Study On The Evaluation Of Rock Brittleness Of Glutenite Reservoir Of Baikouquan Formation In HM Sag

The glutenite reservoirs are one of the important types of oil and gas reservoirs in China.Compared with conventional oil and gas reservoirs,the porosity and permeability of glutenite reservoirs is generally poor,and the heterogeneity is strong,which controlled by the size of gravel diameters,composition,distribution and strength.As a result,the natural productivity of glutenite reservoirs is relatively low.In order to meet the industrial production requirements,reservoir stimulation is usually required to induce fracture system in the surround formation and increase the flowability of crude oil.Studies have shown that the brittleness index of the rock can characterize the fracturing of the reservoir.In view of this,the paper has carried out systematic research aims at the logging evaluation method of rock brittleness index,on the basis of rock mechanics experiments.Taking the glutenite in the Baikouquan Formation of HM depression as an example,we comprehensively analysed the data from basic physical properties experiments(including density,porosity,permeability,vertical and horizontal wave time difference),and rock mechanics experiments(compression,tensile),based on the distinctions of different evaluation methods of rock brittleness.This paper explored the brittleness logging evaluation method of the glutenite in Baikouquan Formation of HM depression,and established the prediction model of rock brittleness index.The main results achieved are as follows:(1)The pores and micro-cracks in the glutenite in Baikouquan Formation of HM depression constitute the original microscopic defects of the glutenite.Under the external force,such microscopic defects will extend and connect with each other to form complex multidimensional rupture surfaces,so that the glutenite exhibits brittle failure properties.(2)The results of rock mechanics tests of different blocks of the glutenite show that the heterogeneity of the glutenite is strong,and the mechanical parameters such as elastic modulus,Poisson's ratio,compressive strength and tensile strength of different blocks are different,The stress-strain curves of the glutenite show obvious linear elasticity,in the early stage of axial stress loading,there was no obvious pore-crack compression stage.In addition to the impact of confining pressure,the characteristic of tight and hard in glutenite is also very important reason to explain the phenomenon above.Before the rock sample is destroyed,the plastic deformation stage is not obvious.When the peak stress is reached,the axial strain is generally less than 1%,which shows that the glutenite has obvious brittle characteristics.The destruction mode is dominated by splitting destruction and high angle single shear failure.(3)The porosity and elastic modulus of the glutenite in the study area have a good linear correlation with the rock brittleness index.The brittleness prediction model based on density,porosity and acoustic time difference is established by multiple regression.Based on the logging data of the glutenite in the study area,the paper also validated the prediction model.The results show that the prediction model has some practical value.