Flow regime associated with vertical secondary migration

Guy Vasseur (1) , Luo Xiaorong (2) , Jianzhao Yan (2) , Didier Loggia (3) , Renaud Toussaint (4, 5) , Jean Schmittbuhl (6, 5)

1 SISYPHE - Structure et fonctionnement des systèmes hydriques continentaux
2 IGG - Institute of Geology and Geophysics [Beijing]
3 Géosciences Montpellier
4 IPGS-GE - Géophysique expérimentale (IPGS)
5 EOST - Ecole et Observatoire des Sciences de la Terre
6 IPGS-Sismologie - Sismologie (IPGS)

Secondary migration is defined as the movement of hydrocarbons through relatively permeable rocks from source to trap: a two-phase flow within a porous medium. Depending on the geometry and capillary pressure distributions of carrier beds, secondary migration has both vertical and lateral components. The present paper focuses on that part of the migration where the movement is mainly vertical. Its objective is to propose a description of the dynamics governing the vertical part of secondary migration based on the main physical aspects of two-phase flow in a homogeneous porous medium. The study is illustrated by laboratory observations performed in a vertical, 2-D Hele-Shaw cell filled with a transparent porous medium where the flow of dyed oil invading a wetting fluid is visually observed. These observations help us to understand the effect of buoyant, capillary and viscous forces on the resulting flow, the relative importance of which is characterized by non-dimensional numbers. Extrapolating these observations to natural media, it is proposed that vertical secondary migration can be described as a percolation of disconnected and vertically-elongated stringers. These stringers do not move continuously but as a succession of snap-off and re-feeding events which result in a jerky upward movement. Using parameters characterizing the physical properties of the fluid and of the porous medium, the geometry and the dynamic behavior of the stringers are estimated. The width of stringers occurring during secondary migration in geological media is centimetric and their vertical size ranges from several centimeters to a few meters. An upper limit of the mean upward velocity of stringers is proposed, as well as an estimate of their spatial density and of the minimum, average horizontal distance (decametric) between two stringers. The stringers are sparsely distributed, resulting in a low average oil loss and a high efficiency of the vertical migration process.

Mots clés: capillary number; Bond number; porous medium; two-phase flow; secondary migration

Domaines: Géologie appliquée; Mécanique des fluides [physics.class-ph]; Mécanique des fluides [physics.class-ph]

Guy Vasseur, Luo Xiaorong, Jianzhao Yan, Didier Loggia, Renaud Toussaint, et al.. Flow regime associated with vertical secondary migration. Marine and Petroleum Geology, 2013, 45, pp.150-158. ⟨10.1016/j.marpetgeo.2013.04.020⟩. ⟨hal-00831370⟩