Numerical Simulation And Experimental Study On Erosion Of Drilling Tools And Wellhead Equipment By Gas Drilling Cuttings

In the last few years the gas drilling well has developed rapidly for some distinct advantages over traditional mud drilling well. It not only increases the rate of penetration (ROP), but also controls drain well and discovers and protect pay zone effectively. However, drilling tools may become fail and wellhead BOP close lax in gas drilling. One of the main reasons is drilling tools erosion. At present, the research about drilling tools erosion is still defective. So the proper erosion evaluation of wellhead, casing and drilling tools is hard. The main jobs of this paper are discussing and researching the law of drilling tools erosion in gas drilling well by analyzing erosion theory, simulation analysis and visualization test. The main jobs are followings:(1)The paper had analyzed the principle of erosion and the factors of erosion on the drilling tools, casing and wellhead in gas drilling well. The results showed that cuttings impact angle belongs to low angle range (0°～50°) and erosion can easily happen in this angle. When the volume of injecting gas increased, the erosion increased. And when ROP increased, the erosion increased.(2)After the computational fluid dynamics simulation software simulated the erosion rate of drilling tools, casing and wellhead in gas drilling well, the results showed that the momentum of cuttings consumed when cuttings hit the surface of drilling tools and casing. However, cuttings speed recovered because of aerodynamic drag, and even increased when cuttings were through small annulus (connector of drilling pipe). So the cuttings hit the surface of drilling tools and casing in faster speed. It leads erosion in surface of drilling tools and casing was serious than it in the connector. The biggest erosion speed was on the slopes of the female connector, but the thickness and strength of the connector is bigger than noumenon. So the erosion was serious in the position that is in the range of 0.2 to 1.8m under the male connector.(3)The orthogonal test was used to find the effect of different parameters in pure gas drilling well, mist drilling well and foam drilling well. It showed that the volume of injecting gas had the biggest effect on erosion of drilling tools, casing and wellhead in gas drilling well. The next one is ROP and the last one was the diameter of cuttings. Volume of injecting gas had the biggest effect on erosion in mist drilling well. The next one is ROP and the last one was the diameter of cuttings.The paper provided a mean to calculate the erosion speed of drilling tools, casing and wellhead in gas drilling well and also find the speed of erosion in pure gas drilling well, mist drilling well and foam drilling well. It had a most important significance to properly evaluate the erosion of wellhead, casing and drilling tools and decrease the possibility of accidents.