The quantification of anisotropy in horizontal wells, common in shale reservoirs, with dipole sonic featuring a unique through-the-bit conveyance is presented. Anisotropy and fracture evaluation with multipole sonic logging provides essential information for designing completions and optimizing perforation performance. Multiple case studies demonstrate the contribution of measurements for optimized completion quality and increased production.
The small-diameter logging tool can be conveyed through the drillstring using mud pump flow to deliver the tool out through a specialized bit to the open borehole. The formation survey is conducted in memory mode while the drillpipe is tripped out of the hole. Based on intensive numerical modeling, the tool structure has been optimized to sufficiently suppress the tool-borne acoustic waves and allow measurements in fast formations. The tool is designed to be well-centralized in horizontal and highly deviated wells to ensure robust cross-dipole measurements for the estimation of anisotropic stress and orientation.
The tool characterization in reference formations with known characteristics indicates that the logging tool response is in agreement with the model predictions; therefore, the tool presence effect can be fully compensated for in the processing as a function of borehole size, formation and mud properties. More than 100 field jobs have verified high-quality, cross-dipole measurements in unconventional horizontal and high-angle wells, from 4 1/2-in. to 8 3/4-in. borehole. Detailed analysis of the measured data confirmed that the tool is well-centralized in real logging conditions of horizontal wells. It was also confirmed that the transmitters generating monopole and dipole waves provide sufficiently wide frequency band excitation to extract information from the borehole signal. Case studies show that anisotropy ranging from 3% to 40% was extracted reliably as later verified with other measurements. Incorporating the anisotropy of the rock into the horizontal stress estimation enabled the operator to optimize engineered completions. The substantially greater confidence in the accuracy and reliability of the completion directly impacted the perforation efficiency and ultimately the well production.
The new tool is an enabler for quantifying anisotropy with cross-dipole as well as fracture analysis with Stoneley to evaluate horizontal and high-angle wells with minimal cost, leveraging a unique low-risk and driller-friendly conveyance system. It can easily be included into existing drilling and tripping plans.