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One of the challenges in reservoir management is determining the fracture density (FVDC) in reservoir rock. Given the high cost of coring operations and image logs, the ability to predict FVDC from various petrophysical input variables using a supervised learning basis calibrated to the standard well is extremely useful. In this study, a novel machine learning approach is developed to predict FVDC from 12-input variable well-log based on feature selection. To predict the FVDC, combination of two networks of multiple extreme learning machines (MELM) and multi-layer perceptron (MLP) hybrid algorithm with a combination of genetic algorithm (GA) and particle swarm optimizer (PSO) has been used. We use a novel MELM-PSO/GA combination that has never been used before, and the best comparison result between MELM-PSO-related models with performance test data is RMSE = 0.0047 1/m; R2 = 0.9931. According to the performance accuracy analysis, the models are MLP-PSO < MLP-GA < MELM-GA < MELM-PSO. This method can be used in other fields, but it must be recalibrated with at least one well. Furthermore, the developed method provides insights for the use of machine learning to reduce errors and avoid data overfitting in order to create the best possible prediction performance for FVDC prediction. [ABSTRACT FROM AUTHOR]

Awareness of uniaxial compressive strength (UCS) as a key rock formation parameter for the design and development of gas and oil field plays. It plays an essential role in the selection of the drill bits and stability of the wellbore's wall. Precise prediction of UCS before or during the drilling, especially in exploration wellbores, is necessary to improve the drilling speed and reduce the instability of the wellbore walls. UCS predictor machine-learning (ML) models are developed in this study using drilling parameters recorded during drilling using least-squares support-vector machine (LSSVM) and multi-layer extreme learning machine (MELM) algorithms hybridized with cuckoo optimization algorithm (COA), particle swarm optimization (PSO) and genetic algorithm (GA) optimizers. In addition, stand-alone LSSVM and convolutional neural network (CNN) models without optimizer enhancements are evaluated. Drilling and petrophysical data recorded for two wells (A and B) from the Rag-e-Safid oil field in southwest Iran were compiled to form the studied dataset. UCS was initially calculated numerically based on data from laboratory tests from petrophysical logs. The Well A dataset was pre-processed to remove outlying data records by applying the quantile regression algorithm. That analysis indicated that 9 data records should be removed from the Well A dataset. A decision tree model was employed for feature selection purposes to identify the more influential variables with respect to UCS. Depth, weight on the drill bit (WOB), drill-string rotation speed (RPM), rate of penetration (ROP), and torque (Trq) were the variables identified as being highly influential on UCS values. Application of the ML models on the training data subset (75% of Well A data records) revealed that the MELM-COA algorithm achieved the lowest root mean squared error (4.6945 MPa) and a higher coefficient of determination (0.9873) value than the other models when predicting UCS in the Well A training and validation data subsets. The Well-A-trained MELM-COA model confirmed its generalizability within the studied field by generating low UCS prediction errors when applied to the independent Well B testing dataset. [ABSTRACT FROM AUTHOR]

A key parameter when drilling for gas and oil is to determine the safe mud weight window (SMWW) to ensure wellbore stability as part of a quantitative risk assessment (QRA). This study determines SMWW by predicting acceptable upper and lower limits of the bottom hole pressure window during over-balance drilling method. A novel machine learning method is developed to predict SMWW from ten well-log input variables subject to feature selection. 3389 data records from three South Pars gas field (Iran) wells include data from: uncorrected spectral gamma ray; potassium; thorium; uranium; photoelectric absorption factor; neutron porosity; bulk formation density; corrected gamma ray adjusted for uranium content; shear-wave velocity and compressional-wave velocity. Combinations of these well logs are tuned to provide predictions of the SMWW, measured in terms of subsurface pore and fracture pressures, using machine learning (ML) algorithms hybridized with optimizers. The ML algorithms assessed are multiple layer extreme learning machine (MELM) and least squares support vector machine (LSSVM), hybridized with genetic (GA) and particle swarm (PSO) optimizers. This new algorithm (MELM) incorporates special features that improve its prediction performance, speeds up its training, inhibits overfitting and involves less optimization in the model's construction. By combining MELM with PSO, its optimum control parameters are rapidly determined. The results reveal that the MELM-PSO combination provides the highest SMWW prediction accuracy of four models evaluated. For the testing subset MELM-PSO achieves high prediction performance of pore pressure (RMSE = 12.76 psi; R2 = 0.9948) and fracture pressure (RMSE = 15.71 psi; R2 = 0.9967). Furthermore, the model demonstrates that once trained with data from a few wells, it can be successfully applied to predict unseen data in other South Pars gas field wells. The findings of this study can provide a better understanding of how ML methods can be applied to accurately predict SMWW. • Four hybrid algorithms used for determining safe mud weight window based on pore and fracture pressures. • MELM-PSO outperforms MELM-GA, LSSVM-PSO and LSSVM -GA models. • Ten petrophysical variables were used as input to determination of safe mud weight window. [ABSTRACT FROM AUTHOR]