Low oil-water ratio invert emulsion mud for unconventional shale reservoirs

Due to stringent environmental regulations on the disposal and management of the traditional diesel oil-based mud used for drilling difficult formations such as shale, there is the necessity to develop an environmentally friendly drilling mud. Vegetable oils such as Jatropha have proven to be a comparable alternative to diesel oil. However, there have been concerns of compatibility of the vegetable oils with the chemical additives and the ability to achieve a low oil-water ratio mud, which is beneficial to low fluid loss for enhanced wellbore stability. The focus of this study is to achieve a novel low oil-water ratio invert emulsion using Jatropha oil and egg yolk as an emulsifier. Shale-fluid interaction and the economic viability of the mud were also evaluated. The findings from this study show that the low oil-water ratio invert emulsion is beneficial to reducing fluid loss for enhanced wellbore stability and the reduction of oil retention on cuttings, thereby reducing cost of disposal and environmental impact. The mud was formulated without a fluid loss additive, wetting agent, secondary emulsifier and the need for high water content, thereby savings could also be made in material costs. The results from this experimental study demonstrated that the electrical stability of the mud emulsified by egg yolk at a test temperature of 48.9 and 120˚C for any variation, were 398 and 289V respectively. Comparatively, the mud emulsified with a standard emulsifier versacleanVB gave stability values of 201 and 188V thus indicating higher stability with the egg yolk. Moreover, the 50/50 oil-water ratio mud gave stability values of 353 and 258V hence, giving plastic viscosity of 36 cP, at the yield point of 17 Ib/100 ft2 and 30 minutes fluid loss of 6ml with filter cake of 1.7 mm. This resulted to 50% reduction in fluid loss over the conventional 70/30 oil-water ratio mud, which was emulsified with the standard emulsifier with stability values of 480 and 393V, plastic viscosity of 31cP, yield point of 17 Ib/100 ft2 and fluid loss of 12 ml with filter cake of 3.2 mm. Using the X-Ray Computed Tomography (CT) Scanner, the shale-fluid interaction also showed a volume increase by 11 and 23% of the core sample when immersed into water based mud from one to 7 days respectively. The result indicates that a high interaction with the fluid are possible, thus leading to a non-stable condition compared to 0.88 and 2.53% obtained from diesel and jatropha oil based muds. There was negligible variation in the structure of the samples exposed to diesel and jatropha oil based muds, which further suggests the suitability of jatropha as diesel substitute. The economic analysis of 50/50 oil-water ratio invert emulsion equally showed a potential saving of57.91% of the $65.31 of the cost of formulation and 47.5% of $60 of the cost of disposal of theconventional diesel oil-based mud. This has the potential to equate to saving of $37.82 per barrel ofinvert emulsion formulated and $28.50 per barrel disposed