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Chapter 6Coupled mass transfer and gelation of TMOS inporous materialsIn the previous chapters the coupled mass transfer and gelation of TMOS in twophasebulk models was considered. Here we turn to the situation in which TMOS,dissolved in oil, is forced into a natural porous material containing (heavy) water.The coupled mass transfer and gel reaction were characterized and monitored byemploying bi-nuclear NMR techniques. The relaxation time T 1 of hydrogen in theoleic phase was measured to determine the mass transfer rate, and the relaxationtime T 2 of deuterium in the aqueous phase was measured to determine the reactionrate. It was found that, like in bulk systems, the mass transfer is predominantlydriven by the hydrolysis rate. Due to the gel treatment, for each core the relativepermeability to water was reduced more than that to oil.6.1 IntroductionWhen an alkoxy-silane solution in oil is forced into a porous material containing water thechemical transfers and reacts with water on a pore scale. Silica gel is then formed, whichalters the pore space or blocks the pores. A series of experiments was done to characterizeand monitor in situ the placement and reaction of TMOS in a natural porous material.Consider a homogeneous porous cylinder (core) with a length L, porosity ϕ and absolutepermeability K abs (see Figure 6.1). The core is fully saturated with an aqueousphase and an oleic phase. The water saturation is given by S w (z, t), where z is the spatialcoordinate along the length of the core. Consequently, the oil saturation S o (z, t) isequal to 1 - S w . The volume fraction of TMOS in the oleic phase is given by φ T (z, t). Amixture of TMOS/oil, with a fraction φ T = φ 0 , is injected with an injection rate Q atthe inlet of the core, which is located at z = −L/2, and subsequently fluids are producedat the outlet which is located at z = L/2. As the TMOS comes in contact with water,the TMOS partitions between both phases. In the aqueous phase the TMOS undergoesa heterogeneous reaction with water and forms a gel.To our best knowledge, the coupled mass transfer and gel reaction of TMOS have sofar not been monitored in situ in natural porous materials. To do so, we developed andemployed dedicated NMR techniques to measure the mass transfer and reaction rates ofthe chemical within small sandstone cores which were prepared at either irreducible wateror residual oil conditions [118]. Discrimination between both phases was done by usingheavy water instead of normal water for the aqueous phase and by employing both 1 H-NMR and 2 H-NMR techniques to measure the relaxation times of the oleic phase and the77