Reservoir Brine Research Articles

Assessment of lithium distribution in associated reservoir brines of oil and gas fields of Western Kazakhstan

Assessment of lithium distribution in associated reservoir brines of oil and gas fields of Western Kazakhstan

Molecular Simulation of Multiphase Interface Characteristics and Microscale Flow Mechanisms of Oil and Brine in Carbonate Reservoir

Molecular Simulation of Multiphase Interface Characteristics and Microscale Flow Mechanisms of Oil and Brine in Carbonate Reservoir

Co-precipitation and grafting of (3-Aminopropyl) triethoxysilane on Ferro nanoparticles to enhance oil recovery mechanisms at reservoir conditions

After primary and secondary recovery processes, a substantial amount of oil remains trapped in the reservoir due to pressure and reservoir heterogeneity. Iron oxide nanoparticles (IONPs) are increasingly being considered for use in the oil and gas sectors for oil spill clean-up, emulsion separation, drilling and enhanced oil recovery (EOR) applications owing to their distinctive magnetic properties. However, the major drawback is that the particles quickly agglomerate to diminish their high surface energy, particularly in the presence of reservoir brine. As a result, dispersion is poor and oil recovery is limited due to reservoir pore plugging which might cause reservoir damage. Previous studies have documented the oil recovery mechanisms of bare IONPs leading to incremental oil recovery however, their research work was conducted at ambient condition, which does not present oilfield condition. Therefore, the oil recovery efficiency of functionalised IONPs at reservoir conditions is still tenuous in literature. In this work, IONPs were functionalized with 3-aminopropyltriethyloxysilane to form a novel nanohybrid with improved chemical − synergistic effects on interfacial tension (IFT), wettability alteration, and emulsion formation. The morphology, surface properties, chemical composition and stability of the functionalized IONPs was determined and compared with the conventional IONPs. Likewise, the ability of the functionalized IONPs to decrease IFT and alter the wettability of rock/fluid at reservoir conditions was examined using K20 Easy Dyne Kruss tensiometer and Kruss drop shape analyzer, respectively. Finally, a high temperature high pressure core flooding equipment (Fars EOR) was utilized to ascertain the oil recovery efficiency of the functionalized IONPs at reservoir conditions and the results compared with the conventional IONPs. High resolution transmission electron microscopy (HRTEM) images revealed that the functionalization approach did not alter the morphology of IONPs. The functionalized IONPs were stable with a zeta potential of + 31.2 mV thereby, decreasing IFT from 25.5 to 7.7 mN/m and altering wettability from oil wet (128°) to water wet (22°) at reservoir conditions. The functionalized IONPs also increased oil recovery by 13.3 % compared to 10.3 % increment by IONPs in distilled water (DW). However, at high salinity conditions, the oil recovery of IONPs decreased by 7.5 % while that of functionalized IONPs increased by 1.4 % relative to DW. Therefore, it can be concluded from this experimental study that functionalization of IONPs increased oil recovery at reservoir condition, owing to production of in-situ emulsions, reducing pore obstruction and improving sweep efficiency. These findings contribute towards understanding the influence of functionalization on the oil recovery mechanism and transportation of IONPs under reservoir conditions.

Geology and colour of Kupalo crater on Ceres

Kupalo is a ∼4 ​Ma old, 26-km diameter impact crater on dwarf planet Ceres, which exhibits extensive areas of bright bluish material. Here we describe, for the first time, the geology of Kupalo on a regional and local scale in detail, based on Dawn Framing Camera (FC) imagery. We find the crater has a complex geology consistent with a brittle and heterogeneous crust in this area. Through analyses of the FC colour data, we identify a correlation between the geologic units and the spectral variations, which can be explained by a mixture of subsurface materials in response to the impact. The brightest sites of Kupalo, located at the upper west wall and the central ridge, show similar FC colour and spectral IR data, which suggest that the bright material in these locations likely has the same origin. To explain the distribution of the bright bluish material in the crater and its vicinity, we propose two scenarios for the structure of the upper Cerean crust. Both require deep-seated brine or salt reservoirs, possibly connected to a brine ocean at the crust-mantle transition. • Geology of Kupalo suggests that Ceres' crust is rather heterogeneous (69). • Mixture of impacted subsurface materials explains correlation of spectra and geology (84). • Bright material in Kupalo would have originally been deposited at a depth of ∼3 ​km (82). • The brightest exposures are linked to subsurface reservoirs of hydrated carbonates (82).

