Impact of Well-To-Fault Distance and Two-Phase Fluids on the Detection of Faults for CO2 Storage Purposes Using Pressure Transient Analysis

The impact of faults on fluid flow in the subsurface reservoirs can never be overemphasized as they can serve as either barriers and/or conduits for the flow of fluids in the subsurface. Faults also play a great role in the structural trapping mechanism for the retention of injected CO2. Hence, the detection and imaging of faults are crucial in structural and dynamic reservoir characterization, especially for CO2 storage purposes. One of the well-established methods for fault detection and characterization is pressure transient analysis (PTA). This paper focuses on the individual and combined influence of well-to-fault distance and two-phase fluids on the detection of faults using PTA conducted during CO2 injection into a saline aquifer. Several numerical well test (WT) simulations and interpretations of the resultant pressure transient behaviour involving single phase fluid (water) for different well-to-fault distances were also carried out as a precursor to determine the characteristic well test PTA signatures for faults in a closed system. Subsequently, several other numerical WT simulations, involving CO2 injection into saline aquifer were performed for different well-to-fault distances. Only the falloff test period was interpreted using the radial composite model and pseudopressure approach. The variations in the CO2 plume migration distance and the diffusion of the pressure disturbance front for the different well-to-fault distances underpins the influence of variation of injection rate and volume on the observed signatures. The results from this study have applications in the design and interpretations of PTA data prior to CO2 injection and for CO2 monitoring, as well as reiterating the importance of integrating other data sources for improved reservoir characterization.