Effect Of Initial Water Saturation Research Articles

Effect of initial water saturation and water film on imbibition behavior in tight reservoirs using nuclear magnetic resonance technique

Initial water saturation has a significant influence on spontaneous imbibition, and it impacts the imbibition rate and imbibed liquid dynamic distribution among pore networks. At present, the effect of initial water saturation on spontaneous imbibition is still unclear, especially the water film effect caused by initial water saturation varies during imbibition. To address these issues, we prepared the samples with varied initial water saturation through vapor adsorption and then conducted spontaneous imbibitions on these samples, which were monitored by nuclear magnetic resonance (NMR). Samples were selected from tight sandstone reservoirs in the eastern Ordos Basin. From the NMR spectrum corresponding to different imbibition duration, the left wing of the left peak at the initial water saturation is usually higher than the ones after imbibition, mainly caused by the water film effect. When the water film on the surface of large pores is too thin, it is prone to be interpreted as water in small pores because the water film has a quick relaxation time than the water in the center part of pores. The water film effect disappears when the whole pores are filled with water, and the inversed small pores decrease. The relaxation time of the water film is shorter than 0.51 ms in the tested samples. This study is conducive to understanding the effect of initial water saturation on liquid dynamic distribution during imbibition, especially the water film effect variation during imbibition and the T2 value of the water film.

Poroelastic response of unsaturated soils to cyclic loads with arbitrary waveforms

AbstractWe develop an analytical solution to the problem of one‐dimensional consolidation of unsaturated soil subjected to cyclic loads with arbitrary waveforms. The solution predicts the excess pore water and pore air pressures and the accompanying vertical compression in a poroelastic, unsaturated soil material. Cyclic loading occurs in a variety of engineering applications and often generates higher excess pore fluid pressures and larger vertical compression than does a time‐invariant load. In the present study, the loading function is allowed to take on any arbitrary waveform represented by a Fourier trigonometric series. Analytical solution to the boundary‐value problem in one dimension is given in closed form describing the frequency‐independent and frequency‐dependent components of the poroelastic response. We verify the analytical solution through representative examples involving cyclic loads with square and triangular patterns. Apart from the shape of the forcing function, we also investigate the effects of initial water saturation, soil texture, and excitation frequency on the system response.

The effects of initial water saturation on retrograde condensation in natural porous media: An in situ experimental investigation of three-phase displacements

In this study, state-of-the-art imaging technology is integrated with a miniature core-flooding system to map pore-scale fluid occupancy during the retrograde condensation process in the presence of brine and in a natural porous medium. Two depletion experiments were performed using a three-component synthetic gas condensate mixture in a Fontainebleau sandstone core sample and after establishing different levels of initial water saturations. The results are analyzed to investigate the impact of water saturation on condensate formation, accumulation, and mobilization and to shed light on the relevant three-phase flow dynamics. The results provide the first direct pore-scale observation of gas, condensate, and brine residing in the pore space. The micro-scale fluid occupancy maps illustrated that the presence of water in the pores delays the pressure at which condensate nuclei form, slows down the initial growth of nuclei, and partially impedes the accumulation of condensate. The higher the water saturation is, the lower the amount of condensate will be accumulated. As the pore pressure decreases, the condensate clusters develop significantly in the pore space triggering chains of displacement events between various pairs of fluids. The key mechanisms include gas-to-brine/condensate and condensate-to-gas/brine. The displacement events eventually reduce the brine saturation and increase the gas and condensate saturations in the pore space. The condensate saturation increases monotonically as the pore pressure reduces and reaches a maximum value. Quantitative pore fluid occupancy data also reconfirm the visual observations and demonstrate that condensate accumulation is associated with displacing gas and brine from small- and medium-sized pore elements.

