The time evolving strain field contains a wealth of information that can
be used to interpret subsurface behavior. For example, injecting or
removing fluids from reservoirs or aquifers causes deformation that can
be used as a diagnostic signal in some cases, while it can interfere
with geodetic interpretations in other cases. We've recently completed a
field study that demonstrated the feasibility of measuring the strain
tensor at a depth of 30 m caused by injection into a reservoir at 530 m
depth. The observed strain signals were interpreted using four
independent analytic and numerical methods that resulted in estimates of
the poroelastic properties and geometry of the reservoir that was
consistent with data from well logs. However, studies like these are
only possible if these deformations can be reliably measured. Advances
in optical fiber sensing systems have led to their introduction in a
number of areas including quasi-static and dynamic subsuface deformation
monitoring. Optical fiber-based interferometers are capable of measuring
very small displacements while being completely passive in their
operation. The low attenuation and significantly reduced bending loss in
rare-earth doped, high numerical aperture glass optical fibers allows
for the embedding of long lengths of fiber into compact, durable and
exceptionally sensitive downhole sensing packages. We have expanded on
years of lab and field work developing and deploying long baseline and
embedded single-component borehole strainmeters to the design of three
novel horizontal tensor strainmeters. Each design represents a unique
embedding approach for measuring directional strain across the diameter
of a borehole with differing advantages in terms of ease of fabrication
and assembly, as well as directional resolution. We will present the
design details along with laboratory calibration results and preliminary
field data comparing their relative performances across tidal and
seismic frequencies.