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Biostratigraphy, Palynology, and Petroleum Exploration: The Scenario

Your company has acquired licenses for several prospective sections of land with the exploration rights from Mannville to surface (Cretaceous or younger age). The stratigraphy indicates a complex erosional unconformity occurring between Lower Mannville and the Rock Creek .

You have spent one month of geological mapping, run a local seismic survey, and isolated a bright prospect. The equivalent sands from the surrounding wells have an ambiguous log character suggesting either a Basal Quartz or possibly interstratified Upper Fernie or Neocomian sands. The log characteristics change dramatically laterally.

You have to make a decision -whether or not you own it -where does the land holding stand legally? You can choose to drill with the hope that your assumptions are correct - but you might discover that you are guilty of trespass and lose all of your investment.

If you drill without the deep rights secured (or shallow rights as the reverse case may be), you risk losing the prospect, and releasing to the public all the geological and production data on the lease. You would be required to rebid for the prospect from the same level as all other companies. Possibly someone owns the rights already. The total loss when it is finished will be great. Ownership is much like scratching a lottery ticket while holding it up to a bright light with empty hopes to see through the opaque wax.

There is yet another option which presently, only a few, most enlightened companies exploit to their advantage,

"calibrating their stratigraphy with BIOSTRATIGRAPHY"

Many geologists look at this science to be rather ethereal, -not exacting, -lacks numbers or -we can do without it. But can you afford to overlook the possibilities? A closer look will show how cost and time effective the use of biostratigraphic consultants can be.

This age problem may be difficult to resolve by normal stratigraphic practices but it is a rather simple one from the standpoint of a palynologist and other specialized paleontologists. Fundamentally, " Is the prospect Jurassic or Cretaceous?"

 

 

The base of the Lower Mannville is Barremian or younger (at 125 MA) and the top of the Rock Creek is Bajocian (at 175MA). The uncomformity accounts for eight stages having a duration of 50 million years. Academically the Jurassic/Cretaceous boundary is slightly ambiguous in Europe and there is a continuous arguement about the exact placement of the golden spike, between the top of the Tithonian and the base of the Berriasian, but this has a maximum of 2 or 3 million years. However, this is effectively negligible when attempting to differentiate these periods in the Western Interior of Canada.

 

Profound changes in the plants and animals occurred with this time frame. If there are fossils present then the problem can be easily resolved. A study involving palynology would require sampling, laboratory preparation, analysis and report generation over a period of one to two weeks costing a minimal one to five thousand dollars. With a small suite of samples a palynologist can often determine the assemblage zone and assign the age within one million years.

You can confidently invest in the area with low legal risk. In fact you will be armed with a lot of additional data on time framework, paleoenvironments and thermal maturation which will enhance your exploration program.

 

PALEONTOLOGY and BIOSTRATIGRAPHY: What Are They?

Paleontology studies the history of life by identifying the large variety of forms of the past and illuminating the processes which have brought life to the present state. The clues from the past will be the windows to the future.

Ancient life is basic to the petroleum industry. Petroleum is generated from the organic components in the rocks. It is as simple to say as,

"No fossils - No production"

Biostratigraphy is best defined as the study of the biosphere and the interaction with the hydrosphere and lithosphere through time and space.

TYPES OF FOSSILS

Nearly every form of life has left an imprint in the sand. Fossils can be represented by trace fossils, preserved fossil remains and altered fossil remains.

Fossils can be the size of large trunks of trees and gigantic ammonoids or as minute as the scales of single celled algae. The greatest fossils are the large reef bioherms which may act as hydrocarbon reservoirs and the smallest are the organic molecules of the petroleum itself.

One of the most common type of fossils which are usually overlooked are microfossils. They exist in great abundances in most types of sedimentary rocks, they form the basis from which petroleum is generated, and they
are the most useful in well correlations and age dating.

