Abstract

One form of tertiary oil recovery that does not require exceptional investments is microbial enhanced oil recovery (MEOR). With abundant and easily producible oil supplies dwindling, MEOR could be an uncomplicated aliment to conventional water flooding. Unfortunately it has not gained credibility in the oil industry due to technical and economic reasons. To better understand this problem, a survey of reported MEOR field trials from across the world was conducted here. The survey shows some widely prevalent practices in most of the trials. Few tests could explain the mechanics of oil recovery or presented any post treatment analysis and explanation of to how results were calculated. And some showed improvements that appeared disproportionate to the treatment size. Based on trends observed in the survey results, recommendations are made to overcome barriers to widespread use of MEOR and gain credibility with more users. One recommendation is to standardize test procedures and reporting of results and analysis. This would be the best way to avoid contradictory interpretations of MEOR results. The initial few trials will be expensive if all the pre-treatment and post-treatment recommendations are followed. But the benefits of conducting a few systematic and well designed tests to fully evaluate the potential of MEOR and bring credibility outweigh the expense.

Introduction

Tertiary recovery has remained an attractive but unrealized prospect for the petroleum industry. It is estimated that approximately 300 billion barrels of oil still remain in the continental United States after waterflooding or gas injection 1. Recovering even a small fraction of this oil can be economically beneficial because of the large volume of oil. Tertiary recovery methods such as polymer flooding, steam flooding, in-situ combustion and chemical surfactant flooding have all been investigated. But these methods were found to be technically complex or uneconomical for widespread use. For example, despite detailed research and numerous field trials, polymer and chemical flooding was confined to a few individual operators because of low oil prices and high adsorption losses that resulted in a high cost per barrel of incremental oil 2.

Microbial enhanced oil recovery was another process that was investigated. Experimental results by Zobell first set the stage for researchers across the world to conduct experiments of their own 3,4. These laboratory experiments consistently showed that certain microbes along with proper nutrients and bio-catalysts could grow under reservoir conditions such as high temperature, pressure and salinity and produce bio-surfactants, alcohols, bio-polymers, gases and acids as metabolic byproducts. These products displaced trapped oil by altering saturations, rock wettability or improving waterflood sweep efficiency resulting in enhanced oil recovery from oil reservoirs. And because the microbes needed plentiful but cheap nutrients to grow and produce these products, MEOR potentially cost less.5 Gas reservoirs were not considered for tertiary recovery because very little gas usually remained in reservoirs at abandonment.

The main advantages of MEOR over conventional tertiary recovery were 2:

  1. Potential low cost.

  2. Multiple mechanisms working simultaneously, thereby improving effectiveness.

  3. Environmentally benign.

  4. Indigenous microbes could be used making it possible to partially overcome adsorption and other losses due to degradation.

But laboratory successes and some successful field trials that served as technology demonstrators have not made MEOR a widespread commercially used technology. A survey of the reports studied here shows that today, except for a waterflood currently being run in Argentina, there isn't a single MEOR field trial anywhere in the world.6 Two important reasons explain the lack of support for microbial enhanced oil recovery in the oil and gas industry; first, the lack of commercial incentive to invest in this method caused by the absence of field tests and data supporting the economic benefits of MEOR and second, the perceived complexity of the process and the inability of its proponents to allay this perception.7 These and some other reasons resulted in MEOR being largely confined to laboratory investigations and scattered field trials across the world.

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