Measurement of Small Surface Displacements Induced by Fluid Flow

Fluid flow to wells produces strain that has been measured as horizontal, vertical, and rotational displacements of reference points fixed on the ground surface. Most linear displacements measured were between 1 and 100 microns, and angular displacements were a few microradians. Of the various devices used to make measurements, a horizontal extensometer proved to be the most accurate and versatile. Most measurements were made of effects produced by pumping wells for 5 to 30 minutes. Such effects are almost entirely elastic, except in some geologically recent materials. Deflections of the land surface resembled the theoretical deflections caused by a point load on a plate of infinite extent resting on an elastic foundation. Significant horizontal strain was measured in all materials tested, suggesting that accepted equations for fluid discharge from wells might be modified for special conditions near the wells.