A composition of matter suitable for increasing the viscosity of liquids comprises tendrillar carbonaceous material (TCM) having a ultra low bulk density of less than about 0.1 g/cm.sup.3 and comprises intertwined tendrils having a diameter (number average) of from about 0.05 to about 0.2 micron and a length (number average) to diameter (number average) ratio greater than about 10, the tendrils comprising carbon fibers and an iron metal component dispersed throughout the carbon fibers as nodules that are intimately associated with and at least partially bonded to the carbon fibers, the tendrillar carbonaceous material comprising from about 0.1 to about 5% by weight iron. The TCM can be used as a viscosifier and for suspending solids in such applications as drilling muds, lubricating oils and greases. The TCM can be prepared by disproportionating carbon monoxide in the presence of iron contained in a blend of (1) previously formed TCM and (2) iron containing particles.

A wellbore fluid having a non-aqueous continuous liquid phase that exhibits an electrical conductivity increased by a factor in order of 10.sup.4 to 10.sup.7 compared to conventional invert emulsion comprises from about 0.2% to about 10% by volume of carbon black particles and one or more emulsifying surfactant(s) selected from the class including nonionic emulsifiers of Hydrophilic-Lipophilic Balance (HLB) less than about 12, and anionic surfactants wherein the counter-ion (cation) is any of alkali metal, ammonium, or hydrogen ions. This wellbore fluid can be used for drilling or completing a well and can be used for providing enhanced information from electrical logging tools, measurement while drilling, logging while drilling, geosteering and the like.

An additive that increases the density of fluids used in a wellbore during the construction or repair of oil, gas, injection, water, or geothermal wells comprises In one illustrative embodiment the additive comprises a weighting agent, and more preferably an ultra-fine weighting agent. Another embodiment includes a wellbore fluid containing an ultra-fine weighting agent that has an increased density with improved suspension stability without a significant viscosity increase. The wellbore fluid as described herein has rheological properties comparable to a conventional wellbore fluid. An illustrative embodiment of the claimed subject matter is further directed to a method for making the ultra-fine weighting agent and a method for using such ultra-fine weighting agent in a wellbore fluid. In one preferred embodiment the additive has a particle diameter between 4 .mu.m to 15 .mu.m. In another preferred embodiment, the additive has a D.sub.50 of approximately 3 .mu.m (1 .mu.m to 6 .mu.m). In another preferred embodiment the additive has a D.sub.90 of approximately 6 .mu.m (4 .mu.m to 8 .mu.m). The additive may be used in any wellbore fluid such as drilling, cementing, completion, packing, work-over (repairing), stimulation, well killing, and spacer fluid, as well as in a dense media separating fluid or in a ship's or other vehicle's ballast fluid.

An additive that increases the density of fluids containing a sized barite weighting agent. The wellbore fluid has rheological properties comparable to a conventional wellbore fluids but does not exhibit problems with sag and resulting variations in density. An illustrative embodiment is directed to a method for making the sized barite weighting agent and a method for using such sized barite weighting agent in a wellbore fluid. In one preferred embodiment the sized barite weighting agent has a particle diameter between 4 .mu.m to 15 .mu.m In another preferred embodiment, the additive has a D.sub.50 (by weight) of approximately 1 .mu.m to 6 .mu.m. In another preferred embodiment the additive has a D.sub.90 (by weight) of approximately 4 .mu.m to 8 .mu.m. The additive may be used in any wellbore fluid such as drilling, cementing, completion, packing, work-over (repairing), stimulation, well killing, and spacer fluid.

An additive that increases the density of fluids containing a sized barite weighting agent. The wellbore fluid has rheological properties comparable to a conventional wellbore fluids but does not exhibit problems with sag and resulting variations in density. An illustrative embodiment is directed to a method for making the sized barite weighting agent and a method for using such sized barite weighting agent in a wellbore fluid. In one preferred embodiment the sized barite weighting agent has a particle diameter between 4 .mu.m to 15 .mu.m In another preferred embodiment, the additive has a D.sub.50 (by weight) of approximately 1 .mu.m to 6 .mu.m. In another preferred embodiment the additive has a D.sub.90 (by weight) of approximately 4 .mu.m to 8 .mu.m. The additive may be used in any wellbore fluid such as drilling, cementing, completion, packing, work-over (repairing), stimulation, well killing, and spacer fluid.