Qiang Zhang

Experimental Study and Prediction Model of Casing Wear in Oil and Gas Wells

With the development of drilling technology and reinforced exploration and exploitation of unconventional reservoirs, there has been a great increase of complex wells. Meanwhile, however, consequent casing wear is and will continue to be a serious problem that causes enormous economic losses and many safety issues. The purpose of this paper is to find out the mechanism of casing wear and establish casing wear prediction model. Casing wear experiment was carried out to study the effect of contact force, rotation speed, and casing grade on wear depth. Meanwhile, wear coefficients under different working conditions were obtained through the normalizing of data. With the extensive research of downhole drag and torque calculation method, a contact force calculation model was established. Through the combination of crescent-shaped model and wear-efficiency model, the past complicated casing wear prediction models and confusing empirical formulae were greatly simplified. Therefore, the wear volume and depth of the casing string can be accurately predicted. Finally, a prediction software was developed to predict downhole casing wear of oil and gas wells. Comparison with the field data confirmed that the established model and software had enough accuracy to help predict and analyze casing wear at field.

Application of Titanium Alloy Tubing in HPHT Gas Wells to Reduce Vibration and Buckling

Tubing string vibration and buckling are primary causes of tubing string failure, sustained casing pressure and production casing wear in HPHT gas wells. In order to obtain an improved understanding of tubing string vibration and buckling, finite element analysis is carried out in this paper. Typical tubing string failures in HPHT gas wells are analyzed, and fracture surfaces are tested. The vibration and buckling characteristics of original nickel-base alloy tubing string and modified tubing string with Titanium alloy tubing are calculated and compared. The results indicate that the application of Titanium alloy tubing can effectively reduce tubing string vibration and buckling. Titanium alloy tubing has lower elasticity modulus, so it transforms more energy into deformation energy rather displacement energy. Therefore, it is concluded that Titanium alloy tubing can effectively reduce tubing axial vibration displacement, so as to prevent tubing fatigue and thread looseness. Original tubing string has contacted with the wellbore under sinusoidal buckling. The sinusoidal buckling of modified tubing string is much slighter and tubing doesn’t contact with the wellbore. The work presented in this paper can provide a technological basis for the reduction of tubing string vibration and buckling, as well as application of Titanium alloy tubing.

Stress Analysis of Tubing Thread of the Gas Seal Test in Deep Gas Well

Seal test of tubing thread in high pressure gas well is a new technology currently, but there is no uniform standard regarding the accurate sealing test pressure, frequently improper sealing test pressure can easily lead to damage and fatigue failure of tubing threads. In order to solve the above problems, in this paper the axisymmetric finite element mechanical model of the BEAR threads based on the theory of elastic-plastic mechanics was established, and the finite element software used to calculate the results. The results showed that when the test pressure was equal to 100 and 50% of the RIP (Resistance to internal pressure) of tubing, the plastic deformation of the tubing thread occurred, and the plastic deformation area generated in the roots of the last three buckle, when the test pressure was equal to 25% of the RIP of the tubing, the maximum stress of all types of tubing threads was less than the yield strength. Based on this model, the stress of the tubing thread of the high-pressure gas well can be quantitatively and fully evaluated, and the gas seal test technology can be provided with theoretical reference.

Numerical simulation of fluid flow and experiment on downhole friction reduction tool

In this article, a new friction reduction tool is designed for drilling of horizontal wells, and its performance is investigated using computational fluid dynamics simulation technique, laboratory experiment, and field testing. According to flow field analysis, the spiral diversion channel has obvious disturbance effect on fluid, which can help cutting transport and reduce cutting bed accumulation. Tensile test is carried out and tensile resistance of the friction reduction tool is 90 ton. Shearing test is also conducted to examine the shear resistance capacity of the pins that support rollers. Under the lateral load of 20 MPa, large deformation of the pins is observed, but they are not broken. The function of friction and torque reduction is verified using experimental apparatus for drill string dynamics of horizontal well. Field testing is also completed in a real well. The accumulated operational time of the friction reduction tool is more than 130 h and its fatigue life reaches up to 3×105 cycles. The simulations and experiments indicate the designed tool can effectively reduce friction and torque in horizontal wells. The work presented in this article can provide a technological basis and scientific reference for the development and application of friction reduction tool in horizontal wells.