An exiting new EM hydrocarbon detection technique has been identified.
The intriguing aspect is that seismic and EM can be exploited for their own merit or in combination, electroseismic and seismoelectric, as conversion takes place at polarised interfaces such as hydrocarbon contacts. The implications of the different mechanisme at work are impressive for structural as well as rock and fluid fill recognition techniques.
There is a catch that strong shallow EM anomalies may occur.These are associated with small amounts of hydrocarbons in shallow rocks (leaked from the much deeper underlying HC reservoirs) dissolved in water .
Within these rocks aerobic bacteria can consume the hydrocarbons and use the available oxygen reducing the pore waters to anaerobic .If there is sufficient sulphate ion and organic material sulphate reducing bacteria flourish and sulphate reduces to sulphide and hydrocarbons to bicarbonates .(Sternberg 1994)These tend to reduce the resistivity contrasts with respect to the conductive minerals in the formations .
Even a negligible content of sulphur compounds in sediments (e.g. pyrites or chalcopyrites) causes significant enlargement of residual rock polarisation.
However the shallow anomalies are an indication of the presence of hydrocarbon seepage but not a guarantee of commercial reserves in the deeper strata. The jury is still out of some of the published new EM claimed hydrocarbon detection results are in fact representation of these shallow anomalies.
This project describes a detailed Russian EM approach to detect hydrocarbons , which in addition claims to create electro (not seismic) subsurface section down to a few kilometres depth. The method uses a electrode source and transmitter and is distinctly different from the seismic method at a fraction of the cost.
The different methods are under review by a major client.