MEOR

The lifecycle of any field consists of three main periods; green, plateau and maturity periods. Currently most of GUPCO fields are brown what made us very concerned to sustain and even increase our production. To achieve that, we have looked at new different options to exploit our resources better. Generally, this can be achieved by whether optimizing current system, applying new technology or evaluating unconventional resources.

One of the high-potential resources that we do have in GUPCO is unconventional resources with many tight carbonate formations. Nevertheless, we did not try to appraise it before since most of our reservoirs are clastics that can be easily characterized and evaluated. On the other hand, tight carbonate formations cannot be characterized or appraised utilizing conventional logging tools or even classical reservoir engineering concepts. It always requires unique techniques relevant to its unique complexity degree especially in presence of micro-porosity and unknown fluid content. This paper sheds light on Appraisal Unconventional Resource Study that resulted in the first successful producer in the company.

GUPCO started to appraise tight carbonate rocks (named Thebes in Lower Eocene) and basaltic intrusion in GoS. This study involved high integration between key disciplines; Petrophysics, Petrology and Reservoir Engineering. To manage uncertainty, we have acquired wide range of data types starting from advanced petrophysical logging tools like Magnetic Resonance, Borehole Imaging and spectroscopy, and full petro-graphic description, reaching to predicting reservoir dynamic performance using measured pressure points (RFT), its analysis and fluid characterization. Ultimately, we have succeeded to completely characterize Thebes formation, and proposing its development plan. The first successful well resulted in 300 BOPD gain as the first successful tight carbonate producer in GUPCO. Development plan is being built to drill new wells targeting unconventional resources including a few possible potential in basalt intrusions, as well.

Dealing with unconventional resources is not an easy task. It requires a lot of work and analysis. Having all of your homework done is not always enough, you have to integrate with interrelated disciplines to link dots and complete the picture. In this paper, we have conceived a new approach in evaluating such formations, and it is a very good example of managing uncertainty by integrating different data to convert hypothesis into reality that can be translated ultimately into oil production and revenues.

Globally, most oil fields are on the decline and further production from these fields is addressed to be practical in cost-effectiveness and oil productivity. Most oil companies are adopting two main technologies to address this: artificial intelligence and enhanced oil recovery (EOR). But the cost of some of these EOR methodologies and their subsequent environmental impact is daunting. Herein, the environmental and economic advantage of microbial enhanced oil recovery (MEOR) makes it the point of interest. Since, there is no need to change much-invested technology and infrastructure, amidst complex geology during MEOR application, it is entrusted that MEOR would be the go-to technology for the sustainability of mature fields.

Despite the benefits of MEOR, the absence of a practical numerical simulator for MEOR halts its economic validation and field applicability. Hence, we address this by performing both core and field- scale simulations of MEOR comparing conventional waterflooding. The field scale is a sector model(fluvial sandstone reservoir with 13,440 active grid cells) of a field in Asia - Pacific.

Here we show that pre-flush inorganic ions (Na⁺ and Ca²⁺) affect the mineralization of secondary minerals which influences microbe growth. This further influences carboxylation, which is relevant for oil biodegradation. Also, as per the sensitivity analysis: capillary number, residual oil saturation and relative permeability mainly affect MEOR. Secondary oil recovery assessment showed an incremental 6% OOIP for MEOR comparing conventional water flooding. Also, tertiary MEOR application increased the oil recovery by about 4% OOIP over conventional water flooding. It was established that during tertiary recovery, initiating MEOR after 5years of conventional waterflooding is more advantageous contrasting 10 and 15years. Lastly, per probabilistic estimation, MEOR could sustain already water-flooded wells for a set period, say, a 20% frequency of increasing oil recovery by above 20% for 2 additional years as highlighted in this study.

Microbial-influenced corrosion (MIC) has been implicated in few corrosion-related challenges in the well-service industry in the past. DuPont is ramping up the commercial-scale implementation of its microbial enhanced oil recovery (MEOR) method after nearly a decade of development and testing of what it says is a low-risk way to improve production from mature fields.

Good diagnostic testing is often painstaking, time-consuming, and costly, but recent studies suggest that a lack of knowledge can be even costlier. Tiny soil samples may contain as many as 300,000 species of microbial life, but a Netherlands-based startup has figured out that between 50 and 200 of them can tell an operator if a drilling location will hold oil and gas reserves. For the past 2 decades, the use of DNA sequencing technology has largely been relegated to the domains of criminal forensics and the healthcare industry. One company is betting that the shale industry soon will join that list. DuPont is ramping up the commercial-scale implementation of its microbial enhanced oil recovery (MEOR) method after nearly a decade of development and testing of what it says is a low-risk way to improve production from mature fields.

