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Geology - microfossil in petroleum exploration
Expert: Manoharan Kothandapani alias Manoharan - 10/31/2009
Question
how does microfossil help in petroleum exploration,role of foraminifera,radiolaria,ostracodont etc.also abt the paleo shore line.plz reply as soon as possible
Answer
Dear Maria,
Thanks for your question,
Microfossils are very much useful in hydrocarbon exploration. A detailed study of study from core samples and mud flows helps in hydrocarbon exploration in identification of geological ages because of their short stratigraphic ranges as zone fossils helps to make age boundaries and thereby marking of index lines and correlating with already known oil bearing horizons. This study also helpful in stratigraphic correlation and sedimentary environment determination by correlation, Tectonic activity in sedimentary basins can also be determined by oscillations in water depth and also charts are been prepared for such oscillations. For example Foraminiferal assemblages and depth wise presence are given as rotalia beccari-30cm-3.5mts, nonoin scapha (3.5mts-40mts, triloculina trigulena-40mts-300mts, globulina pacifica-300mts-2175mts and greater than 2175 mts- by pullenia bulloides.(I have mentioned only some important fossils however few other fossils are also present in each assemblages.) The data obtained are thoroughly analyzed and precise locations of hydrocarbon presence are marked.
Foraminifera: These are important microfossils because they are abundant and helpful in reconstruction of sedimentary environment. They are unicellular and belong to protozoa and found in all sorts of environment at any depth from Cambrian to recent.
Example-textularia-cretaceous to recent, nodosaria-permian to recent, fusulina-middle carboniferous,nummulites-palaeocene to Oligocene.
Ostrocoda- These belongs to Crustacea and phylum Arthropoda; they include both benthoic and free swimming types and are widely distributed from upper Cambrian to present day. A new method called Mutual Ostracod Temperature Range (MOTR), similar to the Mutual Climate Range (MCR) used for beetles, is in development which can be used to infer palaeo temperatures. Some important ostracods are
Leperdita-ordovician to Devonian,primitia-ordovician to Permian,cypris-tertairy to present etc.,
Radiolaria: These are pelagic, marine protozoans occurring in present ocean and form radiolarian oozes and have wide geographic distribution and hence have limited stratigraphic value. These are used only for the local correlation purposes.
Few radiolarians are actinoma, heliosphaera and hexadoridium.
Palaeosea levels: Study of stratigraphic records from sedimentary successions shows that they are cyclical and show constant changing of sea level and further these are also studied in depth in seismic and sequence stratigraphy. These changes in shoreline are due to local tectonics, sea water temperature, continental ice caps, exchange with water on continents, global scale thermo tectonics, changes in rate of formation of oceanic crust and formation and break up of super continents. These are studied to determine ancient
Shore line. These studies are made with the help of seismic reflection profiles, borehole lihology studies and out crop studies. A good study in this subject is made by vail 1977 and huq 1987, 1988. and many others.
You can also refer to elements of micropaleontology by Gerard bignot and principles of stratigraphy by Roy.R.Lemon.
Thanks,
Manoharan Kothandapani alias Manoharan
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