|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
Dynamic saturation distribution of fluids in oil reservoirs is arguably the most important piece of information petroleum engineers and geophysicists need. It allows them to better characterize oil fields, choose right enhanced oil recovery techniques and make accurate recovery forecasts. The main objective of the present paper is to develop and test a novel non-intrusive technology that enables real time in-situ monitoring of fluid saturations in porous media during immiscible floods.
To achieve this goal we designed, constructed and commissioned a high pressure (up to 25MPa) and temperature (up to 200°C) core-holder with an antenna that allows for low power electromagnetic sweeps in the radio frequency range. A novel inversion algorithm was created and incorporated with our core-holder-pump system that enables dynamic acquisition of the oil and water saturations. Experiments were conducted through sand packs saturated with water and then displaced with oils of varying viscosity (drainage) followed by water flooding (imbibition). Reflection and transmission coefficients in the frequency domain were measured while flooding using a commercial vector network analyzer connected to the core holder. Recorded frequency data was processed with the novel high-resolution inversion technique to obtain impulse reflection and transmission responses in the time domain. These responses were further normalized to dynamically track the water-oil volumetric saturations within the porous media. Every displacement experiment has been performed in both vertical and horizontal positions to emulate water-oil override and underride scenarios. Material balance calculations were performed to validate fluid saturation profiles for all imbibition and drainage experiments every 5 % of the pore volume of the fluids injected.
Frequency domain reflection and transmission electromagnetic responses were measured every 1 % of the fluid injected. Material balance was used to validate the measured saturation profiles. The goodness of fit was calculated between these two independent measurements for every flood experiment performed. The mean-square error was calculated to be around 1.26% of the total pore volume on average. Late breakthroughs and piston-like displacement were observed in the floods with favorable mobility ratios. In contrast, much earlier breakthroughs have been registered in all the experiments with unfavorable mobility ratios due to fingering. All our observations are in agreement with the current theory of immiscible displacement in porous media.
The novel automated system paired with the inversion algorithm were developed to allow for virtually real time monitoring of the fluid saturations during imbibition and drainage displacement cycles. Our technology is shown to be a promising candidate to compliment resistive logging measurements in the field.
Water flooding has been applied either along with primary production to maintain reservoir pressure or later to displace the oil in conventional and heavy oil reservoirs. Although it is generally accepted that water flooding of light oil reservoirs in oil-wet systems delivers the least oil compared to either water-wet or intermediate-wet systems, there is a lack of systematic research to study water flooding of heavy oils in oil-wet reservoirs. This research gives some new insights on the effect of injection velocity and oil viscosity on water flooding of oil-wet reservoirs.
Seven different oils with a broad range of viscosity ranging from 1 to 15,000 mPa.s at 25 °C were used in fifteen core flooding experiments where injection velocity was varied from 0.7 to 24.3 ft/D (2.5 × 10−6 m/s to 86.0 × 10−6 m/s). Oil-wet sand (with contact angle of 159.31 ± 3.06°) was used in all the flooding experiments. Breakthrough time was precisely determined using an in-line densitometer installed downstream of the core.
Our observations suggest that drainage displacement does not occur unless non-wetting (water) phase pressure exceeds a critical breakthrough capillary pressure. At the same injection velocity, this non-wetting phase invading pressure is a function of the viscosity of the oil being displaced. For the same viscosity ratio, oil recovery monotonically increases with increasing injection velocity suggesting that the flow regime is viscous-dominant for all the viscosities studied. This is consistent with the classical literature on carbonates (
In this paper, it is demonstrated that in an oil-wet system increasing velocity improves forced drainage to the extent that it takes over viscous fingering. For the viscous oil system (15,000 mPa.s), it was found that wettability critically affects the pressure gradient across the core to the extent that one order of magnitude larger pressure gradient was observed in an oil-wet system compared to the completely same system but water-wet. This notable larger pressure gradient in oil-wet system accompanies with delayed water breakthrough leading to incremental (around 30 % OOIP) oil recovery compared to the water-wet case. This is completely opposite to the classical literature on light oils and needs to be further investigated due to the lack of literature on heavy oil domains. Observations reported in this study can provide some useful information about the sizes of the pores being invaded as a function of oil viscosity and wettability, which is a subject of our future microfluidic studies at the pore scale.
