Zhao Jinzhou

3-D Fracture Propagation Simulation and Production Prediction in Coalbed

In accordance with the fracturing and producing mechanism in coalbed methane well, and combining the knowledge of fluid mechanics, linear elastic fracture mechanics, thermal transfer, computing mathematics and software engineering, the three-dimensional hydraulic fracture propagating and dynamical production predicting models for coalbed methane well is put forward. The fracture propagation model takes the variation of rock mechanical properties and in-situ stress distribution into consideration. The dynamic performance prediction model takes the gas production mechanism into consideration. With these models, a three-dimensional hydraulic fracturing optimum design software for coalbed methane well is developed, and its practicality and reliability have been proved by example computation.

MODEL AND METHOD OF WELL TEST ANALYSIS FOR WELLS WITH VERTICAL FRACTURE

Based on the flow mechanism of hydraulic fractured wells, through integrating linear-flow model and effective well-radius model, a new model of well test analysis for wells with vertical fracture was established. In the model, wellbore storage, the damage in the wall of fracture and all kinds of boundary conditions are considered. The model is concise in form, has intact curves and computes fast, which may meet the demand of real-time computation and fast responded well test interpretation. A new method to determine effective well radius was presented, and the correlation between effective well radius and the fracture length, fracture conductivity, skin factor of fracture was given. Matching flow rate or pressure tested, the optimization model that identified formation and fracture parameters was set up. The automatic matching method was presented by synthetically using step by step linear least square method and sequential quadratic programming. At last, the application was also discussed. Application shows that all of these results can analyze and evaluate the fracturing treatment quality scientifically and rationally, instruct and modify the design of fracturing and improve fracturing design level.

Dynamic production prediction and parameter identification for gas well with vertical fracture

In order to devoid the hard work and factitious error in selecting charts while analyzing and interpreting hydraulic fracturing fracture parameters, on the basis of the non-Darcy flow factor, this paper put out the non-Darcy flow mathematical model of real gas in the formation and fracture, established the production history automatic matching model to identify fracture parameters, and offered the numerical solutions of those models, which took the variation of fracture conductivity in production process. These results offered a precise and reliable method to understand formation, analyze and evaluate the fracturing treatment quality of gas well.

Simulation on Deviatoric Fracture Propagation Path during Refracturing Process

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.

Numerical Simulation of Jet Flow Field for Hydrajet Fracturing

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-ε 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.