考虑岩屑床影响的井内波动压力研究

发布时间：2018-03-15 07:41

本文选题：波动压力　切入点：岩屑床　出处：《西南石油大学》2017年硕士论文　论文类型：学位论文

【摘要】：对于窄安全密度窗口地层,起下钻过程中的井内压力瞬时波动,可能会导致井壁失稳发生井漏、井喷,所以波动压力的准确预测对于井控、控压钻井和钻井参数优化至关重要。在水平井和定向井的钻井过程中,极易在大斜度的偏心环空中形成岩屑床,岩屑床形成后不仅会增大摩阻扭矩,还会对环空流动产生较大影响。为了实现存在岩屑床时的偏心环空波动压力的准确便捷预测,本文首先以流体力学理论为基础,建立同心环空屈服幂律流体闭口管波动压力拟合模型、偏心环空屈服幂律流体闭口管稳态波动压力数值模型和偏心环空屈服幂律流体波动压力比率拟合模型;其次基于Fluent软件,开展考虑岩屑床影响的同心环空和偏心环空波动压力仿真实验。最后在通过引入当量水力直径的基础上,利用CFD仿真结果分别建立考虑岩屑床影响的同心环空和偏心环空波动压力简化模型。取得的主要研究成果有:(1)波动压力随起下钻速度、屈服值和稠度系数的变化呈(拟)线性变化,随流性指数、环空内外径比率和偏心率的变化呈指数性变化;基于同心环空和偏心环空屈服幂律流体波动压力数值模型结果,建立的屈服幂律流体同心环空波动压力拟合模型和偏心环空波动压力比率拟合模型,误差分别为0～+10%和±5%;拟合模型预测结果比较接近于数值精确模型预测结果,即拟合模型具有比较高的计算精度;(2)沿径向方向的"中间疏,两头密"的网格模型适用于考虑岩屑床影响的波动压力预测;同心和偏心环空波动压力随着岩屑床的厚度增加,呈先增大后减小的趋势;当岩屑床厚度相同时,波动压力随着起下钻速度、屈服值、稠度系数、流性指数的增大而增大;(3)同心和偏心环空平均岩屑床壁面切应力随着起下钻度、屈服值、稠度系数、流性指数的增大而增大;同心环空中,当岩屑床厚度小于环空间隙时,岩屑床最易全部清除,当岩屑床厚度刚接触内管壁附近时,岩屑床最难完全清除,偏心环空中,当岩屑床厚度小于环空间隙时,岩屑床最难全部清除,当岩屑床厚度刚接触内管壁附近时,岩屑床最易完全清除;(4)通过引入有效水力直径的方法能够实现考虑岩屑床影响的同心环空和偏心环空波动压力的简单准确预测,与CFD仿真结果相比,修正后当量水力直径拟合模型的预测精度能得到大幅提高,同心环空误差范围为-5%～10%左右,偏心环空误差范围为±11%左右。
[Abstract]:For the formation with narrow safe density window, the instantaneous fluctuation of the pressure in the well during the process of hoisting and drilling may lead to the leakage and blowout of the wellbore instability, so the accurate prediction of the fluctuating pressure is controlled by the well. In the drilling process of horizontal well and directional well, cuttings bed is easily formed in the eccentric annulus with high inclination, and the friction torque is not only increased after the formation of cuttings bed. In order to realize accurate and convenient prediction of eccentricity annulus wave pressure in the presence of cuttings bed, this paper is based on the theory of hydrodynamics. The numerical model of steady state wave pressure of yield power law fluid in eccentric annulus and the fitting model of wave pressure ratio of yield power law fluid in concentric annulus are established. Secondly, based on Fluent software, the numerical model of steady wave pressure of yield power law fluid in eccentricity annulus and the model of wave pressure ratio of yield power law fluid in eccentric annulus are established. The simulation experiment of wave pressure in concentric annulus and eccentric annulus considering the influence of cuttings bed is carried out. Finally, on the basis of introducing equivalent hydraulic diameter, Based on the CFD simulation results, the simplified models of wave pressure in concentric annulus and eccentric annulus considering the influence of cuttings bed are established, respectively. The change of yield value and consistency coefficient is (quasi-) linear and exponentially varying with the flow index, the ratio of inner diameter and outer diameter of annulus and eccentricity, and based on the numerical model of the pressure of yield power law fluid in concentric annulus and eccentric annulus. The fitting model of the concentric annulus pressure of yield power law fluid and the ratio of eccentric annulus wave pressure with the error of 0 ~ 10% and 卤5 respectively, the predicted results of the fitting model are close to those of the numerical accurate model. That is to say, the fitting model has a high calculation accuracy, and the meshing model with "middle thinning and dense at both ends" along the radial direction is suitable for predicting the fluctuating pressure considering the influence of the cuttings bed, and the concentric and eccentric annulus fluctuating pressures increase with the thickness of the cuttings bed. When the thickness of cuttings bed is the same, the fluctuating pressure increases with the increase of drilling speed, yield value, consistency coefficient and flow index. In concentric annulus, when the thickness of the bed is less than the gap of annulus, the bed of cuttings is most easily cleared, and when the thickness of the bed of cuttings is in contact with the inner pipe wall, it is the most difficult for the bed to be completely removed. In eccentric annulus, when the thickness of cuttings bed is smaller than the annular gap, the cuttings bed is the most difficult to be completely removed, and when the thickness of the cuttings bed is in contact with the inner pipe wall, By introducing the effective hydraulic diameter method, the simple and accurate prediction of wave pressure in concentric annulus and eccentric annulus considering the influence of cuttings bed can be realized, and compared with the CFD simulation results. The prediction accuracy of the modified equivalent hydraulic diameter fitting model can be greatly improved. The error range of concentric annulus is about -5% and that of eccentric annulus is about 卤11%.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE21

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