Calcite–Brine Interface and Its Implications in Oilfield Applications: Insights from Zeta Potential Experiments and Molecular Dynamics Simulations

Carbonate reservoirs are made up of predominantly calcite and dolomite minerals and hold significant hydrocarbon reserves globally. However, the production from carbonate reservoirs is limited due to their wettability, which controls the production and fluid distribution. To develop efficient strategies for producing from these formations, it is necessary to understand the underlining mechanisms of carbonate rock wettability. We believe that understanding the native state of the rock mineral in the reservoir environment and how oilfield operations affect the wetting state of minerals is critical to demystifying the change in carbonate rock wettability. Thus, this study extends the understanding of the surface charge development of calcite minerals and provides useful insight into the mineral’s surface charge development. Zeta potential measurements and molecular dynamics (MD) simulations of calcite in different fluids of varying composition and salinity were investigated. We have considered both the mixed brine (seawater and reservoir water) and individual salt brine (i.e., NaCl, MgCl2, and CaCl2). The results show that the calcite mineral surface charge is controlled by the composition and salinity of the surrounding fluids. Indeed, we found that monovalent ions have dominant contributions to the total calcite surface charge. The adsorptions of Na+ and Cl– shape the stern layer structure in the first two calcite hydration monolayers. We found that the interplay between the calcite surface affinity to the brine ions and the hydration-free energies are the two critical parameters shaping the final mineral surface charge. We believe that our study provides essential atomic insights into the calcite–brine interfaces and how ions interact with the surface to control the surface charge, which are vital to the quest for wettability control.

Simulation of Freezing Cryomagma Reservoirs in Viscoelastic Ice Shells

Brine reservoirs in Europa’s icy crust, if they exist, could represent the most accessible liquid water bodies in the outer solar system. Any potential subsurface reservoirs are key for the exploration of ocean worlds and the search for habitability and life beyond Earth. Previous studies have demonstrated that freezing cryoreservoirs might trigger eruptions due to the pressurization associated with volume change as liquid water expands to become water ice, but those studies did not take into account the deformation of the reservoir wall. Viscoelastic deformation of the wall can act to accommodate the growing overpressure and prevent eruptions. Here we utilize a semianalytical numerical approach to calculate the pressure-induced deformation of a freezing cryoreservoir on Europa as a function of the far-field ice temperature. We find that shallow reservoirs located in relatively cold ice deform slightly and can be pressurized by freezing, but that deeper reservoirs located in warmer ice deform more easily and in some cases cannot reach the threshold overpressure required for spontaneous eruption. We identify a transition depth around 4–8 km depending on the reservoir radius, assuming a conductive ice shell structure consistent with current best estimates. Further, we find that shallow lens-shaped reservoirs may store a large volume of cryomagma and can be easily pressurized by freezing; they represent the best candidates for the mobilization of cryovolcanic material at Europa’s surface.

Comparing CO2 and Variable-TDS Waste-Fluid Injection Into Deep Saline Geologic Formations

There is a renewed interest in carbon capture, utilization, and storage technology due to recently expanded US Internal Revenue Service 45Q credits as well as to reduce anthropogenic carbon emissions to the atmosphere. Deep carbonate reservoirs in western Kansas have the potential for CO2 storage because they have experienced low waste-fluid injection volumes to date. Waste-fluid injection in Kansas has not caused felt seismicity for more than seven decades. However, beginning in 2013, the state has experienced increased seismicity due to increased subsurface pressure associated with the injection of large volumes of variable-TDS (total dissolved solids) waste-fluid in US EPA Class I and Class II wells. This work compares CO2, low-TDS, and high-TDS injection practices and quantifies the induced spatial and temporal patterns in overpressure in the caprock, reservoir, and its hydraulically connected crystalline basement, where the majority of induced seismicity in Kansas has been observed. Our results show that pressure buildup is higher in the caprock and lower in the crystalline basement when injecting CO2 as compared to variable-TDS waste-fluid injection. The CO2 plume tends to expand at the top of the reservoir, primarily due to its lower density and viscosity than reservoir brines, creating an overpressure plume that moves the resident brine across the caprock. In contrast, waste-fluid injection moves more resident brine down into the basement, particularly when high-TDS waste-fluid is injected. This result is particularly valid for high-permeability carbonate reservoirs, in which gravity forces dominate over viscous forces and move the CO2 and overpressure plume toward the top of the reservoir. Our study may explain the lack of human-perceivable induced seismicity at operating CO2 injection projects globally.

