Title
Joint optimization of field development and water-alternating-gas recovery strategies
Author
Feng, T.
Leeuwenburgh, O.
Hewson, C.
Hanea, R.G.
Publication year
2017
Abstract
Alternating injection of water and gas (WAG) has been widely applied as an oil recovery strategy since the late 1950s. The expected benefits are improved macroscopic sweep, with the water and gas sweeping lower and upper zones of the reservoir respectively, and improved microscopic sweep due to various effects leading to lowering of the residual oil saturation. Benefits on the microscopic scale are expected especially if the injected gas is miscible with the oil. WAG has been applied to various North Sea assets such as Snorre, Statfjord and Gullfaks. WAG strategies are typically designed using trial simulations of different scenarios. For fields with many wells it is not generally possible to design an optimal strategy without the use of approaches to systematically explore alternative strategies. Mathematical optimization theory provides such methods. Previously, we have applied such methods to determine optimal drilling sequences for new field developments for a number of Norwegian assets under uncertainty. Here we apply similar concepts to additionally optimize the optimal injection and production strategies for drilled wells. The development period may take a number of years if many wells are to be drilled, leading to time-varying capacity to (re-)inject gas that is difficult to take into account when the order in which injectors become available is not a priori fixed. Therefore we investigate alternative approaches to characterize WAG strategies during the field development stage, namely switching time controls and injection type controls, also in combination with injection rate controls. We present a number of examples of numerical experiments for a representative test model. Multiple geological realizations of the model are used to represent the uncertainty. Results indicate that significant improvements in economic returns can be obtained through optimization relative to reasonable base strategies, also if the WAG strategy is optimized for a fixed drilling sequence. We show that not only the expected value can be increased, but that also the value for the worst performing realizations can be improved, thereby reducing risk. Finally, we provide physical interpretations of the optimal strategies in support of decision maturation.
Subject
2017 Geo
AG - Applied Geosciences
ELSS - Earth, Life and Social Sciences
Geological Survey Netherlands
Geosciences
2015 Energy
Gases
Offshore gas fields
Oil well flooding
Optimal systems
Optimization
Petroleum prospecting
Petroleum reservoirs
Planning
To reference this document use:
http://resolver.tudelft.nl/uuid:d75b0b09-9198-4a50-a4f6-06955ffab4c2
DOI
https://doi.org/10.3997/2214-4609.201700326
TNO identifier
777337
Publisher
European Association of Geoscientists and Engineers, EAGE
ISBN
9789462822092
Source
19th European Symposium on Improved Oil Recovery: Sustainable IOR in a Low Oil Price World, IOR NORWAY 2017. 24 April 2017 through 27 April 2017, 1-12
Document type
conference paper