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J.L. Ridgley

Publications and source records attributed to J.L. Ridgley.

5 recordsLinked to original sources
USGS2013

Geology and oil and gas assessment of the Todilto Total Petroleum System, San Juan Basin Province, New Mexico and Colorado: Chapter 3 in Total petroleum systems and geologic assessment of undiscovered oil and gas resources in the San Juan Basin Province, exclusive of Paleozoic rocks, New Mexico and Colorado

Organic-rich, shaly limestone beds, which contain hydrocarbon source beds in the lower part of the Jurassic Todilto Limestone Member of the Wanakah Formation, and sandstone reservoirs in the overlying Jurassic Entrada Sandstone, compose the Todilto Total Petroleum System (TPS). Source rock facies of the Todilto Limestone were deposited in a combined marine-lacustrine depositional setting. Sandstone reservoirs in the Entrada Sandstone were deposited in eolian depositional environments. Oil in Todilto source beds was generated beginning in the middle Paleocene, about 63 million years ago, and maximum generation of oil occurred in the middle Eocene. In the northern part of the San Juan Basin, possible gas and condensate were generated in Todilto Limestone Member source beds until the middle Miocene. The migration distance of oil from the Todilto source beds into the underlying Entrada Sandstone reservoirs was short, probably within the dimensions of a single dune crest. Traps in the Entrada are mainly stratigraphic and diagenetic. Regional tilt of the strata to the northeast has influenced structural trapping of oil, but also allowed for later introduction of water. Subsequent hydrodynamic forces have influenced the repositioning of the oil in some reservoirs and flushing in others. Seals are mostly the anhydrite and limestone facies of the Todilto, which thin to as little as 10 ft over the crests of the dunes. The TPS contains only one assessment unit, the Entrada Sandstone Conventional Oil Assessment Unit (AU) (50220401). Only four of the eight oil fields producing from the Entrada met the 0.5 million barrels of oil minimum size used for this assessment. The AU was estimated at the mean to have potential additions to reserves of 2.32 million barrels of oil (MMBO), 5.56 billion cubic feet of natural gas (BCFG), and 0.22 million barrels of natural gas liquids (MMBNGL).

Colorado;New Mexico↗
USGS2013

Geology and oil and gas assessment of the Fruitland Total Petroleum System, San Juan Basin, New Mexico and Colorado: Chapter 6 in Geology and Oil and Gas Assessment of the Fruitland Total Petroleum System, San Juan Basin, New Mexico and Colorado

The Fruitland Total Petroleum System (TPS) of the San Juan Basin Province includes all genetically related hydrocarbons generated from coal beds and organic-rich shales in the Cretaceous Fruitland Formation. Coal beds are considered to be the primary source of the hydrocarbons. Potential reservoir rocks in the Fruitland TPS consist of the Upper Cretaceous Pictured Cliffs Sandstone, Fruitland Formation (both sandstone and coal beds), and the Farmington Sandstone Member of the Kirtland Formation, and the Tertiary Ojo Alamo Sandstone, and Animas, Nacimiento, and San Jose Formations. Analysis of the geochemistry of Fruitland coal-bed gas and co-produced water suggests that hydrocarbons in Fruitland coal beds began to form early in the depositional history of the Fruitland Formation with the generation of early microbial gas. Source rocks in the Fruitland entered the oil generation zone in the late Eocene and continued to generate minor oil and large quantities of thermogenic gas into middle Miocene time. Near the end of the Miocene, thermogenic hydrocarbon generation and subsidence in the San Juan Basin ceased, and the basin was uplifted and differentially eroded. Late-stage (secondary) microbial gas has been documented in Fruitland coal-bed reservoirs and was formed by microbial reduction of carbon dioxide during introduction of groundwater in the late Pliocene and Pleistocene. Most of this late-stage microbial gas is found just downdip from the northern, western, and southern Fruitland outcrops. The northern part of the Fruitland Formation is overpressured as a result of artesian conditions established in the Pliocene or Pleistocene. South and east of the overpressured area, the Fruitland is either normally pressured or underpressured. Four assessment units (AU) were defined in the Fruitland TPS. Of the four AUs, one consists of conventional gas accumulations and the other three are continuous-type gas accumulations: Tertiary Conventional Gas AU, Pictured Cliffs Continuous Gas AU, Basin Fruitland Coalbed Gas (CBG) AU, and Fruitland Fairway CBG AU. No oil resources that have the potential for additions to reserves in the next 30 years were estimated for this TPS. Gas resources that have the potential for additions to reserves in the next 30 years are estimated at a mean of 29.3 trillion cubic feet of gas (TCFG). Of this amount, 23.58 TCFG will come from coal-bed gas accumulations and 83.1 percent of this total is estimated to come from the Basin Fruitland CBG AU. The remaining 5.72 TCFG is allocated to continuous-type gas accumulations (5.64 TCFG) and conventional gas accumulations (0.08 TCFG). Although the Fruitland Fairway CBG AU has produced the most significant amount of coal-bed gas to date, the area of the AU is limited. New potentially productive wells will come from infill drilling, and the number of these wells will be limited by effective drainage area. Total natural gas liquids (NGL) that have the potential for additions to reserves in the next 30 years are estimated at a mean of 17.76 million barrels. Of this amount, 16.92 million barrels will come from the Pictured Cliffs Continuous Gas AU and the remainder from the Tertiary Conventional Gas AU.

