Measuring Methods for Non-Conventional Natural Gas Recovery

Introduction

Research for sustainable energy supply from conventional and non-conventional sources, energy conversion and storage as well as CO₂ sequestration is of increasing importance in context of problems related with global warming and high energy prices. These energy related processes do usually involve high pressures, high temperatures, corrosive and/or toxic substances.

As a result of that measuring instruments for investigating and improving these processes are required to provide reliable results even under these severe conditions. Gravimetric analyzers equipped with magnetic suspension balances (MSB) can be used for different kinds of measurements – for example thermogravimetric, ad- or absorption, solubility, phase equilibrium – in an extremely wide temperature and pressure range, even with corrosive, toxic and explosive reaction gases and vapors.

Applications

In the presentation an overview about recent research activities of our international customers in the field of energy supply using MSB instruments will be given. The following applications will be discussed particularly:

Coal bed methane recovery and CO₂ sequestration

During the coalification process, significant amounts of CH₄ are generated and retained permanently. The chemistry and the micro-structural features inherited from the original biomass confer to coal a large internal surface area, suggesting that sorption is indeed the main storage mechanism of gas in coal seams. Thus, the ad- and desorption properties of CH₄ on coal samples under geological pressure and temperature conditions are important measures for the development of coal bed methane recovery processes and can be measured with MSB instruments. As an example CH₄ adsorption data at two temperatures on a coal sample is provided in the following diagram [1].

Diagram 1:    CH₄ adsorption data at two temperatures on a coal sample as function of the pressure [1].

Coal bed methane recovery combined with CO₂ sequestration:

It has been suggested, that the recovery of coal bed methane might be enhanced by injecting CO₂ in the coal seam. Through an in situ adsorption/desorption process the displaced methane is produced and the adsorbed CO₂ is permanently stored. This process is called enhanced coal bed methane (ECBM) recovery. For proving the process and determining the necessary data gas mixture adsorption data have to be measured on the coal samples. MSB instrument equipped with gas mixing and dosing systems can perform such measurements and provide reliable gas mixture adsorption data. As an example the excess adsorption of the gas mixture CH₄/CO₂ with two different compositions is shown in the next diagram [2].

Diagram 2:    Adsorption data of CH₄ and CO₂ mixtures with two different feed compositions a coal sample [2].

Shale gas recovery

Although the recovery of non-conventional resources of natural gas – so called shale gas – is controversially discussed in Germany, this application is intensively researched in other parts of the world. Critical for the efficiency and the environmental effects are the agents used currently for the hydraulic fracturing. During this process a liquid mixture is pumped into the geological structure and generates cracks and porosity which leads to improved diffusivity for the natural gas. Additives in the mixture are used to maintain the cracks and porosity even when the liquid is displaced by the gas. These additives are potentially toxic and may migrate into ground water reservoirs. A research topic currently is to generate the required improved diffusivity by using other fracturing agents. One of the potential substances is highly pressurized CO₂. We have developed especially for this research a highest pressure MSB which allows studying the mass change of complete geological bore cores under pressures up to 700 bar. A number of these instruments were installed recently in China. First results for the temperature dependent adsorption of CH₄ on a rock sample are given in the figure below.

Diagram 3:    CH₄ adsorption data on a Chinese shale sample up to highest pressures of 700 bar at three temperatures.

Summary

In the presentation several examples of measurements in the above application fields will be presented. The typical experimental setup, procedure of measurements and results – mainly generated by our customer's in their laboratories - will be presented and discussed.

Literature

[1]   S. Ottiger, R. Pini, G. Storti, M. Mazzotti, R. Bencini, F. Quattrocchi, G. Sardu and G. Deriu, Environmental Progress, Vol.25 (2006), No.4

[2]   S. Ottiger, R. Pini, G. Storti and M. Mazzotti, Adsorption, Vol. 14 (2008)