Research on gas injection to increase coalbed methane production based on thermo-hydro-mechanical coupling

Gas injection to increase coalbed methane production is an effective energy saving and emission reduction technology, with triple benefits of clean energy production, environmental protection and safety production. In this paper, a coupled thermo-hydro-mechanical flow (THM) model is developed, the effects of different injected gases on ECBM are considered, the effect of initial water saturation on CO2/N2-ECBM is quantified using the control variable method. Exploring changes in storage and production during the injection gas mixture enhanced CBM recovery (GM-ECBM). The results show that: The breakthrough time of CO2 injection was much later than N2 injection. The higher the initial water saturation, the lower the CH4 production and gas storage. CO2 injection will reduce the permeability of coal seam and damage it, while N2 injection can effectively restore the permeability. The higher the initial water saturation, the slower the permeability decrease during CO2-ECBM and the slower the permeability increase during N2-ECBM. Increasing the N2 injection concentration before the N2 breakthrough time can promote CH4 production, and increasing the CO2 injection concentration near the N2 breakthrough time will delay the N2 breakthrough time and provide more time for CH4 to migration in the pore space, which will increase the CH4 production. When injecting gas mixture into water-bearing coal seam, the higher the initial water saturation, the slower the coal seam permeability increases when N2 is disturbed, and the slower the coal seam permeability decreases when CO2 and N2 are co-disturbed, while both production and storage will decrease.

Research on the seepage mechanism and influencing law of shale oil fracturing

In order to clarify the characteristics of oil and water seepage during shale oil fracture, the tight reservoir in Jimsar Basin, Xinjiang Province was an example to get the characteristics of two-phase seepage between fracturing fluid and shale oil during fracture through the core experiment during injection. Effects of initial water saturation, viscosity ratio of oil to water, injection pressure, core permeability about imbibition displacement efficiency of fracturing fluid were systematically studied by using an improved one-dimensional core displacement device from Xinjiang tight sandstone artificial core under indoor conditions. The research results show that under constant pressure of 1 MPa, initial water saturation of the core is 43%, permeability is 0.12 md, and oil-water viscosity ratio between shale oil and fracturing fluid is 3:1, drive efficiency about fracturing fluid was about 23.5%. At the same time, results indicated at certain injection conditions, when initial water saturation increases, the permeability gradually decreases, and the viscosity ratio of oil to water gradually increases, the lower drive efficiency of fracturing fluid was, the worse its effect is. This conclusion could be used in the process of shale oil tight reservoirs.

Effect of initial water saturation on the performance of fracturing fluids with and without polyallylamine under simulated EGS conditions

Objectives/scopeStimuFrac (US Patents 9,873,828 B2 and 9,447,315 B2), a CO2-reactive polymer aqueous solution [polyallylamine (PAA) 1wt% in water] combined with CO2, can potentially be used as a less water-intensive fracturing fluid for enhanced geothermal systems (EGS). Our previous results show that in hot dry rock (HDR), PAA/CO2 fracturing fluids outperformed other fluids such as water, CO2, and CO2/water in generating large fractures with less fluid consumed. The objective of this work is to investigate the effect of initial water saturation on the performance of StimuFrac by conducting hydraulic fracturing tests with ½ foot cubic rock samples held under representative EGS stress/temperature conditions and by using cyclic injection strategies (under constant injection rate). The resulting fracture hydraulic conductivities, breakdown pressures, and volumes of fluids required are compared. Methods/procedures/processTo simulate geothermal reservoir conditions, in all tests, the rock sample was held under triaxial confinement and at 200 °C, and different volumes of water were initially injected into the rock sample before any fracturing processes were initiated. For the single-cycle PAA (or water) alternating CO2 (PAG or WAG) injection fracturing experiments, one complete cycle consisted of two steps: (1) injecting a PAA slug (or water slug) followed by (2) injecting CO2 to initiate and propagate the fracture. For experiments involving multiple injection cycles, the CO2 injection pressure is increased until it peaks and begins to decline (indicating fracture initiation at this moment), and then continued being injected for another 30 s to propagate the fracture. Then, these two-step cycles [injection of PAA (or water) followed by CO2 injection (up to 2–4 mL/min)] are repeated. Applications/significance/noveltyThe results of this study suggest that water saturation significantly affects the fracturing fluid transmission into the rock pore space, thus affecting fracture initiation and propagation. In this study, fracturing tests via a single injection cycle or multiple injection cycles were performed. When the rock samples are split in half following testing, it is evident that fracture propagation is considerably restricted under high water saturation conditions (where a three-day initial water injection was conducted) in comparison to stimulation experiments carried out in hot and dry rock. The fractures propagate less than 1/3 of the distance from the wellbore to the outer rock surface, and in some cases, no fracture is generated. This may be caused by leak-off dominating the fracturing process and the fluid injection rate is insufficient to overcome leak-off, even under high injection rate conditions. Additionally, CO2 could be leaking off into the wellbore annulus and this may be making it more difficult to generate sufficiently high-pressure gradients away from the near-wellbore region. Under low water saturation conditions (dry rock or after 1-day initial water injection), PAA/CO2 consistently generated significantly larger fractures compared with the other fluids. CO2 generated large fractures only in the hot dry rock and only when using high injection rates, though data variability is high.

