In this example, four large structural traps contain very high trapping capacities. We place one well in each of these traps in an attempt to exploit this capacity. As will be shown below, this placement of wells is not ideal in terms of pressure buildup. However we use it as a starting point here to highlight the issue of pressure buildup, and show how a different placement can improve the situation.
The initial injection rates are shown (left). These rates are as much as 75 times that which is used at the Sleipner storage site, which is located in the Utsira formation, North Sea. It is unlikely that a single well could be used to inject at such a high rate due to operational limitations, and as such, penalizing pressure buildup is an important factor in obtaining a practical optimal injection strategy.
Simulation of the initial rates (unoptimized) reveals that it is not practical to exploit the full trapping capacity of these four large traps with only four wells. The pressure in the formation increases to more than 6 times that of the overburden pressure around the wells.
Optimizing the injection rates while penalizing leakage suggests a strategy in which the pressure in the formation rises to almost 7 times the overburden pressure around the wells.
Optimizing the injection rates while penalizing both leakage and pressure suggests a strategy in which the wells inject a very small amount (relative to the initial guess). The rates of these wells were restricted due to the low overburden pressure and thus low pressure limit (we used a pressure limit of 90% of the overburden pressure).
Comparion of initial and optimized rates when penalizing leakage only versus both leakage and pressure.
1. R. Allen, H. M. Nilsen, O. Andersen, and K.-A. Lie. On obtaining optimal well rates and placement for CO2 storage. ECMOR XV - 15th European Conference on the Mathematics of Oil Recovery, Amsterdam, Netherlands, 29 Aug-1 Sept, 2016. DOI: 10.3997/2214-4609.201601823
Published December 9, 2016