Analysis of Downhole Temperature-Strain Responses in Multiscale Fractured Reservoirs Using Coupled Geomechanical-Flow-Thermal Simulations and Fiber Optic Data Modelling
Creators: Zhong, Chuanyao
Publisher: name: University of Alberta Library
Year: 2024

<p>Recent advancements in fracture diagnostic tools, particularly fiber optic (FO) technologies such as Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS), have greatly enhanced the real-time monitoring and assessment of fracture development and inter-well interactions in hydraulically fractured unconventional reservoirs. However, accurately and efficiently interpreting these data remains a significant challenge. Recent studies have shown that correlating numerical simulations with fiber optic data can yield more detailed information about fracture properties and the extent of stimulation. Nonetheless, this numerical modelling process is not trivial. First, modelling multi-scale fracture networks and capturing their dynamic interactions with the surrounding matrix is challenging. Second, modelling hydraulic fracturing&#39;s dynamic processes require a coupled geomechanical-thermal-flow simulation approach, but systematic evaluation and validation is needed to ensure it accurately addresses the complexities. Third, a robust framework is needed to model the dynamic behaviours of induced secondary fractures and natural fractures, effectively capturing their effects. On the other hand, to improve interpretation, further investigation is needed into downhole strain responses under complex thermal conditions and the impact of various fracture properties on downhole temperature behaviours. In a parent-child well setup, it&#39;s crucial to understand how inter-well interference (fracture hits) affects FO data. While previous simulations have compared numerical results to DAS responses, few have examined how fracture interference impacts the production of nearby wells. Even fewer studies have incorporated DTS data in analyzing inter-well interference.<br>
We first enhance the fracture-matrix modelling by developing an improved upscaling workflow using the Upscaled Discrete Fracture Matrix (UDFM) approach within the framework of an open-source code: DFNWORKS. The simulation is then coupled with a pressure-dependent apparent permeability (Kapp) updating scheme, capturing the effects of non-Darcy flow mechanisms on the matrix conductivity. Next, to model the dynamic hydraulic fracturing process, we utilize a 3D deformable finite-element geomechanics system coupled with flow-thermal simulations under the Dual-Porosity Dual-Permeability (DPDK) framework within commercial software packages. A dynamic node-splitting technique models the main hydraulic fracture (HF) opening and propagation. The model responses are validated against analytical solutions, asymptotic solutions, and established numerical solutions, which help us identify the most effective modelling strategies for this context. Induced secondary fractures (IFs) are modelled by dynamically updating fracture grid block properties, while pre-existing natural fractures (NFs) are modelled as a DFN using additional control volumes. A novel integrated scheme was developed to model NF reactivation considering tensile and shear fracturing mechanisms, updating stresses and permeability at each time step. <br>
The constructed models are used to study the impacts of non-Darcy flow behaviours, fracture network connectivity, and pressure interference on production. Geomechanical characteristics are analyzed and compared to field Low-Frequency DAS (LF-DAS) data, explaining complex temperature-strain behaviours. A comprehensive analysis is conducted to investigate how operational characteristics and various fracture properties affect temperature behaviours along the wellbore, providing insights for DTS data analysis. Treatment-monitor well interactions (fracture hits) are examined, revealing their significant influences on fracture growth, thermal behaviours, and flowback performance of nearby clusters. Finally, field case studies on the Montney Formation are conducted by correlating our simulations with field DTS and DAS data from an industrial partner.<br>
The proposed modelling strategies are readily applicable to other simulation packages. Our findings enhance the understanding on the effects of hydraulic fracturing, multi-scale fracture networks and inter-well interference on downhole geomechanics and thermal behaviours, as well as flowback performance in unconventional reservoirs. More importantly, we provide a practical framework for enhancing the interpretation of field DTS and DAS signals, advancing the application of FO technologies in fracture diagnosis and treatment evaluation.</p>