Modeling Two-Phase Flow in Tight Core Plugs with an Application for Relative Permeability Measurement

Summary The two-phase flow of immiscible fluids in porous media has been studied for a long time in different disciplines of engineering. Relative permeability (kr) is one of the constitutional relationships in the general equation governing immiscible displacement that needs to be determined. Due to the complexity and nonlinear nature of governing equations of the problem, there is no unique model for relative permeability. The modified Brooks and Corey (MBC) model is the most common model for kr prediction. Here, a practical technique is presented to measure kr for low-permeability tight rocks. We use this experimental data to tune the empirical constants of the MBC model. The proposed method is based on a simple mathematical technique that uses assumptions of frontal advance theory to model the pressure drop along the core plug during two-phase immiscible displacement at constant injection flow rate. We make simplifying assumptions about the highest point on the observed pressure profile and use those assumptions to determine relative permeability of a tight rock sample. In the end, the amount of work for an immiscible displacement is calculated as the area under the pressure-profile curve. The effect of initial water saturation (Swi) and interfacial tension (IFT) is studied on the work required for an immiscible displacement. Using this concept, it is concluded that adding chemical additives such as surfactants to fracturing fluids can help the reservoir oil to remove the water blockage out of the rock matrix more easily while maintaining the flow rate at an economic level.

Transport and targeted binding of Pluronic-coated nanoparticles in unsaturated porous media

The effectiveness of most in situ remedial technologies, including nanoremediation, lies on successful delivery of reagents to a subsurface target treatment zone. Targeted delivery of engineered nanoparticles (NPs) to treat petroleum hydrocarbons present in the unsaturated zone requires an understanding of their transport behaviour in these systems. A series of column experiments explored the effect of initial water saturation, flowrate, input dosage, and porous medium texture on the transport of iron oxide or cobalt ferrite NPs coated with an amphiphilic co-polymer, as well as their targeted attachment to a crude oil zone. As the initial water content increased with a concomitant reduction in air saturation, the degree of tailing present in the NP breakthrough curves (BTCs) reduced, and the mass of NPs recovered increased. Air saturation is positively correlated with the magnitude of air-water interfaces, which provide additional NP retention sites. At a lower injection flow rate, NP retention increased due to a longer residence time and comparatively high air saturation. NP transport behaviour was not sensitive to NP injection dose over the range tested. Increased retention and retardation of the NP BTC was observed in sediments with a higher clay and silt content. NPs coated with a lower concentration of a Pluronic block co-polymer to promote binding were preferentially retained within the crude oil zone. To simulate the asymmetrical NP breakthrough curves observed from the unsaturated systems required the use of a model that accounted for both mobile and immobile flow regions as well as NP attachment and detachment with nonlinear Langmuirian blocking. This model allowed examination of attachment and detachment rate coefficients which captured NP interaction with the porous medium and/or crude oil. It was found that the initial water saturation and flow rate did not have an appreciable impact on the NP attachment rate coefficient, while it increased by ~10× with increasing clay and silt content, and by ~100× in the presence of crude oil, indicating preferential NP attachment within the crude oil zone. As a result of the lower NP polymer concentration coating used to promote increased attachment to crude oil, higher retention was observed near the column inlet and was captured quantitatively by adding a depth-dependent straining term to the model. This retention behaviour represents a combination of irreversible attachment at the air-water interfaces and straining near the column inlet enhanced by the formation of NP aggregates. The detachment rate coefficient decreased with a lower initial water saturation and flowrate, but increased with higher clay and silt content. The findings from this study contribute to our understanding of the transport and binding behaviour of Pluronic-coated NPs in unsaturated conditions and, in particular, the role of initial water content, flowrate and porous medium texture. Demonstrated delivery of NPs to a target zone is an important step towards expanding the utility of NPs as treatment reagents.