Study on the Migration Pattern of Concentrated Brine in Underground Concentrated Brine Storage Reservoir: A Case Study in Ling Xin Mining Area

The discharge of mine water from underground coal mines in arid areas is leading to extensive water loss and secondary pollution. To eliminate the water loss and environmental pollution, sealing the concentrated brine after the mine water treatment in the underground storage and pumping the clean water to the surface for recycling are effective methods. In this study, focusing on the Ling Xin mining area, China, a coupled model of concentrated brine flow and solute transport in underground reservoir was established. The migration patterns of concentrated brine under two simulation scenarios of long-term penetration and sudden leakage were analyzed. At the same time, it also initially revealed the essence of the environmental pollution caused by the penetration and leakage of the concentrated brine in the underground concentrated brine storage reservoir. Results show that the concentrated brine would penetrate the bottom aquifer in about 60 years in long-term penetration while approximately 40 days in sudden leakage. In addition, the storage time, reservoir permeability, and groundwater head difference were important factors affecting the migration of concentrated brine, where the influence of permeability varieties was the most significant. The results of this study provide technical options for the subsequent study of the environmental risk of underground concentrated brine reservoirs and have important technical significance for the study and engineering application of underground reservoirs in arid areas.

Discriminating seismic amplitude pitfall by low saturation gas using controlled-source electromagnetic technology

One of false positives in seismic amplitude associates with the presence of low saturation gas. The amplitude response is ambiguous prominently in shallow subsurface due to similar amplitude of fizz gas to highly saturated gas reservoir. This pitfall is demonstrated in Gassmann’s fluid substitution modelling which drastic velocity reduction is modeled by 5% of gas. The strong reduction induces anomalous bright spot in seismic similarly manifested by a highly gas reservoir. In pore fluid characterization, seismic amplitude of a brine reservoir is well distinguished from gas by change of response polarity from negative to positive amplitude due to higher brine modulus than gas. To a lesser extent, the negative amplitude of gas sand almost identical between commercial and non-commercial gas trap and difficult to distinguish in seismic. The similar negative amplitude of the gas cases caused by a very low gas modulus resulting to sudden drop of rock bulk modulus despite with the presence of low gas percentage. Thus, seismic velocity slows down when travels through a gas sand medium. Integration of controlled-source electromagnetic (CSEM) method in hydrocarbon prediction reduces exploration risk by only detecting commercial hydrocarbon. It exploits resistivity contrast between overburden and hydrocarbon reservoir which highly controlled by hydrocarbon saturation. CSEM normalized response exceeds the cut off response by a minimum saturation of 70% of gas. Less than 70% of gas, CSEM response is below the cut off response which considered as insignificant anomaly in CSEM measurement. It becomes a key strength as this method reduces amplitude uncertainty in seismic due to low saturation gas and potentially improves the chances of economic discovery in hydrocarbon exploration.

Study on Deformation and Fracture Evolution of Underground Reservoir Coal Pillar Dam under Different Mining Conditions

Coal mine underground reservoir water storage technology is an effective technical way to achieve high efficiency of coal mining and protection of water resources. The stability of coal pillar dam plays a decisive role in the safe and stable operation of underground reservoirs. Mining of adjacent working faces and long-term water erosion are the main influencing factors of stability of coal pillar dam. In this paper, a fluid-solid coupling calculation model for the deformation and evolution of coal pillar dam was established by FLAC3D numerical simulation software and the underground brine reservoir of Lingxin Coal Mine of Shenning group as an engineering background. The paper studied systematically the deformation, failure, and stress evolution of the dam with coal pillars soaked in water for a long time under different working face inclining length, coal pillar width, mining height, and water pressure. The simulation results showed that the degree of deformation and failure of the coal pillar dam continued to increase with the continuous advancement of the working face. The plastic zone of the coal pillar dam was increased by approximately 23.53%, the maximum vertical stress was increased by approximately 95.78%, and the maximum vertical deformation was increased by approximately 68.18%. The influence of each factor on the deformation and failure of overburden strata is quite different. The development range of plastic zone, the maximum vertical stress, and the maximum vertical deformation were increasing with the increased of working face inclined length and mining height. The increasing width of coal pillar would lead to the decrease of maximum vertical stress. The increase of water pressure would lead to the decrease of maximum vertical deformation. It can be seen that the inclined length of the working face is the main factor affecting the deformation and failure of the coal pillar dam. Coal pillar width and mining height are the main factors affecting the development of plastic zone. This study reveals the law of deformation and fracture evolution of coal pillar dam under different mining conditions, which can provide a reference for the design of coal pillar dam of coal mine underground reservoir.

