INVESTIGATING GEOPHYSICAL TECHNIQUES TO DETECT HYDROCARBON SEEPS

A magnetic and electromagnetic survey have been undertaken in the Cement Oil Fields (Caddo and Grady counties, Oklahoma State) to investigate suitable geophysics techniques that can help detect electromagnetic anomalies within hydrocarbon seepages areas. The total magnetic field was measured using a G858 magnetometer and the Electromagnetic fields, with both the EM31 and EM 34. The surveys have revealed mainly two types of magnetic anomalies within the Hydrocarbon Induced Diagenetic Alteration (HIDA) Zone.

The first type of anomaly is characterized by the magnetic strength above 53000 nT (53200 nT being the highest along the survey line 11 and from a background of 50 000 nT). This type of anomaly was found to be accompanied with the highest conductivity reading (above 170 mSm from EM31) The higher magnetic strength and conductivity have been interpreted as due to the proximity of a pyritic Zone.

On the other hand the second type of magnetic anomaly is characterized by the magnetic strength of above 55000 nT. The higher magnetic reading is consistent with the highest conductivity of 67 mSm (EM31) and -75 mSm (EM34). The vicinity of dumping site and other buried metal explain this type of anomaly as well as the proximity of pyritic horizon that is located to be on the contact between the red and bleached sandstone.

The present surveys have also revealed that Hydrocarbon Induced Diagenetic Alteration (HIDA) Zone in the Cement oil fields is not composed of uniformly bleached sandstone, instead there are many horizons of red sandstones within the Zone. Also the pyrite zone has been interpreted as a result of microbial activity. This zone plays an important role in the investigation of long term hydrocarbon seeps.