In enriched gas drives, for correct interpretation of slim tube displacement (STD) tests and for determination of minimum miscibility pressure (MMP) or minimum enrichment (ME) required to achieve dynamic miscibility, it is extremely important to identify the correct mechanism of misciblity development. Traditional, pseudo-ternary diagram construction and limiting tie-line method or the criteria of very high (90-95% plus) ultimate oil recoveries or the criteria of breakover point in ultimate oil recovery versus pressure diagram in STD tests, used to determine MMP or ME are not always valid and can lead to solvents designed either too rich or too lean. In this study, STD tests supported by equation-of-state (EOS) predictions were used to evaluate the ability of various solvents such as CO2, n-butane and various mixtures of Prudhoe Bay natural gas (PBG) and natural gas liquids (NGL), to miscibly displace heavy, asphaltic West Sak crude. Results indicate that for enriched gas drives, the development of dynamic miscibility occurs via simultaneous vaporizing and condensing mechanisms. The solvent minimum enrichments for this dual mechanism were obtained from the solvent-oil, pressure-composition isotherms, compositional path in multicontact test (MCT) calculations and the methane spike disappearance phenomena in STD tests and were compared to those determined by condensing type, pseudo-ternary diagram construction method. STD test results indicate that the ultimate oil recoveries, even for first contact miscible (FCM) solvent were considerably lower due to asphaltene precipitation. Asphaltene tests were conducted for various solvent-West Sak crude mixtures to determine the amount of precipitation and it's effect on oil composition. STD results and EOS predictions indicate that CO2 was unable to develop dynamic miscibility with West Sak crude at reservoir pressure and temperature conditions and the process mechanism for CO2 drive is simultaneous vaporizing-condensing drive.

Wellbore drilling in highly fractured and unstable formations has always been one of the greatest difficulties in drilling operations. Failure and collapse of wellbore wall frequently occur in the fractured zone and may ultimately obstruct any further drilling of the wellbore. A number of techniques have been proposed and tested to improve drilling conditions in the fractured and unstable formations, but a highly effective method is still lacking. For many years chemical consolidation techniques have been studied and applied for ground support in underground mine openings. Very successful results have been achieved employing the techniques to stabilize fractured zones surrounding underground openings. For these a number of highly effective chemical materials for consolidation have been developed. In order to examine the feasibility of this technology for enhancing wellbore stability, a series of laboratory experiments have been carried out in this study. These experiments included uniaxial compressive strength tests, triaxial compressive strength tests, shear bond strength tests, indirect tensile strength tests and thick wall cylinder tests. Chemical grouts Terraset B1000, Webac 4110 and others were used in these tests and their mechanical properties were assessed. The results of the experiments show that chemical grouting is likely to improve the stability of wellbore in fractured and unstable rock formations. Among the grouting materials tested, the Webac 4110 had the best performance. Its use increased the shear strength by 100-150%.