Geology topics

Charles N. Threlkeld

Publications and source records attributed to Charles N. Threlkeld.

3 recordsLinked to original sources

USGS1989

Characterization and origin of natural gases of the Anadarko Basin

Natural-gas production in the Anadarko basin is from three geographically separated areas that can be differentiated by age of reservoir and by inferred nature of thermal origin of the gases. In the central basin, nonassociated gases are produced mainly from Upper Mississippian and Pennsylvanian sandstones. Gases become isotopically heavier (δ 13 C 1 values range from -49.8 to -33.2 ppt) and chemically drier (C 1 /C 1–5 values range from 0.74 to 0.99) with increasing level of thermal maturity. Gas samples are from depths as much as 21,600 ft. Gases were generated mainly from interbedded shales with type-III kerogen during the mature and postmature stages of hydrocarbon generation. Deviations from the trend are due to mixing and migration of gases generated at different levels of thermal maturity over the past 250 m.y. In the giant Panhandle-Hugoton field, nonassociated gases are generally produced from Permian carbonates at depths <3,000 ft. Gases display little compositional variation δ 13 C 1 values range from -46.4 to -39.9 ppt, C 1 /C 1–5 values range from 0.69 to 0.96). Because organic-rich, mature source rocks are not present in the area, gases probably were generated in the central basin from Pennsylvanian or older source rocks during the mature stage of hydrocarbon generation. This implies migration over distances as much as several hundred miles. In the Sooner trend, associated gases are produced from Silurian, Devonian, and Mississippian carbonates at depths as great as 9,600 ft and were generated from type-II kerogen during the mature stage of hydrocarbon generation. Associated oil correlates with extracts of the Upper Devonian and Lower Mississippian Woodford Shale. Gases are isotopically lighter (δ 13 C 1 values of -47.3 to -40.6 ppt) and chemically wetter (C 1 /C 1–5 values of 0.67 to 0.99) than those derived from type-III kerogen at an equivalent level of thermal maturity.

Oklahoma↗

USGS1984

Geochemistry of a naturally occurring massive marine gas hydrate

During Deep Sea Drilling Project (DSDP) Leg 84 a core 1 m long and 6 cm in diameter of massive gas hydrate was unexpectedly recovered at Site 570 in upper slope sediment of the Middle America Trench offshore of Guatemala. This core contained only 5–7% sediment, the remainder being the solid hydrate composed of gas and water. Samples of the gas hydrate were decomposed under controlled conditions in a closed container maintained at 4°C. Gas pressure increased and asymptotically approached the equilibrium decomposition pressure for an ideal methane hydrate, CH 4 .5-3/4H 2 O, of 3930 kPa and approached to this pressure after each time gas was released, until the gas hydrate was completely decomposed. The gas evolved during hydrate decomposition was 99.4% methane, ∼0.2% ethane, and ∼0.4% CO 2 . Hydrocarbons from propane to heptane were also present, but in concentrations of less than 100 p.p.m. The carbon-isotopic composition of methane was −41 to −44 permil(( 0 00 "> 000 ), relative to PDB standard. The observed volumetric methane/water ratio was 64 or 67, which indicates that before it was stored and analyzed, the gas hydrate probably had lost methane. The sample material used in the experiments was likely a mixture of methane hydrate and water ice. Formation of this massive gas hydrate probably involved the following processes: (i) upward migration of gas and its accumulation in a zone where conditions favored the growth of gas hydrates, (ii) continued, unusually rapid biological generation of methane, and (iii) release of gas from water solution as pressure decreased due to sea level lowering and tectonic uplift.

Middle America Trench↗

USGS1978

Analyses of natural gases from Gulf of Mexico Outer Continental Shelf

This report contains analyses and related source data for natural gas samples from 32 fields in the Gulf of Mexico OCS (Outer Continental Shelf). The interpretation of this data, along with analyses from other fields in Texas, is still in progress.

Gulf of Mexico Outer Continental Shelf↗