MPOG® (Exploration)

Basis oft Microbial Prospecting for Oil and Gas

The basis of MPOG^® is that oil or gas fields emit a conti­nuous stream of light hydro­carbon gases to the earth’s surface known as macro- and micro-seepages.

In all shallow soil and sediment layers a variety of specia­lized micro-organisms (hydro­carbon oxidizing bacteria) exists, able to utilize extremely low concen­tra­tions of short-chain hydro­carbons (10^-6 %vol/vol). Based on a conti­nuous hydro­carbon supply active popula­tions of hydro­carbon degrading bacteria can develop. This long term supply is almost exclu­sively found at micro-seepages above hydro­carbon bearing struc­tures. Under these condi­tions detec­table popula­tions of bacteria develop with signi­fi­cantly increased cell numbers and a high bioche­mical activity.

For oil and gas explo­ration two well distin­gu­is­hable groups of bacteria are relevant:

• Hydro­carbon oxidizing bacteria
• Methane oxidizing bacteria (Methy­lo­trophic)

Due to high specia­lization of methane-oxidizing bacteria, the MPOG^® method allows methane-oxidizers to be isolated from all other bacteria and bioche­mi­cally analyzed. A signi­fi­cantly increased activity and cell number of methane oxidizing bacteria represents an indication for methane occur­rence in soil samples.

Another bioche­mical group of micro­or­ga­nisms uses short-chained hydro­carbons (C₂ — C₈) as energy source. These micro-organisms are not able to metabolize methane. Short alkanes namely ethane, propane and butane can be utilized by a large variety of bacteria. Detection of active bacteria which oxidize n‑alkanes with chain lengths of 2 to 8 carbon atoms without any adapt­ation period indicates the existence of oil signa­tures in the area investigated.

On the basis of a complex micro­bio­lo­gical test scheme to determine bacterial count and bioche­mical activity of specific bacteria, an oil and gas indication factor will be recorded for each soil or sediment sample. Maps with identified microbial hydro­carbon anomalies show position and extent of hydro­carbon indications.

The higher the calcu­lated measure units (cell numbers and activity), the more intense the hydro­carbon supplies to bacteria and the greater the proba­bility of finding hydro­carbon accumu­la­tions at these positions.

MPOG^® data can easily be integrated into existing explo­ration data sets (e.g. seismic) or used for pre-selection of parti­cu­larly interesting areas for subse­quent, cost-intensive explo­ration techniques (wild-cat exploration).griert werden oder zur Vorauswahl besonders inter­es­santer Flächen für nachfol­gende, kosten­in­ten­sivere Verfahren genutzt werden (Wild-cat exploration).

Application of Microbial Prospecting for Oil and Gas

Basically no geolo­gical or seismic data is required to carry out a geo-microbial explo­ration survey. In areas which have not yet been inves­ti­gated by geophysics, the MPOG^® technique can be applied as a wild-cat explo­ration tool, in order to identify hydro­carbon signa­tures in green field areas. In this way subse­quent geolo­gical and seismic inves­ti­ga­tions can thus be focused on hydrocarbon-prospective areas. Measu­rement points are laid over the area to be inves­ti­gated in the form of a map grid. The stationary interval is from 500 m to a maximum of 2,000 m depending on the expected reservoir size.

In those regions where structure data of the sub-surface already exists, the stationary interval can be reduced to 250 — 500 m, in order to generate a more detailed picture of the hydro­carbon distri­bution. Likewise, this approach does not require any knowledge of the position of geologic struc­tures. As a result therefore, the seismic structure maps and microbial anomalies, which have been recorded independently from one another, can be compared and contrasted.

A further appli­cation of microbial prospecting is reservoir charac­te­rization. In this case the distance between two measuring points should not exceed 200 m. The area of inves­ti­gation is restricted to an already known structure. This method is parti­cu­larly suited for evaluation of the reservoir dimen­sions and altera­tions of the oil-water contact due to long-term oil production processes.Additional appli­ca­tions of MPOG^® are frequent measu­re­ments within a safety monitoring program at under­ground gas storages or along pipelines.

Sampling procedure

Onshore, soil samples are taken in the field at pre-defined positions using an environ­men­tally friendly hand auger set at a depth of 1 — 2 m. At each measu­rement point about 200 g of soil shall be packed in airtight sterile sampling bags. A tempo­r­arily storage at 4 — 10°C and trans­por­tation to the laboratory should not exceed a period of 14 days.

Offshore, seabed core samples are taken by means of a vibro-coring system or grab-sampler approx. 0.5 — 2 m below sediment surface. Sampling material for MPOG^® analyses can easily be sub-sampled from cores on board a vessel.

