No abstract

Well productivity in gas condensate reservoirs is reduced by condensate banking when the bottom hole flowing pressure drops below the dew point pressure. Among the several methods which have been proposed for condensate removal, wettability alteration of reservoir rock to intermediate gas wetting in the near wellbore region appears to be one of the most promising techniques. In this work, we report use of a nanofluid to change the wettability of the carbonate and sandstone rocks to intermediate gas wetting. Application of nanofluid in the wettability alteration of carbonate and sandstone rocks to gas wetting has not been reported previously and is still an ongoing subject. Static and dynamic contact angle measurements, along with imbibition tests, have been performed to investigate the wettability of carbonate and sandstone rocks in presence of nanofluid. It was found that the nanofluid used in this work can considerably change the wettability of both surfaces to preferentially gas wetting in just one day of ageing time. We also report the effect of initial oil saturation and ageing time on the nanofluid capability for wettability change. Initial oil saturation reduces the impact of the nanofluid on wettability change, and hence, a pre-treatment before using nanofluid is necessary. In addition to these small slab-scale experiments, applicability of nanofluid in wettability alteration of sandstone rocks to gas wetting is also investigated in core scale. The results of core displacement tests confirm the ability of nanofluid to change the rock wettability from liquid wetting to gas wetting in core samples. They also show the effectiveness of chemical treatment in subsurface conditions.

Several facultative bacterial strains tolerant to high temperature and salinity were isolated from the oil reservoir brines of an Iranian oil field (Masjed-I Soleyman). Some of these isolates were able to grow up to 60 degrees C and at high concentration of NaCl (15% w/v). One of the isolates grew at 40 degrees C, while it was able to grow at 15% w/v NaCl. Tolerances to NaCl levels decreased as the growth temperatures were increased. Surfactant production ability was detected in some of these isolates. The use of biosurfactant is considered as an effective mechanism in microbial-enhanced oil recovery processes detected in some of these isolates. The surfactant producers were able to grow at high temperatures and salinities to about 55 degrees C and 10% w/v, respectively. These isolates exhibited morphological and physiological characteristics of the Bacillus genus. The partial sequencing of the 16S ribosomal deoxyribonucleic acid gene of the selected isolates was assigned them to Bacillus subtilis group. The biosurfactant produced by these isolates caused a substantial decrease in the surface tension of the culture media to 26.7 mN/m. By the use of thin-layer chromatography technique, the presence of the three compounds was detected in the tested biosurfactant. Infrared spectroscopy and (1)H nuclear magnetic resonance analysis were used, and the partial structural characterization of the biosurfactant mixture of the three compounds was found to be lipopeptidic in nature. The possibility of use of the selected bacterial strains reported, in the present study, in different sectors of the petroleum industry has been addressed.