Fracture permeability and high initial water cut in a carbonate gas reservoir

Conference · Fri Feb 01 04:00:00 EST 1985 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:5783139

Major, R P

Waveland field in Hancock County, Mississippi, produces gas and condensate from the Lower Cretaceous Mooringsport Formation at approximately 13,400 ft. Total gas reserves have been estimated at 256 bcf. The reservoir is a fractured lime packstone, containing milliolid and orbitolinid foraminifers, mollusk fragments, and echinoderms. Core plug permeability is low, commonly below 1 md, yet productive wells flow at rates of as much as 8000 MCFGD. Short-term flow tests can be misleading, as productive wells may initially produce an uneconomically high water cut for several days. The trap is a south-southwest-plunging anticline with no apparent structural closure to the north. A map of averaged, thickness-weighted porosity values for productive stratigraphic intervals indicates that porosity does not decrease across the northern limit of production. In order to compare the productivity potential of zones with varying porosity and water saturation, Buckles Numbers (product of porosity and water saturation) were mapped for zones within the productive stratigraphic interval. Averaged, thickness-weighted Buckles Numbers indicate that productivity potential does not decline across the northern limit of the field. Thus, it is concluded that the northern (updip) extent of effective fracture permeability controls the northern limit of production at Waveland field. High initial water cut indicates that water is in the fractures and gas and water are in the matrix. The presence of water in fractures adjacent to rock with much narrower effective pore-throat radii is a normally unstable situation, as capillary pressure would be expected to result in the matrix imbibing water and releasing gas to the fractures. It is proposed that fracturing occurred after hydrocarbon migration and that there is little or no fluid exchange between fractures and matrix prior to wellbore drawdown.

• Research Organization: Univ. of Colorado, Denver
• OSTI ID: 5783139
• Report Number(s): CONF-850322-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 69:2
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200* -- Natural Gas-- Reserves
Geology
& Exploration
CRETACEOUS PERIOD
FEDERAL REGION IV
GAS CONDENSATE FIELDS
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGY
MESOZOIC ERA
MINERAL RESOURCES
MISSISSIPPI
NATURAL GAS DEPOSITS
NORTH AMERICA
PERMEABILITY
PETROLEUM DEPOSITS
RESERVOIR ROCK
RESOURCES
STRATIGRAPHY
USA