Projecting Petrophysical Logs at the Bit through Multi-Well Data Analysis with Machine Learning

The vertical distance from logging while drilling (LWD) sensors to the bit is often more than 30m (98 ft), which leads to difficulty in performing real-time comparison of LWD and drilling data. This study aims to predict the petrophysical data at the drill bit with the objective of determining the best supervised machine learning algorithm to incorporate to reduce the sensor offset problem. The bulk density and porosity logs are predicted at the bit in this paper using petrophysical and drilling parameters. The results of the model will be used to perform lithology identification in real-time that can be used in real-time drilling analysis.

To predict the bulk density and porosity logs at the bit, data from four different wells located in the Norwegian continental shelf in the North Sea was used as a training dataset. The data from a fifth well from the same field was used as a validation dataset. The prediction was based on input variables of the Gamma ray (GR) log data recorded close to the bit, along with other drilling parameters measured at the bit using Measurement while Drilling (MWD) sensors. The five regression models used for prediction and comparative analysis were: Multi-linear regression (MLR), K-nearest neighbor (KNN) regression, Random forest regression (RFR), Support vector machine (SVM) regression and Artificial neural network (ANN).

All five models were tested for their accuracy in predicting porosity and bulk density, and it was determined that the KNN model was more effective for predicting both porosity and bulk density. The coefficient of determination (R²) value for the KNN model for porosity and bulk density predictions were 86% and 74% respectively with the least mean square error (MSE) calculated on the blind dataset (data from a well not included in model training). SVM was found to be the least effective model for predicting both porosity and bulk density, as it had the highest MSE value.

Prediction of porosity and bulk density logs at the bit using multiple machine learning techniques to eliminate the sensor offset problem have not been performed extensively in the past. The developed machine learning model will improve real-time drilling analysis.