Pressure constraints on the CO ₂ storage capacity of the saline water-bearing parts of the Bunter Sandstone Formation in the UK Southern North Sea

Abstract

The Bunter Sandstone Formation (BSF) in the UK sector of the Southern North Sea is thought to have a significant potential for the injection and storage of anthropogenic CO 2 within periclines that lie above salt domes and pillows formed by halokinesis in underlying Zechstein strata. During the formation of the periclines, the BSF and its overlying top seals were subjected to extensional stresses and, in consequence, are commonly cut by seismically resolvable faults that present a risk to the containment of gas and buoyant fluids such as supercritical CO 2 . Although most of the closed structures in the BSF are saline water-bearing, eight gas fields (total gas initially-in-place >72 bcm (billion cubic metres)) have been discovered to date. The seismically resolved structure of these gas fields demonstrates that two different top seals, the Haisborough Group and the Speeton Clay, can seal gas columns of up to 128 and 104 m respectively, despite the presence of faults with small displacements above the field gas–water contacts. The observed gas columns are equivalent to CO 2 columns of up to around 100 m in height. Simple geomechanical modelling suggests that existing optimally orientated faults may dilate or be reactivated if the pore-fluid pressure increase as a result of CO 2 injection exceeds a gradient of about 13.4 MPa km –1 , potentially resulting in loss of storage integrity.

Multiphase Flow Characteristics of Heterogeneous Rocks From CO2 Storage Reservoirs in the United Kingdom

“…The Leman formation also contains two natural CO 2 accumulations, the Fizzy and Oak gas fields both of which contain 50–90% CO 2 (Pearce et al, ; Underhill et al, ), providing an analogue to CO 2 storage. Closed structures without gas charge, which provide structural traps for saline aquifer storage, have been identified in the Ormskirk formation (Kirk, ) and Bunter formation (Holloway et al, ; Noy et al, ; Williams et al, ).…”

In-situ stress orientations in the UK Southern North Sea: Regional trends, deviations and detachment of the post-Zechstein stress field

“…This is associated with the presence of the Permian-aged Zechstein Group (Ask 1997;Fejerskov & Lindholm 2000;Hillis & Nelson 2005;Williams et al 2014), which comprises a thick evaporite sequence. Halokinesis has occurred in the centre of the UK SNS, with Cenozoic halokinesis particularly in the Silverpit Basin (Figure 1) resulting in folding of the post-Zechstein cover rocks into a series of anticlinal ridges and associated synclines (Griffiths et al 1995;Stewart & Coward 1995;Underhill 2009).…”

“…This suggests that the stress regime differs from the dominantly strike-slip state of stress observed in adjacent areas in the onshore part of the UK (Evans & Brereton 1990;Baptie 2010), and which is also thought to be prevalent in the basement rocks beneath the UK SNS. which the well was drilled, and parallel to the orientation of crestal extensional faults (Williams et al 2014). Teufel (1991) reported variable S Hmax orientations around a similar structure in the Norwegian sector of the North Sea where a normal faulting stress regime prevails.…”

Permeability of the Mercia Mudstone: suitability as caprock to carbon capture and storage sites

“…Potential has been identified to store CO 2 in Lower Triassic Sherwood Sandstone Group (SSG) reservoirs and saline aquifers onshore and offshore UK, including in the East Irish Sea Basin and Southern North Sea Basin (Williams et al 2014). In the East Irish Sea Basin, there has been careful study of the potential for CCS within existing petroleum fields and also in structures that do not contain petroleum but could feasibly trap sequestered CO 2 Heinemann et al 2012).…”