Reservoir Petrology of Analogous Middle Jurassic Sandstones from Haltenbanken, Norway, and Jameson Land, East Greenland
Chris J. Cheatwood, Charles F. Mansfield
Stratigraphically equivalent Middle Jurassic sandstones from wells in the Haltenbanken area, offshore Norway, and outcrops in Jameson Land, east Greenland, are petrographically similar. Both are subarkosic and display similar diagenetic features, notably well-developed secondary porosity.
The well-exposed Jurassic strata of east Greenland provided effective depositional and stratigraphic models for the prolific oil fields of the North Sea and Norwegian shelf, because sediments were deposited in closely related tectono-stratigraphic settings. Conversely, the productive Middle Jurassic sandstones of the North Sea and Norwegian shelf suggest analogous reservoirs should occur on the east Greenland shelf.
Potential reservoir sandstones of east Greenland are moderately to well sorted and fine to medium grained, with porosity ranging from 10 to 30%. Much of the porosity is secondary, created by the dissolution of framework grains and carbonate cements. The pores are commonly oversize, elongated, and bridged by clusters of sutured quartz grains. Pore throats are large, suggesting high reservoir permeability.
Two types of nonreservoir sandstones are observed: (1) slightly finer grained versions of the reservoir sandstones that are tightly cemented by up to 40 vol. % carbonate cement and smaller amounts of authigenic kaolinite, and (2) fine-grained sandstones rich in micrite lithic fragments (rip-ups) and detrital micas. The variation of porosity with grain size implies influence by original porosity and permeability that is ultimately controlled by depositional environment.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.