Troll Phase 3: The Next Step for a Groundbreaking Giant

An important driver for maximizing value creation for the Troll Phase 3 gas project offshore Norway was to identify means to reduce the pressure drop in the value chain from the reservoir to the onshore terminal. Using a design-to-cost approach in the concept selection phase, this has affected design of the wells, subsea production system, pipeline and the new inlet separator on the Troll A platform; all of which have been designed to preserve the energy from the reservoir as much as possible. The final design has enabled a significant increase of the project value by accelerated gas deliveries, reduction of the energy consumption and thus lowering the CO2 emissions. Calculations show that 1 bar pressure drop in the Troll Phase 3 value chain increases the project NPV (8%, pretax) with approx. 45 Million USD and reduces the power consumption by 11 GWh/year. The well tubing size was increased to 9 5/8", reducing the required number of wells by ~40%. Factoring both wells and subsea facilities, this optimized well concept alone represents a total cost saving of nearly 300 million USD. The project has piloted a modification to the Vertical X-Mas Tree (VXT) design featuring an increase from 5 1/8" to a 7" production wing outlet to minimize the pressure drop across the subsea production system. This VXT design has become the new company standard for gas field developments. The big bore wells and subsea production system design also ensures acceptable gas velocities in the late production phase with low reservoir pressure. The total reduced pressure drop obtained through these and other measures is estimated to 19 bar, realizing a project NPV improvement of approx. 850 million USD (8%, pretax).