In general, every energy form is affected by stress due to the anisotropy in materials. Regionally, tectonics acting on rock mass will cause a slight increase in matter density due to elevated horizontal stress. That in turn will cause a re-orientation of the horizontal gravity field in the direction of maximum horizontal stress (SH max).

SFD® detects characteristic directional changes that deviate locally from the established large scale background trends. These local deviations form the basis of SFD® anomalies.

SFD® anomalies can be correlated to horizontal subsurface stress anomalies caused by the development of traps, shear fault system and lithologic boundaries.

Why isn’t rotational information detectable with other types of gravity methods?

For the accurate measurement of density changes, traditional gravity methods require a large ‘proof’ mass. The problem is that a large mass requires a significant time to settle in order to attain a high level of accuracy. In addition, the inertia of a large ‘proof ‘mass prevents the detection of any rotational information. In contrast, the detection of small disturbances in orientation require a small mass that is insensitive to the effects of vertical and horizontal acceleration yet still able to provide adequate interrogation time for rotational investigation while in motion.

How does SFD® isolate and analyze the directional/rotational effects in the gravity field?

To reveal the twists and perturbations in the gravitational field the effects of any force that causes changes in magnitude need to be minimized. The SFD® sensor element, with near zero mass, reduces the effects of any accelerating force and thus the directional/rotational effects in the horizontal gravity field are detectable.

SFD®’s sensitivity to perturbations is accomplished by a proprietary approach which utilizes wave-particle duality of matter based on the De Broglie-Bohm interpretation of quantum mechanics.

How does regional background horizontal stress field orientation develop?

The regional stress direction is primarily influenced by the tectonic forces acting on the layers of the earth. In the foothills the maximum horizontal stress would be oriented perpendicular to the mountains.

How is the local stress orientation changed by the existence of a trap?

Locally, the background stress orientation would be deflected by the changes in shear encountered in and around a trap.

How does SFD® detect stress anomalies?

Locally, subsurface discontinuities (faults, traps, reservoirs, etc.) will alter the regional direction of horizontal stresses and this results in perturbations in the horizontal gravity field.

The SFD® method investigates the weak horizontal interactions of gravity; responding to minute perturbations (rotations/twists) as the sensor is flown from one point to another.

How can reservoir level stress field changes be discriminated from the cumulative stress in stratigraphic column?

SFD® interpretation process uses spatial and character based discriminators to identify anomalies. Regional stress orientations changes are generally more gradual and become part of the background SFD® signal and are not recognized as anomalous. A strong lithologic edge or fault will be recognized as anomalous but will only effect the SFD® at one location. As coherent orientation changes propagate through the stratigraphic column, spatially it will dominate over other chaotic or random changes in accumulated stress field. Additionally, reservoir anomalies have strong changes in orientation that are highly localized, ordered and correspond to the spatial configuration of the reservoirs in the region.