Traditionally, resources encountered in low-permeability (‘tight’) formations such as shales are deemed uneconomical for production. Advances in horizontal drilling and reservoir stimulation have shifted this perspective to render shale gas reservoirs one of the most promising hydrocarbon resources around the world. A profound understanding of the transport processes manifesting in shale gas reservoirs will contribute to more effective Enhanced Gas Recovery (EGR) schemes, lower production costs and, at the same time, improve the forecasting of gas production.
To gain more insights into the mechanics of gas production from shale formations, this thesis proposes a geometrically accurate model inspired from Scanning Electron Microscopy (SEM) imaging. Discretising the computational domain, the equations of flow were solved considering the mechanisms of Fickian and Knudsen diffusion, Klinkenberg’s permeability, real gas compressibility and adsorption/desorption processes. The gas flowrate was determined and the pressure variations were deduced inside shale porous media at the micro-level. A non-dimensionalisation approach was developed that permits the comparison between micro-scale modelling results with actual core measurements several orders of magnitude apart in spatial and temporal scales. Non-dimensional micro-scale modelling results exhibit excellent agreement with actual core data shedding light on some of the important aspects which govern gas flow.
To ensure that the adsorption mechanism is thoroughly captured, the calculated isotherm profile should replicate experimental measurements within the whole pressure range. The adopted Klotz isotherm profile closely matches the core measurements, and this promotes a better understanding of the adsorption processes in the shale matrix. In parallel, a flowrate sensitivity analysis was conducted in the context of the matrix and the fluid properties. The sensitivity analysis revealed that, although permeability is the most prominent parameter governing gas flow rates, reservoir pressure requires even more attention, since it changes considerably during the lifetime of a gas field and it can be managed by a suitable production strategy. Ultimately, the effort to tie the prevailing theoretical understanding with experimental observations was deemed significant for boosting the productivity of gas from shale formations.
Integrating Micro-scale Modelling with Core Measurements to Improve Shale Gas Production
- PhD thesis
- Sciences and Engineering -- Engineering