Dr. Jan ter Heege
- shale gas
- unconventional gas
- hydraulic fracturing
- rock physics
The development of successful exploration and production strategies for tight gas reservoirs require good insight into the (local) porosity-permeability distribution. TNO is building a quick screening tool that predicts porosity-permeability on the basis of rock type, burial history, lamination and tectonic stress regime.
The tool will be integrated in basin modelling software to investigate the typical porosity-permeability evolution of key stratigraphic units for realistic basin formation scenarios, with results evaluated against porosity-permeability predictions based on geological modelling in a case study of a well-characterised tight gas reservoir. One such case could come from the offshore Rotliegendes gasfields, NW of the Netherlands. If information on the spatial distribution of sedimentary facies is available, the tool can be used in combination with rock typing and basin modelling to predict the spatial distribution of porosity-permeability. The predictions are compared with porosity-permeability maps that are produced using well log correlation, petrophysical analysis of rocks and geological modelling of facies distribution. The tool thus helps to optimise completion strategies in problematic gas systems.
The tool is particularly useful for areas where a lack of data hampers conventional porosity-permeability prediction. The evolution of porosity-permeability of reservoir rocks over geological time is predicted by modelling compaction and cementation during diagenesis, with compaction by grain fracturing and solution-precipitation processes in a closed system modelled as a base case. Experimental and field data are combined with discrete element models to model these processes for the full range of relevant conditions and compositions. The base case can be extended to include other diagenetic processes, such as illite cementation, in situations where these processes play an important role and data is available. The tool requires rock properties, pressure-temperature-time paths, and stress conditions of rocks during burial as input. The input is provided by a combination of rock typing and basin modelling.
Rock typing is performed to obtain a classification of rock types with characteristic rock properties that are linked to depositional environment. Rock properties, such as clay content, grain size distribution and pore throat geometry can be used as input for the porosity-permeability prediction tool. By running the tool for different rock types and burial histories, both the distribution of porosity-permeability within stratigraphic units and the potential for developing tight gas reservoirs can be determined. Realistic scenarios for the formation of sedimentary basins use state-of-the-art basin modelling software to investigate typical burial histories of rocks. Related pressure-temperature-time paths and stress conditions are used as input for the porosity-permeability tool. By combining basin modelling and rock typing, the tool can be used to determine the evolution of porosity-permeability for a specific rock type and burial history.