Hydrocarbons  Nine component hydrocarbon analysis, with Eh, pH, and umhos measurements! GRDC provides complete multiparameter surveys.

Eh, ph, umhos (ORP)  This suite of tools was pioneered by GRDC and introduced in 1986. They can be used as a reconnaissance method as well as part of GRDC's hydrocarbon method.

Microbial  Inexpensive reconnaissance tool.  Non-specific aerobic bacteria detection.

Radiometrics      Digitally Acquired Full Spectrum (DAFS) gamma ray surveys.  GRDC is not limited to the standard four channel surveys for Total Count, Potassium, Bismuth, or Thorium.

Iodine   A proven tool since its introduction in 1979 Pioneered by GRDC.

Indirect evidence of hydrocarbon micro seepage includes chemical, geobotanical, and mineralogical anomalies, as well as magnetic, radiation, or related geophysical anomalies. Surface geochemistry can be a valuable extension to any exploration program when applied properly. Staging the exploration program so that samples are acquired judiciously is the most often prescribed survey practice. This minimizes cost while maximizing sample placement. However, due to the noisy nature of geochemical data, staging sample collection can present some problems. Multiple reconnaissance surveys are acceptable to asses the presence of hydrocarbons, but prior to drilling a detailed survey of closely spaced hydrocarbon samples should be run in addition to reoccupying the reconnaissance sample locations.

Many of the geochemical methods currently in use can yield spurious anomalies. False anomalies can be detected if 1) the sample spacing is sufficiently close to determine the discontinuous nature of the anomaly, 2) a sufficient number of samples are taken to obtain an adequate population to differentiate an anomaly from background, 3) the method used meets of exceed an expected signal to background ratio.

Surface geochemical surveys can be one of two types of hydrocarbon indicators, direct or indirect. Direct methods are those that directly detect hydrocarbons at the surface, primarily as soil gas. Indirect methods usually detect a non-hydrocarbon anomaly associated with hydrocarbon induced alteration. Methods using very near surface soil samples are usually indirect methods.

Surface geochemical anomalies are manifested in two distinct signatures, halo and apical. Halo signatures occur towards the edge of the seepage area, sometimes encircling the prospective zone. Apical signatures occur over the seepage area, thus delineating the area of greatest potential.

Sample spacing is the hardest of all geochemical survey parameters to justify with respect to efficiency and cost. Grids are efficient but costly when a large area is to be covered. Traverses yield some data relative to a specific geographic site but can be ambiguous when lines are widely spaced. Factors that affect sample spacing are

- size of target
- faults and fractures
- cost of the method being used
 

GRDC subscribes to the use of either a grid or closely spaced sample traverses. A usual reconnaissance survey grid uses 660 foot sample intervals while a reconnaissance traverse is spaced at no more than 330 foot intervals. Intervals of 1320 feet are the maximum distance between samples that can be interpreted. The greater the data resolution the better the interpretation. It is important to keep in mind that with any geochemical technique a given sample has an approximate 50 foot ( 16m) maximum radius of investigation. This is a very important consideration when attempting to track stream channels or small pinnacle reefs.

The purpose of a reconnaissance survey is to roughly identify the location of an anomalous area. Subsequent detailed surveys yields a clear, though considerably more complex picture of the potential prospect. GRDC recommends a normal sample interval of 528 to 660 feet for reconnaissance grids, 330 foot spacing for reconnaissance traverses, and 330 feet or less for detailed survey grid. Sample intervals greater than 1320 feet tend to miss much of the detail required for an accurate interpretation and are not recommended.

Remember that surface geochemical detection is not meant to define structure but locates areas of hydrocarbon microseepage. Therefore survey orientation does not play a significant role. Orienting survey lines in simple north-south or east-west grids or traverses will suffice for anomaly detection.