Science Drivers for the Future Exploration of Ceres: From Solar System Evolution to Ocean World Science

Abstract Dawn revealed that Ceres is a compelling target whose exploration pertains to many science themes. Ceres is a large ice- and organic-rich body, potentially representative of the population of objects that brought water and organics to the inner solar system, as well as a brine-rich body whose study can contribute to ocean world science. The Dawn observations have led to a renewed focus on planetary brine physics and chemistry based on the detection of many landforms built from brines or suspected to be emplaced via brine effusion. Ceres’ relative proximity to Earth and direct access to its surface of evaporites that evolved from a deep brine reservoir make this dwarf planet an appealing target for follow-up exploration. Future exploration, as described here, would address science questions pertinent to the evolution of ocean worlds and the origin of volatiles and organics in the inner solar system.

Brine residues and organics in the Urvara basin on Ceres

Ceres is a partially differentiated dwarf planet, as confirmed by NASA’s Dawn mission. The Urvara basin (diameter ~170 km) is its third-largest impact feature, enabling insights into the cerean crust. Urvara’s geology and mineralogy suggest a potential brine layer at the crust-mantle transition. Here we report new findings that help in understanding the structure and composition of the cerean crust. These results were derived by using the highest-resolution Framing Camera images acquired by Dawn at Ceres. Unexpectedly, we found meter-scale concentrated exposures of bright material (salts) along the crater’s upper central ridge, which originate from an enormous depth, possibly from a deep-seated brine or salt reservoir. An extended resurfacing modified the southern floor ~100 Myr after crater formation (~250 Myr), long after the dissipation of the impact-generated heat. In this resurfaced area, one floor scarp shows a granular flow pattern of bright material, showing spectra consistent with the presence of organic material, the first such finding on Ceres beyond the vast Ernutet area. Our results strengthen the hypothesis that Ceres is and has been a geologically active world even in recent epochs, with salts and organic-rich material playing a major role in its evolution.

Molecular dynamics study on the use of Deep Eutectic Solvents for Enhanced Oil Recovery

The suitability of using Deep Eutectic Solvents for chemical Enhanced Oil Recovery operations is analyzed from the nanoscopic viewpoint using classical molecular dynamics simulations. Four different eutectics were considered based on Choline Chloride, as hydrogen bond acceptor, plus urea, glycerol, ethylene glycol or levulinic acid, as hydrogen bond donors. Two main effects were studied to study their suitability: i) eutectic solutions – oil interfacial tension and ii) wettability of oil droplets on calcite surfaces in presence of eutectic solutions to study the possible evolution from oil wet to water wet behavior. Different eutectic concentrations in water halide solutions, as a model of brine in reservoirs, are studied. The main physical properties such as interfacial tension or contact angle are analyzed as well as the behavior of the oil in presence of the eutectic solutions in terms of intermolecular forces, energy of interactions, molecular arrangements and adsorption at the corresponding interfaces. The reported results allow to infer the nanoscopic effects on the basis of the use of eutectics for enhanced oil recovery operations, thus providing the information which may contribute to the development of environmentally friendly operations using these low-cost green solvents.

Concepts for the Future Exploration of Dwarf Planet Ceres’ Habitability

Abstract Dwarf planet Ceres is a compelling target for future exploration because it hosts at least regional brine reservoirs and potentially ongoing geological activity. As the most water-rich body in the inner solar system, it is a representative of a population of planetesimals that were likely a significant source of volatiles and organics to the inner solar system. Here we describe possible medium-class (around $1 billion) mission concepts that would determine both Ceres’ origin and its current habitability potential. Habitability is addressed through a combination of geological, geophysical, and compositional investigations by (i) searching for evidence from orbit of past and ongoing geological activity near landforms interpreted as brine-driven volcanic structures and (ii) probing the brine distribution below one of these regions with electromagnetic sounding (in situ). Two approaches were considered for compositional measurements, which address both habitability and origins: (1) in situ exploration at two sites and (2) sample return from a single site. Both concepts targeted material at Occator crater, which is one of the youngest features on Ceres (∼20 Ma) and a site rich in evaporites evolved from recently erupted brine sourced from a region >35 km deep. We conclude that a sample return architecture from these young evaporite deposits offers greater science return by enabling high-resolution analysis of organic matter (trapped in salt minerals) and isotopes of refractory elements for a similar cost and less science risk than in situ analyses. This manuscript describes the six science objectives and the two implementation concepts considered to achieve those objectives.

