I can’t hear you, speak up — A case study of passive seismic monitoring of the CO2 injection at Delhi Field, Louisiana

Abstract

Passive seismic monitoring has a variety of applications, most widely to monitor hydraulic fracturing in tight sandstone or shale reservoirs. For hydraulic fracturing, microseismic events can help to define the affected zone of the reservoir and the stress state. For enhanced oil recovery (EOR), wastewater, and carbon capture and storage (CCS) injection projects, passive seismic can aid in understanding the impact of injection on the reservoir or the surrounding formations. In any injection programme, containment and caprock integrity are always a concern. Passive seismic data can help to identify potential fracturing within the reservoir area or the overlying formations. The goal of an enhanced oil recovery (EOR) is not to fracture the reservoir and not to lose CO2 out of zone. CO2 seeping into non-reservoir zones wastes resources. Furthermore, there are potential environmental and legal consequences if CO2 is allowed to migrate closer to the surface. Thus, monitoring is a key component of an injection project. Programmes using passive seismic to monitor CO2 injection have experienced mixed results. A primary research field for fluid injection microseismicity is Weyburn field in Canada. Throughout the project, about 100 events were located up to 1600 ft from a downhole array with event magnitudes ranging from -3 to -1. The majority of events occurred at the start of CO2 injection, with lower levels of activity after (White, 2009). CSS projects, with injection into deeper formations, can have a greater level of microseismic activity (Bauer et al., 2015). In a CO2 injection project analysed by Verdon et al (2010), a number of small events were detected close to the monitor well. The majority of events occurred at the start of injection. A number of campaigns did not record microseismicity at all during injection, such as the Pembina oil field in Alberta, Canada (Martinez-Garzon et al., 2013). Additionally, analysis by Soma and Rutledge (2013) found the microseismicity in Aneth oil field was related to salt water disposal not the CO2 injection. The success of different monitoring campaigns is related to a number of factors including geology, geomechanics, and acquisition geometry.