(724b) The Development and Demonstration of Best-Practice Guidelines for the Start-up Injection of CO2 into Highly-Depleted Gas Fields
AIChE Annual Meeting
Thursday, November 17, 2016 - 3:34pm to 3:53pm
The most effective way of transporting the captured CO2 for subsequent sequestration using high-pressure pipelines is in dense phase. The CO2 arriving at the injection well will typically be at pressure greater than 70 bar and at temperature between 4 and 8 ºC. Given the substantially lower pressure at the wellhead, the injection of CO2 will result in its rapid, quasi-adiabatic Joule-Thomson expansion leading to significant temperature drops. This could pose several risks, including hydrate and ice formation around the wellbore and thermal shocking of the wellbore casing steel, leading to its fracture and ultimately escape of CO2.
Despite its importance, the modelling of the flow dynamics taking place during the start-up injection of CO2 has been devoted mainly to either steady-state operations1 or flows where only pure CO2 is injected2. The steady-state flow model is inappropriate as it ignores important phenomena, such as expansion wave propagation and bubble nucleation, occurring during the rapid depressurisation process. In addition, there is little work in the literature regarding the impact of the injection rate and the upstream inlet conditions (e.g. temperature and pressure) on the degree of cooling along the well3. Moreover, all previous work has been confined to pure CO2. In practice the injected CO2 will have a range of different impurities which will have a profound impact on the CO2 fluid phase behaviour and hence its injectivity4.
The aim of our work is twofold. First, we present in detail a homogeneous relaxation flow model for the numerical simulation of the highly transient phenomena taking place in the wellbore. Mass, momentum, and energy conservation equations are considered in the tubing. Wall friction, gravitational force, and heat transfer between the fluid and the surrounding formation are also taken into account. The phase equilibrium and thermodynamic properties for CO2 are determined using the Peng-Robinson equation of state, which guarantees both accurate and computationally efficient predictions of VLE data for CO25. Operational envelopes for the injection well are obtained from data already available in the literature3. Second, by performing a sensitivity analysis on various injection rates and temperatures, we propose optimal transient-operation design and develop best-practice guidelines for the minimisation of the risk associated with start-up injection of CO2 into highly-depleted gas fields.
1. Hughes D., Carbon storage in depleted gas fields: Key challenges, Energy Procedia, 1, 2009, 3007-3014.
2. Galic H., Cawley S. and Bishop S., CO2 injection into depleted gas reservoirs, SPE 123788, 2009, 1-8.
3. Li X., Xu R., Wei L. and Jiang P., Modeling of wellbore dynamics of CO2 injector during transient well shut-in and start-up operations, International Journal of Greenhouse Gas Control, 42, 2015, 602-614.
4. Brown S., Beck J., Mahgerefteh H. and Fraga E. S., Global sensitivity analysis of the impact of impurities on CO2 pipeline failure, Reliability Engineering & System Safety, 115, 2013, 43-54.
5. Oosterkamp A. and Ramsen J., State-of-the-art overview of CO2 pipeline transport with relevance to offshore pipelines, Technical Report, PolyTec.