studies that focused on the Rio Grande Embayment documented structural styles that include coastperpendicular faults, diapiric shale, and subbasins. Present work involves mapping the structural styles in the Houston Embayment and comparing the deformation pattern in both basins using 3D seismic data from four different surveys. Two of the seismic surveys (surveys #1 and #2) are located in Refugio County in the Rio Grande Embayment. The other two are located in the Houston Embayment one (survey #3) within Calhoun County, and the other (survey #4) straddling Calhoun and Jackson counties and Matagorda Bay. Methods of investigation consist of seismic interpretation, 3D visualization, and seismic-attribute extraction. Our investigation shows that although the studied areas within the Rio Grande and Houston embayments are separated by ~40 55 km (~25 34 mi), and although both basins have been affected by extensional tectonic forces, deformational patterns of strata on either side of the San Marcos Arch are different. In the Rio Grande Embayment, in addition to coast-parallel synthetic and antithetic faults, structural styles also include a northwest-southeast-trending curvilinear anticline, and prominent coast-orthogonal faults and shale ridges. However, in the Houston Embayment, the dominant structural style consists of coast-parallel synthetic growth faults and shale diapirs. Originally published as: Ogiesoba, O. C., and A. K. Eluwa, 2018, Structural Styles of Eocene Jackson and Oligocene Vicksberg formations within the Rio Grande and Houston embayments near the San Marcos Arch, Refugio and Calhoun counties, South Texas Gulf Coast: Gulf Coast Association of Geological Societies Transactions, v. 68, p. 357 370. 1
Structural Styles of Eocene-Jackson and Oligocene-Vicksburg Formations within the Rio Grande and Houston Embayments near the San Marcos Arch, in Refugio and Calhoun Counties, South Texas Gulf Coast Osareni Ogiesoba and Angela Eluwa Bureau of Economic Geology, The University of Texas at Austin
Objective Previous work by Ogiesoba and Hernandez (2015) showed that in addition to the synthetic and antithetic growth faults, the dominant structural features in the Rio Grande in the vicinity of the San Marcos Arch are coast-orthogonal shale ridges, sub-basins, and coastorthogonal faults. Our current work builds on Ogiesoba and Hernandez (2015) work by extending the previous interpretation into the Victoria County and the Houston Embayment in the vicinity of the San Marcos Arch. Our objective is to determine the similarity between the deformational pattern in the Vicksburg Formation within the Rio Grande and the Houston Embayments in the vicinity of the San Marcos Arch.
Overview Review of previous work in the area Present work: Location of study area and database Interpretation method Results Summary and Conclusions
Previous Work: San Marcos Arch, Rio Grande, and Houston Embayments 1. Culotta et al. (1992), published results of the COCORP (Consortium for Continental Reflection Profiling) San Marcos Arch survey a single 2D seismic line, composed of 3 segments and covering a distance of 250 kilometers from Port Lavaca on the central Texas coast to the southeastern side of the Llano Uplift. 2. Coleman and Galloway (1990), discussed oil and gas fields within the Vicksburg Formation in the Rio Grande and Houston Embayments and in the vicinity of the San Marcos Arch. 3. Ogiesoba and Hernandez (2015), discussed coast-orthogonal shale ridges and sub-basins in the Rio Grande Embayment in the vicinity of the San Marcos Arch axis.
Previous work: Culotta et al., 1992--COCORP San Marcos Arch Survey Benton Uplift Llano Uplift Sabine Arch Monroe Arch Devils River Uplift Rio Grande Embayment Gulf of Mexico Modified after Culotta et al., 1992
Previous work: Culotta et al., 1992--COCORP Line TX6 TX5 TX4 V.E. = 3x V.E. = 4x Modified after Culotta et al., 1992 Luling Uplift? Depth (km) Precambrian Grenville Bend Data Gap Diapir? TX6 Depth (km) Two-way time (s) Bend
Previous work: Coleman and Galloway (1990) Modified after Coleman and Galloway (1990) 42 g o Gas field Oil field Oil and gas field Upper Vicksburg production Lower Vicksburg production Seismic line Field location number > 1,000,000 MCFG cumulative production > 1,000,000 MCFG cumulative production
Present Work: Study Area and Database 200,000 600,000 1,000,000-600,000-200,000 0 0 500,000 ft A Refugio Co. Victoria Co. G A G TX4 B D F H C D C F H B Calhoun Co. 1,600,000 2,000,000 2,400,000 2,800,000 20 km
Present Work: Interpretation Method Perform well-to-seismic tie and identify key stratigraphic horizons Track horizons using auto-dip mode where data quality is good; and point-to-point mode where data quality is fair to poor In surveys #3 and #4 where drilled wells did not penetrate the Vicksburg Formation, top Vicksburg is recognized by identifying the first major unconformity surface below Frio Formation onto which lower Frio strata downlap by employing seismic stratigraphic principles Use 3D visualization tool to display mapped horizons in 3D and observe shale ridges and valleys