Microbial Prospecting for Oil and Gas – case histories

The following case studies compare and contrast results of geo-microbial surface prospecting (MPOG^®) with seismic and geolo­gical data. At the time of micro­bio­lo­gical inves­ti­gation, the authors did not have knowledge of any of the data on geolo­gical struc­tures of the inves­ti­gation areas, apart from already existing wells. The case studies were selected on basis of their exemplary character and different geolo­gical setting.

The map on the right shows the positions of surveyed areas both onshore and offshore in Central Europe.

The following colors repre­senting MPOG^® data were used for the maps discussed here.

A division of recorded microbial activities into four levels is mainly based on inves­ti­ga­tions in regions with ecolo­gical condi­tions like in central Europe and the North Sea. Under extreme ecolo­gical condi­tions (e.g. in desert regions) the average of measured activities can decline. Nevert­heless, a reliable identi­fi­cation of positive microbial anomalies is guaranteed because of decreased background level.

The background level, which is mainly of biogenic origin, does not indicate any signi­ficant fluctua­tions. The additional hydro­carbon supply from oil and gas fields (e.g. from depths of ca. 2,000 m), which is confirmed by isotope analyses (delta ¹³C₁ = ‑30 to ‑40 (‰) PDB), causes signi­ficant microbial anomalies.

By separately identi­fying methane and hydro­carbon oxidizing bacteria, it is possible to diffe­ren­tiate between oil and gas reser­voirs, and oil reser­voirs with a gas cap. Oil fields without a free gas cap have either no or small methane indica­tions, but do have signi­ficant oil indica­tions. Oil fields with a free gas cap create measurable methane anomalies and increased oil indica­tions. Gas fields in the North Sea, which contain beside methane also aliphatic hydro­carbons (ca. 15%) show oil indica­tions as well as signi­ficant methane indica­tions. The intensity of these oil indica­tions however is normally below the indication level for oil fields.

• Baum, M., M. Schmitt, M. Wagner, C. Westerlage (2008)
   Geoche­mical and Micro­bio­lo­gical Surface Inves­ti­gation in Northern Germany Indicates Interesting Hydro­carbon Potential: Oil Gas European Magazine 1/2008; 10–14
• Trappe, H.; Wagner, M.; Bleschert, K.; Piske, J.: (2004)
   Verknüpfung von mikro­bieller Oberflä­chen­pro­spektion mit seismi­schen Attri­buten am Beispiel einer osteu­ro­päi­schen Öllagerstätte;Vortrag auf der Frühjahrs­tagung der DGMK, Celle, Germany
• Wagner, M., et.al.: (2003)
   MPOG- Microbial Prospection of Oil and Gas; Field Examples and their Geolo­gical Background, Lecture on the Inter­na­tional Symposium “Recent Trends in surface geoche­mical Prospecting and Risk Reduction for hydro­carbon Explo­ration and Develo­pment”; Hyderabad, India
• Wagner, M., M.Wagner, J. Piske, R. Smit (2002)
   Case Histories of Microbial Prospection for Oil and Gas Onshore and Offshore in north-west Europe
   AAPG-SEG Special Publi­cation — Appli­cation of Surface Explo­ration Methods to Explo­ration, Field Develo­pment and Production, edited by D. Schumacher and L. Le-Schack
• Wagner, M., M. Wagner, (1999)
   Microbial Prospection for Oil and Gas — Case Histories on- and offshore:
   Confe­rence Ravenna, Italy, 2, 1061–1067.
• Wagner, M., H.J. Rasch, J. Piske, and B. Ziran, (1998)
   Mikro­bielle Prospektion auf Erdöl und Erdgas in Ostdeutschland:
   Geolo­gi­sches Jahrbuch, 149, 287–301.
• Wagner, M., M. Wagner, H.J. Rasch, J. Piske, and M. Baum, (1998)
   MPOG — Microbial prospection for oil and gas. Field examples and their geolo­gical background:
   Confe­rence Cracov, Poland, AO-05, 118–121.
• Baum, M.G., M. Wagner et.a. (1997)
   Appli­cation of Surface Prospecting Methods in the Dutch North Sea
   Petroleum Geoscience 3, 171–181
• Wagner, M. (1966)
   Ergeb­nisse der mikro­bio­lo­gi­schen Prospektion im Küsten­be­reich der Ostsee
   In Vorträge des Inter­na­tio­nalen Symposium „Erdöl­mi­kro­bio­logie“, Brno 1964 (Malek & Schwartz, Ed.), Akademie Verlag Berlin