From Paper to Action: How Operation Agility and Synergies will Unlock CCS at Scale in Offshore Context

Abstract This paper details a unique offshore operation in the United Kingdom (UK) North Sea to deploy a light and agile spot seismic monitoring solution in less than 3-4 days. The objective was establishing the first seismic baseline for monitoring CO2 storage in a depleted gas field, using only 12 seismic receivers and 3 source locations. This novel operational model includes several variables (such as the vessel, the seismic equipment to be used) that can be fine-tuned. The paper describes how real-time tuning of these parameters during baseline acquisition enables a safe and sustainable monitoring solution applicable throughout the storage life cycle. The monitoring system's first layer utilizes spot seismic, an ultra-light acquisition method needing only one source and one receiver per spot location to detect subsurface fluid and/or pressure changes. The goal is to deploy a spot seismic operational model (10 to 30 spots by campaign) that can be frequently repeated with a minimal environmental footprint and at a low cost, offshore. It is essential to: 1) adapt the source and recording devices to ensure optimal detection while limiting environmental impact; 2) identify synergies to reduce operational costs during the survey design; and 3) carefully plan operations while maintaining the flexibility to adapt timing, equipment, or personnel in real-time to ensure optimal acquisition conditions. The preliminary results of the offshore baseline acquisition show a repeatability with a normalized root mean square (nRMS) below 5%, on repeated static shots indicating high-quality results. During the baseline survey, quality control (QC) on a spot monitoring test provides decisive information for tuning source parameters. For instance, determining the relevant number of shots needed to ensure a higher signal-to-noise ratio at target helps reduce rental and operational costs while minimizing environmental impact, achieving up to 90% noise reduction compared to conventional seismic methods, which is beneficial for marine mammals. Careful pre-planning allows daily adaptation onboard to ensure optimal operational conditions, directly enhancing data quality. To ensure cost-efficiency, synergies were carefully studied beforehand. The spot acquisition is performed from a vessel of opportunity chartered annually. Offshore maintenance operations continue during the night shift while acquisition pauses. Additionally, the baseline acquisition operation is planned simultaneously with a vertical seismic profile (VSP) baseline. This paper presents the first application of the spot seismic light and agile operational model for CO2 storage surveillance in a depleted gas reservoir. First QC and operations conducted demonstrated the suitability for Carbon Capture and Storage (CCS) with an acquisition successfully achievable in less than a day.