Strain analysis of top seals
Loss of top seal integrity by high strain and fracturing is an important cause of dry holes and partially filled traps.[1][2] Although fracturing is commonly predicted from stress, the advantage of strain analysis is that it provides a practical tool prior to drilling for evaluating prospects using seismic data.
Rates of leakage[edit]
Even a small amount of fracturing can result in staggering leakage rates. The volume of hydrocarbon that could be lost from a typical North Sea field, assuming a fractured top seal with a relatively low fracture permeability of only 0.05 md, is more than 100 billion bbl/m.y..[2]). Fracture permeability can be as high as tens of darcys ([3] and leakage rates consequently can be much higher.
Natural seeps confirm these high rates of hydrocarbon loss. The Palos Verde fault in Santa Monica Bay, California, seeps oil at the rate of 10–15 bbl/d or more than 5 billion bbl/m.y. The Coal Point seep in the Santa Barbara Channel, California, is leaking 50–70 bbl/d or more than 25 billion bbl/m.y.[4]
See also[edit]
- Seal ductility
- Estimating ductility of top seals
- Estimating strain in top seals
- Example: evaluating top seal integrity
References[edit]
- ↑ Skerlec, G., M., 1982, Risking top seals in the Central Graben: Exxon Production Research Company internal report.
- ↑ 2.0 2.1 Skerlec, G., M., 1990, SEALS: A short course for risking top seal and fault seal: Franklin, Pennsylvania, SEALS International, 600 p.
- ↑ Stearns, D., W., Friedman, M., 1972, Reservoirs in fractured rock: AAPG Memoir 16, p. 82–106.
- ↑ Wilkinson, E., R., 1971, California offshore oil and gas seeps: California Oil Fields–Summary Operations, vol. 57, no. 1, p. 5–28.
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