Numerical Simulation And Experimental Study On Ice Drilling Hole Wall Hydraulic Fracturing

In the polar ice drilling project, in order to prevent hole shrinkage problems caused by ice creep of after stress relief of hole wall, the low temperature drilling fluid maintaining the balance of stress in hole is essential. But for various engineering design and construction issues, drilling fluid pressure is often locally over the hole wall-situ stress, causing the oversize pressure difference which can cause hydraulic fracturing phenomenon of hole wall and a huge loss of drilling fluid. And then may cause instability of the cell walls, drilling-buried problems and accidents. So the study of initiation pressure and prevent crack propagation of ice drill hole wall hydraulic fracturing is considered to be very feasible for preventing ice drilled hole wall hydraulic fracturing phenomenon.For a long time, on the rock layer and seam, the issue of hole wall hydraulic fracturing has been considerable research, but for hydraulic fracturing drilling of the ice drilling hole wall is no systematic study. And low intensity, great temperature effect,creep and crystal properties of ice, making hydraulic fracturing research difficult extending from rock to ice. But the study of hydraulic fracturing is inseparable from the traditional "three-step" ideas: theoretical analysis, numerical simulation and experimental verification. From the mechanical model and crack initiation guidelines of theory to numerical simulation of hydraulic fracturing process, and finally verification and discuss initiation and crack propagation in hydraulic fracturing experiments, use three-phase comparative analysis to find a reliable initiation and guidelines calculation equation, realizing guidance to the actual project parameters. In this paper, for hole wall hydraulic fracturing issues of ice drilling, from three aspects of ice characteristics and theoretical formulas, numerical simulation and experiments explore the relationship between cracking pressure of hydraulic fracturing and drilling depth, and the main crack expansion trend.Combine the main contents and elements of the rock hydraulic fracturing research in theory, and summarizes the theoretical development at some extent. Combine physical and mechanical properties of ice and ice structure and build drilling hole wall hydraulic fracturing initiation pressure calculation equation based on the theory of plane strain mechanical model and the maximum tensile strain strength criterion, and transformed into initiation pressure- depth curve equation.Use MATLAB language to compile hydraulic fracturing initiation judgment program, as well as calculation program of stress, strain distribution and hole wall strain- bore column pressure relationship near the hole wall, in order to calculate a continuous distribution of stress and strain. Use RFPA-2D Seepage Edition(real fracturing process simulation program) to simulate hydraulic fracturing of different confining pressure, that is, different depths, to get the corresponding initiation pressure value, and fracture morphology diagram, at the same time get trend line of initiation pressure – depth. Then compare it with the theoretical analysis of the equation.Use modified oil shale hydraulic fracturing experiment system, to take hydraulic fracturing experiments on frozen ice samples. Analyze development of main crack, and get hydraulic fracturing pressure curve for the confining pressure corresponding to numerical simulation results and then process it for initiation pressure value, then several experiments were averaged. According to the draw-point average initiation pressure get trend line of initiation pressure- depth, and compare it and numerical simulation, phase theoretical equation, to get initiation pressure prediction equation of each ice depth for guidance to specific ice status.