Constraints on bed scale fracture chronology with a FEM mechanical model of folding: The case of Split Mountain (Utah, USA)

W. Sassi (1) , M.L.E. Guiton (1) , Y.M. Leroy (2) , J.-M. Daniel (1) , Jean-Paul Callot (3)

1 IFPEN - IFP Energies nouvelles
2 LGENS - Laboratoire de géologie de l'ENS
3 LFCR - Laboratoire des Fluides Complexes et leurs Réservoirs

A technique is presented for improving the structural analysis of natural fractures development in large scale fold structures. A 3D restoration of a fold provides the external displacement loading conditions to solve, by the finite element method, the forward mechanical problem of an idealized rock material with a stress-strain relationship based on the activation of pervasive fracture sets. In this elasto-plasticity constitutive law, any activated fracture set contributes to the total plastic strain by either an opening or a sliding mode of rock failure. Inherited versus syn-folding fracture sets development can be studied using this mechanical model. The workflow of this methodology was applied to the Weber sandstone formation deformed by forced folding at Split Mountain Anticline, Utah for which the different fracture sets were created and developed successively during the Sevier and the syn-folding Laramide orogenic phases. The field observations at the top stratigraphic surface of the Weber sandstone lead to classify the fracture sets into a pre-fold WNW-ESE fracture set, and a NE-SW fracture set post-dating the former. The development and relative chronology of the fracture sets are discussed based on the geomechanical modeling results. Starting with a 3D restoration of the Split Mountain Anticline, three fold-fracture development models were generated, alternately assuming that the WNW-ESE fracture set is either present or absent prior to folding process. Depending on the initial fracture configuration, the calculated fracture patterns are markedly different, showing that assuming a WNW-ESE joint set to predate the fold best correlates with field observations. This study is a first step addressing the complex problem of identification of fold-related fracturing events using an elementary concept of rock mechanics. When tight to complementary field observations, including petrography, diagenesis and burial history, the approach can be used to better constrain fractured reservoir characterization. © 2012.

Mots clés: Burial history; Chronology of fracture sets development; Complex problems; Constitutive law; Development model; Displacement loading; Field observations; Fold structures; Folding process; Fracture pattern; Fractured reservoir; Geomechanical modeling; Joint set; Laramide; Mechanical model; Mechanical modeling; Mechanical problems; Natural fracture; Rock failures; Rock materials; Sandstone formations; Sliding modes; Stratigraphic surfaces; Stress-strain relationships; Total plastic strain; USA; Landforms; Loading; Petrography; Petroleum reservoirs; Restoration; Sedimentology; Stratigraphy; Stress-strain curves; Three dimensional computer graphics; chronology; displacement; elastoplasticity; finite element method; folding; fracture; rock mechanics; sandstone; strain analysis; stress-strain relationship; structural analysis; three-dimensional modeling; United States; Utah

Domaines: Sciences de la Terre

W. Sassi, M.L.E. Guiton, Y.M. Leroy, J.-M. Daniel, Jean-Paul Callot. Constraints on bed scale fracture chronology with a FEM mechanical model of folding: The case of Split Mountain (Utah, USA). Tectonophysics, 2012, 576-577, pp.197-215. ⟨10.1016/j.tecto.2012.07.025⟩. ⟨hal-00872233⟩