Investigation On Two-Phase Flow Characteristics In A Pipeline-Catenary Riser System With The Gas And Liquid Mixture Transportation

Gas-liquid mixed transportation is a method adopted normally in oil and gas industry. With the development of offshore drilling, a horizontal/declination pipeline- catenary riser system is often used to transport oil and gas resources from seabed to the platform. Compared with a horizontal/vertical pipeline system, gas-liquid two-phase flow is more complex for such a horizontal/declination pipeline-catenary riser system,and the transportation effect is different from a vertical riser normally adopted in offshore drilling.Severe slugging phenomenon is a special flow pattern occurred in such a system where the slug length may have several times of the riser's height. As a result, severe slugging phenomenon is commonly encountered, causes drastic fluctuations for pressure and outlet flow, and then results in some harmful consequences. Therefore, investigation on such a flow phenomenon has of theoretical and realistic significance.In the first part of this thesis, the severe slugging phenomenon in a horizontal/ declination pipeline-catenary riser system was studied experimentally. The mechanism and flow characteristics of the severe slugging were analyzed. The main contents and conclusions are as follows:Two flow patterns are observed in the horizontal pipeline, including stratified flow and intermittent flow respectively. There are also three flow patterns in the catenary riser, including severe slugging,occasional flow and intermittent flow, where severe slugging can be divided into type I, II and III respectively. The flow pattern maps of the two-phase flows for the horizontal pipeline and catenary riser were also obtained.The flow characteristics of the severe slugging were analyzed. It was found that severe slugging is strictly cyclical, and the cycle length decreases with the gas and liquid superficial velocity increasing, the pressure fluctuations change with the gas and liquid superficial velocity change, and the maximum value of the pressure fluctuation occurs at the boundary of the severe slugging I and II.The pressure fluctuations are much related to the gas and liquid superficial velocities. The amplitude first increases and then decreases with the gas superficial velocity increasing. On the left side of the extreme points, smaller liquid superficial velocity corresponds to bigger pressure fluctuation amplitude,while on the other side,bigger liquid superficial velocity corresponds to bigger pressure fluctuation amplitude.In the last part of this thesis, Based on the consistence principle for the severe slugging formation condition, a CFD (computational fluid dynamics) method was proposed for numerically simulating the gas-liquid severe slugging in a pipeline-riser system by means of translating the 3D pipeline-riser system into a 2D equivalent one. Numerical simulations were conducted for the gas-liquid flow patterns of the severe slugging in a horizontal/declination pipeline-catenary riser system according to the experimental cases presented in the reference, and the pressure characteristics including period and its amplitude were analyzed due to such a severe slug flow, the numerical results are good agreements with the experimental ones in the refrence showing that the proposed method is effective.