Effect of Initial Water Saturation on Oil Displacement Efficiency by Nanosuspensions

This article deals with the study of the initial water saturation effect of a porous medium on the oil recovery factor using a water-based nanosuspension. The initial water saturation of the porous medium in the computations varied within the range from 0 to 90%. The nanoparticle SiO2 concentration varied from 0 to 1 wt%. The particle sizes were equal to 5, 18, 22, and 50 nm. Experimentally measured wetting angles and the interfacial tension coefficient depending on the concentration and size of nanoparticles were used in computations. A mathematical model was developed, describing the transfer and diffusion of nanoparticles within the aqueous phase during immiscible displacement of oil by nanosuspension from a porous medium. Using the developed model, a systematic computational study of the effect of the initial water saturation of the core micromodel on the oil recovery factor using nanosuspension was carried out. It was revealed that with an increase in the initial water saturation, the oil recovery factor monotonically decreased in the case of displacement both by water and nanosuspension. It was shown that with an increase in the concentration of nanoparticles and a decrease in their size, the oil recovery factor increased. At that, the relative increase in the recovery factor had a maximum at an initial water saturation equal to 60%.

Effect of Initial Water Saturation on the Performance of Fracturing Fluids with and Without Polyallylamine Under Simulated Egs Conditions

Effect of Initial Water Saturation on the Performance of Fracturing Fluids with and Without Polyallylamine Under Simulated Egs Conditions

The Effect of Initial Water Saturation on Enhanced Water Imbibition by Surfactant for Fractured Tight Porous Media

SummaryThe main objective of this research was to investigate the effect of initial water saturation on the oil recovery from tight matrices through surfactant-enhanced water imbibition. Two flooding/soaking experiments using fractured tight cores with/without initial water were performed. The experimental results were analyzed by the material balance for the components oil, brine, and surfactant. The analysis resulted in a quantitative evaluation of the imbibed fraction of the injected components (brine and surfactant).Results show that the surfactant enhanced the brine imbibition into the matrix through wettability alteration. The initial efficiency of the surfactant imbibition increased when brine was initially present in the matrix. The imbibition of brine was more efficient with no initial water in the matrix. A possible reason is that the presence of initial water in the matrix was able to increase the initial efficiency of the surfactant imbibition; however, the increased amount of surfactant in the matrix lowered the interfacial tension (IFT) between the aqueous and oleic phases; therefore, the efficiency of brine imbibition was reduced. Another possible reason is that capillary force was lower in the presence of initial water in the matrix, resulting in weaker imbibition of brine.Although the two cases showed different characteristics of the mass transfer through the fracture/matrix interface, they resulted in similar values of final water saturation in the matrix. Hence, the surfactant injection was more efficient for a given amount of oil recovery when there was no initial water in the matrix.

