| The gas drilling technology is developing rapidly in recent years. But people always ignore the design requirements of sediment delivery pipeline which is used to return annular rock debris. Because during the process of gas drilling, it’s not the mud but the crushed rock debris which is brought out by the strength from underground, therefore, When velocity of carrying rocks by gas is higher, sediment delivery pipeline will be continually washed out and worn by rock debris particles. As a result, sediment delivery pipeline will tend to be pierced especially the elbow part. And some elbows even cease to be effective after they are used for a few days. If the sediment delivery pipeline leaks, a large number of rock debris which are carried by gas will come out from the pierced place, resulting in serious consequences:Firstly, when we drill in hydrogen sulfide or air in gas drilling process, it is easy to cause a fire or even a major accident of staffs be poisoned; secondly, it is likely to cause serious environmental contamination, affect the normal daily life of the staff and lead to the damage of diesel engine, air compressor, etc.; thirdly, it will force the staff to stop the normal gas drilling, repair sediment delivery pipeline and we need sand washing operation before maintenance, lift drilling tools, prevent burying the drills, stop the air compressor or other gas equipment, drain the gas in the well. It will cost a few hours to replace elbow part of sediment delivery pipeline which severely reduced drilling effectiveness.Concerning this issue, based on the FLUENT software, the paper present the numerical simulation analysis of flow field in the sediment delivery pipeline. And it will give us a comprehensive study of the gas flow pattern within the sediment delivery pipeline as well as a detailed analysis of erosion of the pipeline by rock debris under various conditions. In order to reduce the erosion of sediment delivery pipeline, this paper proposes a new structural t-branch pipe, explains its working mechanism, and illustrates through simulation analysis method. Our analytic works are mainly as follows:(1) simulation analysis of sediment delivery pipelines under different conditions, such as different diameters, different bending diameter ratio as well as different angles of elbows. We will find that the Erosion rate decreases as the diameter increases;(2) Simulation Analysis of the air flow (velocity), and the sediment delivery pipeline with the different speed of rock debris entrance, as its increases, the Erosion rate of the sediment delivery pipeline gradually increases;(3) proposing a new t-branch pipe structure, we will analyse and optimize its structure;(4) comparing DPM concentration in various conditions in sediment delivery pipeline to explain the relation between DPM concentration and the Erosion rate of the sediment delivery pipeline.From above, we can draw a conclusion that in the on-site engineering practice, under the permit condition, we can use sediment delivery pipeline with large diameter or big bend diameter. At the same time because the reduction of Erosion rate of90°-120°degree elbow is very small, and the limitation of spatial pattern, we can take a90°elbow to connect the sediment delivery pipeline. In order to meet the requirements of carrying rocks, we should minimize the air flow rate (speed). The reduction of Erosion rate by reducing speed of rock debris entrance can be achieved by the way of additional back pressure at the wellhead. |
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