Indigenous Microorganisms in Connate Water of Many Oil Fields: A New Tool in Exploration and Production Techniques

Abstract

Abstract A microbiological investigation was carried out on water samples taken from producing wells on 24 oil field. The fields were all of a different nature and located in different places. Many of the samples contained microorganisms and it has been demonstrated that some of their associations do really originate in the connate water concerned and often contain unknown species. These bacteria differ according to the nature of the geological formations and to the physico-chemical state of the water and the oil found in the various reservoirs. The nutrients which they need and the products of their metabolism thus vary substantially. They have been able to modify the state of oil and gas accumulations quite considerably and may continue to do SO. The result is that practical applications can already be established and there are many other potential uses. Some of them concern exploration and. by analogy, can be used to improve the rate of discovery. Others give rise to the reappraisal of certain aspects of reservoir management, in particular that of biodegradation of hydrocarbons and the aquifer regime. Other aspects concern production and the protection of installations, i.e. the fight against biocorrosion and souring. Introduction The origin of this research is based on the fact that the action of microorganisms has punctuated the history of oil: formation of the original biomass. initial bio-transformations including the generation of CR4, and then all the stages of biodegradation of the oil formed, biogenesis of CO2, in situ bioformation of H2S during production, biocorrosion of installations, especially pipelines, tubings and casings. All these specific actions, whether their consequences are good or detrimental, are due to microorganisms which have been able to proliferate in the water which always coexists with the oil, from the moment of its formation until the time of its production. The idea of looking for microorganisms in connate water and studying their characteristics is simply the result of this reflection. It was encouraged by the periodic publication of papers describing certain microorganisms found in these water. However, a justified criticism which was put forward on numerous occasions threw some doubt on this new concept. How could it be proved that the microorganisms recovered from connate water did not result from recent contamination? Right from the first well, the mud used is a potential carrier of erogenous bacteria from the surface. During the course of production, there are numerous other occasions when contamination could take place. The main opportunity is during water injection as, even if care has been taken with water sterilization. this remains incomplete. In order to be convincing, it was necessary to carry out an initial microbiological investigation on connate water taken from a sufficient number of oil fields of a highly diversified nature and to find irrefutable proof of the indigenous character of the microorganisms identified. This paper describes the first results of this investigation which provide much new information. Experimental microbiological approach The accurate microbiological study of a large number of connate water samples using comprehensive methods of cultivation and characterization of bacterial flora would have required a considerable amount of time and money. The results presented here were obtained by three types of methodological procedures. They provide data of increasing precision concerning the composition of the bacterial systems:–on 66 samples, detection of microorganisms and their enumeration, using epifluorescence microscopy,–on 29 of these samples, distribution of the main groups of bacteria making up the revivable population, using various methods of culture. P. 467^