The paper presents:
the challenges associated with modelling CO2 injection into depleted reservoirs
the application of Integrated Asset Modelling in planning CO2 injection into depleted reservoirs.
Depleted gas fields represent an opportunity for CO2 storage. However, low reservoir pressure, as advantageous as it may seem, will present a significant challenge for CO2 injection due to CO2 phase behaviour issues. This behaviour will significantly constrain the operating injection parameters during the early stages of CO2 injection.
It has been recognized that an efficient way of understanding and possibly resolving these flow assurance problems is to adopt an Integrated Asset Modelling (IAM) approach. The benefits of this approach are that it recognises the interaction between all the system elements and enables the user to observe the effects of many parameter changes within the whole system.
The PETEX IAM suite of tools was selected to complete this task as follows:
PVTP to characterise reservoirs fluids and CO2
REVEAL to model the reservoir
PROSPER to model well performance
GAP to model the injection system
RESOLVE as an overall controller and integrator.
An integrated asset model was built for CO2 injection into a UK Southern North Sea depleted gas field, allowing various scenarios to be run and providing important data on CO2 injection. This comprised a full field reservoir description and well distribution, injection rates and time frame, trunkline (main CO2 delivery pipeline) and injection hardware requirements, and the impact of external parameters such as seasonal ambient temperature changes etc.
This methodology, workflow, benefits and challenges of this novel approach will be presented in this paper, giving a deeper insight into the CO2 injection planning process.
The case study modelled a BP-operated asset located in the offshore UK Southern North Sea (UK SNS) for CO2 injection. The main project objectives were to:
understand the CO2 injectivity and storage potential of the asset
identify any additions or modifications required to the existing infrastructures for CO2 service
test different injection scenarios to maintain a plateau injection rate governed by a CO2 delivery schedule
understand what operational issues might pertain, particularly during the early period of injection.