For this case study, a Permian basin operator deployed wireline dipole acoustic shear wave imaging through five stacked cased hole wells to determine the extent and orientation of sub-seismic, water bearing faults prior to completing eight closely spaced horizontal wells. Operator encountered continuous and uncontrollable water flows throughout drilling and casing of the first horizontal well on the multi-well pad. To minimize the risk on $50 million dollars in capital and potential long-term operating expenses associated with excessive water production, cased hole logs were acquired in four additional horizontal wells off-line operations. Acoustic log data was recorded in five of the eight wells from two adjacent drilling pads. Reflected geologic features cutting across these wellbores were correlated with drill breaks, gas influxes, and changes in drilling mud properties which helped identify the geohazard connecting the wells to this large water bearing fault. The faulted zones were left uncompleted and production results indicates the study wells performance exceeded that of neighboring wells in the field on a per completed lateral foot basis.
Waveform acquisition was extended in time to expand detection radius away from the wellbore. Advanced processing was performed to bring out acoustic reflections several tens of feet away from the wellbore. Images were exported in orthogonal planes and viewed in earth coordinates to correlate reflective features, in a 3D visualization space, between the adjacent boreholes.
Several important observations and conclusions are drawn from this study. Cement quality directly impacts formation wave coupling on monopole data, the lower frequency dipole source did not generate significant casing ring, and generated quality images through intervals with poor cement bond. Direct logging measurement methods resolve observations on drilling reports, and indirect seismic methods lack the resolution required to guide an engineered completion design.
Smaller, sub-seismic features are difficult to detect and cause significant operational issues. Operators can leverage higher resolution log data to identify geologic events not resolved by surface seismic data. Deep acoustic wave imaging presents a unique post-drill technology to interrogate, in either open or cased hole condition, the extent of intersecting and non-intersecting geological features proximal to the wellbore. Close well spacing may benefit total recovery, however, a single fault network can impact several wells, thus, geohazard risk is compounded in tight spacing developments.
Many operators avoid open hole evaluation services due to the rig time costs and conveyance risks in horizontal sections. These risks are minimized by deploying acoustic tools in a cased hole environment. Wireline tools can be rigged up from a crane and deployed through the horizontal section on a wireline tractor. In Drilled but Uncompleted (DUC) stage of wells, the casing inside is clean and operational risk is greatly reduced. The offline operation eliminates significant standby costs of drilling rig or fracturing fleet.