| dc.description.abstract | I explore the capability of terrestrial controlled source electromagnetic (CSEM) methods to detect electrically conductive injected fluids associated with hydraulic fracturing of unconventional reservoirs. An existing finite element program is modified to incorporate a rectangular mesh for implementation of geologic features such as slabs with given dimensions and conductivities, and is validated by comparisons to analytical responses. Local mesh refinement around the lateral wellbore in conjunction with a transverse conductance argument enables a first order approximation for modeling the long slender wellbore, since its realistic dimensions are not feasible to model. My numerical results find that responses from the lateral wellbore are ~5 orders of magnitude greater than those from fluid-filled fracture zones. Inline responses provide more information than broadside responses, including the depth of a lateral wellbore and the lateral location of a fluid-filled fracture zone.
Host sediment conductivity is an important factor, as the response to a fracture zone is 100 times larger in terrestrial sediments than clays. If both lateral wellbore and fluid zones are present, the wellbore response dominates. Once the response of the wellbore is removed, the residual response remains dominated by a residual wellbore signature. This is likely caused by mutual inductance of the wellbore and fluid zones. The composite signature provides scant information regarding the location of the fluid zone; though the signature of the latter is somewhat preserved. The wellbore, especially its toe, is shown to act as a secondary source. Further tests suggest that the wellbore-fluid coupling is inductive rather than galvanic, although the latter cannot be discounted. The detection of fracture zones likely depends on the source used, the host sediment conductivity, and the ambient electromagnetic noise levels, which vary from site to site and from day to day. | en |
