Development of ANN-based predictive model for miscible CO₂ flooding in sandstone reservoir

Up to 2010, 44.55% of 312 EOR's project for light oil implemented around the world in sandstone reservoirs were come from continuous miscible gas CO₂ injection which contributed to an incremental Recovery Factor (RF) of about 34.5% for less than 10 years of production period. This fact has triggered many oil industries to apply this potential and proven technogy for their assets. This potential comes with the needs of having a robust tool to forecast additional recovery due to CO₂ injection. This work focuses to development of predictive model using artificial neural network (ANN). More than 6000 series of input-output parameters for ANN training and validation/testing data are extracted from numerical reservoir simulator of 1/8 of five-spot pattern models. The models are set as combination of reservoir geometry, rock, fluid and well operating condition parameters within the range of CO₂ EOR screening criteria. The main objective of this work is to find the best ANN architecture/model which accurately matches reservoir simulation results, especially the relationship of RF, total volume of injected CO₂ (GI) and the reservoir characteristics and well operating conditions. Trial and error of ANN architectures and parameters are done on number of hidden layers, number of neurons for each hidden layer, learning rate (LR) value, and momentum constant (MC) with minimization algorithm (Lavenberg-Marquardt) in Feed-Forward Back Propagation (FFBP) schemes under log-sigmoid transfer function. An optimum result of ANN model is achieved with an architecture of 18-26-11-2. The relative error of RF and GI of the ANN model are within range of 3 to 10% respectively. A better average relative error of RF and GI of 2.8% and 4.15% respectively are obtained after removing the outliers (unrealistic combinations of input data) from training process of the ANN model. Furthermore, it is clearly found that oil viscosity plays the most the important factor in CO₂ EOR method.