Abstract: A method of estimating one or both of compaction or subsidence of a subterranean formation with gravity measurements. The free air gradient at surface is measured and compared with gravity measured in a borehole that intersects the formation. At a later point in time, values for gravity are re-measured, differences between the measured values at the initial point in time, and the later point in time are estimated. The differences are used to estimate the compaction or subsidence. A gravimeter can be used for measuring gravity, markers in the formation can be used in conjunction with the gravimeter.

Abstract: Methods, systems, and devices for characterizing a water-flooded zone in an earth formation resulting from injection of water to the formation through an injector well borehole intersecting the formation. The method includes estimating horizontal elongation of the water-flooded zone using a gravity field change in the injector well borehole. Estimating horizontal elongation may include predicting a gravity field change for each of a plurality of model water-flooded zones for the borehole, wherein each model water-flooded zone is an elliptical cylinder having finite height and semi-axes; and fitting the gravity field change to one of the predicted gravity field changes corresponding to one of the plurality of elliptical cylinder model water-flooded zones. The gravity field change may comprise a difference between a first estimated gravity field in the injector well borehole before injection and a second estimated gravity field in the injector well borehole after injection.

Abstract: A method of estimating one or both of compaction or subsidence of a subterranean formation with gravity measurements. The free air gradient at surface is measured and compared with gravity measured in a borehole that intersects the formation. At a later point in time, values for gravity are re-measured, differences between the measured values at the initial point in time, and the later point in time are estimated. The differences are used to estimate the compaction or subsidence. A gravimeter can be used for measuring gravity, markers in the formation can be used in conjunction with the gravimeter.

Abstract: Methods, systems, and devices for characterizing a water-flooded zone in an earth formation resulting from injection of water to the formation through an injector well borehole intersecting the formation. The method includes estimating horizontal elongation of the water-flooded zone using a gravity field change in the injector well borehole. Estimating horizontal elongation may include predicting a gravity field change for each of a plurality of model water-flooded zones for the borehole, wherein each model water-flooded zone is an elliptical cylinder having finite height and semi-axes; and fitting the gravity field change to one of the predicted gravity field changes corresponding to one of the plurality of elliptical cylinder model water-flooded zones. The gravity field change may comprise a difference between a first estimated gravity field in the injector well borehole before injection and a second estimated gravity field in the injector well borehole after injection.