The Study On Mechanical Characteristics Of Natural Fractures In Fractured Reservoirs

Natural fractures are abnormal development in fractured reservoirs,and these messy natural fractures have had a significant impact on its production.Previous research results mainly considered the changes which is the state of natural fractures under the high effective stress but they have little studied that the natural fractures will become which state under low effective stress.Therefore,the study of mechanical characteristics of natural fracture is necessary.Firstly,based on vectors and the lower hemisphere projection can analysis the overall distribution of natural fractures.Secondly,based on the Mohr-Coulomb and Maksimovic peak shear strength criterion,using the three-dimensional Mohr circle to determine the state of natural fractures under the different stress field condition,which are steady state,sliding,dilatant and opened state.And then,discusses the mechanism of stimulation of natural fracture under different mechanical states.At last,using a study case of Southwest region analyze that changes of oil and gas reservoir pressure have influence on mechanical characteristics of natural fractures.The studies have shown that the depletion of oil and gas reservoir leads to the decrease of oil and gas reservoir pressure,causing natural fractures closure and its permeability reduced.However,in waterflood development or hydraulic fracturing,it can cause natural fractures sliding,dilatant or opened,which increase the permeability of the reservoir.The conclusions of the paper have a certain referential value to the development of fractured reservoir.