For this month’s ResFrac Office Hours, we had a presentation from Jiehao Wang, Geomechanics Specialist with Chevron, titled “Drainage Fracture Height Characterization Using Rayleigh Frequency Shift Distributed Strain Sensing (RFS-DSS) in a Vertical Monitoring Well from HFTS-2.”
Abstract: Understanding drainage fracture height is critical for optimizing multi-bench unconventional reservoir development and improving forecasting reliability. Rayleigh Frequency Shift Distributed Strain Sensing (RFS-DSS) can measure strain changes along fiber during hydraulic fracturing and production. RFS-DSS data acquired from fiber installed in vertical offset wells show potential for characterizing drainage fracture height. This study revisits the HFTS-2 dataset and provides new insights into the potential of RFS-DSS for drainage fracture height characterization through cross-disciplinary data analysis and numerical modeling.
This study first conducts a series of synthetic simulations using a fully coupled reservoir geomechanics model to characterize the strain responses induced by pressure depletion. Then, a cross-disciplinary analysis of the HFTS-2 dataset was performed, including RFS-DSS, low-frequency DAS, microseismic, pressure gauge, geochemistry, and geological lithology data. It enables a comparison between drainage height interpreted by RFS-DSS and created/drainage fracture height determined by other surveillance methods. This is followed by a field-scale fracturing and production simulation to further validate the interpretation.
Simulation results from synthetic cases with various fracture and reservoir configurations were used to build a reference catalogue that supports the interpretation of RFS-DSS data in field applications. The RFS-DSS data in HFTS-2 was acquired during a well interference test. Pressure gauges show continuous pressure decrease in far-field even when wells are shut-in, enabling the interpretation of drainage height using this dataset. After 13 months of production, the RFS-DSS-interpreted drainage height was approximately 40% of the created fracture height. This interval is effectively bounded by calcite-rich layers above and below. A field-scale model of HFTS-2 successfully reproduced the observed RFS-DSS strain pattern during the interference test and confirmed that the compressive strain zone corresponds to the drainage height.
This paper demonstrates the potential of RFS-DSS in characterizing drainage fracture height and performing production allocation. RFS-DSS in vertical monitoring wells provides a more complete picture of vertical drainage profile compared to pressure gauge arrays and geochemistry methods, thanks to its spatially continuous measurement. Its application in multi-bench unconventional reservoirs has the potential to support the optimization of development strategies and completion designs, as well as the improvement of production forecasting.