Characteristics of Fracture Properties from Simulated High-Resolution Distributed Strain Sensing Data During Stable Production
Authors: Ma Wei , Wu Kan , Jin Ge 
Published: September 2023

ABSTRACT
Distributed fiber optic monitoring has been demonstrated to be an invaluable technique for characterizing fracture geometries and analyzing the completion effectiveness. Distributed Strain Sensing through Rayleigh Frequency Shift (DSS-RFS) is a novel fiber optic diagnostic method, which enables continuous, real-time measurement of strain changes along the fiber during production. The DSS-RFS strain change measurement can provide critical information about fracture characteristics. The strain changes are measured during both shut-in and stable production periods in the Hydraulic Fracturing Test Site-2 (HTFS-2) test site. The negative strain changes are observed at perforation locations during stable production. However, the mechanism of strain changes during stable production in a multistage fractured horizontal well remains unclear. Therefore, in this paper, we use a coupled geomechanics and fluid flow to simulate the DSS strain change during stable production. The different strain change profiles along the fiber are investigated through a sensitivity analysis during stable production in a multistage fractured horizontal well. Based on sensitivity analysis, tornado plots are presented to rank the effects of fracture properties on DSS strain changes. This study provides valuable insight on the DSS strain change during stable production and demonstrates the potential for utilizing the DSS-RFS datasets without shut-in the well.

INTRODUCTION
The economical development of unconventional reservoirs has been enabled by the multistage hydraulic fracturing technique in a horizontal well. Many uncertainties remain in understanding and evaluating unconventional development. Accurately characterizing the fracture geometry is crucial for optimizing completion design and evaluating the well production (Pan et al. 2022). Various fracture diagnostic techniques are widely used for characterizing and evaluating the hydraulic fracturing stimulation, such as, microseismic monitoring (Fisher et al. 2004), pressure monitoring (Haustveit et al. 2020), tracers (Karmakar et al. 2016), and geochemical fingerprinting (Liu et al. 2020).
Fiber optic monitoring is recently being proven to be a promising diagnostic tool to characterize fracture geometries and assess the stimulation effectiveness (Jin and Roy 2017; Ugueto et al. 2021, Liu et al. 2021; Jin et al. 2021, Srinivasan et al. 2022). Recently, a new fiber optic diagnostic technology known as Distributed Strain Sensing based on Rayleigh Frequency Shift (DSS-RFS) has been demonstrated for fracture characterization during production in the Hydraulic Fracture Test Site 2 (HFST-2) project (Ugueto et al. 2018). This technology measures relative strain changes along the fiber with a high spatial resolution of 20 cm and high measuring sensitivity of less than 1 με. The detailed principle of the DSS-RFS can be found in Jin et al. (2021). The measured DSS strain changes during the shut-in period provide crucial information about understanding fracture characteristics and optimization of completion design and production performance (Jin et al. 2021; Ugueto et al. 2021). The field applications of DSS-RFS measurements have been demonstrated in the HFTS-2 project (Ugueto et al. 2021). The strain changes have been measured twice during shut-in and reopening periods (February 2020 and September 2020). The extensional DSS-RFS strain changes are observed at the perforation locations during the shut-in period and locations of the strain change peaks show good correspondence to the Distributed Acoustics Sensing (DAS) measurements during the stimulation (Jin et al. 2021). Liang et al. (2022) and Dhuldhoya et al. (2022) also demonstrated the successful field applications of DSS-RFS measurements for near-well and far-field fracture characteristics and development optimization.