Ali Saeedi

Permeability Prediction from Mercury Injection Capillary Pressure: An Example from the Perth Basin, Western Australia

For shale gas reservoirs, permeability is one of the most important—and difficult—parameters to determine. Typical shale matrix permeabilities are in the range of 10 microdarcy–100 nanodarcy, and are heavily dependent on the presence of natural fractures for gas transmissibility. Permeability is a parameter used to measure the ability of a rock to convey fluid. It is directly related to porosity and depends on the pore geometry features, such as tortuosity, pore shape and pore connectivity. Consequently, rocks with similar porosity can exhibit different permeability. Generally, permeability is measured in laboratories using core plugs. In some cases, however, it is difficult to obtain suitable core plugs. In these instances, other approaches can be used to predict permeability, which are chiefly based on mathematical and theoretical models. The approach followed in this peer-reviewed paper is to correlate permeability with capillary pressure data from mercury injection measurements. The theoretical and empirical equations, introduced in the literature for various conventional and unconventional reservoir rocks, have been used to predict permeability. Estimated gas shale permeabilities are then compared with results from transient and steady state methods on small pieces of rocks embedded in a resin disk. The study also attempts to establish a suitable equation that is applicable to gas shale formations and to investigating the relationship between permeability and porosity.

Multiphase Flow during CO2 Geo-Sequestration

Both quantitative and qualitative evaluations of multiphase flow in porous medium is necessary in order to understand the processes involved and optimum management of the underground reservoirs subjected to either production or injection of fluids. The flow of fluids through pipes and conduits is relatively easy to model. However, due to the complex nature of the geological porous medium, analysing multiphase flow through them involves complex formulation and cannot be described explicitly.

Interpretation, Analysis and Discussion

Apart from the basic routine core analysis, 20 cyclic core-flooding experiments and 11 NMR measurements were conducted on a total of 13 sandstone core samples during the experimental work carried out throughout this research. In addition, two chemical composition analyses were also done on the brine samples taken during the flooding tests. The results obtained through running the above-mentioned experiments were presented in details in the previous chapter. This chapter, however, is dedicated to the interpretation, analyses and discussion of those results, to find out how they help achieving the research objectives outlined earlier.

Experimental Setup, Material and Procedure

A major part of the experimental work related to this research, consisting of a number of different types of core-flooding experiments, was carried out using the state-of-the-art, high pressure-high temperature, three-phase steady-state core-flooding apparatus located within the Department of Petroleum Engineering at Curtin University. To be able to achieve the objectives of this research program, various types of flooding experiments were designed and carried out using the above-mentioned core-flooding rig. In the first part of this chapter a detailed description of the experimental apparatus and its various components is presented.

Summary Conclusions and Recommendations

A range of variable factors are expected to influence multiphase flow during CO2 geological sequestration. In order to, qualitatively and quantitatively, investigate the effects of a number of these factors, a range of specially designed core-flooding experiments (complemented by some other minor laboratory work) was carried out. The investigated factors which were expected to have moderate to strong effect on the multiphase flow characteristics of the rock-fluids system during subsurface CO2 disposal included: cyclic CO2-brine flooding, flow direction (horizontal versus vertical), change in the reservoir net effective pressure and existence of residual natural gas (represented by CH4 here) saturation.