A multiphase flow is a fluid flow that comprises more than one phase of matter. The phase defines the different chemical and physical properties of the matter, and the interface between different phases should be physically distinguished for multiphase flow. The same matter in different states, such as gas, liquid and solid, is considered as different phases. Insoluble chemicals with the same state are also considered as different phases. For instance, the fluid flow of ice and water, or vapor and water, is a multiphase flow. The fluid flow of oil and water is also a multiphase flow. However, the fluid flow of salt and water solution is not, because this solution is a homogeneous fluid without any physical interface between the two components.
The study of multiphase flow started at the beginning of the 20th century. Multiphase flow is widely applied in industry, such as in power generation, nuclear reactor technology, food production, chemical process, aerospace, automotive industries and petroleum engineering. From the 1970s, multiphase flows in the oil and gas wells especially became more and more important, because of the increasing dependence of world economy on petroleum, and the development of drilling and production engineering.
1.1 Multiphase flow in the well
Basically, most of the fluid flows in the petroleum engineering are multiphase flows. For instance, the drilling fluid, during the common drilling of oil and gas wells, is a gas-solid phase. Crude oil, during the production, is normally a gas-oil-water mixture. However, there are well-established methods to solve these fluid problems for conventional processing in petroleum engineering. In this book, we focus on the multiphase flow for unconventional processing, especially in drilling. These problems include underbalanced drilling, well control for kicking, well control for the acidic gas well, and the well control for deepwater drilling.
Underbalanced drilling uses low-density drilling fluid to keep the wellbore pressure lower than formation pore pressure, which protects the formation during the drilling. This demands very precise pressure control of the drilling fluid, otherwise disasters such as kicking and well collapse will easily happen. Injecting air to the drilling fluid is the most popular approach to lighten the drilling fluid. The prediction for this gas-liquid system in the complicated pressure and temperature conditions of the wellbore is challenging.
Safety is of key importance for the petroleum industry. Kicking and blowing are disasters that can damage the drilling facilities, and even kill the crews in many cases. These lead to serious social and economic losses. The early prediction of kicking, and well control when kicking or blowing happens, could efficiently prevent these losses.
In the 21st century, oil fields have been extended to offshore, where efficient lifting and multiphase transfer techniques are the common means for oil and gas development. How to increase the pumping efficiency and metering accuracy is related to multiphase flow theory. Therefore, the development of multiphase flow theory has a close relationship with petroleum engineering.
Due to the complexity of the multiphase flow, there are still many theoretical problems that have not been solved so far – such as flow regime transition,...
