N267 Petrophysics for Shale Gas Reservoirs

Shale gas reservoirs present a significant petrophysical challenge compared to conventional oil and gas reservoirs. The basis of petrophysical evaluation in conventional reservoirs involves the simple separation of solids and fluids but is problematic when considering fine grained successions of mudstones, or shale gas plays.  Core analyses must be adapted for these low permeability formations, while traditional logs are best supplemented by more recently developed measurements.

This seminar-style course will present an overview of mudstones, and how in shale gas plays the physical and chemical properties are central to any petrophysical evaluation. The course starts from the conventional petrophysics viewpoint, considers the nature of mudstone systems, and then uses a variety of approaches appropriate for evaluating shale gas using core and log data within a geological framework. 

The course will cover the following items:

Day 1: Introduction to shale gas reservoirs and petrophysical models for shale gas; case study 1.

1. Introduction: Shale gas resources and shale gas petrophysics.
2. Shale gas reservoirs. Mudstones: what do we mean by the term shale? Grain size, shape, mineralogy, pore sizes and shapes. Depositional environments, compaction, dewatering, diagenesis, temperature and pressure. TOC, kerogen, organic maturity, chemical and physical properties.
3. Petrophysical models for shale gas. Introduction to shale gas petrophysics. Adsorption and desorption. Mineralogy, chemistry and physical properties. Calculating gas in place.
4. Shale gas: case study 1.

Day 2: Review of petrophysics and introduction to shale gas core analysis.

1. Review of petrophysics as applied to conventional reservoirs. Petrophysical properties; porosity, saturation, density, permeability, capillary pressure; gross, net and pay. Review of core analysis procedures. Review of geophysics and petrophysical relationships. Review of downhole logs.
2. Shale gas core analysis. Coring, core handling and core preservation. Porosity, permeability and saturation. Core sub-sampling. Desorption tests. Langmuir isotherms. Total organic carbon, kerogen, thermal maturity, gas analysis. Geomechanical properties.

Day 3: Shale gas log analysis, petrophysical models revisited, geomechanical properties, and an integrated workflow.

1. Routine log analysis and new approaches (e.g. induced gamma ray spectroscopy, NMR, imaging, stress and dielectric measurements). TOC from logs. Density and porosity. Saturation from Archie, from shaly sand resistivity models and from mineral models. Integrated analysis of core and log data.
2. Worked example: case study 2.
3. Petrophysical models revisited; shale gas in place calculations.
4. Geomechanical properties.
5. Integrated workflow. Review of possible steps, problems, pitfalls, and future directions. Summary of how shale gas varies from conventional reservoirs, and how the variable nature determines the petrophysical approach.