Abstract
In June 2006, in a production well in a tight sandstone shale sequence, on-shore USA, two borehole seismic arrays were deployed in separate wells during a proppant-baring hydraulic fracture treatment. The intent was to delineate the treatment-generated fracture network by recording the microseisms triggered by the treatment, map the microseism source locations, and then use the map as an overlay to delineate the fracture network. The treatment was one facet of a proprietary, multi-faceted injection strategy with microseismic mapping used to determine if neighboring fracture networks overlap. In addition to mapping the network, the objective of this facet was to compare maps from the two arrays. One array was in a remote well, the other in the treatment well. The remote array was offset ~700 ft from the treatment well and at the injection depth. This array was ~500 ft long; self-locking; contained 15, 3-component motion sensors; and operates on a fiber-optic cable. The treatment-well array, the "TABS" or TriAxial Borehole Seismic array (licensed by ExxonMobil Upstream Research), is ~75 ft long; self-locking; operates on a standard, 7-conductor wireline; and includes (1) 3, 3-component motion sensors, (2) an ambient fluid pressure sensor, and (3) a gyroscopic, sensor orientation package. During the treatment, a 45-minute injection immediately followed by a 1-1/2-hour well shut-in, the remote array failed to detect any discernable treatment-triggered, microseisms. However, TABS, which recorded microseismicity only during the shut-in, recorded ~400 microseisms. During the operation, the remote array maintained one position; TABS was unlocked, repositioned, and relocked twice; Moving TABS allowed different perspectives for recording the microseismicity, improving the accuracy of mapping and enhancing additional characteristics extractable from the microseismic waveforms.
