How do petrophysics and geomechanics work together in well log interpretation?

Petrophysics is fundamental to understanding the properties of oil and gas reservoirs both for initial static volumes in place and potential and actual dynamic performance. It lies at the centre of all subsurface activities, whether in the context of open-hole evaluation of new wells, cased-hole operations on producing wells, or in an integrated team building reservoir models for asset evaluation, field development or reservoir management.

Petrophysics is the study of the physical and chemical properties of rocks and their interactions with fluids, particularly in the context of petroleum exploration and production. It involves analyzing well log data to characterize reservoir properties such as porosity, permeability, and fluid saturation. For example, petrophysicists use well logs like gamma-ray, neutron, and resistivity logs to assess rock lithology and pore fluid content, providing crucial information for reservoir evaluation and production optimization.

In geomechanics we measure geomechanical properties in the lab. The well log derived geomechanical properties had to be calibrated against the lab data. In the contrary, the stress and pressure of formation cannot be measured in the lab and had to be measured or estimated by in situ tests. Geomechanical is not only important for oil and gas it’s also critical for CCS, energy storage and geothermal energy.

Geomechanics is the study of the mechanical behavior of rocks and their response to stress and strain within the Earth's crust. It encompasses understanding how rocks deform, fracture, and interact with fluids under various conditions, including drilling and production operations. For example, geomechanics analyses assess the stability of boreholes during drilling, predict formation damage, and optimize hydraulic fracturing operations in unconventional reservoirs. When combined with petrophysics in well log interpretation, geomechanics provides insights into reservoir properties, wellbore stability, and hydraulic fracturing design, enhancing overall reservoir characterization and production optimization.

Geomechanics plays an important role in many aspects of petroleum exploration and development, such as formation pressure prediction, casing program design, directional well trajectory design optimization, wellbore stability analysis, reservoir fractured performance evaluation, fracture effectiveness evaluation, induced fracture network prediction, stimulation scheme optimization, perforation interval selection, sand production mechanism analysis, early warning of casing failure, fault activity evaluation, productivity prediction, well placement optimization, geological modeling of fractures, in CO2 storage and coupling numerical simulation.

Petrophysics is very important for understanding of geomechanical behavior of rock. These two disciplines are working together. For example, when you measure your sonic and density logs, they will be used for the calculation of geomechanical elastic properties. Therefore geomechanics engineers need to talk with petrophysic engineer and make sure that his input data are correct. If sonic logs are affected by gas saturation, they need to be corrected before being used in geomechanics models.

By combining petrophysical data on rock properties (e.g., porosity, permeability) with geomechanical insights into rock behavior under stress, engineers can assess reservoir quality, predict wellbore stability, and optimize hydraulic fracturing designs. For example, integrating petrophysics and geomechanics can help identify sweet spots for drilling in unconventional reservoirs, optimize completion strategies to minimize formation damage, and improve reservoir management practices for enhanced hydrocarbon recovery and overall field performance.

One challenge is reconciling different data scales and resolutions from petrophysical and geomechanical datasets. For instance, petrophysical logs provide detailed rock properties at a small scale, while geomechanical data like seismic surveys cover larger areas with less detailed information. Another challenge is the complexity of integrating diverse datasets, methodologies, and interpretations, requiring interdisciplinary collaboration and advanced data integration techniques to overcome these challenges effectively.

Recent advancements in integrating petrophysics and geomechanics in well log interpretation involve sophisticated data fusion techniques and machine learning algorithms. These advancements enable the simultaneous analysis of petrophysical properties and geomechanical behaviors from well logs, providing a more comprehensive understanding of reservoir characteristics and mechanical properties. Future trends include the development of advanced modeling tools that incorporate real-time data from drilling operations to optimize well placement and completions, leading to enhanced reservoir performance and production efficiency.

Petrophysical and geomechanical parameters help to determine horizontal well orientation, to select drilling mud densities for stable drilling operations, to assess the suitability of specific zones in a formation for hydraulic fracturing, and to assess required hydraulic fracturing pressures.