| http://www.w3.org/ns/prov#value | - Yet another illustrative embodiment of the present invention includes an invert emulsion drilling fluid that includes: an oleaginous continuous phase, a non-oleaginous discontinuous phase, a biodegradable surfactant including a di-fatty acid ester of triglycerol in which the fatty acid has the formula RCO2H and R is an alkyl or alkenyl having 10 to 20 carbon atoms, and a weighting agent.
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