Research On The Micro-Mechanism Of The Sand Production And Dynamic Behavior Of The Weakly Cemented Sandstone

The weakly cemented sandstone reservoirs are suffering from sand production seriously,which are distributed widely all around the world.And it is one of the important factor that confine the oil fields production increase.At present,the study on sand production is confined to macro-geological structure and various influencing factors,and do not think of the weakly cemented sandstone's micro-structure.The sand production mechanism of shear failure and tension failure can't clearly describe the sand production process.Aiming at the problems of the study on weakly cemented sandstone sand production and based on the research on the domestic and foreign,The weakly cemented sandstone sand production is researched from the macro into sand particles.And the new sand production mechanism is put forward.Accroding to analysis the micro-structure,the sand particles of weakly cemented sandstone are consisted of frame sands and cohesionless sands.And cohesionless sands movement?chemical action and frame sands denudation of sand production mechanism are put forward.Depending on the production practice of oilfield,the rocess of sand production is divided into three stages.According to analysis the force of the cohesionless sands and the frame sands,the calculation model of critical flow velocity and denudation critical velocity are established,and the movement and denudation regular patterns are analysised.The results show that with the cohesion force increasing?the sand size increasing?the formation fluid viscosity decreasing?the formation porosity increasing?the smooth decreasing,the critical velocity of cohesionless sands movement and frame sands denudation increases and the wells are not easy to sand production.On study the frame sands denudation by stress,the universal models of stress distribution on hole are established.The regulation of frame sands denudation is researched.The result showed that sanding plane is not circular and it is depended on the direction of hole and principle stress.In the same situation,when the hole is along the vertical stress direction,the frame sands denudation is easier to be denudated than that the hole is along the horizontal stress direction.The results concluded from this paper can provide theoretical support for the sanding prediction and it can guide the sand control completion design of weakly cemented sandstone.