Sill morphology and comparison of brittle and non-brittle emplacement mechanisms

Abstract

Since the first seismic data acquired in the Parnaíba Basin during the1970s to the present day, there has been a technological advance that allowed to improve the seismic imaging of the subsurface data, as well as the geological knowledge of the basin, which has resulted in several gas discoveries. The petroleum system considered for these discoveries is defined as atypical, where the magmatism is a critical point for generation processes, as well as important to the processes of migration and preservation of hydrocarbons, becoming in this case, part of the elements of the system as trap and seal. The evolution of a magmatic event can compromise the petroleum system if the timing of the igneous intrusion is not adequate for the trap and the seal be ready before the hydrocarbon migration. This work aimed to analyze the importance of the two magmatic events in the basin previously described as Triassic-Jurassic and Cretaceous ages, to understand what their contribution to the processes of generation and preservation. For that, thousands of kilometers of seismic data were mapped, dozens of wells were studied and from them, a great set of geochemical data from intrusive rocks was collected, and a highresolution U-Pb (ICP-MS and TIMS) dating was performed on part of those samples previously analyzed Using wells drilled up to the Devonian age sequence it was possible to estimate at least 128,000Km 3 of volume of magma emplaced in this interval, which raises the largest volume estimation for the basin so far in about 20%. The geochronological analyses indicate for intrusions whitin Poti Formation, 217 ± 6My to the well 1-OGX-114-Ma and 192 ± 4My to the well 1-OGX-22-MA and for rocks intruded whitin Tiagua Formation 201.22 ± 0,11My to the well 1-OGX-22-MA, which is an event related to Penatecaua magmatism of the Triassic / Jurassic limit, with no association to the Cretaceous event. The geochemical analyses from the subsurface did not allow to separate Mosquito and Sardinha formations into geographical domains as postulated by several authors. Finally, based on the data obtained and the seismic interpretation, an events chart was proposed for the plays already proved in the basin, being defined that the critical point on the traps and seal is related to the Triassic / Jurassic magmatism according to the geochronological analyses, being the Cretaceous magmatism, possibly associated with the tectonism that occurred during the breakup of the Gondwana and possibly responsible for open traps already formed.

Mechanisms of overburden deformation associated with the emplacement of the Tulipan sill, mid-Norwegian margin

“…Our data also highlight the occurrence of hydrothermal vent complexes (Figures 6-8) (see also Kjoberg et al, 2017), which result from local fluidization and gas generation within the host rock (Einsele et al, 1980;Svensen et al, 2004;Schofield et al, 2010Schofield et al, , 2012aJackson et al, 2013;Aarnes et al, 2015). Nevertheless, these authors show that any fluidization occurs dominantly close to the intrusions, and the resulting structures are likely of subseismic scale and, so, invisible on our seismic data.…”

“…For example, pore fluid expulsion within the thermal and/or structural aureole of the intrusion can lead to a significant volume reduction of the host rock ( Figure 1c) (Einsele et al, 1980;Morgan et al, 2008;Schofield et al, 2010Schofield et al, , 2012aSchofield et al, , 2014Jackson et al, 2013;Magee et al, 2013). This volume reduction resulting from a decreased porosity reduces the effect of active mechanical doming due to the emplacement of the intrusion.…”

“…These models typically assume that uplift occurs via elastic bending, and sometimes failure, of the overburden, causing forced folding and fracturing due to the intrusion. However, field observations, seismic studies, and recent 3D laboratory models show that substantial synemplacement inelastic (elastoplastic) deformation, such as local compaction and fluidization, can also affect the growth of these domes (e.g., Cosgrove and Hillier, 1999;Hansen and Cartwright, 2006;Schofield et al, 2010Schofield et al, , 2012aSchofield et al, , 2014Magee et al, 2013). In addition to the synemplacement mechanisms, seismic data indicate that postemplacement differential compaction may also play a role in forming or modifying dome structures above sills (e.g., Einsele et al, 1980;Cosgrove and Hillier, 1999;Hansen and Cartwright, 2006;Agirrezabala, 2015).…”

Unravelling intrusion-induced forced fold kinematics and ground deformation using 3D seismic reflection data

“…At shallowlevels in sedimentary basins, intrusions often develop sill-like geometries as magma is emplaced along mechanical contrasts between layered strata, weak sedimentary rocks, and/or the minimum principal stress axis rotates to vertical [e.g. Kavanagh et al 2006;Gudmundsson 2011;Schofield et al 2012;Magee et al 2016;Walker et al 2017]. As intrusion continues and the sill inflates, space can be generated by uplift of the overburden and free surface to form forced folds [e.g.…”

“…Initial formation of S1-S4 likely occurred in the Katiki or Moreaki formations at various structural levels, where host rock properties or stress conditions favoured sill emplacement [e.g. Kavanagh et al 2006;Gudmundsson 2011;Schofield et al 2012], and were at least partly accommodated by forced folding (e.g. Figure 2 and 3).…”