Quantitative Characterization Method And Application Of Fracturing Performance Of The Tight Glutenite

The tight glutenite contains different contents of gravel and a matrix composed of sand and clay.The presence of gravel leads to strong heterogeneity of the tight glutenite reservoirs,and it dramatically affects the mechanical properties.At present,most of the standard fracturing performance evaluation methods for formations are aimed at shale and sandstone reservoirs,and they are not suitable when used in tight glutenite reservoirs.Therefore,it is necessary to observe the fracture characteristics of the tight glutenite and the influence of gravel and cementation strength on the fracture process of the tight glutenite based on rock mechanics experiments.Optimizing the brittleness index characterization method of the tight glutenite to study the influence of gravel and cementation on its fracture toughness.Finally,the fracturing characterization method of the tight glutenite is established to provide technical support for the fracturing reform of the tight glutenite reservoirs.Firstly,a triaxial compression test machine was used to conduct uniaxial compression experiments and triaxial compression experiments on 11 natural tight glutenite samples and 12 groups of 48 artificial conglomerate samples.The experimental results show that the content of gravel and the strength of gravel cementation are the main controlling factors for the brittleplastic mechanical behavior of tight sandy conglomerate.As the confining pressure increases,the brittleness index of the rock decreases,and the plasticity increases.The brittleness index evaluation method based on mineral content and compressive strength conflict with the results of the triaxial compression experiment,and it is impossible to evaluate the tight glutenite reservoir’s brittleness accurately.The brittleness index calculated by Young’s modulus is consistent with the characteristics of the stress-strain curve,so the Rickman method can be used to characterize the brittleness index of the tight glutenite.Secondly,using SEM and CT to observe the fracture morphology of the sample after the triaxial test,it is found that the gravel content has a controlling effect on the mechanical properties of the rock.The results of the three-point bending test and the micro indentation test on the tight sand and conglomerate samples show that the modulus of the gravel is 38.81-41.55GPa;the modulus of the mixed matrix is 8.92-13.19 GPa,the clay cement is the smallest,the siliceous cement is the largest,and the interface bonding strength is distributed in 1.1-3.2 MPa.The experimental results analysis found a correlation between the gravel content and cementation strength and the fracture toughness of the tight glutenite.A method for evaluating the fracture toughness of the tight glutenite through gravel content and cementation strength is established.Finally,through the experimental measurement of acoustic velocity,gravel content,cementation strength,and density of the tight glutenite,it is found that the cementation strength of the tight glutenite reservoir can be quantitatively calculated by using density logging and acoustic velocity logging.Based on the production method of various influencing factors,a model for quantitatively characterizing the fracturability index of the tight glutenite formations using sonic logging and density logging has been established.The application results in well H of Baikouquantight glutenite formation in Mahu well area show that the model can quantitatively characterize the fracturing performance of the tight glutenite reservoir.