The Application of High Integrity Protection Systems to Prevent Topside Overpressure which Caused by Water Injection

Abstract

Abstract The Tang South-East platform is unmanned and a combined wellhead and process platform in the North Sea, it was installed to produce and separate the well streams into a vapour phase and a liquid phase, and transfer the gas and liquid in two separate pipelines to another field. There was no automatic relief system or flare system on the Tang South-East platform, and the High Integrity Protection Systems (HIPPS) was built to protect the export gas and liquid pipelines. When water injection is applied later in Tang South-East field, it will lead to possible overpressure for the topside process systems under the situation of direct water hit through fracture. Our solutions to prevent this overpressure can be divided into two parts: First, design new HIPPS. Three transmitters and one Emergency Shut Down Valve (ESDV) are proposed to build downstream of each manifold, working with the other items, including Emergency Shut Down (ESD) and Independent Emergency Shut Down (IESD) panels, Master Control Valves (MCV) and Wing Control Valves (WCV). A reliability study is carried out; the resulting unavailability of the HIPPS is 9.716 x 10–5, which meets the requirement of better performance than a standard relief valve which has an unavailability of 2.12x10–4. Second, change the process system upstream of ESDV according to new design pressure. This paper shows how to define this new design pressure which is higher than original design pressure. HIPPS are chosen in this project basically because they offer lower install cost of flowlines and process systems, and they do not discharge to the environment. Introduction The Tang South-East (TSE) platform is unmanned and a combined wellhead and process platform, it is located in the North Sea. The design of the process system on TSA platform includes production from 7 wells, including 2 gas wells and 5 oil wells. TSA platform is installed to produce and separate the well streams into a vapor phase and a liquid phase, and transfer the gas and liquid in pipelines to some other fields. There is no water injection on the TSA platform now. On the TSA platform, each well is connected by flowlines to two production manifolds for separation and export as well as to the test manifold. The crude can be led to High Pressure (HP) separator, Low Pressure (LP) separator, and multiphase test meter from three different manifolds respectively. There is no automatic relief system or flare system on the TSA to protect the flowlines and process systems. The export pipelines are protected against overpressure by High Integrity Pressure Protection Systems (HIPPS). If water injection is applied later in the field life, it may have an influence on the wellhead and the topsides. This will in some case lead to an overpressure and result in a requirement for additional protection. Mechanism of Overpressure On TSE platform, to ensure that the reservoir can be safely isolated, wellhead and parts of the topsides piping system was designed to a pressure which is higher than the maximum pressure that the reservoir can generate at the topsides. This pressure is defined as the initial pressure in the reservoir minus a gas gradient to the surface, and this pressure can also called tubing head pressure.