(731c) 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)