Abstract: An alkaline-reserve-free, oil-based drilling fluid is disclosed as comprising an oleaginous liquid, and an amine surfactant having the structure R-NH.sub.2, wherein R represents a C.sub.12 -C.sub.22 alkyl group or alkenyl group. Such fluid is particularly useful in the drilling of subterranean wells in which CO.sub.2, H.sub.2 S or other acidic gases which adversely effect the rheologies and other properties of the drilling fluid are encountered. The alkaline-reserve-free oil-based drilling fluid permits the logging of acidic gases which otherwise could not be logged in the presence of lime or other alkaline.

Abstract: By the use of small amounts of novel amide resin reaction products of dibasic dimerized or trimerized fatty acids, an alkanolamine and a polyalkylene polyamine, improved drilling mud formulations are obtained. In those oil mud drilling formulations that contain organophilic clays, one is able to maximize the viscosity and gelation of the formulations, resulting in less preparation time and less material usage, especially the clay. In accordance with the invention, one is able to thicken or gel oil-mud systems at usual operating temperatures even when using low viscosity/low aromatic oils as the external phase, and to maximize the yield of organophilic clays readily in a short period of time, at low shear rates. The amide resin extends the utility of organophilic clays in low viscosity oil-mud systems. They produce more shear thinning fluids, higher yield points and quicker gel strengths while maintianing low plastic viscosities.