Role of Faults in Hydrocarbon Leakage in the Hammerfest Basin, SW Barents Sea: Insights from Seismic Data and Numerical Modelling

Abstract

Hydrocarbon prospectivity in the Greater Barents Sea remains enigmatic as gas discoveries have dominated over oil in the past three decades. Numerous hydrocarbon-related fluid flow anomalies in the area indicate leakage and redistribution of petroleum in the subsurface. Many questions remain unanswered regarding the geological driving factors for leakage from the reservoirs and the response of deep petroleum reservoirs to the Cenozoic exhumation and the Pliocene-Pleistocene glaciations. Based on 2D and 3D seismic data interpretation, we constructed a basin-scale regional 3D petroleum systems model for the Hammerfest Basin (1 km × 1 km grid spacing). A higher resolution model (200 m × 200 m grid spacing) for the Snøhvit and Albatross fields was then nested in the regional model to further our understanding of the subsurface development over geological time. We tested the sensitivity of the modeled petroleum leakage by including and varying fault properties as a function of burial and erosion, namely fault capillary entry pressures and permeability during glacial cycles. In this study, we find that the greatest mass lost from the Jurassic reservoirs occurs during ice unloading, which accounts for a 60-80% reduction of initial accumulated mass in the reservoirs. Subsequent leakage events show a stepwise decrease of 7-25% of the remaining mass from the reservoirs. The latest episode of hydrocarbon leakage occurred following the Last Glacial Maximum (LGM) when differential loading of Quaternary strata resulted in reservoir tilt and spill. The first modeled hydrocarbon leakage event coincides with a major fluid venting episode at the time of a major Upper Regional angular Unconformity (URU,~0.8 Ma), evidenced by an abundance of pockmarks at this stratigraphic interval. Our modelling results show that leakage along the faults bounding the reservoir is the dominant mechanism for hydrocarbon leakage and is in agreement with observed shallow gas leakage indicators of gas chimneys, pockmarks and fluid escape pipes. We propose a conceptual model where leaked thermogenic gases from the reservoir were also locked in gas hydrate deposits beneath the base of the glacier during glaciations of the Hammerfest Basin and decomposed rapidly during subsequent deglaciation, forming pockmarks and fluid escape pipes. This is the first study to our knowledge to integrate petroleum systems modelling with seismic mapping of hydrocarbon leakage indicators for a holistic numerical model of the subsurface geology, thus closing the gap between the seismic mapping of fluid flow events and the geological history of the area.

Dynamic and history of methane seepage in the SW Barents Sea: new insights from Leirdjupet Fault Complex

“…Seafloor features related to fluid expulsion processes e.g. pockmarks and craters are widespread and their formation, in some cases, is related to the destabilization of methane hydrates 19 , 30 fed from leaking Mesozoic hydrocarbon reservoirs 31 – 34 . In addition, the Barents Sea is a paleo-analogue of the Antarctic 35 , and therefore may help better predict the evolution of the modern gas hydrate systems beneath the marine-based West Antarctic Ice Sheet.…”

Role of Warming in Destabilization of Intrapermafrost Gas Hydrates in the Arctic Shelf: Experimental Modeling

“…A wealth of data on subsea permafrost in the Arctic shelf collected through Russian and international research projects [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] has revealed large-scale methane emission from bottom sediments into water and on into the atmosphere. The gases in the Arctic shelf are often attributed to increasing microbial methane generation, migration of gas through taliks and faults, as well as to decomposition of intrapermafrost and subpermafrost gas hydrates during progressive degradation of subsea permafrost [11,[16][17][18][19][20][21]. The dissociation of hydrates related to subsea permafrost degradation has been largely discussed lately as the main mechanism maintaining the emanation of methane [4,14,18,[22][23][24][25][26].…”

Geohazard detection using 3D seismic data to enhance offshore scientific drilling site selection

“…This helps improve both safety and the chance of success of future scientific drilling. Improved 3D seismic acquisition and processing workflows have led to significant improvements in 3D resolution and a reduced reliance on dedicated site surveys (Games and Self, 2017;Oukili et al, 2019). Comparison of the 3D seismic volumes as pseudo site surveys within Proposal 909, against the recently acquired 2D UHR site survey lines, shows that the quality and resolution of imaging are mostly consistent across the two data types, confirming its suitability (comparison in Figs.…”

“…Today, the acquisition of large-scale 3D seismic reflection datasets in frontier basins provides spatial coverage that far exceeds most conventional site surveys (Games and Self, 2017). The processing of these datasets has improved sufficiently to provide a vertical resolution that approaches that of a traditional site survey and often provides a horizontal resolution exceeding that of even closely spaced 2D seismic site surveys (Games and Self, 2017;Oukili et al, 2019). Three-dimensional seismic surveys thus minimize the need for additional data, except for particularly complicated areas (Hill, 1996;Selvage et al, 2012;Sharp and Badalini, 2013;Williams and Andresen, 1996;Roberts et al, 1996).…”