Modeling tracer flowback behaviour for a fractured vertical well in a tight formation by coupling fluid flow and geomechanical dynamics

In this work, a pragmatic technique has been developed to describe tracer flowback behaviour for a vertically fractured well in a tight formation by coupling fluid flow and geomechanical dynamics. More specifically, the Barton-Bandis model is employed to describe the relationship between effective stress and fracture permeability, while tracer flowback profiles, which can reveal the fracture properties, are quantified by taking tracer dispersion and adsorption into account. Subsequently, this method considering two main mechanisms (i.e., tracer flow behaviour and fracture propagation dynamics) is separately validated with previous analytical solutions and then extends its application to a field case. In addition to tracer flowback concentration, the tracer recovery factor (TRF) is generated to analyze the tracer flowback behaviour. With considering geomechanics, the TRF is nearly 20% higher than that without considering geomechanics. During the flowback period, tracer concentration profiles appear to be unimodal for reservoirs with a single fracture, while tracer concentration increases quickly at the initial stage and then decreases slowly as time proceeds. An increase in matrix permeability increases tracer flowback concentration and the TRF. A larger tracer dispersion coefficient leads to earlier arrival time for the tracer flowback concentration peak together with a lower TRF. Also, the stronger the tracer adsorption is, the lower the tracer flowback concentration and the TRF will be. A higher Young's modulus results in a lower tracer flowback concentration and TRF. An increase in minimum horizontal stress increases tracer flowback concentration. Other parameters, including maximum horizontal stress, fracture closure permeability, and normal fracture stiffness, are also examined and analyzed though less sensitive.

在这项工作中，通过耦合流体流动和地质力学动力学，开发了一种实用技术来描述致密地层中垂直裂缝井的示踪剂返排行为。更具体地说，采用巴顿 - 班迪斯模型来描述有效应力与裂缝渗透率之间的关系，同时通过考虑示踪剂的弥散和吸附来量化能够揭示裂缝特性的示踪剂返排剖面。随后，这种考虑两个主要机制（即示踪剂流动行为和裂缝扩展动力学）的方法分别用先前的解析解进行了验证，然后将其应用扩展到一个现场实例。除了示踪剂返排浓度外，还生成了示踪剂采收率因子（TRF）来分析示踪剂返排行为。考虑地质力学时，TRF比不考虑地质力学时高出近20%。在返排期间，对于单裂缝储层，示踪剂浓度剖面似乎是单峰的，示踪剂浓度在初始阶段快速增加，然后随着时间推移缓慢下降。基质渗透率的增加会提高示踪剂返排浓度和TRF。较大的示踪剂弥散系数会导致示踪剂返排浓度峰值的到达时间提前，同时TRF降低。此外，示踪剂吸附越强，示踪剂返排浓度和TRF就越低。较高的杨氏模量会导致较低的示踪剂返排浓度和TRF。最小水平应力的增加会提高示踪剂返排浓度。其他参数，包括最大水平应力、裂缝闭合渗透率和法向裂缝刚度，也进行了检查和分析，尽管它们不太敏感。