GEOLOGICAL SURVEY CIRCULAR 800 Geological Studies of the COST GE-1 Well, United States South Atlantic Outer Continental Shelf Area Geological Studies of the COST GE-1 Well, United States South Atlantic Outer Continental Shelf Area By Peter A. Scholle, Editor GEOLOGICAL SURVEY CIRCULAR 800 1979 United States Department of the Interior CECIL D. ANDRUS, Secretary Geological Survey H. William Menard, Director Use of brand names in this report is for descriptive purposes only and does not constitute endorsement by the U.S. Geological Survey. Free on application to Branch of Distribution, U.S. Geological Survey, 1200 South Eads Street, Arlington, VA 22202 CONTENTS Page Abstract 1 Introduction 1 Acknowledgments 3 Geologic setting, by William P. Dillon, Kirn D. Klitgord, and Charles K. Paull 4 Regional stratigraphy and structure of the Southeast Georgia Embayment, by Page C. Valentine 7 Data summary and petroleum potential, by Peter A. Scholle 18 Lithologic descriptions, by E. C. Rhodehamel 24 Petrophysical summary, by E. K. Simonis 37 Petrographic summary, by Robert B. Halley ,- 42 Foraminiferal biostratigraphy, paleoecology, and sediment accumulation rates, by C. Wylie Poag and Raymond E. Hall 49 Calcareous nannofossil biostratigraphy and paleoenvironmental interpretation, by Page C. Valentine 64 Radiometric age determinations, by E. K. Simonis 71 Geothermal gradients, by E. I. Robbins 72 Organic geochemistry, by R. E. Miller, D. M. Schultz, G. E. Claypool, M. A. Smith, H. E. Lerch, D. Ligon, C. Gary, and D. K. Owings 74 Geophysical studies, by R. C. Anderson and D. J. Taylor 93 Structure of the Continental Margin near the COST No. GE-1 drill site from a common-depth- point seismic-reflection profile, by William P. Dillon, Charles K. Paull, Alfred G. Dahl, and William C. Patterson 97 Conclusions 108 References cited 109 ILLUSTRATIONS Page Figure 1, Locality map 2 2. Regional geologic and bathymetric features in relation to the COST No. GE-1 well, other wells, and USGS seismic line TD-5 5 3- Location of wells, cross-sections lines, and structural features of the Southeast Georgia Embayment ° 4. Section XX' through offshore Southeast Georgia Embayment 9 5. Section YX' through Southeast Georgia Embayment 12 6. Sections YY" and ZZ' through Southeast Georgia Embaymentr 14 7. Generalized lithologies and depositional environments for COST No. GE-1 well 19 8. Porosity and permeability data as a function of depth 21 9. Comparison of various measures of thermal maturity as a function of depth 22 10. Lithologic log 25 11. Porosities of conventional and sidewall cores 39 12. Permeabilities of conventional and sidewall cores 40 13. Core porosities as related to core permeabilities 41 14- Photomicrograph of chalk 45 15. Photomicrograph of chalk 45 16. Photomicrograph of calcareous shale 45 17. Porosity depth relations of chalks in COST No. GE-1 well compared with other chalks 46 Page 18-25. Photomicrographs: 18. Oolite 47 19. Oolite 47 20. Moldic porosity in blocky calcite cement 47 21. Oomoldic porosity 47 22. Fine-grained arkose 48 23. Medium-grained arkose 48 24. Quartz ite 48 25. Volcanic rock (trachyte) 48 26. Biostratigraphic column for Albian through Pleistocene rocks 50 27. Paleoecological dip section of Cenozoic rocks, Southeast Georgia Embayment 52 28. Paleobathymetry, accumulation rates, and subsidence rates of rocks in the COST No. GE-1 well 58 29. Sediment accumulation rate curve for COST No. GE-1 well 59 30. Comparison of Cenozoic sediment accumulation rates at COST No. GE-1 well and nearby core holes 60 31. Diagrammatic examples of subsidence rate calculations 61 32. Temperature data for the COST No. GE-1 well 73 33. Gas-chromatographic analyses of saturated hydrocarbons of Tertiary rocks 79 34. Gas-chromatographic analysis of saturated hydrocarbons of Tertiary and Upper Cretaceous rocks 80 35. Gas-chromatographic analyses of saturated hydrocarbons of Upper and Lower Cretaceous rocks 82 36. Summary and comparison of organic-richness analyses of samples from the COST No. GE-1 well 84 37- Gas-chromatographic analyses of mud drilling additives, COST No. GE-1 well 85 38. Gas-chromatographic analyses of unfractionated sediment samples, COST No. GE-1 well 86 39. Summary profiles of types of organic matter present in the COST No. GE-1 well 88 40. Maturity profiles of organic matter from the COST No. GE-1 well 89 41. Summary of light-hydrocarbon analyses from the COST No. GE-1 well 90 42. One-dimensional synthetic seismograms derived from the COST No. GE-1 well transit- t ime curve 94 43. Two-way vertical travel time as a function of depth in the COST No. GE-1 well 96 44. Interval velocity, average velocity, and root-mean-square velocity as a function of vertical two-way travel time, COST No. GE-1 well 96 45. Line drawing interpretation and