MODELLING SHALE GAS FLOW USING THE IDEA OF APPARENT DYNAMIC PERMEABILITY
The basic idea behind this research is to propose a work flow to model gas flow in numerical simulators, which would take into consideration all the complexities of the multiple porosity systems that exist in shale matrix and the different dynamics of flow involved within them. The concept of a multi porosity system that is composed of the organic part (kerogen), inorganic matter, and natural and hydraulic fractures is used here. Kerogen is very different from other shale components because of its highly porous nature, capability to adsorb gas and abundance of nano-pores on its surface.
Some theories have been put forward for the physics involved in shale on a micro scale level. However, when working with reservoir scale models, the details as described for porosity systems in micro scale models is lost. To overcome this problem, the idea of dynamic apparent permeability, which is a function of matrix pressure, is used. It helps in up-scaling the particulars of the micro scale model to a reservoir one and aids in modelling Darcy flow, Fickian diffusion and transition flow in between the matrix and fractures.
Our assumptions are validated by working with the case of a horizontal well model, producing gas from the Barnett shale formation, that doesn’t take into consideration the relevant flow phenomenon. History matching the model after integrating diffusion and desorption reveals that considering these additional processes impacts the assumed SRV region, affecting its volume as well as its properties. This would be a critical factor in optimizing completion design, to lower down the well cost for same or ever greater production. Similarly, this can play a vital role in well spacing for effective field development.
We summarize our findings from production forecasts that matrix contribution towards production is under estimated when relevant assumptions for shale are not modelled. This signifies the importance of better understating the transport phenomenon occurring in shale, which would enable us to have a greater insight to scrutinize production data and later to predict changes in production as completion methods are changed. This means that a multi stage high density fracturing job might not optimize the well in terms of its value. Decreasing our expenditure on well completions, such that their design results in lower production rates at the initial time period along with lower decline rates, would enable us to produce these wells longer for the same recovery. This would enable us to push the production in future where oil and gas prices might be better。