Numerical study on the injection of heated CO2 to enhance CH4 recovery in water-bearing coal reservoirs

ABSTRACTA hydraulic-mechanical-thermal coupled numerical model for enhanced CBM recovery by injecting heated CO2 (CO2-ECBM) is established, which fully couples the gas-water two-phase flow, competitive adsorption, and temperature change as well as coal deformation. Through the finite element simulation software COMSOL Multiphysics, the model is used to investigate the effects of initial water saturation, CO2 injection temperature and pressure on the CO2-ECBM process from the perspectives of CO2 storage, CH4 production and the evolution of reservoir permeability. The coalbed water hinders the migration of gases in the reservoir. The CO2 migration distance is always negatively correlated with the initial water saturation in the reservoir, even after the coalbed water is discharged. Interestingly, in the early stage of drainage and recovery, the rapid decrease of pore water pressure facilitates the desorption of adsorbed CH4, especially near the producing well. The increase of CO2 injection temperature and pressure is conducive to the transport of CO2 in the reservoir, allowing more opportunities for CO2 to come into contact with coal, which promotes CO2 sequestration and thus enhances CH4 recovery. The coalbed water can delay the decline of permeability induced by CO2 adsorption by impeding CO2 migration. The increase of CO2 injection temperature and pressure can exacerbate the reduction of absolute permeability by inducing more CO2 to be adsorbed.

Magnetic Resonance Imaging of Methane Hydrate Formation and Dissociation in Sandstone with Dual Water Saturation

This paper reports formation and dissociation patterns of methane hydrate in sandstone. Magnetic resonance imaging spatially resolved hydrate growth patterns and liberation of water during dissociation. A stacked core set-up using Bentheim sandstone with dual water saturation was designed to investigate the effect of initial water saturation on hydrate phase transitions. The growth of methane hydrate (P = 8.3 MPa, T = 1–3 °C) was more prominent in high water saturation regions and resulted in a heterogeneous hydrate saturation controlled by the initial water distribution. The change in transverse relaxation time constant, T2, was spatially mapped during growth and showed different response depending on the initial water saturation. T2 decreased significantly during growth in high water saturation regions and remained unchanged during growth in low water saturation regions. Pressure depletion from one end of the core induced a hydrate dissociation front starting at the depletion side and moving through the core as production continued. The final saturation of water after hydrate dissociation was more uniform than the initial water saturation, demonstrating the significant redistribution of water that will take place during methane gas production from a hydrate reservoir.

Impact of water saturation and cation concentrations on wettability alteration and oil recovery of carbonate rocks using low-salinity water

In this study, the effect of initial water saturation on the oil recovery for carbonate rocks is investigated using spontaneous imbibition experiments. The experiments are performed using 20 times diluted sea water as imbibing fluid and the sea water as initial water. In addition, the impact of pH and Ca2+, Mg2+, Na+, and K+ cations concentration change of imbibing fluid are investigated during tests. These results help to identify the active cations in the wettability alteration process of carbonate rocks during the low-salinity water injection. A mechanism is proposed to describe the effect of initial water saturation on the oil recovery by low-salinity water injection. The impact of initial water saturation on the wettability alteration might be positive or negative depending on its value and the rock permeability. The comparison of divalent cations concentrations shows that the minimum adsorption of Ca2+ and maximum desorption of Mg2+ lead to maximum oil recovery of spontaneous imbibition. The results confirm that three cations of Ca2+, Mg2+, and Na+ are active for wettability alteration of carbonate rocks in the presence of sea water as initial water and diluted sea as imbibing fluid, whilst the amounts of potassium remain constant.

Drying of Recycled Aggregate Concrete: Plastic Shrinkage, Cracking Sensitivity, and Durability

This paper presents the results of experimental research on recycled concrete at early age and long term. It consists in studying the effect of initial water saturation of recycled concrete gravel (RG). Five mixtures were investigated, one mixture with natural aggregates only (reference concrete) and the second with 100% of RG using four initial water saturations: 30%, 70%, 100% and 120% of saturated surface dried (SSD) state. A stress/strength approach was used to quantify the risk of cracking at early age. It is based on experimentally assessed parameters. At long term the effect of initial water saturation on the ultimate drying shrinkage was investigated. The drying shrinkage was correlated with drying depth and the natural carbonation was also studied. At early age the results indicate RG affected the properties of the recycled concrete. However, the concrete with oversaturated RG showed a behavior close to reference concrete in terms of cracking sensitivity. At long term, the drying shrinkage is weakly depending of initial water saturation, but the durability of concrete can be affected by the drying depth. A good correlation between compressive strength at one day and the carbonation depth at 18 months was observed

