This paper presents an overview of the development and implementation of a Topsides safety and control system to mitigate the risk of a downhole caprock breach in the BC-10 Phase 2 waterflood development.
For the water injection development in deep water offshore Brazil (SS-BC-10 Phase II), there is a strict operational pressure envelope for the water injectors. Excessive pressurization of the sand can lead to fault reactivation and/or a breach of cap rock (shale) integrity. A breach in turn can lead to out of zone injection, propagation of the injected water to the seabed and release of hydrocarbons to the environment. The efflux of reservoir fluids to the seabed constitutes a major HSE hazard with potentially significant impact to environment and company reputation.
Current subsea pressure measurements cannot be utilized in any Safety Instrumented Function (SIF), as these measurements are transmitted by equipment that is not rated for use in safety systems. Instead, we derived a relationship between the pressure of the water injection distribution header (WIDH), and the subsea pressure. From this relationship, we calculate a maximum pressure for the WIDH as the trip setting for a high pressure SIF.
To implement this we have designed a Water Injection Pressure Protection System (WIPPS) that includes a safeguarding function as well as control funtion. The safeguarding function will provide a dynamic trip setting and will stop the water injection pump, and will close an isolation valve on the water distribution header. The control function consist of an override pressure controller for each water injection well, which will limit the flow of injection water if any injection well's pressure exceeds a specified setpoint.
We concluded that the safeguarding and control system are compliant with our requirement for a Safety Integrity Level 3 (SIL3) safeguarding system. The safeguarding system requires regular testing and calibration to maintain this SIL. The WIPPS has been commissioned succesfully without any HSE incident and to date there has been no demand on the safeguarding function.
We realize that it would be better to safeguard the injection wells by using direct measurements that are close to the injection point. However, this will require us to have a means to securely communicate subsea pressure measurements to the Safety Logic Solver (SLS). For this purpose we are developing new instruments that make use of a secure communications framework called Black Channel Communications.