Visible surface features such as oil seeps, natural gas seeps, pockmarks (underwater craters caused by escaping gas) provide basic evidence of hydrocarbon generation. However, most exploration methods depend on highly sophisticated technology to detect and determine the extent of these deposits using exploration geophysics. Areas thought to contain hydrocarbons are initially subjected to a gravity survey, magnetic survey or regional seismic reflection surveys to detect large scale features of the sub-surface geology. Features of interest (known as leads) are subjected to more detailed seismic surveys which work on the principle of the time it takes for reflected sound waves to travel through matter (rock) of varying densities and using the process of depth conversion to create a profile of the substructure. Finally, when a prospect has been identified and evaluated and passes the oil company’s selection criteria exploration well is drilled in an attempt to conclusively determine the presence or absence of oil or gas.
Oil exploration is an expensive, high-risk operation. Very large corporations or national governments generally undertake offshore and remote area exploration. Typical Shallow shelf oil wells (e.g. North sea) cost $10 – 40 Million, while deep water wells can cost up to USD$100 million plus. Hundreds of smaller companies search for onshore hydrocarbon deposits worldwide, with some wells costing as little as $200,000 USD.
BakhtarRadar Forced-Resonance Imaging (FRI) is a novel technique for oil/gas exploration in land and marine environments. It uses the BakhtarRadar platform designed based on Radar principle in which the electromagnetic energy is forced-resonated at an extremely low-power (below 10 dBm) using a pair of specially designed “forced resonating” (FR) “dipole” and “horn” antennae onto a geologic formation (land, frozen ground and ocean including sea-floor). The low-power EM energy is transmitted via FR dipole/horn antennae in “reflection” mode in which transmitter and receiver are located on one side of the test bed during interrogation. Test area interrogation is done by antennae traversing on a moving platform at a constant speed. An integrated “differential” global positioning system (GPS) enables tracking of the search area with respect to a fixed reference point (RP). The transmit antenna force-resonate the energy onto the ground/water/seabed and backscattered signal from various layers along the path is collected by the receiving antenna. Energy transmission is done through a pre-programmed number of discrete frequency steps having duration (dwelling time) at the order of 0.005 to 0.002 seconds at each step within a selected frequency band of operation in MHz regime.
The detection concept is based on detecting the absorption of energy in the transmitted signal at the frequency emission spectral bands – quantum emission bands — of energy of the hydrocarbons as detected in the signal acquired by the receive antenna. The Bakhtar Associates uses transmit and receive antennas that are impedance matched to the near/far field. The transmitter and receiver are low noise designs enabling the energy transmission loss due to the energy absorbed by the hydrocarbons to be detected using signal processing on the received signal. The detection concept is anticipated to have an effective range, due to its low power transmit power levels and noise limiting in transmit and receive system at the order of 3500 meters. In a single transmitted sequence or trace of 51 or 201 frequency steps, within a selected frequency band of operation (MHz) in 0.6 second, the transmitted energy intercepts the suspect hydrocarbon reservoir in the antenna field of view. If a hydrocarbon layer is present the oil/gas selectively absorbs the energy at the quantum emission frequency bands associated with that reservoir (oil/gas). The absorption is such that the magnitude intensity of received signal in a single trace on the target reservoir is less, on average that the signal received with no oil/gas present. The difference is discern in the signal processing through application of either “linear” or “exponential” Scale Factor and Bakhtar Statistical Trace-per-Screen Discriminator (BSTSD) filter.
