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Hydraulic Fracture Monitoring Using a Downhole Sliding Array: an Innovative Single-Well Solution


Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman",serif;} Understanding the geometry of the hydraulically induced fracture network is key to the effectiveness of any stimulation program because fracture surface area directly impacts production performance. Microseismic monitoring of hydraulically induced fracture networks maps failure loci detected using a variety of monitoring geometries (e.g., nearby single- and/or multiwell downhole 3C arrays; 1C and 3C surface networks; 1C and 3C shallow grid, fiber-based arrays). Each type of acquisition geometry has its pros and cons in terms of deployment, acquisition, resolution limitations, and cost. Surface and shallow arrays are limited in their ability to detect small-magnitude microseismic events given the large distance from the treatment zone (e.g., attenuation) and near-surface noise. Although borehole arrays are closer to the treatment zone, they are generally restricted to the availability of nearby wells, which limits the number of arrays and tools and the overall monitoring aperture that can be deployed. Typically, a single monitor well deployment is used, although multiwell, multi-array deployments can increase raypath coverage to improve microseismic event detection and location. We propose a unique and innovative single-well, downhole array setup and show with modeling results that it improves event location and attribute extraction. This array monitoring geometry uses two decoupled 3C sensor subarrays with variable lengths of split between them, positive mechanical clamping, and onboard shakers. The decoupled split subarrays can be deployed in multiple sections of the monitor well, in the vertical and/or in the horizontal and near the toe and/or near the heel of the monitor well. The location of the lower half of the split array can be adjusted to allow the array to remain close to the entire treatment zone, which results in increased detectability of small-magnitude events. Velocity model calibration is also improved using the split levels as a result of having tools deployed in multiple sections of both the vertical and lateral. Microseismic event hypocenter location accuracy, source parameter estimation, and moment tensor solutions are improved using a near-optimally constrained velocity model and by the proximity of the monitoring array. The variable-length subarrays provide a virtual continuous array for improved sensitivity and hypocenter determination precision.