Molecular diffusion is a transport mechanism often ignored in conventional, non-fractured multi-component petroleum upstream simulations due to the predominance of convection. In unconventional fractured reservoirs, diffusion plays a vital role in hydrocarbon production. A "shale" reservoir is characterized by thin, ultra-tight matrix blocks surrounded by natural or induced fractures. This creates conditions in which diffusion fluxes could be significant. In ultra-tight formations, convection is a slow process, and the presence of thin blocks surrounded by fractures increases the contact area, both of which favors diffusion.
In this paper, we discuss the application of cyclic gas injection to enhance recovery in tight reservoirs in the gas condensate window. A fully implicit model is implemented with the objective to investigate the impact of diffusion on liquid dropout and vaporization on a matrix level. Diffusion fluxes are implemented considering a gradient in total chemical potential as driving force. Additionally, since capillary forces are significant in ultra-tight formations, phase equilibria calculations are modified to account for nano-confinement effects. Sensitivity is performed on matrix block size and injection gas composition (pure C1, a mixture of C1 and CO2, and a mixture of C1, C2 and C3), and the role of diffusion is evaluated for each scenario.
As gas is injected, the composition of heavier hydrocarbon fractions in the gas phase significantly increases due to vaporization of condensate. Molecular diffusion helps to spread composition banks. As a result, liquid dropout is delayed during the subsequent production stages. Heavier fractions remain in the gas phase for longer periods, which ultimately enhances its recovery. In addition to that, retention of heavier fractions due to condensate dropout is intensified as the size of the matrix block increases. Longer matrix blocks result in lower swept length for the same number of cycles. As a result, liquid dropout occurs earlier because feed of gas at in-situ composition diffuses from the center of the matrix block towards the fracture boundary.
We demonstrate that heavier components recovery is more affected by molecular diffusion than lighter components. Furthermore, it is observed that molecular diffusion strongly influences time and location of occurrence of liquid dropout in tight gas condensate reservoirs. Implementation of a rigorous model that includes convection, diffusion, adsorption and phase change allowed to investigate the commingling effects of different physics involved in enhanced recovery in unconventional reservoirs.
In preparation for a field pilot of cyclic solvent injection (CSI) on two depleted cold heavy oil production with sand (CHOPS) wells, a series of oilsands coreflood experiments were conducted to evaluate the effectiveness of various commercially available solvents and make a solvent recommendation for the pilot. Oil recovery and solvent recovery were the key performance indicators used to compare CSI effectiveness of each solvent blend. The operating pressure for each test was kept relatively constant for each solvent blend tested. Tested solvents included blends of methane/propane, carbon dioxide/propane, methane/ethane, 100% ethane, and nitrogen. Sensitivities for depletion rate and blowdown pressure are also presented. Overall the 100% ethane test performed the best with the highest oil recovery and solvent recovery in the fewest cycles. Due to the lack of commercial ethane supply and the industry experience with methane/propane in Husky Edam's CSI pilot, a methane/propane blend was recommended for the field pilot in Manatokan East near Bonnyville Alberta Canada.
In preparation for a field pilot of cyclic solvent injection (CSI) on two depleted cold heavy oil production with sand (CHOPS) wells, a series of oilsands coreflood experiments were conducted to evaluate the effectiveness of various commercially available solvents and make a solvent recommendation for the pilot. Oil recovery and solvent recovery were the key performance indicators used to compare CSI effectiveness of each solvent blend. The operating pressure for each test was kept relatively constant for each solvent blend tested. Tested solvents included blends of methane/propane, carbon dioxide/propane, methane/ethane, 100% ethane, and nitrogen. Sensitivities for depletion rate and blowdown pressure are also presented. Overall the 100% ethane test performed the best with the highest oil recovery and solvent recovery in the fewest cycles. Due to the lack of commercial ethane supply and the industry experience with methane/propane in Husky Edam’s CSI pilot, a methane/propane blend was recommended for the field pilot in Manatokan East near Bonnyville Alberta Canada.