Initial water saturation and imbibition fluid affect spontaneous imbibition into Barnett shale samples

Spontaneous imbibition has been widely investigated due to its significant impact on gas/oil recovery from conventional sandstone and carbonate reservoirs. Unlike conventional reservoir rocks with relative high porosity and permeability, shale is characterized by its low porosity (<10%), ultra-low permeability (∼10−18–10−23 m2), complex wettability, and strong heterogeneity at multiple scales. This study is to understand the effects of initial water saturation and imbibing fluid on spontaneous imbibition of Barnett shale core samples taken from three different depths of Blakely #1 well in Wise County of Texas. Two partial, and yet uniform, water saturations of shale samples were achieved by equilibrating the samples inside closed containers at specific relative humidity controlled with over-saturated salts. The effect of imbibing fluids (water or oil-phase n-decane) on spontaneous imbibition behavior is evaluated by conducting replicate experiments. Our results show that the spontaneous imbibition behavior of shale samples could be affected by the initial water saturation conditions, and the effects are different for shale samples with different mineral compositions. The imbibition curves of shale samples with a high clay content show a poor reproducibility during water imbibition experiments due to the water sensitivity of clay minerals. In addition, n-decane could not be completely removed after its imbibition experiment. The interaction between remnant n-decane and shale matrix may change the sample wettability towards more oil-wet, which is indicated by a higher imbibition slope of second n-decane imbibition experiment on the same sample. Overall, this work helps understand the mechanism controlling fluid loss and ultimate gas/oil recovery in unconventional hydrocarbon exploration, which is significant for optimizing the selection of fracturing and treatment fluids to enhance recovery rate and minimize environmental risk.

Simulation of microwave stimulation for the production of gas from methane hydrate sediment

Natural gas hydrates dissociate via an endothermic process. One of the key requirements for any production technique is to supply the heat necessary for this dissociation. In this study, first, a microwave stimulation model for the production of gas from methane hydrate sediment is developed, which includes mass transport, energy conversion and conservation, and intrinsic kinetic reactions as the governing equations. In addition, the theoretical mixing rule of Lichtenecker and Rother is introduced for calculating the average dielectric data of the sediment containing methane hydrates, which affects the penetration of microwaves into the sediment. Next, simulations are performed for investigating gas production, as well as effects of initial water saturation, initial hydrate saturation, and sediment thermal properties induced by microwave stimulation. Moreover, the energy efficiency ratio is employed in the simulation. The simulation results show that microwave stimulation provides timely energy conversion sufficient for promoting the dissociation of hydrates, with rapid, continuous gas production. Temperature gradients caused by the decrease of the microwave penetration depth appear in the reservoir, leading to a rapid dissociation rate in the upper part of the sediment. The energy efficiency ratio for all simulations ranges between 3.752 and 6.452. Hydrate saturation and the specific heat capacity of porous media are two factors that significantly affect energy efficiency. High hydrate saturation contributes to a rapid gas generation rate and a long rapid gas generation lasting time, leading to a high energy efficiency. A low specific heat capacity of porous media can decrease the loss of heat to the sediment, increase the gas generation rate, and improve energy efficiency. Furthermore, high initial water saturation can cause a rapid decrease in the microwave penetration depth and lead to large temperature gradients in the sediment. The thermal conductivity of porous media mainly affects gas generation in the latter period of hydrate dissociation. Macroscopic heat conduction in the sediment decreases the temperature gradients in the reservoir and promotes homogeneous hydrate dissociation.

