Lee Hunt1, Eric Street1, Graham Hack1, Jason Schweigert2 and Matthew Allen2




We present a new strategy, which we call Theseus 24D, to increase the capital efficiency of seismic monitoring, measurement, and verification (MMV) plans for carbon capture and storage (CCS) projects onshore. Theseus is needed because CCS is currently socially and environmentally desirable but has a discouragingly high capital intensity. Also, the repeat, or time-lapse, seismic elements of CCS bear a material amount of the MMV cost for these projects. MMV rarely endures a critical business evaluation in the literature—papers have predominantly focused on whether MMV is effective, but not whether it is efficient. Theseus proposes to maintain effectiveness and improve efficiency by taking a realistic look at the seismic elements of CCS, and how the physical nature of carbon dioxide’s (CO2) seismic response can be used to create an advantage. Theseus does this through three primary means: first, by choosing seismic methods that are more realistic to onshore CCS projects and the primary goals of the seismic therein, second, by integrating all seismic activities and their scheduling, and lastly by minimizing the excess amount of repetition, or redundancy, in the area covered by the repeat seismic surveys. We therefore first discard vertical seismic profile (VSP) methods as unrealistic for new projects. VSP analysis makes sense for onshore pilot studies and for the early analysis of plume growth, and while there may be some cases where it is needed for near wellbore monitoring, its expense and limited offset range of coverage make it ill-suited for general business use, which is long-term. We also note that most onshore CCS seismic response is limited to mapping the plume front. Next, we integrate the two seismic techniques most capable of being effective through all stages of a CCS project—2D and 3D surface seismic. The integration is brought about through a special design within the baseline 3D, termed 24D. The 24D design comes at a similar cost of a standard baseline 3D, but also comprises the baseline 2D. Repeat seismic is undertaken by either 2D or 3D methods, scheduled in a way that minimizes capital and sees interaction between the two survey types. Finally, by recognizing that the seismic response of a CO2 plume stabilizes and changes little after a small cut-off saturation, we build upon the well-known Ship of Theseus thought experiment to define a protocol for reducing unnecessary redundancy in the repeat seismic operations. This increase in efficiency cuts repeat data beyond the plume, as well as inside it, creating in some cases a ‘coring’ of the repeat 3D surveys around the injector wells. The net effect of all these changes can be a reduction on the order of 26% of the capital used for seismic in MMV, and up to a 30% reduction in surface disturbance at closure.

This is part 1 of a 3-part series and treats the new MMV strategy from a high level, focusing mostly on the 3D aspects of the problem. Parts 2 and 3 extend the idea to its limits, particularly with the 24D 2D and 3D integration concept.