Print this pagePotential Tracers of Gas Diffusion in Petroleum Reservoirs and Caprocks
Magnier, C., A. Prinzhofer, S. Kara, A. Battani, IFP, Rueil Malmaison, France
Noble gases are chemically inert but are sensitive to physical partitioning.
They have been used as natural tracers for evaluating distances and direction
of migration of hydrocar-bons(Prinzhofer et al. 2000). Our objectives is to test their potential as monitoring tools
for gas storage and cap-rocks studies.
This methodology may be very promising to assess a risk of
upward gas leakage. Our approach is based on experimental work that uses the
diffusive properties of noble gases through different mineral assemblage in
water
saturated media. The apparatus consists of a stainless steel reactor with
two separated gas chambers filled with different gases, one is carbon dioxide
and noble gases, the other pure oxygen, both having similar diffusive rates and
solubility in water. In the middle of the reactor, a synthetic carbonate,
sandstone or a real cap-rock sample is placed.
The experiment
quantifies the flux of gas through the rock and the chemical and isotopic
fractionation of different components as a function of the porosity and
permeability. When sampling was made early on in the diffusion experiment,
important chemical (4He/20Ne etc...) and isotopic fractionations (3He/4He) were
observable. The rates of diffusion in porous media were simulated by taking
into account two water domains, bound water and free water. The proportion of
bound water was studied and tentatively adjusted by a 1D model. The bound water
has a complex behavior but clearly varies with salinity, pH and atom size.
Furthermore, it induces changes in the gas solubility and rates of diffusion.