Doctor of Philosophy (PhD)
The well-known condensate blockage problem causes severe impairment of gas productivity as the flowing bottom-hole pressure falls below the dew point in gas-condensate reservoirs. Hence, this study attempts to investigate the concept of modifying the spreading coefficient and wettability using low-cost surfactants in the near wellbore region, to prevent the gas flow problems associated with condensate buildup. This study also examines the effect of brine salinity and composition on wettability, spreading and adhesion in condensate buildup regions, to evaluate the ability of brine salinity/composition for enhanced gas productivity in gas-condensate reservoirs. In this study, experiments were performed at both ambient and reservoir conditions using reservoir fluids. Water-advancing and receding contact angles were measured using the Dual-Drop-Dual-Crystal (DDDC) technique and sessile drop method to characterize reservoir wettability and spreading behavior. Interfacial tension was measured using pendent drop shape analysis (DSA) technique and capillary rise techniques. Anionic and nonionic surfactants and nine multi-component brines varying in salinity as well as ten single-salt brines with two different salinities were tested. Oil-water relative permeabilities were generated by history matching condensate recovery and pressure drop data obtained from the coreflood experiments using Berea sandstone core. Wettability was altered from strongly oil-wet to intermediate-wet by the anionic surfactant. The declining trend of spreading coefficient resulted from the presence of surfactants indicating the possibility of enhanced gas productivity and condensate recovery by surfactants. Coreflood results substantiated the wettability alteration to intermediate-wet induced by the anionic surfactant and 82% improvement in gas relative permeability was obtained at ambient conditions. The variation of brine salinity and composition had little effect on wettability and interfacial tension in condensate-brine system. However, large water-receding angles were observed due to the condensate drop spreading on the quartz surface through changing brine salinity and composition. This spreading behavior was more pronounced in high salinity brine systems. This study thus demonstrates that surfactant-induced wettability alteration and spreading coefficient reduction have the benefits for improving gas and condensate production by mitigating the condensate blockage problem. This study also indicates the potential of controlling the spreading behavior of condensate using low salinity brines.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Zheng, Yu, "Effect of surfactants and brine salinity and composition on spreading, wettability and flow behavior in gas-condensate reservoirs" (2012). LSU Doctoral Dissertations. 1314.
Rao, Dandian N.