Automatic Control Algorithms of Water-Gas Mixture Injection under Implementation of SWAG Technology

Abstract

AbstractSWAG technology is planned to be implemented in a large oil field currently being at the initial stage of development. SWAG (Simultaneous Water-Alternating-Gas) is a method of the oil fields development by pumping water and gas mixture in reservoir to maintain the reservoir pressure. In addition to maintaining the reservoir pressure, SWAG is also used to enhance the efficiency of field development due to oil recovery increase with disposal of produced associated petroleum gas (APG). The objective of this project is to create automatic control system (ACS) of reservoir pressure maintenance (RPM) pipeline system to ensure stable and steady injection of water-gas mixture (WGM) into reservoir in accordance with the target flow rates of water and gas under potential perturbations.While performing the work two software complexes were used together: a hydraulic simulator to create mathematical model of RPM pipeline system and special design system to build ACS. Based on the results of dynamic processes analysis, control algorithms were developed both for ACS of a single injection well and for ACS of RPM pipeline system.The study of the behavior of RPM pipeline system showed that it is a complicated control object having the properties of nonlinearity and multistability. These features were taken into account when choosing the structure of ACS. As a result, low-level multi-loop ACS was created on the basis of PID-regulation with a cascade contour to control wellhead pressure. Also, high-level control algorithm was developed that ensures distribution of incoming gas volumes between injection wells according to their operating regime.Testing of designed ACS was performed on experimental-industrial site which was created for WGM injection experiments into two wells. Test results confirmed that developed control algorithms were correct and could be scaled up for full implementation of SWAG (i.e. ACS could be quickly rebuilt in case of changes in number of injection wells of RPM pipeline system).The described approach to the synthesis of ACS of RPM system and developed algorithms can be applied to similar projects of simultaneous water-gas injection into the reservoir using RPM system.