BakhtarRadar provides a portable, cost effective, user friendly and autonomous device for oil and gas exploration. The “simplified” ground and sea borne versions of BakhtarRadar hardware configurations are shown in Figures 1 to 5. BakhtarRadar has promise not only be the most economical but best alternative to seismic survey which is used as the final stage to create a profile of the substructure associated with an oil/gas reservoir. The size of the forced resonating dipole antennae is directly proportional to the required depth of detection. Depth conversion is done through initial EM characterization of a potential site. For ocean interrogation, it is best to submerge the antennae at a fraction of the averaged wavelength as shown in Figure 5. Deployment of a command ship with unmanned (UAV) submarine for pulling antennae close to the sea floor may prove to be the best approach for oil/gas exploration far below cap rock in the ocean. This scenario is illustrated schematically in Figure 5. A 4 page note attached to this document highlights technical issues that should be discussed with interested parties for oil/gas exploration using BakhtarRadar “forced-resonance imaging” (BFRI) technique.
The most significant aspect of BakhtarRadar oil/gas exploration technique is the ability to “force-resonate” (FR) EM energy at extremely low-power onto the heterogeneous and anisotropic geologic formation. Forced-resonating the energy allows separation of the return signal from noise floor in a detectable manner at enhanced signal-to-noise (S/N) ratio. The detection depth can be controlled by adjusting the width of operating frequency band without compromising resolution in MHz regime. In recent tests observed by scientists and geophysicists the ability of BakhtarRadar with forced-resonating antennae to overcome skin-depth and Faraday’s cage effects was clearly demonstrated. This contradictory finding was demonstrated to the scientists through laboratory experiments simulating depth below cap rock at the order of several kilometers. The test bed consisted of 1-m3 completely sealed lead box containing 3.5% salt saturated sand. Resistive and conductive materials were introduced inside the sealed lead box and successfully detected and discriminated using BakhtarRadar with FR horn antennae under “transmission” and “reflection” modes (Figures 6 and 7).
The Bakhtar radiators (dipole and horn Antennae) are of “forced-resonating” design invented by the founder of Bakhtar Associates. They have the ability to radiate into any geologic formation and allow the return portion of reflected energy to discern for detection and discrimination. The depth of penetration is controlled by adjusting the frequency band of operation and intermediate frequency (IF) selected for internal processing of received signal in frequency domain. Post deign, each antennae is electromagnetically hardened and environmentally sealed to meet any adverse field conditions to which they are subjected.
Operation under submerged conditions would require antennae to be adapted to the deployed platforms that include command ships or submarines as depicted in Figure 5. Objectives of such operations are achieved through evaluation of the available or proposed platform and provision for attaching the radiators to the moving platform through flexible or semi-rigid links dragging the antennae at a certain depth in the ocean or on the sea-floor. It is important to remove any slacks from the connecting links allowing antennae movement at constant speed within a depth of water or on ocean floor.
Frozen ground interrogation is conducted by dragging the large forced-resonating dipole antennae via a motorized platform as depicted schematically in Figure 8. Dipole antennae circuitry is mounted on a polyethylene skid to enable overcoming asperities and surface roughness along the travel path. Deployment of a GPS unit at the center of the dipole antennae assembly enables location tracking as well as facilitating superposition of interrogated area on the GIS maps. It is envisaged that frozen ground interrogation is by far the best application of the BakhtarRadar for oil/gas exploration.
Figure 1 – Simplified Line Diagram of BakhtarRadar
Figure 2 – Ground Based BakhtarRadar for Subsurface Exploration
Figure 3 – Schematic Representation of BakhtarRadar Configuration for Sea-Floor Interrogation
Figure 4 – Sea Borne BakhtarRadar for Submerged Exploration
Figure 5 – Schematic Illustration of Ocean and Sea-Floor Interrogation by Submerging Bakhtar Forced Resonating (FR) Antennae at Fractions of Operating Wavelength
Figure 6 – Section through a Double Shielded Sealed Aluminium-Lead Container Used for Marine Environment Simulation (Bakhtar, 2007)
Figure 7 – Sealed Aluminium-Lead Container Test Configurations
Figure 8 – Schematic Illustration of Frozen Ground Interrogation Using BakhtarRadar with Forced-Resonating Antennae and an Integrated GPS Unit