Petroleum Geologyand the Permian Basin Andrew McCarthy Concho Resources
Petroleum System • Source: organic-rich mudrock • Heat (burial) and time • Reservoir: porous rock • Seal: low-permeability rock • Trap
Source 3,850,000 EJ burial Sol (our sun) Fusion (of hydrogen and helium) 3,000 EJ Earth 3,850,000 exajoules per year – Solar radiation 3,000 exajoules per year – captured by plant life 500exajoules per year – total human use (fossil, nuclear, etc.)
Source Shale: high organic material Gas (methane, ethane, propane) H2S CO2 N2 + Kerogen Heat and pressure Kerogen: geo-plastic or geo-chocolate. Lipids, proteins, carbohydrates Texas tea (light, sweet crude)
How much heat? • Low temps yield nothing: <60 C • High temps yield oil: 60C-120+C • Higher temps yield gas: 120+C
100% natural and organic Yummy! • Oil is 100% natural and organic • 95%++ of all oil ever generated has been naturally leaked to the surface • Millions of natural oil seeps exist around the planet, many under the oceans Natural Oil seeps (BP not Involved) Not Iced tea
An oil reservoir at the surface Oil reservoirs are exposed and eroded away. The light oil is biodegraded, tar remains.
OK. So far we have: • Source • Heat and time • Now we need a reservoir, a seal, and maybe a trap
Reservoir The first key to a reservoir rock is porosity intergranular fracture
Reservoir The second key to a reservoir rock is permeability
Seal We need something to slow the upward migration of oil and gas. A seal will do: it’s a layer of very low permeability. Microscopic view of clay layers Imagine if this were clay…
Traps Required for conventional reservoirs…
A very conventional petroleum system: Concho oil sealing shale sand organic shale
Today: Unconventional plays Tight carbonate (seal/frac barrier) Organic mudstone, silty shale, with varying carbonate and silica content 1 source 2 reservoir 3 seal Tight carbonate (seal/frac barrier)
Today Active petroleum systems
Basins Low areas; tend to fill with sediment Typically covered with water (ocean, sea or lake) Nature’s landfill Rivers Coral reefs Wind blown basin Pelagic rain deep basin slope shelf
Before the Permian Basin • Shales: Devonian Mississippian Barnett • Before 370 Ma (Devonian) Ron Blakey, Colorado Plateau Geosystems, Inc.
Early Permian Basin • 315 Ma • Late Miss/Early Penn time • Shale deposition Ron Blakey, Colorado Plateau Geosystems, Inc.
Late Permian • 255 Ma • Carbonates (shallow marine carb factory) • Later, evaporites Ron Blakey, Colorado Plateau Geosystems, Inc.
Sources Organic-rich shales
Reservoirs *Just about everything! carbonates sands Shale/silt
What does a geologist do? • Exploration very little data! • Seismic, basin geochem, remote sensing • Everything changes with the first well • Development increasing amounts of data! • Well logs, core, production data • Operations • Day-to-day drilling • When do we have “the answer”?