The disciplines of microfossil study are subdivided primarily on the basis of the wall composition of the tests or cysts which is often systematically differentiated:

 

The term Micropaleontology usually refers to the study of calcareous tests of a variety of minute animals such as ostracodes, foraminifers, and other protozoans. Phosphatic worm teeth or conodonts are also included. Botanical microfossils are represented by nannofossils (the tiny calcareous scales of the chrysophycean algae), the siliceous tests of diatoms and silicoflagellates, and the organic-walled palynomorphs .

Each group of fossils has its own utility range within time and environmental space. Every discipline requires a highly-specialized person with a keen interest in his science. Usually the paleontologist studies one part of the geological column and one geographic region.

The latter group of organic-walled microfossils has been placed into a separate category, namely Palynology, due to its recent development and radical extraction techniques. The broad microfossil spectrum of palynomorphs encompasses the three living kingdoms: animals, plants and protists, such as: testate amoebians (protozoans) and scolecodonts (worm teeth), but more commonly as aquatic acritarchs and dinoflagellates (algal resting cysts), and the pollen and spores from terrestrial land plants.

The word Palynology is derived from the Greek word for dust palyn which is the root for the word pollen (latin- pollinis = fine flour). As the dust of the oceans over 50,000 palynomorphs may be recovered from one gram of rock with specimen counts
commonly attaining 1,000 to 10,000 in shales and siltstones from non-marine to abyssal environments. With such large numbers distributed over a wide range of depositional environments, palynomorphs have become important geological tools in petroleum exploration.


Palynomorphs are extracted from the rocks by a series of stringent acids (hydrochloric and hydrofluoric) to remove the mineral matter, followed by upgrading the organic residue with heavy liquid separation, selective oxidation and microsieving. They are then mounted on glass slides and examined utilizing high powered light microscopes or electron microscopes.

Palynology was in an infantile stage since the late 1800's until it was discovered to be highly useful in the exploration of oil and gas in the late 1950's. A great wealth of knowledge has been gathered over the last thirty years paralleling the petroleum industry.


Development in sample processing, optical technology, and computer accessibility have changed the ability of the palynologist to make a direct impact on an active exploration program. As short as five years ago, most biostratigraphic data was recorded by hand on scribble pads. The large number of species required a superbrain to remember all the latin names. The occurrences were plotted by hand on large matrices called rangecharts. The applied palynologist required the assistance of a number of people including a typist, a draftperson, technicians and computer specialists.

Coordination of these people in order to complete a study in a time-frame that would make the data relevant to the exploration geologist was next to impossible. Report generation would take approximately same amount of time again as the fossil analysis.

Today a revolution has taken place with the advent of the personal computer. The modern palynologist can input the data directly into a personal computer during the microscopic analysis. With a full dictionary of species names loaded one does not need to handle the data repetitively and can present the complete data set in a number of formats with low error occurrences. Free flow from the microscope to colour log charts and word-processors has reduced the time for report writing from weeks to a matter of hours for a small project.

OTHER USES

 There is a host of applications other than regulatory biostratigraphy in the petroleum industry. The most often use of biostratigraphy is establishing the age and time duration of lithostratigraphic formations. Fossil assemblages can be utilized to appraise reservoir correlations, identify sedimentary tracts and sequences, assign depositional facies and evironments, discern paleoclimatic changes, determine the thermal maturation and calibrate the geohistory reconstructions.

These techniques are extremely useful in complex fault patterns, incised valleys, homogenous acoustic impedience, reservoir distribution controls, horizontal drilling, channel migration, GPP allocations, and frontier drilling control.

Biostratigraphy is efficacious in creative application, especially when integrated with other geological specialties to solve stratigraphic problems. Can you afford not to consider the potential benefits on you exploration program?

By Dr. Edward H. Davies
Ph.d, P.Geol.

 

 

 

 

 

 

 

 

 

 

 

 

 

© Branta Biostratigraphy Ltd.
Edward H. Davies Ph.D., P.Geol.