Abstract
Abstract. Drilling fluid infiltration during well drilling may induce pore pressure and strain perturbations in neighbored reservoir formations. In this study, we report that such small strain changes (∼20 µε) have been in situ monitored using fiber-optic distributed strain sensing (DSS) in two observation wells with different distances (approximately 3 and 9 m) from the new drilled wellbore in a shallow water aquifer. The results show the layered pattern of the drilling-induced hydromechanical deformation. The pattern could be indicative of (1) fluid pressure diffusion through each zone with distinct permeabilities or (2) the heterogeneous formation damage caused by the mud filter cakes during the drilling. A coupled hydromechanical model is used to interpret the two possibilities. The DSS method could be deployed in similar applications such as geophysical well testing with fluid injection (or extraction) and in studying reservoir fluid flow behavior with hydromechanical responses. The DSS method would be useful for understanding reservoir pressure communication, determining the zones for fluid productions or injection (e.g., for CO2 storage), and optimizing reservoir management and utilization.
Highlights
The utilization of underground reservoirs includes the exploitation or storage of resources such as groundwater, oil/gas, heat, and more recently, the CO2 for mitigating the effect of CO2 emission on global warming (Benson et al, 2005), as well as storage of compressed air for electric energy storage (Mouli-Castillo et al, 2019) in underground reservoirs
distributed temperature sensing (DTS) data have been useful for understanding fluid flow behavior and reservoir characteristics owing to the hydrothermal coupling in addition to heat transport monitoring (Bense et al, 2016; Freifeld et al, 2008; Luo et al, 2020; Maldaner et al, 2019; des Tombe et al, 2019)
The results suggest that the formation strain pattern during well drilling could be associated to two causes: either by the permeability structure or drilling-induced formation damage
Summary
The utilization of underground reservoirs includes the exploitation or storage of resources such as groundwater, oil/gas, heat, and more recently, the CO2 for mitigating the effect of CO2 emission on global warming (Benson et al, 2005), as well as storage of compressed air for electric energy storage (Mouli-Castillo et al, 2019) in underground reservoirs. An understanding of fluid flow and reservoir characteristics is required for more manageable and optimized operations. Geophysical methods, such as site-scale seismic, electrical methods, and well logging, have been widely applied for reservoir characterization and monitoring. There have been numerous application studies using distributed temperature sensing (DTS) and distributed acoustic sensing (DAS) in subsurface monitoring. DTS data have been useful for understanding fluid flow behavior (such as flow rate and active fluid flow zone) and reservoir characteristics owing to the hydrothermal coupling in addition to heat transport monitoring (Bense et al, 2016; Freifeld et al, 2008; Luo et al, 2020; Maldaner et al, 2019; des Tombe et al, 2019). The usage of distributed strain sensing (DSS) for subsurface monitoring of quasi-static deformation is comparatively less
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