Modeling tracer flowback behaviour for a multifractured horizontal well in a tight oil reservoir using the embedded discrete fracture model

Abstract

Tracer flowback testing has been proven as an efficient method to characterize hydraulic fractures and predict the performance of a hydraulically fractured well in a tight oil reservoir; however, few efforts have been made to characterize such fracture networks by quantifying tracer flowback behaviour due to the associated technical challenges. In this work, an efficient and effective numerical model based on the embedded discrete fracture model (EDFM) was developed, validated, and applied to characterize complex fracture networks and evaluate tracer flowback behaviour for a multistage fractured horizontal well. More specifically, such a model is applied to deal with complex fractures by dividing the fractures into segments using matrix grid boundaries and creating non-neighbouring connections (NNCs) using structured grids, while the complex fracture networks can be characterized by matching tracer flowback profiles with consideration of tracer dispersion and adsorption effects. Then, tracer flowback profiles for a fractured horizontal well with different fracture network patterns, including bi-wing fracture network (BWFN), opening-fissure fracture network (OFFN), fractal-like fracture network (FLFN), and mutually orthogonal fracture network (MOFN) are obtained. It should be noted that tracer flowback concentration (TFC) varies greatly with different fracture network patterns. Sensitivity analyses have been performed to examine the influence of different parameters (i.e., fracture width, fracture porosity, fracture conductivity, tracer adsorption, and tracer adsorption capacity) on the tracer flowback response for a fractured horizontal well with the BWFN and OFFN. It is found that the TFC increases as the fracture conductivity increases, while it decreases as the adsorption capacity increases. The higher the tracer dispersion coefficient is, the lower the tracer flowback peak concentration will be. Also, this model was validated and then extended to a field case, indicating the accuracy and efficiency of the newly proposed method to characterize the fracture networks compared with the microseismic events.