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Hydrajet fracturing is a novel stimulation technique developed in recent years, with mechanism that inner static pressure boosts by transforming flow kinetic energy into the static pressure energy resulted from the continuous flow velocity decrement after being injected into the perforation, based on the Bernoulli principle. The formation of the inner-outer perforation pressure difference is the key point for the successful field application and it is important to find the relationship between the inner pressure field and outer ambient pressure as well as the influence factors. Based on the continuous medium theory and considering the high speed jet, the jet flow control equations are put forward and through the numerical simulation of inner flow field with standard k-e two-equation model, analysis on influence factors is further conduct in this paper. It is suggested from the research results that the jetting pressure is positively correlated with boost pressure while jetting distance is negative. The higher the jetting pressure is, the more favorable for hydra jet fracturing, and the longer the jetting distance is, the more unfavorable. The outer ambient pressure is uncorrelated to the boost pressure with little influence.

Produced water in oil field is generally recycled back to the formation, and the dynamic analysis of formation pressure during water injection has always been a research hotspot. It is difficult, however, to apply current numerical models to formation pressures analysis during water injections due to the models' complexity. Furthermore, actual formation conditions are quite different from the generic analytical models that assume homogeneous and circular boundaries. Therefore, this paper takes the anisotropy of formation into account for the first time and establishes a mathematical model for unsteady flow when water injection well is located at any position of a rectangular formation. This paper also considers the well as line source instead of point source, and this research adopts an orthogonal transformation method to deduce the exact solution of the model. It is of great significance to easily and exactly analyze formation pressure behaviour during water injection. Calculation program is compiled to analyze the key factors affecting formation pressure during water injection. Results show that: initial injection bottom hole pressure is proportional to time on semi-log scales, and the pressure increases rapidly, but the increase slows down later on in time, the model correctly reflects the propagation mechanism of pressure-wave, which can be applied to analyze the pressure behaviour of reservoirs during water injection.

Refracturing is an important technique treatment for enhancing oil or gas well productivity at the middle and late stage of low-permeability reservoir development. On the theoretical study of refracturing, most of researchers only focused on the reorientation of refracture while few studies focus on the refracture propagation path simulation. Due to the refracture propagation path depending on the stress field before refracturing, based on elasticity fracture mechanics and fluid-solid coupling theory, the mathematical solving model of induced stress field on the refracturing well is set up, which is combined with the propagation criteria of fracture, the computing method of refracture propagation path is deduced and the correlating calculation program is developed. The calculation results show that the reversal of stress orientation may occur owing to the effect of induced stress field near the well, and refracture will propagate at 90 degrees to the initial fracture azimuth at stress reversal region, until it reaches the stress isotropic point, where after, the refracture starts to reorient itself at some direction beyond the isotropic point, finally the refracture will propagate in a direction parallel to the initial fracture. For the simulation deviatoric path, the main factor affecting the refracture deviatoric distance is the straight length between the isotropic point and well bore, which perpendicular to the initial fracture azimuth.