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Utilisation of microorganisms as an enhanced oil recovery (EOR) method has attracted much attention in recent years because it is a low-cost and environmentally friendly technology. However, the pore-scale mechanisms involved in MEOR that contribute to an additional oil recovery are not fully understood so far. This work aims to investigate the MEOR mechanisms using microfluidic technology, among others bioplugging and changes in fluid mobilities. Further, the contribution of these mechanisms to additional oil recovery was quantified.

A novel experimental setup that enables investigation of MEOR in micromodels under elevated pressure, reservoir temperature and anaerobic and sterile conditions was developed. Initially, single-phase experiments were performed with fluids from a German high-salinity oil field selected for a potential MEOR application: Brine containing bacteria and nutrients was injected into the micromodel. During ten days of static incubation, bacterial cells and in-situ gas production were visualised and quantified by using an image processing algorithm. After that, injection of tracer particles and particle image velocimetry were performed to evaluate flow diversion in the micromodel due to bioplugging. Differential and absolute pressures were measured throughout the experiments. Further, two-phase flooding experiments were performed in oil wet and water wet micromodels to investigate the effect of in-situ microbial growth on oil recovery.

In-situ bacteria growth was observed in the micromodel for both single and two-phase flooding experiments. During the injection, cells were partly transported through the micromodel but also remained attached to the model surface. The increase in differential pressure confirmed these microscopic observations of bioplugging. Also, the resulting permeability reduction factor correlated with calculations based on the Kozeny-Carman approach using the total number of bacteria attached. The flow diversion of the tracer particles and the differences in velocity field also confirmed that bioplugging occurred in the micromodel may lead to an improved conformance control. Oil viscosity reduction due to gas dissolution as well as changes in the wettability were also identified to contribute on the incremental oil. Two-phase flow experiments in a newly designed heterogeneous micromodel showed a significant effect of bioplugging and improved the macroscopic conformance of oil displacement process.

This work gives new insights into the pore-scale mechanisms of MEOR processes in porous media. The new experimental microfluidic setup enables the investigation of these mechanisms under defined reservoir conditions, i.e., elevated pressure, reservoir temperature and anaerobic conditions.

The method that uses microorganisms to increase oil recovery from reservoir rocks is called Microbial enhanced oil recovery (MEOR). Using this method, the microorganisms are injected to the reservoir and produce the metabolic product which is used in MEOR. There are 6 main metabolic products (bio-products) that can be effected to the reservoir fluid and rock. The 6 main bio-products are bio-surfactant, bio-polymer, bio-mass, bio-solvent, bio-gases and bio-acid. Every bio-product has a different effect on the reservoir and is produced by different microbes, with its purpose being to decrease the residual oil saturation that is left behind in the reservoir rock.

Bio-surfactant can reduce the interfacial tension between oil and the formation water and bio-polymers control the mobility of water that is used in waterflooding. Biomass can plug the reservoir pores and then change the flow direction of fluid flow in the rock. Bio-gas increases reservoir pressure and then forces the oil out of the rocks. Bio-acid can dissolve rock particles and open pore mouths, thus increasing rock porosity and permeability and allowing more fluid to flow, especially in Limestone.

A MEOR field trial was successfully applied at ‘X’ Field X in Indonesia, involves 10 wells. It can decrease oil viscosity, increase in Oil API Gravity and decrease of the oil pour point. Oil production rate increased from 8 to 66%. Scale is observed as a disadvantage of successful MEOR. The results from this field trial demonstrate that MEOR is potential and offers some benefit to increase oil production.

