Study On Failure Criterion And Strength Parameters Of The Rock In The Deep Formation

Rock mechanics is the basic theory of the exploration and exploitation of the oil or gas.In practice,a lot time and process are necessary for comprehensively understanding and knowing the rock mechanics of the rock in the deep formation of an area.The rock mechanics in the deep formation can not be understood unless the files of drilling and logging are analyzed after the completion of a series of wells.So how to acquire the rock mechanics in the deep formation and how to shorten the process are the common study direction of rock mechanics.The researchers all over the world has studied the rock strength parameters through the rock strength criterion and the test of rock mechanics.But these studies mainly considered the rock only in the earths surface.For the rock in the deep formation,the thesis focus on the sandstone,basalt and granite.The adaptation of rock strength criterion for the high stress and the high temperature environment was analyzed through the test data.And the testing method which only uses a few specimens was also studied through theory analysis and tests.The adaption of this testing method was very well for the rock in the deep formation.The rock strength criterion for the rock in the deep formation was also known.The main study content of the thesis is as below:(1)Various rock strength criterions and testing datum were investigated.The difference between the rock in the deep formation and which in the earth's surface was analyzed.Based on a lot theory,The adaptation of rock strength criterion for the deep formation was studied.(2)Accorrding to the count of the specimens which the test need,the rock mechanics testing method can be divided into common testing method and the testing method for a few specimen.This thesis analyzed the rock strength,the curves of stress and strain,the stress paths and the failure mode based on the data of these tests.The testing result interpreted that the strain-hardening phenomenon is the main reason which caused the high strength of the rock in the multi-stage triaxial tests with the high compression pressure.The strength was in direct proportion to the cumulative radial strain in the process of increasing the comfining pressure.(3)The testing result of the sandstone,the basalt and the granite indicated that the sandstone has a high level of the strain-hardening phenomenon.The correction model for this testing result was established.Through the software computing and in contrast to the common testing data,this correction model modified the relative error of the result of the multi-stage triaxial test for sandstone into under 10%.Various rock strength criterions were compared,especially the Mohr-Coulomb criterion,was adapted to only the conventional testing data of the sandstone and all the testing data of the basalt.The exponential type strength criterion—the double-parameter Bieniawski criterion,was adapted to all the testing data of the sandstone,and was not adapted to the multi-stage triaxial testing data of the basalt.