Measurements and interpretation of crude Oil-Water/Brine dynamic interfacial tension at subsurface representative conditions

Interfacial tensions (IFTs) between crude oil and water or brine systems are critically important in many processes. Exhibited dynamic behavior often remains poorly studied and requires in-depth analysis. In this study, 27 series of dynamic IFT measurements were conducted for three different crude oils in combination with three different aqueous phases (pure water and two synthetic reservoir brines) at temperatures of 298.15, 343.15 and 393.15 K and pressures up to 30 MPa. This study provides a large database of crude oil-water/brine IFTs encompassing reservoir conditions of temperature and pressure. Specific effects of temperature, pressure, and fluid composition on the crude oil-water and oil-brine IFTs were evaluated. The dynamic evolution of the IFT between the crude oils and aqueous phases was categorized according to typical relationships observed. The most commonly observed evolution was an initial rapid decline in IFT, over a period of 100 to 1,000 s, followed by levelling off at a nearly-constant long-term value. However, in certain cases, the initial rapid decline was followed by a broad minimum and a subsequent slow increase towards a nearly-steady long-time value. In either case, the initial decline is described by a simple model based on diffusion of surface-active components in the oil and their subsequent adsorption at the interface. The longer-term behavior may be further attributed to a combination of saturation, rearrangement and dissolution of the surface-active components.

Green materials for carbon storage in depleted oilfields: An experimental study

The incessant rise in global temperature due to the large increase in anthropogenic carbon emissions over the past century threaten to undo gains made by human civilization and it has become essential that techniques to reduce atmospheric carbon be explored. For this, carbon-negative technologies like carbon geo-storage hold high vitality for industrial applications. In carbon geo-storage, captured CO2 is injected into the subsurface formations like depleted oilfields. However, the injected CO2 tends to undergo viscous fingering, bypassing small pore throats and consequently, the volumetric storage efficiency is reduced. Thus, there is a need for new mobility control agents which not only improve the volumetric storage efficiency of CO2 but also help alter rock surface for longer CO2 retention. Thus, in this study, the use of a novel green surfactant (S) has been explored in conjunction with natural polymers (P), guar gum and xanthan gum for CO2 mobility control. The composition of the SP solution was finalized via contact angle studies in presence of CO2. Following this, CO2 injection at varying flow rates (30–90 ml/h) was investigated in sand-packs of porosity 27–31% and permeability ≈682–812 mD which was saturated with a residual reservoir brine of 4 wt% NaCl. The role of the green SP solution was validated by injecting a slug of 0.3 pore volume (PV) before CO2 injection and the time to breakthrough for gas, the liquid return before breakthrough and the pressure drop profiles were carefully analyzed. It was found that the inclusion of green surfactant improved carbon retention by a factor of 3–4.5 (in the presence of other polymers) which was also demonstrated by an increase in areal coverage inside the sand-pack (as established from the pressure drop studies). Thus, the use of a green SP solution is proposed as a mobility control agent for carbon storage in depleted oilfields.

Geochemical Evaluation of Formation Water, Mauddud Reservoir, Khabbaz Oilfield, Kirkuk Area, Northern Iraq

In this study, formation-water samples were collected by NOC Staff, during drilling time, from the Mauddud Formation reservoir of the Khabbaz Oilfield, for this reason four samples from four wells; Kz-3, Kz-4, Kz-7, and Kz-23 were selected to geochemical analysis. Analyzed geochemical parameters include TDS and the concentrations of the different dissolved cations and anions present in brines (Ca+2, Mg+2, Na+1, SO4-2, Cl-1, HCO3-1, and NaCl). Variations among the resulted data are discussed by comparison with other Cretaceous Brines. Geochemical ratios of Na/Cl, (Na-Cl)/SO4) and (Cl-Na)/Mg+2 was calculated for formation water classification following Bojarski, (1970). The calculated geochemical ratios of the studied samples in the studied four wells indicate that all of these waters are "chloride calcium" type under subsurface conditions, this type reflect closed system isolated associations reservoir, which are becoming high hydrostatic in deeper zones without influence by infiltration waters. A major transversal fault cutting the structure at its SE plunge had participated in the dilution of the Mauddud reservoir brine effectively.

The Influence of Oil Composition, Rock Mineralogy, Aging Time, and Brine Pre-soak on Shale Wettability.

