Study On Water Flooding Percolation Characteristics Of Metamorphic Double Medium Reservoir

As an important part of fractured reservoirs,metamorphic double medium reservoirs play an important role in the exploration and development of oil and gas fields in China.Fracture and matrix systems have great differences in storage and infiltration capacity.The fracture system has strong stress sensitivity and permeability decreases rapidly.The productivity of matrix and fracture system varies greatly,and the degree of utilization is different.The law of seepage is different,so it is necessary to study its seepage characteristics.Taking Jinzhou 25-1S reservoir as an example,we carried out the experiment of fractured core seepage boundary,the stress sensitivity experiment of fractured cores,the static imbibition experiment of matrix cores and the three-dimensional physical simulation experiment of dual medium.On the basis of physical experiments,integrated reservoir numerical simulation,theoretical derivation and other methods,the characteristics of percolation boundary limit of fractured cores,the stress sensitivity characteristics of different fractured cores and the static imbibition characteristics of matrix rocks are clarified.The characteristics of water flooding percolation and residual oil distribution in the double medium reservoir of metamorphic rock under different water injection mode and different reservoir infiltration mode are explored.The results show that when the permeability is greater than the limit of fracture permeability,the whole fracture system is involved in percolation,tiny cracks can be used,and it is also conducive to the occurrence of matrix system imbibition.Permeability grade difference limit is 18.8,when the difference is less than 18.8,both high permeability and low permeability cores are involved in percolation,when the difference is greater than 18.8,only the high permeability pipe is involved in the seepage.The stress sensitivity of high angle crack is stronger,and the decrease of fracture permeability is more obvious under the same confining pressure.The smaller the size of the rock mass,the lower the remaining oil saturation.Ignoring the gravitational effect,it is difficult to carry out the imbibition when the interfacial tension is low.The oil saturation in the middle part of the matrix is high and the circumference is low,which has the symmetrical distribution center.Under the joint participation of capillary force and gravity,the effect of imbibition is obvious,and the distribution of the whole remaining oil saturation has the characteristic of axisymmetric.The front edge of the imbibition is perpendicular to the opening boundary and propelling to the center of the rock block.When the two open surfaces are adjacent,the water saturation is arc-shaped at the contact surface,and the more the matrix rock’s open boundary,the better the seepage effect.In the process of dynamic imbibition,the imbibition recovery increases first and then decreases with the increase of displacement speed.The development of metamorphic double-medium reservoir water flooding can be divided into three stages: water-free oil recovery period,rapid rise period of water cut and slowly rising period of water cut.The smaller the reserve ratio of the fracture matrix system is,the stronger the fracture system heterogeneity is,the shorter water-free oil production period of the reservoir is and the smaller the water-free recovery is.Periodic injection and asynchronous injection of water can reduce the moisture content to a certain extent,improve oil recovery.The greater the longitudinal heterogeneity of the reservoir is,the better the periodic water injection and the asynchronous water injection is.For the fractured reservoirs of metamorphic rocks in the buried hill,the matrix system is the main residual oil-rich area,but because of the very low permeability of the matrix system,it is very difficult to tap the residual oil.