Engineer Level Automated Interpretation of Geothermal Well Logs Using
Convolutional Neural Networks
Abstract
Geothermal well log analyses consist of utilizing pressure and
temperature data measured along the wellbore to predict feed zones,
reservoir temperature, and reservoir pressure. Interpreting geothermal
production logs can be subjective and require great expertise to achieve
repeatability. In situations where there may be several log data,
interpreting the logs may be time consuming for quick decision-making
processes. This work discusses the implementation of a multi-layered
deep learning convolutional neural network to automatically diagnose
sets of temperature and pressure well logs. The algorithm achieves
results similar to those of a professional engineer. This algorithm
enables the interpretation of many well logs in just a few seconds. Data
input for this project is synthetic well data that mimics real data.
10,000 datasets were used. The data was split as follows: 9,800 and 200
for training and validation respectively. The algorithm used takes as
input three “depth-series” logs of temperature, pressure, and
temperature gradient, passes the data through a convolutional neural
network including a flat layer and then a fully connected layer with
five output variables which are the depths of the feed zones, the
reservoir temperature, the reservoir pressure and the depth at which the
reservoir pressure is known. The cost function for this model was the
mean squared error. The optimizer algorithm used was Adam, and the
learning rate had an exponential decay. The algorithm recorded the model
state that had the lowest mean absolute validation error. The
architecture was implemented in Keras with a TensorFlow backend. The
best model found during the process of hyper-parameter tuning was used
to predict the reservoir characteristics for the validation and testing
data sets. The results show a good match between the predicted data and
actual data with a training error of 0.9%, validation error of 2%, and
test error of 7%. Future works will involve adding more real data to
the training and validation set, increasing the number of feedzones that
can be identified, and performing sequential analysis using
interdisciplinary data.