A Comparison of Volumetric and Dynamic CO2 Storage Resource Estimation Methodologies in Deep Saline Formations

Review of CO2 storage efficiency in deep saline aquifers

“…The analytical results of Szulczewski et al (2014) were recently corroborated by a numerical study performed at the Energy and Environment Research Centre at the University of North Dakota (IEAGHG, 2014;Craig et al, 2014;Gorecki et al, 2015) of CO 2 injection in two deep saline aquifers, one with no recharge and discharge areas, hence closed, and one open. The authors calculated the volumetric storage capacity according to relations (5) and (14), and also conducted numerical simulations of injection to investigate the effects of boundary conditions, well configurations and injection (and extraction) strategies, with the goal of determining the effective storage efficiency by using a large number of injection wells, with focus on pressure build-up and pressure interference.…”

“…Active reservoir management to relieve pressure build-up, increase injectivity and manipulate CO 2 migration is analyzed by Buscheck et al (2012), including vertical and horizontal wells and well spacing. The use of horizontal wells does not lead to a marked increase in storage capacity, hence storage efficiency, but it may reduce the number of wells needed for CO 2 injection (Gorecki et al, 2015). Optimization of well placement and brine extraction, and use of multiple 5-spot well patterns for CO 2 injection and water production are discussed by Cihan et al (2014) and WesselBerg et al (2014), respectively.…”

“…While the references quoted so far present cases of water production simultaneous with CO 2 injection, Buscheck et al (2014) present a storage management approach in which dual-mode wells are used first for water extraction and subsequently for CO 2 injection. Generally, as pointed out by Gorecki et al (2015), water extraction is the biggest single factor that increases storage capacity, hence storage efficiency, particularly for closed systems, while maintaining pressure below allowed limits.…”

“…Storage resource estimates are theoretically time and space independent in the sense that the entire aquifer, or storage assessment unit, is considered, and the estimate represents what would be achieved "at the end of time", i.e., in a time period much longer than a project life-time (several decades), but, more importantly, in a time period much longer than the period of time needed to achieve climate stabilization under current scenarios (scale of a century or so). Indeed, for open aquifer systems, given a sufficient large number of wells and a long injection time, and utilizing the full usable extent of the aquifer, the dynamic storage capacity, hence storage efficiency, will asymptotically approach the volumetric storage capacity (reserves will approach resources) (see IEAGHG, 2014, andGorecki et al, 2015), but this will be realized for continuous CO 2 injection in multi-well patterns for time periods much longer than any relevant period of interest. However, the use of multiple injection wells to reach all available pore space (resource) will lead to pressure interference between the wells.…”

“…Of these measures, only the fourth one leads to an increase in CO 2 storage capacity, hence storage efficiency. Pressure management through increasing the number of injection wells (with corresponding reduced injection rate per well) is proposed by Bergmo et al (2011), while generally increasing the number of injection wells to reach more pore space, control pressure build-up and achieve the desired storage capacity is proposed by Wang et al (2013), Craig et al (2014) and Gorecki et al (2015). Simultaneous CO 2 injection and passive brine extraction are proposed by Bergmo et al (2011) (passive brine extraction occurs when, as a result of general pressure build-up in the storage aquifer, hydraulic heads at offset/producing wells are higher than the hydrostatic pressure in those wells, while active brine extraction involves pumping of aquifer water).…”