This paper presents a new method for forecasting post-fracturing responses in a tight oil reservoir using historical hydraulic fracturing data. The methodology is based on a nonlinear regression method called Variable Structure Regression (VSR). Data for 80 frac jobs were used to calibrate and predict responses. Information per fracturing job included feet of perforation, number of perforations per stage, number of stages, pad volume, slurry volume and sand volume. Information for a set of hydraulically fractured vertical wells was used to test the proposed technique.
The VSR method establishes the optimal nonlinear dependencies of variables to predict the cumulative liquid production after fracturing. This method determines the relationships between fracturing parameters and post-fracturing productions in the form of linguistic terms, thereby providing a physical understanding of the process. The exact mathematical structure of these linguistic terms and the number of terms are established simultaneously, thereby freeing the end user from time-consuming trial and error studies. Meanwhile, the knowledge of domain experts can be preserved as qualitative expert knowledge and may be combined with quantitative data.
A Monte Carlo simulation of 5-fold cross-validation method on fracture optimization data set shows the practical accuracy of the VSR model on forecasting post-fracturing performance. The VSR method achieved satisfactory prediction accuracy as well as statistical performance given the relatively small training data size and the complexity of the problem. The final result shows increase prediction accuracy for all the wells that outperforms other existing methods.