Emission estimates for the Coal Oil Point Seep Field
1. Seep gas discharge is on the order of 100,000 m3/day estimated by calibrated sonar methods and direct gas capture. Range of values is 100,000 to 200,000 m3/day. Field area is approximately 18 km2, including seep area of approximately 3 km2.
2. At sea surface the gas is approximately 30% air and 70% hydrocarbons including mostly methane, ethane and propane and smaller amounts of higher hydrocarbons.
3. Oil seepage is estimated at 100 bbl/day based on prior work of others and by our research group; high estimate is 170 bbl/day.
4. Gas seepage around Platform Holly and gas captured by the Seep Tents (see maps) has decreased 50% or more since 1989.
5. Subsurface reservoir pressure in the oil reservoir tapped by wells on Platform Holly has decreased over past 30 years and leveled off in past few years. This drop is pressure may explain the drop in seepage around the platform.
6. Reactive Organic Gas (ROG) emissions from the seeps include propane, butane and higher hydrocarbons. These gasses are precursors to air polluting ozone. ROG emissions from the gas seepage are estimated at 11 metric tons/day. ROG emissions from the seep oil are estimated at 8 metric tons/day. The total amount (19 tons/day) is approximately equal to ROGs emitted from vehicle exhaust in Santa Barbara County each day.
7. About 40 metric tons of methane gas is emitted daily from the seep field.