Event Description

HYDROCARBONS ASSOCIATED WITH IGNEOUS ROCKS

Explorationists generally disregard igneous rocks and their immediate environs, condemning the surrounding sediments as overmature and the igneous rocks themselves as nonporous crystalline masses. However, these are misconceptions, and there is opportunity in moving beyond them. The direct maturation effect of igneous activity is often overrated. Most shallow igneous intrusions are too small to affect a large volume of rock; even thick piles of flood basalts cool too quickly to have a marked effect. Most thermal effects are due to regional heating or hydrothermal circulation.

Porosity in igneous rocks may be due to fracturing, particularly fracturing developed during cooling. Some extrusive rocks are also vesicular or may have a clastic texture, especially airfall or hyaloclastic rocks. Retrograde metamorphism may provide significant porosity by creating what is essentially vuggy texture.

Igneous rocks can also provide their own traps. Variations in porosity can produce a pseudo-stratigraphic trap. However, thick intrusive bodies (such as laccoliths and plugs) and volcanic cones can also provide trapping structures. Dikes can block migration pathways. Syndepositional sedimentary and igneous facies may also provide traps, as well as post-emplacement draping over noncompacting igneous bodies.

Exploration methods need to be as variable as the igneous reservoirs. Seismic expression is frequently ambiguous. Some igneous rocks contain abundant iron, and have strong magnetic signatures; others do not. Notably, one of the earliest plays in Texas, the "serpentine" trend, was instrumental in developing many of the early geophysical techniques. Likewise, log results may be so variable as to be nondiagnostic. Some features may be recognizable, but the nature of the igneous rocks and their relationships must be considered.

Due to the lack of "rules" and systematic study, the best available approach to exploration in and around igneous rocks is to look for analogs. The search for analogs cannot be limited to one area or continent; a global view is needed. Analogs from around the world have applicability to North America. Thus, an extensive selection of possible analogs should be considered, which can be incorporated into forward models of possible traps and reservoirs.

Comments

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Attachments


Event Contact	Event Coordinator
Patty Abney	Patty Abney
(972) 824-2655	(972) 824-2655

DGeolS Luncheon

Tuesday 13-Apr-10 11:30 AM to 1:00 PM CDT

Speaker Steve Schutter

Company: Murphy Oil

Biography

Steve Schutter received his graduate degrees in geology from the University of Iowa, where he worked on the depositional environments of Ordovician and Pennsylvanian shales. At Exxon Production Research, he worked on Paleozoic eustasy, carbonate facies, and salt tectonics, as well as on several regional studies. This was followed by work at Subsurface Consultants and now at Murphy International E & P. In addition to Paleozoic eustasy and the depositional environments of shales, he has published on hydrocarbons associated with igneous rocks.