This multidisciplinary paper presents microbial Huff and Puff project results with objectives: 1) to understand the mechanisms through relating laboratory work results, field implementations and a history matching process during reservoir simulation (2) to seek reliability of the microbial Huff &Puff based on improvements of the production performance parameters. After a thorough screening work was done, detail laboratory works produced fluid samples from selected wells was conducted, implementation programs were designed, and a set of equipment consisting of a cultivation tank, a mobile laboratory, and other supporting facilities was installed at the field. The implementation basically involves three stages: (1) preflush, cultivation solution, and post flush (2) injection of cultivation solution and post flush, and (3) injection post flush. Finally, this project conducted a 6-month monitoring program of microbe population and compositional analysis of the produced fluid samples, and production performance analysis of wells production data. The overall growth of bacteria had increased from 2×10³ CFU / mL to 5×106 for 176 days in Well MJ122, on the other hand, Well MJ-125 can reach much higher up to 500×106 bacteria (CFU/ml) in 122 days. Using the GC/MS composition analysis for semi-quantitative analysis with standards internal reference marker ratio of Pr/Ph shows monthly biodegradation samples percentage before and after application up to about 34% at the 3rd month of monitoring. The well MJ-125 Structure Analysis of Bacteria Community resulted from Single Strand Conformation Polymorphism (SSCP) Method indicated that the number of Operational Taxonomy Unit (OTU) change during the production was relatively stable and this correspond to their Sorensen Index values. But, MJ-122 well indicated unstable community structure, however, the interaction between microbes which were injected with indigenous microbes was not competitive. The wells water cut versus gross rate profiles show that the MJ-122 water cut drop occurs at low production rate, whereas, the MJ-125 water cut drop occurs drastically both in low and high production rates. The well MJ-125 average oil rate gain is about 20%. However, both wells show peculiar production profiles by depicting a cycle of "a valley of low values". Finally, a history matching process supports understanding of the mechanisms.

Under certain conditions, injection of water or other solutions may result in H₂S production, which creates additional challenges for EOR applications. Besides serious health and safety concerns, this can cause significant production problems such as reduced quality of hydrocarbons, reduced productivity of wells and increased corrosion. The numerical assessment of the souring and its successful inhibition for an MEOR (Microbial Enhanced Oil Recovery) application in a Wintershall mature oil field is the subject of this paper. The numerical assessment of the biogenic souring for the field studied was performed in three successive steps. In the first step the potential H₂S generation as well as its partitioning between various phases was calculated by analytical methods. The spatial distribution of the potential H₂S generation was predicted by using the CMG Stars reservoir simulator on a sector model representing the reservoir portion relevant for the application. In a third step a reactive transport model was used to evaluate the implications of an H₂S inhibitor injection due to reactions with formation water and rock.

A significant H₂S formation potential was determined considering the formation water sulfate content and the MEOR metabolism. Its portitioning in various phases was calculated for various thermodynamic conditions of the production sequences. The spatial modeling of the H₂S generation was done in a previously performed CMG Stars implementation of the MEOR simulation for the case studied. The stoichiometry of the reactions applied was calibrated by using laboratory growth and metabolism data. Various strategies were studied to inhibit the souring at laboratory scale with nitrate being one of the inhibitors tested. Potential microbial induced calcite precipitation (MICP) when using nitrate and its effect on the storage and conductivity properties of a reservoir was modelled using the reactive transport computer code TOUGHREACT. The results obtained led to the key decision for testing other souring inhibitors for the field application. The results of the numerical assessment are discussed in terms of its contribution to the decision quality of the risk management concept developed and applied in the field pilot.

Wintershall is conducting a technology project for development and field application of MEOR (Microbiologically Enhanced Oil Recovery) in collaboration with BASF. The successful results of the laboratory phase led to a first small confined pilot Huff'n’ Puff (HnP) in a Wintershall mature oil field to prove that the laboratory-developed concept works in the field under reservoir conditions.

A suitable well for the MEOR operation was selected in the studied field based on selection criteria. The selected well is a former producer approximately 900 m deep. After a USIT run it was decided to recomplete it. Prior to MEOR HnP pilot, an injectivity test was performed to allow for re-assessment of the current petrophysical and geological properties around the well. In order to establish the baseline for the pilot evaluation, a comprehensive monitoring program consisting of microbiological, chemical and petrophysical surveys commenced just after the well recompletion.

The surface set-up designed for follow-up MEOR field operations was installed in the field. The mixing of the MEOR solution with the injection water was regulated automatically by measuring the injection rate. The injection took four days, followed by an incubation period of five weeks. During the nutrient injection, the injectivity was significantly lower than the one obtained from a previous injectivity test. As a result, the total volume of injected nutrient was lower than initially planned. Nevertheless, the volume was sufficient to achieve the pilot objectives.

The injection was carried out under matrix conditions by keeping the pressure below the fracture pressure. The injected fluid temperature was somewhat lower than planned, but according to downhole measurements, still high enough for microbial growth. It was observed that there was an oxygen ingress into the system through the injection pump, however no detrimental effect was seen on microbial activity. After the shut in period, a comparable volume of the injection fluid was produced back. The tracer concentration in the back produced fluid was used to calibrate the chemical and microbiological effects of MEOR.