Environmental constraints concerning drilling fluids require new formulations that are non toxic for replacing mineral oil based muds. Water based muds are good candidates but new drilling conditions (deep drilling, slimhole drilling, extended reach drilling, multilateral drains) rise specific technical problems in particular concerning lubrication and risk of differential pressure sticking. Good lubricating properties of the mud can improve greatly drilling operation efficiency.
This paper describes extensive laboratory tests and also results from field tests showing the performances of an ester based lubricant for reducing torque and pipe drag when using water based muds. Efficiency of the lubricant has been confirmed by an extensive testing under strictly controlled laboratory conditions simulating actual drilling conditions. The lubricant is very efficient on many different water based formulations even highly densified or in presence of large quantities of salts or solids. The ester based lubricant is also very efficient for low solids formulations used for slimhole drilling. It is readily dispersible in water based muds, does not affect mud rheology nor any other mud property and in some cases it even improves the filtrate loss reduction. Furthermore this highly efficient additive is completely biodegradable and non ecotoxic. Field tests carried out in Africa, US and North Sea have largely confirmed the laboratory results presenting, for instance, a torque reduction of at least 30%.
When drilling and particularly in directional drilling the friction between drill pipe and walls of the borehole may be large enough to interfere with running the pipe in and out of the hole. Large friction between the drill pipe and the wall also increases torque and power required to rotate the drill pipe and the stress on the drill pipe. This in turn cause danger of twist-offs of the pipe and can decrease the drilling rate.
These different phenomena are emphasized and may become critical when drilling horizontal and extended reach wells. The use of water based muds for such wells could be detrimental because of their poor properties in such conditions. Improvement of WBM mud lubricity, rheology, hole cleaning properties is not only necessary to meet environmental regulations but also for allowing good drilling operations.
An extensive research programme has been undertaken by IFP and FINA for developing a new performant and non toxic lubricant in order to increase drilling rates in operations using water based muds. The major goal set forward when starting the ester based lubricant R and D programme was to achieve superior performance combined with full ecological and human safety. After the screening of many likely formulations, the final version of the ester based lubricant was subjected to extensive testing under strictly controlled laboratory conditions simulating actual drilling operation. The main results of this research programme are given in this paper as well as the results of the first field tests carried out in Zaire, Louisiana and North Sea.
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