Colorado;New Mexico↗
USGS2002

Unconventional shallow biogenic gas systems

Unconventional shallow biogenic gas falls into two distinct systems that have different attributes. Early-generation systems have blanketlike geometries, and gas generation begins soon after deposition of reservoir and source rocks. Late-generation systems have ringlike geometries, and long time intervals separate deposition of reservoir and source rocks from gas generation. For both types of systems, the gas is dominantly methane and is associated with source rocks that are not thermally mature. Early-generation biogenic gas systems are typified by production from low-permeability Cretaceous rocks in the northern Great Plains of Alberta, Saskatchewan, and Montana. The main area of production is on the southeastern margin of the Alberta basin and the northwestern margin of the Williston basin. The huge volume of Cretaceous rocks has a generalized regional pattern of thick, non-marine, coarse clastics to the west and thinner, finer grained marine lithologies to the east. Reservoir rocks in the lower part tend to be finer grained and have lower porosity and permeability than those in the upper part. Similarly, source beds in the units have higher values of total organic carbon. Patterns of erosion, deposition, deformation, and production in both the upper and lower units are related to the geometry of lineament-bounded basement blocks. Geochemical studies show that gas and coproduced water are in equilibrium and that the fluids are relatively old, namely, as much as 66 Ma. Other examples of early-generation systems include Cretaceous clastic reservoirs on the southwestern margin of Williston basin and chalks on the eastern margin of the Denver basin. Late-generation biogenic gas systems have as an archetype the Devonian Antrim Shale on the northern margin of the Michigan basin. Reservoir rocks are fractured, organic-rich black shales that also serve as source rocks. Although fractures are important for production, the relationships to specific geologic structures are not clear. Large quantities of water are coproduced with the gas, and geochemical data indicate that the water is fairly fresh and relatively young. Current thinking holds that biogenic gas was generated, and perhaps continues to be, when glacial meltwater descended into the plumbing system provided by fractures. Other examples of late-generation systems include the Devonian New Albany Shale on the eastern margin of the Illinois basin and the Tertiary coalbed methane production on the northwestern margin of the Powder River basin. Both types of biogenic gas systems have a similar resource development history. Initially, little technology is used, and gas is consumed locally; eventually, sweet spots are exploited, widespread unconventional reservoirs are developed, and transport of gas is interstate or international. However, drilling and completion techniques are very different between the two types of systems. Early-generation systems have water-sensitive reservoir rocks, and consequently water is avoided or minimized in drilling and completion. In contrast, water is an important constituent of late-generation systems; gas production is closely tied to dewatering the system during production. Existing production and resource estimates generally range from 10 to 100 tcf for both types of biogenic gas systems. Although both system types are examples of relatively continuous accumulations, the geologic frameworks constrain most-economic production to large geologic structures on the margins of basins. Shallow biogenic gas systems hold important resources to meet the increased domestic and international demands for natural gas.

American Association of Petroleum Geologists Bulle↗