Study On Dynamic And Static Damage Constitutive Model Of Sandstone And Mechanism Of Rock Breaking

Efficient rock breaking is an important foundation forbit designing and drilling technology, there are two different paths to solve the problem:research structure, manufacture and the dynamic problems of bit; Studies the physical properties, broken and crushing method of the rock. In nearly two hundred years of the development of oil and gas industry the first has been widely attention and development significantly, while many issues of the latter had been unresolved.As an object of bit broken, rock material is one of nature’s breeding and has a multi-scale native fracture micro cracks, pore, and random probability distribution of physical parameters, the anisotropy mechanical properties and different response under dynamic and static load. Taking sandstone as an example which widely distributed in reservoir, relying on NNSF of China "research and application of rock dynamic stress-strain relationship in the whole process after loading and unloading of single impact ", from the microscopic features, the stochastic characteristic and dynamic-static mechanical response of sandstone, modeling the macroscopic damage constitutive model of sandstone, respectively using ANSYS and LS-DYNAfor secondary development, combined with experimental research, used the custom damage constitutive model for reserching crushing mechanism of sandstone under the dynamic-static load of teeth.A lot of pioneering work had done based on the theory of rock mechanics, rock crushing, impact dynamics, and the finite element method and the secondary development has made, specific content as follows:(1) Summarized the two kinds of research path to solve the problem of efficientlyrock broken, put forward a opposite and effective way-researchthe rock characteristics for rock effectively.Firstly classified the characteristic of rock about effectly rocks broken, discussesed the multiple relationship between rock properties and drill design.Analyzed and summarized rock damage under different load, primary pore, the strain rate effect and broken form under different stress state are.(2) based on the micrographs of rock "pore-particles-cement ", proposed rock skeleton infinitesimal model, getrock damage constitutive mode by rock elastic-plastic mechanics, verify the modelby sandstone experiments Using ANSYS to do secondary development of the constitutive model, verify the custom damage constitutive by single tooth pressure into the experiment. Put forward a new crushing work ratio based on custom damage constitutive model, use of the crushing work ratio model to evaluate effecttion of rock teeth.(3) considering impact speed range and the strain rate under the actual drilling rock, puts forward the broken rock is in low strain rate response.Parallel Bingham, Maxwell and sandstone damage body tomodel dynamic damage constitutive modelof low strain rate, and using the experimental model to verify.Using ls-dyna software tosecondary developthe custom dynamic damage constitutive model.Compare with sandstone sample experimental data, verified that the custom dynamic constitutive model is correct.(4) analysis dynamic load of drill rock fragmentation mechanism of the rock bit, PDC bit and swivel, based on the experimental phenomena under teeth impact rock, considering the teeth impact and low speed of pressure, fixed spherical empty expansion theory model.Using the similarity theory and MATLAB software to solve the compacted zone, cracking zone and elastic zone, and obtained theoretical solution and numerical solution.Using LS-DYNA software and custom probability damage constitutive model to simulating single tooth impacting rock underlow velocity, got the dynamic change law of the rock and tooth, analyzed, stress, the change of porosity and damagein the rock breaking under different impact velocity.