Comparison of Remote Sensing Methods

• Conventional aeromag and aerogravity surveys have been an integral part of the oil and gas industry for
   decades. They provide geological indicators on basin features. Magnetic resolution has reached its peak but
   gravimeters enjoy a renaissance in the industry

• In recent years satellite gravity gradiometer observation methods were introduced, starting with CHAMP
   in 2000, followed by GRACE in 2002 and GOCE in 2004 [1]. These systems were based on new concepts
   and offered improvement in accuracy-resolution over conventional airborne methods

• NXT’s Stress Field Detection (“SFD”) technology is the latest introduction in airborne exploration techniques.
   The SFD system virtually eliminates inertial effects and permits remote investigation of hydrocarbon potential
   for the first time

AEROMAG	AEROGRAVITY
Measures the variations in the earth’s magnetic field based on the susceptibility of magnetizable materials [2]	Measures the variations in the acceleration of gravity based on the density of matter [3]
Problem: hydrocarbon systems lack magnetic materials in general. No direct trap or reservoir detection possible	Hydrocarbon systems exhibit subtle density characteristics. Gravimeter data allows interpretation and mapping of differential crustal densities
If there is no inherent magnetic signal present in connection with oil & gas accumulations, then the degree of resolution is irrelevant	Problem: “test mass” of gravimeters is too large to respond fast enough to subtle density changes. In addition, inertial effects introduce large measurement errors
Conclusion: there is little room for further technological improvement	Resolution in milli-gals; no direct trap or reservoir detection possible
	Conclusion: New methods are needed to overcome these limitations

SATELLITE GRAVITY	SFD (STRESS FIELD DETECTOR)
Measures minute distance variations caused by gravity between two accelerometers aligned to the vertical on earth’s orbit [4]. Based on matter density changes	SFD is not a gravimeter. SFD sensor element responds to minute distortions in the gravity field in an induced microgravity environment
Reduction of inertial effects in microgravity environment improves resolution	SFD responses are strongly associated with subsurface stresses (Poissson’s ratio [5]) caused by geological events
Higher resolution attainable but not enough to resolve potential petroleum systems, individual traps or reservoirs	Removal of main gravity field is possible, which then permits sensor element coupling to the force field of gravity, virtually reducing inertial effects to zero
Limitations: no gravimeters can distinguish between inertial and gravitational accelerations. Inertial corrections require long time periods leading to bandwidth reduction	An SFD sensor transduces these interactions into electrical signal output
Further improvement is required	Increased bandwidth is attainable, which allows the identification of potential petroleum systems, individual traps, and reservoirs