Richardson, William D. L. (University of Calgary) | Schoeggl, Florian F. (University of Calgary) | Maini, Brij (University of Calgary) | Kantzas, Apostolos (University of Calgary) | Taylor, Shawn D. (Schlumberger-Doll Research Center) | Yarranton, Harvey W. (University of Calgary)
The oil-production rate of in-situ heavy-oil-recovery processes involving the injection of gaseous hydrocarbons partly depends on the diffusivity of the gas in the bitumen. The gas diffusivities required to model these processes are determined indirectly from models of mass-transfer experiments. However, the data in the literature are scattered partly because different methods and model assumptions are used in each case. In this work, the pressure-decay method is examined with a focus on accounting for swelling and the dependence of the diffusivity on the solvent content. To assess these issues, the diffusion of gaseous propane into bitumen is measured at conditions where significant swelling occurs. A numerical model is developed for the pressure-decay experiment that accounts for swelling (including excess volumes of mixing) and variable diffusivity. For gases, such as propane, with a relatively high solubility in bitumen, the error in the calculated diffusivity reached 25% when swelling was not included in the model. The error in the height of the gas/oil interface reached 15%. Nonideal mixing had no effect on the calculated diffusivity and only a small effect on the height of the interface. It was found that the diffusion data from a single experiment could be modeled equally well with a constant or a solvent-concentration-dependent (or viscosity-dependent) diffusivity. However, the apparent constant diffusivities for each experiment were different, confirming their dependence on the solvent content. The constant diffusivity approximately correlated to the viscosity of the oil. A larger data set is required to fully develop and test a correlation, and this work will be presented in Part II of this study (Richardson et al. 2019).
Al-Murayri, Mohammed Taha (Kuwait Oil Company) | Hassan, Abrahim Abdelgadir (Kuwait Oil Company) | Kamal, Dawood Sulaiman (Kuwait Oil Company) | Batôt, Guillaume (IFP Energies nouvelles, The EOR Alliance) | Cuenca, Amandine (Solvay, The EOR Alliance) | Butron, Jessica (Perm. Inc.) | Kantzas, Apostolos (Perm. Inc.) | Suzanne, Guillaume (Beicip Franlab, The EOR Alliance)
Foam has been extensively investigated as a method to improve the mobility control of non-condensable gases in the EOR context. Recently, there has been renewed interest in foam applied to steam injections. However, steam is a condensable gas and thus steam-foam requires special analyses that differ from classical foam assessments. This work presents the coreflood results of a steam-foam process evaluation for the Ratqa Lower Fars (RQLF) heavy oil reservoir in Kuwait.
Using specifically designed foaming surfactants, coreflood tests in the absence and presence of heavy crude oil are performed in native sandpack cores under RQLF reservoir conditions (220°C; 360 psi). In order to limit steam condensation due to the build-up of the foam pressure, steam has been supplemented with a small amount of non-condensable gas (nitrogen, about 1 - 5 mol.%). Interstitial velocity was decreased from 40 ft/day down to 1 ft/day (CWE). Phase equilibria at the core inlet were estimated based on thermodynamics flash calculations. From these calculations inlet steam quality was varied from 10 to 70 wt.%. In absence of oil, the apparent viscosity of the generated steam-foam is measured between 25 and 50 cP, depending on the interstitial velocity and inlet steam quality. Indeed, beside the classical shear-thickening behaviour observed with the decreasing flow rates, the critical or optimal steam quality is found to be closed to 30 wt.%. Furthermore, even at higher steam quality the foam is still stable and efficient with a viscosity higher than 25 cP. Experiments in the presence of crude oil were carried out under the same conditions in native cores at a steam residual oil saturation of 7% and 13%. These experiments showed that the optimal steam quality is shifted to approximatively 10 wt.%. Furthermore, the foam flow curve shows a shear-thinning behavior that is elaborated upon. Finally, the viscosity in the presence of heavy crude oil of the generated steam-foam is within the range of 7 to 22 cP, depending on the oil saturation and on the injection conditions. Considering the oil viscosity (2 to 3 cP) under the same conditions, this means that the foam effect should translate into efficient improved conformance control of the steam within the reservoir.
For the first time, an efficient and stable steam-foam is generated in coreflood experiments. The generated foam achieved high apparent viscosities, even in the presence of oil, and this has not been reported in the literature to date. The results presented here are far more than a proof of concept as they bring new evidences regarding steam-foam efficiency and mechanisms with heavy crude oil.