depth section of USGS seismic profile TD5 across Southeast Georgia Embayment 98 46-49. Photographs: 46. Section of seismic profile through COST No. GE-1 well drillsite to upper Florida-Hatteras Slope 100 47. Section of seismic profile across lower Florida-Hatteras Slope and inner Blake Plateau 101 48. Section of seismic profile showing outer Blake Plateau and inner Blake Spur 103 49. Section of seismic profile showing outer Blake Spur and western Blake Basin 104 TABLES Table 1. Comparison of biostratigraphic analyses from the COST No. GE-1 well 20 2. Porosity and permeability values from conventional cores of the COST No. GE-1 well- 37 3. Porosity and permeability values from sidewall cores of the COST No. GE-1 well 38 4. Petrography of carbonate rocks from the COST No. GE-1 well 43 5. Petrography of clastic terrigenous, metasedimentary, metamorphic, and metamorphosed volcanic rocks from the COST No. GE-1 well 44 6. Calcareous nannofossil biostratigraphy of the COST No. GE-1 well 65 7. Rb-Sr whole-rock analyses from the COST No. GE-1 well 71 8. Circum-Atlantic offshore geothermal gradients 72 9. Lithologic descriptions of samples used for organic geochemical analyses 76 10. Organic-carbon and thermal-evolution analyses for the COST No. GE-1 well 77 11. Organic carbon and extractable organic matter, COST No. GE-1 well 78 12. Velocity data from the COST No. GE-1 well- 95 Geological Studies of the COST No. GE-1 Well, United States South-Atlantic Outer Continental Shelf area By Peter A. Scholle, Editor ABSTRACT hydrocarbons, is thermally immature, and has a very poor source-rock potential. The interval The COST No. GE-1 well is the first deep from 3,600 to 5,900 ft (1,100 to 1,800 m) has a stratigraphic test to be drilled in the southern high content of marine organic matter but part of the U.S. Atlantic Outer Continental appears to be thermally immature. Where buried Shelf (AOCS) area. The well was drilled within more deeply, this interval may have significant the Southeast Georgia Embayment to a total depth potential as an oil source. The section from of 13,254 ft (4,040 m). It penetrated a section 5,900 to 8,850 ft (1,800 to 2,700 m) has composed largely of chalky limestones to a depth geochemical characteristics indicative of a poor of about 3,300 ft (1,000 m) below the drill oil source rock and is thermally immature. platform. Limestones and calcareous shales with Rocks below this depth, although they may be some dolomite predominate between 3,300 and marginally to fully mature, are virtually barren 7,200 ft (1,000 and 2,200 m), whereas of organic matter and thus have little or no interbedded sandstones and shales are dominant source-rock potential. Therefore, despite the from 7,200 to 11,000 ft (2,200 to 3,350 m). thermal immaturity of the overall section, the From 11,000 ft (3,350 m) to the bottom, the upper half of the sedimentary section penetrated section consists of highly indurated to weakly in the well shows the greatest petroleum source metamorphosed pelitic sedimentary rocks and potential. meta-igneous flows or intrusives. Biostrati- graphic examination has shown that the section INTRODUCTION down to approximately 3,500 ft (1,060 m) is Tertiary, the interval from 3,500 to 5,900 ft Until the completion of the COST No. GE-1 (1,060 to 1,800 m) is Upper Cretaceous, and the well, all information on the stratigraphic section from 5,900 to 11,000 ft (1,800 to 3,350 framework of the Southeast Georgia Embayment had m) is apparently Lower Cretaceous. The come from onshore wells, offshore bottom indurated to weakly metamorphosed section below sampling or shallow coring, geophysical surveys, 11,000 ft (3,350 m) is barren of fauna or flora or extrapolation from the COST No. B-2 well but is presumed to be Paleozoic based on (Scholle, 1977b) located more than 750 mi (1,200 radiometric age determinations. Rocks deposited km) north of the GE-1 drill site. Between at upper-slope water depths were encountered in February 22 and May 31, 1977, however, the first the Upper Cretaceous, Oligocene, and Miocene deep stratigraphic test was drilled in the parts of the section. All other units were southern portion of the U.S. Atlantic Outer deposited in outer-shelf to terrestrial environ­ Continental Shelf (AOCS) by the Ocean Production ments . Company acting as operator for a group of 25 Examination of cores, well cuttings, and original participating companies, the Conti­ electric logs shows that potential hydrocarbon- nental Offshore Stratigraphic Test (COST) reservoir units are present within the chalks in Group. This hole, designated the COST No. GE-1 the uppermost part of the section as well as in well, was drilled on the outer part of the sandstone beds to a depth of at least 10,000 ft Continental Shelf about 74 mi (119 km) east of (3,000 m).