Characterization of geothermal reservoirs’ parameters by inverse problem resolution and geostatistical simulations

BTES (borehole thermal energy storage)systems exchange thermal energy by conduction with the surrounding ground through borehole materials. The spatial variability of the geological properties and the space-time variability of hydrogeological conditions affect the real power rate of heat exchangers and, consequently, the amount of energy extracted from / injected into the ground. For this reason, it is not an easy task to identify the underground thermal properties to use when designing. At the current state of technology, Thermal Response Test (TRT) is the in situ test for the characterization of ground thermal properties with the higher degree of accuracy, but it doesn’t fully solve the problem of characterizing the thermal properties of a shallow geothermal reservoir, simply because it characterizes only the neighborhood of the heat exchanger at hand and only for the test duration. Different analytical and numerical models exist for the characterization of shallow geothermal reservoir, but they are still inadequate and not exhaustive: more sophisticated models must be taken into account and a geostatistical approach is needed to tackle natural variability and estimates uncertainty. The approach adopted for reservoir characterization is the “inverse problem”, typical of oil&gas field analysis. Similarly, we create different realizations of thermal properties by direct sequential simulation and we find the best one fitting real production data (fluid temperature along time). The software used to develop heat production simulation is FEFLOW 5.4 (Finite Element subsurface FLOW system). A geostatistical reservoir model has been set up based on literature thermal properties data and spatial variability hypotheses, and a real TRT has been tested. Then we analyzed and used as well two other codes (SA-Geotherm and FV-Geotherm) which are two implementation of the same numerical model of FEFLOW (Al-Khoury model).

Characterization of vascular wall progenitor cells and their role in therapeutic angiogenesis and Monckeberg's sclerosis

Recently, the existence of a capillary-rich vasculogenic zone has been identified in adult human arteries between the tunica media and adventitia; in this area it has been postulated that Mesenchymal Stem Cells (MSCs) may be present amidst the endothelial progenitors and hematopoietic stem cells. This hypothesis is supported by several studies claiming to have found the in vivo reservoir of MSCs in post-natal vessels and by the presence of ectopic tissues in the pathological artery wall. We demonstrated that the existence of multipotent progenitors is not restricted to microvasculature; vascular wall resident MSCs (VW-MSCs) have been isolated from multidistrict human large and middle size vessels (aortic arch, thoracic aorta and femoral artery) harvested from healthy multiorgan donors. Each VW-MSC population shows characteristics of embryonic-like stem cells and exhibits angiogenic, adipogenic, chondrogenic and leiomyogenic potential but less propensity to osteogenic ifferentiation. Human vascular progenitor cells are also able to engraft, differentiate into mature endothelial cells and support muscle function when injected in a murine model of hind limb ischemia. Conversely, VW-MSCs isolated from calcified femoral arteries display a good response to osteogenic commitment letting us to suppose that VW-MSCs could have an important role in the onset of vascular pathologies such as Mönckeberg sclerosis. Taken together these results show two opposite roles of vascular progenitor cells and underline the importance of establishing their in vivo pathological and regenerative potential to better understand pathological events and promote different therapeutic strategies in cardiovascular research and clinical applications.