First Break - Volume 42, Issue 4, 2024

Modern marine-streamer time-lapse (4D) seismic projects generally use broadband processing flows that compensate source and receiver ghost effects. They are mostly very successful, but it can occasionally be difficult to achieve an accurate match between the surveys at low frequencies. A test project using data from the Heidrun field, offshore Norway, suggested that broadband processing can exacerbate minor issues that are typically insignificant for non-broadband flows. Seismic surveys acquired with multisensor marine streamer systems tend to undergo wavefield separation and other processing during acquisition, with different acquisition contractors using differing workflows. This can cause discrepancies between the surveys that the 4D processing contractor cannot compensate. Similarly, ancillary datasets, such as farfield signatures, may be generated inconsistently. We recommend that time-lapse seismic processing begin with raw measurements wherever possible so that identical processing flows may be used for each survey. Even then, it may not be possible to completely compensate the impact of differing acquisition systems.

Carbon sequestration within sedimentary basins (e.g., sandstone reservoirs, saline aquifers) is one of the promising solutions for reducing GHG emissions. However, this will require the current rate of CO2 injection to be increased by several orders of magnitude. In practice this will be a shift from a scattered set of pilot projects worldwide e.g. Sleipner, Quest) to large-scale, regional CO2 injection across a range of sedimentary basins. As a result, there will be a large variety of different ‘CO2 systems’, with critical and sometimes challenging variations in both the reservoir and caprock conditions, both locally and regionally. As the CCUS industry scales it will become increasingly important to understand how the simultaneous injection of CO2 across extensive clustered sites will impact overpressure. Research on naturally occurring fluid migration systems shows that when critical boundaries are crossed for regional overpressure, release of gases can occur from the subsurface via different physical mechanisms. To enhance our understanding of this, we utilise analogue and numerical modelling in combination with seismic analysis to identify potential areas of further research within this previously largely unexplored risk category.

Mitigating flood risk of heavily urbanised coastal regions by geo-engineered surface uplift via CO2-sequestration may help to create commercially viable storage opportunities for greenhouse gases like CO2. Recent projections for increased global flood risk due to sea level rise induced by rising CO2-emissions are briefly reviewed. Next, a practical geo-mechanical model is presented, suitable for quick technical assessments of the key physical parameters that contribute most to achieving a specific surface uplift rate required to outpace the projected relative sea level rise for a certain region at risk. The model allows for probabilistic inputs to (1) capture the uncertainty in the value of key input parameters, and (2) link and rank the sensitivity of the surface uplift, to the individual input parameters (in tornado and spider graphs). Three uplift scenarios are given to demonstrate the feasibility of flood mitigation with CO2-sequestration. Finally, a discussion places the emergence of CO2-injection projects in a historic perspective, and highlights the critical key factors in the future screening of any CO2-injection prospects. These factors include the evaluation of technical challenges, potential risks, stakeholder management, public education and perception management.

A Measurement, Monitoring and Verification (MMV) plan is a requirement for subsurface CO2 injection and storage, and developing an appropriate plan requires holistic assessment. A complete MMV plan must take into account the features of the structure, including geology and mineralogy. It must consider how the CO2 will be introduced to the storage space, the potential for plume movement within the containment area, and a well-defined approach to monitoring over time. The plan also must address risk management, including the potential impact if containment is compromised, how it will be controlled, and the extent to which control measures will be effective.

This study explains how experts developed an MMV plan to manage CO2 produced as associated gas from hydrocarbon production. The project design includes a plan for transporting CO2 in dense phase from an onshore facility to offshore platforms for injection into depleted reservoirs. The study details the development of a site-specific MMV plan that considers geological features, identifies operational challenges, and anticipates conditions that could develop over 15 years of CO2 injection. Identified site specific risks are directly tied to the selection of suitable monitoring technologies.