ABSTRACT

When there are anomalous high pressure wells in the development of deep water oil and gas field, the conventional full-pressure design concept with excessive design pressures for manifolds, jumpers, and flowlines increase investment and reduces economic benefits. As a safety protection system, the subsea high integrity pressure protection system (subsea HIPPS) is used to reduce the design pressure of subsea facilities. In the Lingshui 25-1 gas field, the subsea HIPPS was installed for three anomalous high pressure wells in the South China Sea, OLGA dynamic simulation software was used to study the key technical parameters of subsea HIPPS application and optimize the testing and pressure relief process. The results show that setting two layers of mutually independent overpressure protection system for anomalous high pressure wells, with 21.9 MPa shut-off pressure for the production valve of the Christmas tree and 25 MPa shut-off pressure for the subsea HIPPS, which can reduce the subsea HIPPS trigger shut-off under the premise of ensuring safety; setting a fortified zone length of 700 m downstream of the subsea HIPPS can ensure the safety of the downstream low-pressure production facilities. HIPPS testing and pressure relief design is an integrated process, which can simplify the system process, reduce 2 subsea control valves and piping systems, and reduce the weight of the HIPPS body by 0.6 tons. The subsea HIPPS was used in Lingshui 25-1 gas fieldfor the first time in the South China Sea, and the research results can provide references for other oil and gas fields developed in the subsea mode in the future.

INTRODUCTION

Deepwater oil and gas field development is characterized by high technology, high risk, high investment and high economic return, however, any possible accident may increase the operating time and cost greatly, and in serious cases may lead to catastrophic consequences (Deli G, 2020). In the subsea production system, in the process of the host platform gathering, the low-temperature natural environment of the deep-sea floor cause the blockage of wax or hydrate in the flowline easily, the pressure in the flowline will increase to the shut-in pressure in the well (Jing G et al., 2020). To avoid the accidents and environmental pollution caused by the overpressure of the subsea production system, the design pressure of the subsea production facilities is usually taken as the highest shut-in pressure of all production wells, but for deep water anomalous high pressure gas fields, high design pressure will not only cause the extra heavy weight of the production manifold and difficult installation, but also result in large wall thickness of the flowline, low construction efficiency, increase the investment costs, and even restrict the floating platform development scheme feasibility due to the hanging weight of the riser (API, 2015). The Lingshui 25-1 gas field is the first deep-water high-temperature and super-pressure gas field in the South China Sea (Renjun X et al., 2021), with a reservoir pressure of 68.6 MPa and shut-in pressure of 58.8 MPa, and three production manifolds in the field. The production fluids of each well are gathered to the central manifold through the gas infield flowline, and then transported to the shallow host platform with a water depth of 88 m through a single 113 km flowline. The impact of anomalous high pressure on the design pressure of gas field production facilities is one of the main challenges for gas field development.

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