Estimation of Utsira CO2 Storage Capacity Based on Water Producing Modelling and Identification of Proper Water Producer Architecture

Abstract

Utsira aquifer is well known from the CCS community as Sleipner gas project is storing CO2 in that aquifer since 1996. More than 17 million tons of CO2 have been injected to date. According to previous studies, CO2 storage capacity of the Utsira varies between 0.3 and 50.4 Gt. In this study, assuming specific parameters, the storage capacity is estimated about 1.7 Gt using analytical method. A full scale flow model of the aquifer has been used to model CO2 storage, considering CO2 migration and pressure raise to estimate the CO2 storage capacity, with or without water production. Water-CO2 relative permeabilities are selected based on a vertical equilibrium approach and validated when CO2 migration is compared to high resolution grid refinement around the injector areas. Optimizing injector well locations lead to an estimation of CO2 storage capacity of about 1.6 Gt without water production. This capacity can be increased to 3 Gt with about 1 Gt of formation water being produced during injection. The location and architecture of the water production wells were optimized: the wells should be subsea and should be operated with minimal requirement. Two production methods were compared: eruptive wells, producing water based on the formation overpressure induced by the CO2 storage; and activated wells using electrical submersible pumps (ESP). For each scenario, an optimization is proposed in terms of well count, well locations and well architecture designs. For the reservoir depth ranging between 500–1200 m below sea level and for such a high water production rate, the electrical submersible pumps (ESP) technology is a suitable application.