The results of a study that aims to identify the realistic potential for microbially enhanced oil recovery (MEOR) have just been published and point to rather mixed results – some good, but others poor.
The study, funded by UK ITF (Industry Technology Facilitator) members, applied reservoir engineering principles to provide quantitative estimates of the increase in crude oil recovery possible from a typical North Sea reservoir by a range of MEOR mechanisms.
It concluded that there is good potential for microbial plugging of high-permeability zones in fractured reservoirs – and thus increasing recovery by driving the oil out of bypassed regions. But most of the other MEOR mechanisms studied were considered to be poor prospects for field-wide offshore application.
The term, MEOR, does not really refer to a single technology, but rather to a range of proposed mechanisms for enhancing oil recovery which share in common the involvement of microbes.
When bacteria grow, they increase in number and volume – or in other words, produce biomass – and may also excrete byproducts such as gas, surfactants or polysaccharides.
The mechanisms that have been proposed for MEOR fall into two broad categories – alteration of oil/water/rock interfacial properties, such as through the action of surfactants, or changes in flow behaviour, such as via the plugging of fractures with bacterial biomass and polymeric byproducts.
Gert de Jonge, technology initiatives consultant, Chevron Upstream Europe, and ITF board member, said of the study: “There was a strong interest among ITF members in the potential offered by MEOR.
“However, despite all the past work that has been done, there was still insufficient understanding of the process, and field-wide application has been limited. Some experts have questioned whether the technology is inherently feasible.
“Consequently, the group felt that there was a need for a realistic in-depth assessment of the various potential mechanisms reported for MEOR. This study is intended to provide that.”
The work was carried out by a team of reservoir engineers and microbiologists led by Professor Murray Gray at the University of Alberta.
The researchers were provided with real data from a typical sandstone North Sea petroleum reservoir with light crude oil and given the remit of addressing all science and engineering aspects of the mechanisms involved, including chemical and reservoir engineering as well as microbiological considerations.
The study was focused on microbial processes whose objective is to enhance recovery factor rather than single well (stimulation) treatments, which have been frequently documented and are available commercially.
Prof Gray said: “The potential benefits of different MEOR mechanisms – interfacial tension reduction, wettability changes, changes in flow patterns, gas production and acid production – were examined for a representative North Sea reservoir.
“In each case, the material input requirements were calculated in relation to the projected incremental oil production. The heart of the assessment process was to check the mass balance, to determine the potential oil recovery versus the amount of input materials required.
“The literature on MEOR contains many examples where a simple mass balance has not been considered in evaluating a proposed scheme.”
The study highlighted some interesting issues. For example, one proposed mechanism for MEOR is the opening of flow paths by organic acids produced by bacteria.
The study concluded that the prospects for this mechanism are poor because biomass volume would exceed the volume opened by the acid. Mechanisms based on gas or solvent production ranked poorly because of the large amounts of nitrates and nutrients they would require.
De Jonge said: “Some people may be surprised by the findings, and hopefully the study will stimulate some interesting discussions – after all, that is an integral part of the R&D process.”
For more information, contact Duncan Anderson, ITF subsurface technology manager, at email@example.com. The results of the study are summarised in SPE (Society of Petroleum Engineers) paper 114676-PP