Fracturing Mechanisms And Experiments Assisted With High Pressure Water Jets

After developing for more than half a century, the fracturing technology has made a great progress in such aspects as fracture height control, fracturing to control sand in high penetration formation, and multi-grade fracturing with a large amount supporting sand, etc. However, there still exists the following problems: hard to control its initial position and propagation direction, higher initial pressure, liquid loss in open hole fracturing(especially with natural fractures), only initiation at the top of the horizontal open hole, etc. These will increase the fracturing cost and negate its effectiveness. Fracturing assisted with water jet will be possible to solve the above problems.This dissertation used theoretic analysis, numerical simulation, experiments and field test, to study those problems. The principles of fracture initiation and propagation was analyzed according to Fracture Mechanics of Rock and Rock Breaking Mechanics; adopted finite element method, the author simulated the law of fracture initiation and propagation; the initial pressure, initial time and the fracture shape were experimented by changing the perforation perimeters in cement samples; also, the fracture shape was analyzed using Fractal Theory; finally, on the basis of the previous results and establishing operation procedure, field test was performed and brought an obvious effectiveness.The main results include: (1) in theoretical aspect, we analyzed the stress distribution on the perforation wall, getting the relationship between the initial position and the in-situ stress; the condition of micro-fracture reaching critical propagation state and its continuing propagating were concluded from the point of analyzing the stress intensity factor; (2) the effect of perforation parameters on initial pressure and fracture shape were made through numerical method; (3) the author experimented the effect of perforation parameters on initial pressure and initial time, and the results were shown in different curves; (4) the author analyzed the fracture shape, extracted from the experiments, using fractal theory, and calculated the fractal dimensions. This proves that the fractures has the obvious fractal features, which provided guides for judging the fracture shape in field fracturing operation; (5) the author put forward a new concept of"hydro-seal", calculated the pressure difference between the inside and outside of the perforation when blasting, and worked out several operation schemes for field test; (6) according to the above results, we conducted a field test in a well, enhancing its production remarkably after the performance.