Experimental and field studies have indicated that surfactants enhance oil recovery (EOR) in unconventional reservoirs. Rock surface wettability plays an important role in determining the efficacy of this EOR method. In these reservoirs, the initial wettability of the rock surface is especially important due to the extremely low porosity, permeability, and resulting proximity of fluids to the solid surface. This study is designed to investigate the effect of oil components, rock mineralogy, and brine salinity on rock surface wettability in unconventional shale oil/brine/rock systems. Six crude oils, seven reservoir rocks, and seven reservoir brine samples were studied. These oil samples were obtained from various shale reservoirs (light Eagle Ford, heavy Eagle Ford, Wolfcamp, Middle Bakken, and Three Forks) in the US. SARA (saturates, aromatics, resins and asphaltenes) analysis was conducted for each of the crude oil samples. Additionally, this study also aims to provide a guideline to standardize the rock sample aging protocol for surfactant-related laboratory experiments on shale reservoir samples. The included shale reservoir systems were all found to be oil-wet. Oil composition and brine salinity showed a greater effect on wettability as compared to rock mineralogy. Oil with a greater amount of aromatic and resin components and higher salinity rendered the surface more oil-wet. Rock samples with a higher quartz content were also observed to increase the oil-wetness. The combination of aromatic/resin and the quartz interaction resulted in an even more oil-wet system. These observations are explained by a mutual solubility/polarity concept. The minimum aging time required to achieve a statistically stable wettability state was 35 days according to Tukey’s analysis performed on more than 1100 contact angle measurements. Pre-wetting the surface with its corresponding brine was observed to render the rock surface more oil-wet.

Incorporation of Partially Hydrolyzed Polyacrylamide With Zwitterionic Units and Poly(Ethylene Glycol) Units Toward Enhanced Tolerances to High Salinity and High Temperature

Partially hydrolyzed polyacrylamide (HPAM) was widely implemented to improve the rheological properties of displacing fluids, but the high temperature and salinity of the reservoir brine limited their applications. Herein, copolymers including HPAM, zwitterion-modified HPAM (z-HPAM), PEG-modified HPAM (p-HPAM), and zwitterion/PEG-modified HPAM (zp-HPAM) were prepared by free radical polymerization in an aqueous solution. The viscosity of these copolymers under different temperature and salinity was measured in aqueous solution. It is found that the viscosity of the HPAM under the harsh condition (90oC, 20 × 104 mg/L salinity) is only 9.6% of that value under the normal condition (25oC, pure water), while the z-HPAM can significantly improve salt resistance by the effects of salting-in effect and intermolecular electrostatic crosslinking, showing a viscosity retention of 22.9% under the harsh condition. The addition of PEG-containing monomer can strengthen hydrogen bonding between the polymer chains and form a sterically ordered structure with improved salinity and temperature resistance. The synergistic effect of zwitterion units and PEG units endows the zp-HPAM with good salinity and temperature resistance; thus, the sample viscosity under the harsh condition remains 170 mPa s, which retains 29% of the value under the normal condition. The enhanced rheology properties of the zp-HPAM under the harsh condition are significant for the enhanced oil recovery of water-soluble polymer flooding.

Bio-hydrogen production under pressure by pressure-adapted subsurface microbes

Microorganisms can produce bio-hydrogen (H2) during their metabolism, and especially dark fermentative production from carbohydrates is a promising option. However, the technology still suffers from low H2 production rates due to product inhibition of the H2-producing enzymes. In this study we investigate if subsurface (reservoir) microbes can be relevant bio-H2 producers and a source of high-pressure adapted enzymes. In addition, we also investigate the potential H2 productivity using an indigenous reservoir community, thereby proposing a preliminary screening workflow for mature oil fields to be used as potential in-situ H2 bioreactors. We cultured two H2-producers Marinitoga hydrogenitolerans and Thermotoga napthophila, which were isolated from high-pressure environments, and a freshly obtained oil reservoir brine containing a fermentative community under atmospheric and pressurized conditions (15–16 bar). All cultures produced H2 under atmospheric conditions with different productivities. Marinitoga shows the same cell number increase and glucose consumption under high pressure compared to atmospheric but with a significantly decreased H2 productivity of −86%. The productivity decline of the reservoir community was less pronounced with −35%. The mole fraction of H2 in the produced gas was in both cases high (0.64 and 0.82 respectively). Our results indicate strong differences in the pressure-related enzyme adaptations and may be used for screening of pressure-tolerant microbes and enzymes for enhanced bio-H2 production.