In unconventional tough gas reservoirs (e.g. tight sandstones or shales) the presence of fractures, either naturally formed or hydraulically induced, is almost always a prerequisite for hydrocarbon productivity to be economically viable. This project studies the formation of fractures in tough gas reservoir rocks (3D fracture geometry and connectivity) by use of laboratory fracturing experiments combined with 3D visualization of fracture planes using high-resolution X-ray tomography techniques.
The proposed research will particularly focus on the effect of rock heterogeneity on the resultant fracture network, how the permeability evolves during the formation of those fracture networks and what the acoustic characteristics are of the shales during development of 3D fracture networks. In addition, this project aims to determine novel strategies in e.g. fluid pressure or stress cycling to optimize the connectivity of the complex fracture networks and as such maximize the hydrocarbon productivity of tough gas reservoir rocks.
The TKI Upstream Tough Gas program, initiated in 2013, has initiated a close and strong collaboration on fractures in tough gas reservoirs between the 5 Tough Gas projects of the three universities (UU, TU/e and TU Delft). Together with our industry partners, we have created an overall multi-year strategy named 2F2S that is built around the knowledge that efficient predictions of producibility of tough gas plays, such as gas shales, tight sands or coal seams, can be only achieved a) by adopting a multi-scale approach (cover the 105 -10-5m range) to understand the behaviour and transport properties of both natural and man-made fracture systems and intervening rock matrix under in-situ P-T-chemical conditions, and b) by consciously integrating the different disciplines needed to link the multiple scales involved, i.e. numerical modelling studies, laboratory experiments and field observation and verification studies.
Four overarching challenges have been defined within our 2F2S program with the aim of aligning and integrating the universities’ different expertise and activities covering both the relevant processes (Challenges 1-3) and regional tectonic evolution aspects (Challenge 4) (Figure 1)
The research proposed here falls within Challenge 2 which focusses on the fracture networks developed in natural rocks.