Real-time decision making, field surveillance, and production optimization improve the performance of existing operations to increase hydrocarbon recovery and reduce emissions. In this regard, the oil and condensate flow metering in offshore gas condensate platforms is always confronted by environmental, economic, and operational challenges resulting in uncertain production management plans. Although production forecasting of unconventional gas condensate systems is more challenging than for conventional wells, it is of great interest to support decisions by knowing the future of the wells as far as possible. The virtual flow metering techniques make it possible to utilize daily production data sets and extract information on how wells and reservoir will respond to different operational conditions. The objective of this study is to embed artificial intelligence algorithms in reservoir uncertainty modeling and present a mechanistically-supported data-driven model applicable for production forecasting of gas condensate wells with higher confidence. The outcome entails a new set of mathematical models, implemented using Apache Spark cluster computing engine with APIs in Python, that enables rigorous and robust optimization of the recovery process, designing and discovering hidden patterns in production data, and extracting reservoir information indirectly in seconds. The observations used to demonstrate the performance of the proposed hybrid model include 1600 well-testing data points together with 420 days of production history of an offshore gas condensate platform. The daily platform production is allocated efficiently to individual wells using a multilayer perceptron neural network model adaptively trained with well-testing and daily production datasets, and supported by the Energy and mass balance equations.
Thermal and solvent-based EOR methods are not applicable in many of thin post-CHOPS heavy oil reservoirs in Western Canada. Alkaline-surfactant flooding has been suggested as an alternative to develop these reservoirs. The main mechanism behind these processes has been attributed to emulsion-assisted conformance control due to the effect of synthetic and/or natural surfactants. Because nanoparticles (NPs) offer some advantages in emulsion stabilization, here we combine surface-modified silica NPs and anionic surfactants to enhance the efficiency of heavy oil chemical floods.
Based on the results of bulk fluid screening experiments, in the absence of surface-modified silica NP surfactant concentration should be tuned at the CMC (between 1 and 1.5 wt. %) to achieve the highest amount of emulsion. These emulsions are much less viscous than the originating heavy oil. However, at surfactant concentrations far from the CMC, complete phase separation occurs 24 hours after preparation. In the presence of surface-modified silica NP this emulsification was achieved at much lower surfactant concentration. The mixture of 0.1 wt. % anionic surfactant and 2 wt. % surface-modified silica NP produce a homogeneous emulsion of heavy oil in an aqueous phase. This observation was not observed when aqueous phase contains only either 0.1 wt. % anionic surfactant or 2 wt. % silica NP.
Preliminary tertiary chemical floods with water containing 0.1 wt. % surfactant and 2 wt. % surface-modified silica NP yielded an incremental oil recovery of 48 % OOIP, which is remarkably higher than that of either surfactant or NP floods with incremental recoveries of 16 and 36 % OOIP, respectively. Tertiary recovery efficiency, defined as ratio of incremental recovery factor to maximum pressure gradient during the tertiary flood, is six times greater for the surfactant/NP mixture than for the surfactant-only flood. This enhancement in recovery efficiency is of great interest for field applications where high EOR and large injectivity are desired.
Chemical flooding has been suggested as an efficient conformance control technique to develop many of thin post-CHOPS heavy oil reservoirs in Western Canada. In-situ formation of oil in water emulsions due to the effect of surfactant/natural soap has been reported as the main mechanism behind chemical EOR. In this work, the effect of surface-modified silica NPs to enhance the efficiency of surfactant to emulsify heavy oil (14,850 mPa.s and 980 kg/m3 at 25 °C, from the Luseland field) in water has been investigated.
Bulk fluid screening experiments were conducted using different surfactants and surface-modified silica NPs for selecting the best heavy oil emulsifier. Complementary experiments such as interfacial/surface tension, NP zeta potential and size measurements, and elemental analysis were conducted to understand the interactions between NPs and surfactant molecules.
In the absence of NPs, concentration of both anionic and cationic surfactants should be tuned within a narrow window, near CMC, to create stable heavy oil in water emulsions. It was found that there is a threshold for IFT, obtained at the CMC, which should be met to have stable oil in water emulsions. The created oil in water emulsions break easily at surfactant concentrations higher than the CMC, yielding IFTs higher than the threshold. This observation was also seen in a system containing dodecane. At the CMC of both anionic and cationic surfactants, the IFT between dodecane and an aqueous phase is negative, producing stable dodecane in water emulsions for over three months.
In the presence of surface-modified silica NPs heavy oil emulsification is achieved at surfactant concentrations much lower than the CMC. In this case, IFT is remarkably (54 %) reduced, well below the threshold value, due to the combined effect of 2 wt. % negatively-charged silica NPs and only 0.1 wt. % anionic surfactant. These results suggest that the repulsive interaction between negatively-charged NPs and anionic surfactant may result in pushing the surfactant molecules back towards the oil-water interface to enhance IFT reduction.