Experimental study on scaling and adhesion characteristics in water-producing gas wellbore

Abstract

A water-producing gas well in deep water encounters problems of high cost and substantial operational difficulties in scale prevention and descaling. To determine the characteristics of wellbore scaling and its influencing factors, it is important to accurately predict the scaling risk in deepwater gas wells so that anti-scale measures can be optimized. In this study, a high-temperature and high-pressure reactor and aslim metal tube at atmospheric pressure were used to simulate the scaling process of formation water in a gas wellbore under static and flowing conditions. The amount of scaling, distribution of scaling particles, and wellbore blockage risk were investigated. The results show that: (1) Carbonate scaling in formation water occurs at high temperature and low pressure. The scaling ion concentration, CO2 partial pressure, gas phase proportion, and MEG content are the main factors affecting the scaling amount. Only a part of the scaling particles attaches to the tube wall. The remainder will disperse in water, and can be produced out or stranded in the wellbore, depending on the hydrodynamic conditions in the wellbore. The scaling particles easily precipitate and block in horizontal and inclined well sections. (2) The adhesion of scaling particles on the tube wall is severely affected by the scaling tendency of the formation water. As the scaling tendency of water increases, the scaling ions tend to transfer to the tube wall and scale on the tube wall. However, when the scaling tendency is sufficiently high, more scaling particles will be produced in water because of the limited mass transfer speed. (3) The production of gas and water has an important influence on wellbore scaling, output, and distribution. A large water rate results in a large amount of scaling, but the scaling particles in the wellbore are distributed widely and are easy to produce, which causes a small blockage risk in the wellbore. In comparison, gas production has little influence on the amount of scaling, but it can make the scaling particles deposit more intensively in the wellbore and increase the risk of blockage. The knowledge gained in this study can provide baseline information for the accurate prediction of scaling and plugging risk in gas wellbores.

Keywords

• Deep water gas reservoir
• Wellbore flow
• Scaling kinetics
• Prediction model