Preliminary discussion on accumulation mechanism of sand lens reservoirs

Abstract

Petroleum accumulation of sand lens is a long controversial problem,because some sand lenses immerged in source rocks form reservoirs but others not.The accumulation mechanism of sand lens is discussed from hydrocarbon-generation dynamics,capillary pressure and fluidic exchange on surface between source and reservoir rocks,and demonstrated by physical simulation experiments.The study shows that fluidic pressure difference drives the petroleum generated from source rocks towards the sand lens,capillary pressure difference drives the petroleum situated at the contact belt into the sand lens,and buoyancy has the petroleum accumulated on the top of the sand lens.Meanwhile,water in the sand lens naturally escapes from sandstone to mudstone under the capillary pressure difference.So the sand lens can form reservoirs.The sand lenses without forming reservoirs may be relative to the insufficiency of hydrocarbon-driving dynamics and the stop of fluidic exchange passage due to the hydrocarbon-generating peak period being later than the diagenesis and cementation periods.