Effect of Initial Water Saturation on Bypassed Oil Recovery during CO2 Injection at Different Miscibility Conditions

During gas injection in oil reservoirs, oil might be bypassed in either a micro- or macroscopic scale, because of different kinds of heterogeneities. However, it can be recovered by vaporization, diffusion/dispersion, swelling, and cross-flows (viscous, gravity, and capillary). Oil recovery depends upon the injected gas properties, injection type (immiscible, near-miscible, or miscible), presence of connate water, and frequency of dead-end pores. In this study, a special setup is used to investigate the effect of initial water saturation (Swi) on the recovery of bypassed oil during CO2 injection at different miscibility conditions. Further, analytical calculations of dimensionless numbers are used to study the dominant forces and mechanisms. Regardless of the amount of initial water, the maximum amount of oil recovery was achieved at near-miscible injection. Because the main recovery mechanism at immiscible conditions was gravity drainage, the presence of Swi could hardly change the oil recovery factor. H...

Effect of initial water saturation on crude oil recovery and water cut in water-wet reservoirs

Crude oil recovery and water cut are key parameters in petroleum industry. Note that ‘crude oil’ was reduced to ‘oil’ for simplicity in many cases in the rest of this article. Both theoretical prediction and experimental results have shown that oil recovery could increase or decrease with initial water saturation at a core scale. However, there have been few studies on this once-considered peculiar phenomenon at a reservoir scale. Initial water saturation and its distribution in oil reservoirs depend upon oil-water capillary pressures. In this study, effect of initial water saturation on oil production, oil recovery, and water cut in reservoirs with bottom water was investigated numerically in horizontal wells. Distribution of initial water saturation as a function of reservoir height was either calculated using the oil-water capillary pressure or determined as constant values. The numerical simulation results were compared with experimental data. The results demonstrated that some of the numerical simulation results at a reservoir scale were consistent with the theoretical results from models derived at a core scale as well as the experimental data in the core samples, but the others were not. Experiments conducted in small core samples were often doubted because of the small size compared with the reservoir scale and the poor representation of large-scale reservoirs. The consistence of the results at both core and reservoir scales implies the importance of core analysis experiments and is of great significance in petroleum industry. Copyright © 2014 John Wiley & Sons, Ltd.

Pressure Evolution and Production Performance of Waterflooding inn-Heptane-Saturated Fired Berea Cores

SummaryThis work presents experimental results and interpretation of injection pressure and recovery performance of waterflooding in strongly water-wet fired Berea cores saturated with n-heptane. The experiments were conducted at constant injection rate at room conditions, and the effects of injection rate and initial water saturation on the oil-recovery performance and dynamic-injection pressure were investigated. Elements of surprise were observed in the injection-pressure data. The pressure profiles showed four distinct regimes, each governed by capillary or viscous forces. At low capillary numbers (Ca=uμ/σ&amp;lt;10–6), capillarity governed two pressure regimes, corresponding to the core inlet and outlet. In the early part of waterflooding, pressure stayed constant for a considerable time before hydrodynamic pressure gradient could overcome the capillary pressure gradient. After viscous forces dominated, a linear increase in injection pressure over time was observed up to breakthrough time. A sudden pressure rise was observed close to breakthrough because of capillary retention at the core outlet. The pressure became constant after the breakthrough when the water- and oil-saturation distributions were stabilized. Changing the injection rate by an order of magnitude in the range from 2.2 to 22.2 pore volumes (PV)/D (equivalent to Ca = 10–7 to 10–6) did not appreciably change the oil-recovery performance; similar breakthrough time and final oil recovery were observed. The effect of initial water saturation was also investigated. When lowering the initial water saturation beyond that established in oil flooding, production performance and injection pressure were similar to those of a core without the initial water saturation. The injection pressure at breakthrough was found to decrease with increase of the initial water saturation. Waterflooding was modeled by including the capillary pressure and excellent agreement was obtained with experimental results of production and injection pressure. We find that in the absence of in-situ saturation measurements, the injection pressure is a better variable for tuning the model parameters compared with the production history alone.