Well J 1.0 Well D Well A A A TF Sonic log 1.5 TV TJ 2.5 TWT (s) F-CV Frio F-HB GR log Refugio Co. A 3.0 TD Survey #2 is ~8 km (10 km) southwest of the arch 3.5 4.0 +ve 4.5 Jackson? Vicksburg 2.0 TD TD A W Survey #1 Miocene Seismic Interpretation Results SESW EW Survey #2 5.0 km -ve 20 km SE
TWT (s) 1.5 2.0 3.0 4.0 5.0 5.5 6.0 Seismic Interpretation Results B South Miocene +ve -ve GR log SP log Shale-prone sediments 5.0 km Well K B Resistivity log Fault F-U orth Vicksburg? Frio Anahuac Shale 20 km Calhoun Co. B B Well K Total Depth (TD): ~14,780 feet (~4,500 m) Survey #4 ~37 km (~40 km) northeast of the arch axis
H Survey #3 2.0 Miocene F Survey #4 F F H Calhoun Co. 4.0 Shale-prone strata Vicksburg? Shale-prone strata Vicksburg? TWT (s) 3.0 5.0 +ve 5.5 6.0 F Frio H Anahuac Shale Miocene H -ve 5.0 km SE W -ve +ve 5.0 km W Frio 1.5 Anahuac Shale Seismic Interpretation Results 20 km SE
Seismic Interpretation Results 2.0 C C Survey #3 Miocene D D Anahuac Shale 1.5 Survey #4 C D D C Shale-prone strata Vicksburg? TWT (s) Shale-prone strata Calhoun Co. Frio Fault-A 3.0 4.0 5.0 5.5 6.0 SW Survey #4 ~37 km (~40 km) northeast of the arch axis 5.0 km E SW Survey #3 ~22 km (~20 +ve km) northeast of the arch axis -ve 20 km E
Results: Map at Top Vicksburg in survey #1 1380 2010 South curvilinear anticline Well J orth curvilinear anticline 5.0 km
Results: Map at Top Vicksburg in survey #2 1980 G Fault F-HB SD 1 SB 1 2960 SB 4 Synthetic faults SD 2 Synthetic faults SD 3 SB 3 Well A Well D SB 2 Coast-orthogonal fault Coast-orthogonal fault G SD 4 Coast-orthogonal fault 5.0 km
Seismic Interpretation Results: Cross Section Line G G Well D G G Sonic log GR log 1.0 Miocene 0.5 Anahuac Shale Frio G 2.5 Refugio Co. Jackson? Vicksburg TWT (s) 2.0 G 3.0 3.5 +ve 4.0 4.5 SB 4 SW SB 3 2.0 km SB 2 -ve 20 km Survey #2: ~8 km (10 km) southwest of the arch SB 1 E San Marcos Arch Axis 1.5
Results: Map at Top Vicksburg in surveys #3 and #4 3760 Survey #4 3850 Survey #3 5030 4400 Well M Survey #4: ~3.7 km east of survey #3 5.0 km Houston Embayment
Seismic Interpretation Results: Cross Section Line K K TWT (s) 1.5 2.0 3.0 4.0 5.0 5.5 6.0 K SP log Shale-prone strata W Well M +ve -ve Miocene Resistivity log Refugio Co. Poor data/ Shale-prone? 5.0 km K Victoria Co. SE Vicksburg? Frio Anahuac Shale Calhoun Co. Well Total Depth (TD) ~13,300 feet (~4,050 m) 20 km K From Blue Arrow to TD, Shale zone is ~750 feet (~230 m) Resistivity dropped rapidly to ~ 0 (OHMM) Conductivity increased to maximum ~ 2000 (MMHO) Suggesting overpressured shale K
Results: Comparison of COCORP TX4 and Seismic Line H--H 1.0 W COCORP LIE TX4 B1 Ranch SE TX4 1.0 H H 2.0 H TWT (s) 2.0 Anahuac Shale H Victoria Co. Frio Calhoun Co. 3.0 3.0 Refugio Co. Diapir? Vicksburg? 4.0 Growth Faults Shale prone stata 4.0 Culotta et al., 1992 +ve 5.0 20 km 5.5 W 5.0 km -ve SE
Results: Map at Top Vicksburg in surveys #1 through #4 3760 Survey #4 1380 Well M 1980 5030 3850 2010 Survey #3 2960 4400 Houston Embayment Survey #1 Survey #2 Rio Grande embayment 20 km
3D Display of Map at Top Vicksburg in Surveys 1 & 2 1380 2010 1980 Survey #1 Synthetic faults SD 3 SB 4 SD 2 SD 1 SB 3 SB 2 SB 1 Coast-orthogonal fault 2960 Survey #2 Coast-orthogonal fault SD 4 Coast-orthogonal fault 10.0 km V.E: 11 : 1
3D Display of Map at Top Vicksburg in Survey 3 Well M 3760 5030 10.0 km V.E: 13.6 : 1
3D Display of Map at Top Vicksburg in Surveys 3 & 4 Well M Survey #4 Survey #3 3760 5030 3850 10.0 km V.E: 11 : 1 4400
3D Display of Map at Top Vicksburg in Surveys 1 thru 4 3760 Survey #4 1380 2010 1980 2960 5030 Survey #3 3850 4400 Survey #1 Survey #2 20 km V.E: 11 : 1
Summary & Conclusions In the Rio Grande, in addition to the synthetic and antithetic faults, the dominant structural style includes prominent alternating coast-orthogonal shale ridges, sub-basins, and coast-orthogonal faults. In contrast, in the Houston Embayment, the dominant structural styles are synthetic faults and coast-parallel sub-basins and coast-parallel shale ridges. Antithetic faults are few to none. In the Houston Embayment, top Vicksburg is deeper (4,600 5,850 m), and appears to be more deformed than it is in the Rio Grande Embayment, where it occurs at about 1,550 3,380 m. The severity of deformation increases with nearness to the axis of the San Marcos arch. Finally, although the prevailing mechanisms of deformation in both basins were extensional tectonics, strata deformational pattern in each basin are different.
Acknowledgments Landmark Graphics T. C. Oil eumin Exploration Brigham Exploration (now part of Statoil)