The revolutionary development of unconventional resources during the last two decades has been largely enabled by horizontal drilling and multistage hydraulic fracturing. With geosteering, horizontal wells as long as 7,000 meters can now be placed within a stratigraphic target window as thin as 2 meters, maximizing the wellbore exposure to the reservoir. The philosophy of engineered completions is to place perforation clusters in “like rock” so that all perforation clusters fracture simultaneously, and not have one cluster dominate the others. Petrophysical data are needed as a foundation for engineered completion efforts to maximize stimulation effectiveness. Driven by constant efforts to reduce rig time, offline casedhole logging has been tested as an alternative to openhole wireline logging along horizontal wells. Acquisition of petrophysical data in cased hole is possible, but there are additional complications that do not exist when logging in open hole. If not properly accounted for, they can result in the logging objectives not being met. The intent of this paper is to communicate those complications and potential pitfalls as well as recommendations to help ensure success. Here we show a case study of casedhole formation evaluation along horizontal wells in unconventional reservoirs, and share lessons learned from an operator’s perspective. The casedhole logging suite includes spectral gamma ray (SGR), current-generation pulsed-neutron, and monopole and dipole sonic logs, with objectives to evaluate porosity, mineralogy, total organic carbon, Poisson’s ratio, and Young’s modulus along the lateral wellbore. We emphasize the impact of completion design and hardware on casedhole measurement, which would require additional casing and cement corrections for pulsed-neutron spectroscopy logs and impose special requirements on sonic tool properties and functionalities. For instance, the iron and calcium elemental measurements from pulsed-neutron spectroscopy logs need to be corrected for completion hardware, such as casing clamps and centralizers, and variable cement-bond quality along the circumference and lateral direction, respectively, before a correct interpretation is possible. A sonic tool used in horizontal wells needs to be stiffer and shorter than a regular sonic tool and should be able to fire and acquire both monopole (for compressional slowness) and four-component crossed-dipole (for fast and slow shear slowness) modes. Casedhole monopole sonic logs can be dominated by the casing signal when pipe is not fully bonded to cement. The significant impact of the casedhole environment can be more efficiently accounted for by integrating azimuthal cement-bond data as a quantitative input to the analysis of the nuclear and sonic logs, but advances in workflows and environmental corrections will be required to make this practical.
Lessons Learned From Casedhole Formation Evaluation Along Unconventional Horizontal Wells
Sullivan, Michael, Wang, Haijing, Bolshakov, Alexei, Song, Lisa, Lazorek, Michael, Tohidi, Vahid, and Yegor Se. "Lessons Learned From Casedhole Formation Evaluation Along Unconventional Horizontal Wells." Petrophysics 61 (2020): 253–272. doi: https://doi.org/10.30632/PJV61N3-2020a1
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