Absolute pore size distributions from NMR

NMR measurements on core samples saturated with brine returns valuable information on the porous structure of the rock core. Monitoring a single fluid component in a relaxation experiment reflects the pore size distribution and thus the degree of sorting of the porous rock. The basic assumptions are that the mobility of the component confined in the porous rock is of such a value that a small fraction of the probing molecules experience the surfaces of the pores and that the surface relaxation strength is fairly independent of pore size. Then one may combine diffusion measurements at short observation times returning a value for the average surface to volume ratio with ordinary relaxation time measurements to obtain an absolute pore size distribution instead of the standard T2 distributions or T1-T2 correlated two dimensional distributions

Microbial hydrogen consumption leads to a significant pH increase under high-saline-conditions: implications for hydrogen storage in salt caverns

Salt caverns have been successfully used for natural gas storage globally since the 1940s and are now under consideration for hydrogen (H2) storage, which is needed in large quantities to decarbonize the economy to finally reach a net zero by 2050. Salt caverns are not sterile and H2 is a ubiquitous electron donor for microorganisms. This could entail that the injected H2 will be microbially consumed, leading to a volumetric loss and potential production of toxic H2S. However, the extent and rates of this microbial H2 consumption under high-saline cavern conditions are not yet understood. To investigate microbial consumption rates, we cultured the halophilic sulphate-reducing bacteria Desulfohalobium retbaense and the halophilic methanogen Methanocalculus halotolerans under different H2 partial pressures. Both strains consumed H2, but consumption rates slowed down significantly over time. The activity loss correlated with a significant pH increase (up to pH 9) in the media due to intense proton- and bicarbonate consumption. In the case of sulphate reduction, this pH increase led to dissolution of all produced H2S in the liquid phase. We compared these observations to a brine retrieved from a salt cavern located in Northern Germany, which was then incubated with 100% H2 over several months. We again observed a H2 loss (up to 12%) with a concurrent increase in pH of up to 8.5 especially when additional nutrients were added to the brine. Our results clearly show that sulphate-reducing microbes present in salt caverns consume H2, which will be accompanied by a significant pH increase, resulting in reduced activity over time. This potentially self-limiting process of pH increase during sulphate-reduction will be advantageous for H2 storage in low-buffering environments like salt caverns.publishedVersio

A strategy for low cost, effective surfactant injection

Ideally, in a chemical flooding process, one would like to inject a surfactant solution that has good solubility at the relevant conditions, ultralow interfacial tension (efficient oil mobilisation) and low loss of surfactant (better economics) in the porous medium. The key question is – can you have low loss of surfactant, i.e. low retention, at ultralow interfacial tension? To answer this question, we have undertaken a systematic study of surfactant solubility, phase behaviour, interfacial tension and retention as a function of salinity for a given surfactant formulation. The idea is to explore the interrelationship between these properties and find the best condition(s) for combined low interfacial tension and low retention in a surfactant flooding process. For the investigated surfactant formulation, ultra-low interfacial tensions (<0.01 mN/m) can be found in the Winsor III region at optimal salinity. The aqueous solution at optimal salinity is, however, turbid, and retention values are high. On the other hand, for light oils, there are regions in the Winsor I area where (i) interfacial tensions are low (0.01 mN/m<IFT<0.1 mN/m), but not ultralow, (ii) aqueous solutions are clear and (iii) retention is 10 times lower than at optimal salinity. The search for an optimum surfactant formulation has to consider solution properties and retention in addition to the low interfacial tension. Based on our result, we therefore propose that Winsor I phase behaviour is the best option for a compromise between the properties in question

Management of High-Water-Cut and Mature Petroleum Reservoirs

An increasing number of oil and gas companies reach their economic limit after years of production, exhausting the support of natural-pressure drive mechanisms in the reservoir and the benefits of water or gas injection [...

Management of High-Water-Cut and Mature Petroleum Reservoirs

An increasing number of oil and gas companies reach their economic limit after years of production, exhausting the support of natural-pressure drive mechanisms in the reservoir and the benefits of water or gas injection [...

Absolute pore size distributions from NMR

NMR measurements on core samples saturated with brine returns valuable information on the porous structure of the rock core. Monitoring a single fluid component in a relaxation experiment reflects the pore size distribution and thus the degree of sorting of the porous rock. The basic assumptions are that the mobility of the component confined in the porous rock is of such a value that a small fraction of the probing molecules experience the surfaces of the pores and that the surface relaxation strength is fairly independent of pore size. Then one may combine diffusion measurements at short observation times returning a value for the average surface to volume ratio with ordinary relaxation time measurements to obtain an absolute pore size distribution instead of the standard T2 distributions or T1-T2 correlated two dimensional distributions

PROBING THE CONNECTIVITY BETWEEN PORES IN ROCK CORE SAMPLES

ABSTRACT By Nuclear Magnetic Resonance (NMR) measurements of relaxation and diffusion at a predefined observation time in 100 % brine saturated rock core samples it is possible to probe the connectivity between the pores within the sample. By plotting the observation time dependent diffusion coefficients as a function of the surface-to-volume ratio characteristic for each sample, it is possible to compare the connectivity between rock core samples

Absolute pore size distributions from NMR

NMR measurements on core samples saturated with brine returns valuable information on the porous structure of the rock core. Monitoring a single fluid component in a relaxation experiment reflects the pore size distribution and thus the degree of sorting of the porous rock. The basic assumptions are that the mobility of the component confined in the porous rock is of such a value that a small fraction of the probing molecules experience the surfaces of the pores and that the surface relaxation strength is fairly independent of pore size. Then one may combine diffusion measurements at short observation times returning a value for the average surface to volume ratio with ordinary relaxation time measurements to obtain an absolute pore size distribution instead of the standard T2 distributions or T1-T2 correlated two dimensional distributions