Natural hydraulic fracturing example, North Sea

Exploring for Oil and Gas Traps
Series	Treatise in Petroleum Geology
Part	Predicting the occurrence of oil and gas traps
Chapter	Evaluating top and fault seal
Author	Grant M. Skerlec
Link	Web page
Store	AAPG Store

Trap description

A trap in the Central Graben, North Sea, appears to have been bled dry by natural hydraulic fracturing. This trap is a low-relief salt structure with a dry hole and has less-than-sufficient strain to fracture the top seal.

Evidence

Evidence for hydraulic fracturing and seal rupture include the following:

• A fossil oil—water contact exists at the synclinal spill point of the trap. The trap was once filled with hydrocarbon, but something happened after trap fill to bleed off hydrocarbons.
• Hydrocarbon shows exist throughout the sediment column above the reservoir. These hydrocarbons are direct evidence of a breached top seal.
• The pore pressure is close to the theoretical fracture pressure. In adjacent fields, the pore pressure is significantly less than P_f.
• Cores show vertical, open extension fractures rather than the more common shear fractures found in adjacent fields. These fractures are identical to fractures produced by hydraulic fracturing.

Figure 10-44 shows that the pore pressure is close to the fracture pressure at the base of the top seal (approximately depth::1300 ft). The pore pressure is inferred from mud weight and RFT measurements (solid dots). Leak-off tests (LOT) help constrain the fracture pressure. The fracture pressure is close to the lithostatic pressure or overburden pressure.

Figure 10-44 . Copyright: Esso Exploration and Production, U.K.

See also

• Overpressure and natural hydraulic fracturing
• Natural hydraulic fracturing of top seals
• Fracture threshold in the real world
• Overpressure and hydrocarbon distribution, gulf coast

External links

find literature about Natural hydraulic fracturing example, North Sea

• Original content in Datapages
• Find the book in the AAPG Store