Showing papers by "Hongjun Zhu published in 2014"

A New Model for Predicting Dynamic Surge Pressure in Gas and Drilling Mud Two-Phase Flow during Tripping Operations

Abstract: Investigation of surge pressure is of great significance to the circulation loss problem caused by unsteady operations in management pressure drilling (MPD) operations. With full consideration of the important factors such as wave velocity, gas influx rate, pressure, temperature, and well depth, a new surge pressure model has been proposed based on the mass conservation equations and the momentum conservation equations during MPD operations. The finite-difference method, the Newton-Raphson iterative method, and the fourth-order explicit Runge-Kutta method (R-K4) are adopted to solve the model. Calculation results indicate that the surge pressure has different values with respect to different drill pipe tripping speeds and well parameters. In general, the surge pressure tends to increase with the increases of drill pipe operating speed and with the decrease of gas influx rate and wellbore diameter. When the gas influx occurs, the surge pressure is weakened obviously. The surge pressure can cause a significant lag time if the gas influx occurs at bottomhole, and it is mainly affected by pressure wave velocity. The maximum surge pressure may occur before drill pipe reaches bottomhole, and the surge pressure is mainly affected by drill pipe operating speed and gas influx rate.

Coupling Analysis of Fluid-Structure Interaction and Flow Erosion of Gas-Solid Flow in Elbow Pipe:

Abstract: A numerical simulation has been conducted to investigate flow erosion and pipe deformation of elbow in gas-solid two-phase flow. The motion of the continuous fluid phase is captured based on calcul...

Theoretical and experimental analyses of casing collapsing strength under non-uniform loading

Abstract: Failure data from oilfield showed that casings which were designed according to API standards were deformed and collapsed in salt formations. The main reason for decrease in strength may be caused by non-uniform loading (NUL) that was not considered in traditional casing collapsing strength design or that the designing method should be improved and developed. Obviously, the calculation of casing collapse strength is one of the key factors in casing design. However, the effect of NUL on casing collapse strength was generally neglected in the present computational methods. Therefore, a mechanical model which can calculate casing collapse strength under NUL was established based on the curved beam theory of the elasticity and was solved using displacement method. Simultaneously, three anti-collapse experiments were performed on C110 casing under NUL, and the strain and deformation laws of three casings in the process of collapse were obtained by the electrical method. Yield limit of every casing was obtained by analyzing those data. Experimental results are consistent with the results of calculation of new model. It indicates that the model can be used to calculate yield limit loading of casings under NUL.

Experimental Validation on a New Valve Core of the Throttle Valve in Managed Pressure Drilling

Abstract: This paper is concerned with experimental investigation of the linear opening-pressure drop (L−ΔP) relationship of new valve core in managed pressure drilling (MPD). Based on the linear L−ΔP relationship in theoretical results, the actual L−ΔP relationships are obtained by testing the flow rate, displacement of the valve core, and pressures at the import and export. Under all three working conditions, the theoretical L−ΔP relationship almost agrees with the experimental result, and the accuracy of the theoretical design is validated. In addition, the flow coefficient (Cv) is also tested in the experimental process to judge the throttling characteristics of the new valve core and the proper working conditions.

Numerical analysis of the effects of fluctuations of discharge capacity on transient flow field in gas well relief line

Abstract: Transient gas flow in relief line is computed to determine the effects of fluctuations of discharge capacity on flow field. Based on the theories of computational fluid dynamics and aerodynamics, the solution and the analysis were carried out using finite volume CFD solver FLUENT 13.0. Flow fields in seven working conditions were simulated in the numerical investigation and their results were compared. The results showed that the fluctuations of discharge capacity, including extent and period, exert obvious effects on transient gas flow field in relief line. The larger the fluctuation extent and the shorter the fluctuation period, the more significant is the effect. The application method of simulation results is provided to guide the laying and fixing of pipelines, which is verified by filed measurement.

Numerical investigation of temperature distribution in an eroded bend pipe and prediction of erosion reduced thickness.

Abstract: Accurate prediction of erosion thickness is essential for pipe engineering. The objective of the present paper is to study the temperature distribution in an eroded bend pipe and find a new method to predict the erosion reduced thickness. Computational fluid dynamic (CFD) simulations with FLUENT software are carried out to investigate the temperature field. And effects of oil inlet rate, oil inlet temperature, and erosion reduced thickness are examined. The presence of erosion pit brings about the obvious fluctuation of temperature drop along the extrados of bend. And the minimum temperature drop presents at the most severe erosion point. Small inlet temperature or large inlet velocity can lead to small temperature drop, while shallow erosion pit causes great temperature drop. The dimensionless minimum temperature drop is analyzed and the fitting formula is obtained. Using the formula we can calculate the erosion reduced thickness, which is only needed to monitor the outer surface temperature of bend pipe. This new method can provide useful guidance for pipeline monitoring and replacement.

Numerical Investigation of Gas Mixture Length of Nitrogen Replacement in Large-Diameter Natural Gas Pipeline without Isolator

Abstract: Nitrogen replacement is a key process for natural gas pipeline before it is put into operation. A computational fluid dynamic model coupled to a species-transportation model has been used to investigate the gas mixture length of nitrogen replacement in large-diameter pipeline without isolator. A series of numerical simulations are performed over a range of conditions, including pipe length and diameter, inlet rate, and inclination angle of pipe. These affecting factors are analyzed in detail in terms of volume fraction of nitrogen, the maximum gas mixture length, and gas mixture length varied with time. Gas mixture length increases over time, and the maximum gas mixture length is present at outlet of pipe. Long and large-diameter pipe and fast speed of nitrogen lead to long length of mixed gas, while large inclination angle of pipe brings about short length. Several fitting formulas have been obtained, which can predict the maximum gas mixture length in gas pipelines. The used method of fitting formula is shown in the paper by examples. The results provide effective guidance for practical operation of nitrogen replacement.