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Abstract Low recovery of fracturing water is partly due to fracturing fluid leak-off into formation and water trapping in matrix. In our previous studies (Soleiman Asl et al. 2019 and Yuan et al. 2019), we showed that using surfactant solutions in fracturing fluid can significantly enhance imbibition oil recovery. However, there is one critical question remained unanswered: What are the consequences of these additives on well performance during flowback and post-flowback processes? Can they block the pore-throats of rock matrix and induce formation damage? To answer this question, we develop and apply a comprehensive laboratory protocol on a tight core plug to simulate leak-off and flowback processes under reservoir pressure, with and without initial water saturation (Swi). We evaluate the possibility of pore-throat blockage by comparing pore-throat size distribution of the core plug and size distribution of the particles formed in a microemulsion (ME) solution. We also investigate the effects of Swi on effective oil permeability (ko) after the flowback process. The results of leak-off and flowback tests using tap water as the base case shows that ko after flowback is lower than that before the leak-off, mainly due to phase trapping. However, results of the tests using the ME solution show that ko after flowback is greater than ko before leak-off. This observation suggests that the leak-off of ME solution enhances regained oil relative permeability during flowback by reducing phase trapping and water blockage. When Swi = 0, the blockage of leaked-off fluid reduces ko during the flowback process. The mean size of self-assembled structures (referred to as "particles" here) formed by mixing the ME solution with water is around 10-20 nm. The MICP profile of the core sample shows that around 95% of pore throats are bigger than the size of formed particles, suggesting low chance of pore-throat blockage by the suspended particles.
- North America > Canada > Alberta (0.93)
- North America > United States (0.68)
- North America > Canada > British Columbia (0.68)
- Geology > Geological Subdiscipline (0.93)
- Geology > Mineral > Silicate (0.70)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.69)
Abstract This paper demonstrates the effect of pore systems and mineralogy on imbibition capillary pressure (Pci) of carbonate rocks. A systematic workflow is developed and followed to ensure the data quality of Pci, minimize uncertainty in deriving the Pci from centrifuge tests, and analyze the data together with pore-size distribution from mercury injection capillary pressure (MICP) and mineralogy from Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN). The workflow starts with assessing the centrifuge production data for gravity-capillary equilibrium at each speed. Then the quality-checked data is used to produce six different Pci curves using the analytical and numerical models. The analytical and numerical solutions assess the variability in solutions for various rock types, and ultimately, lead to the selection of the most-representative Pci curve. Finally, the representative Pci curves of varying rock types are analyzed together with the MICP and QEMSCAN data to examine the change in Pci curves as a result of changes in the number and character of pore systems, dominant pore throat radii, and mineralogy. Findings from this study present insights into the impact of mineralogy and pore systems on the behavior of the Pci curves. From the mineralogy perspective, the presence of dolomite, microporous calcite, or rutile and anatase (TiO2) within the rock composition has a strong influence on the Pci behavior of carbonate rock. The data reveals that the contrast between the micropore and macropore systems of bi-modal carbonates has the strongest influence on Pci. We find that Pci can be clustered based on mineral content for bi-modal carbonate rocks and the degree of communication between micropore and macropore systems. The novel approach presented in this study links the MICP and QEMSCAN data to the imbibition process making the way toward a better dynamic rock typing.
- North America (0.93)
- Asia > Middle East (0.46)
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Dolomite (0.36)
Abstract Laboratory studies of unconventional reservoirs are faced with considerably more challenges than those of conventional reservoirs. The assessment of Enhanced Oil Recovery potential in unconventional reservoirs (UCR EOR) in particular needs to address the characterization of static and dynamic properties given the tightness of the rocks, available sample size and simulation of EOR under elevated pressure and temperature conditions. This paper summarizes a laboratory study designed and performed for a potential EOR pilot utilizing cyclic gas injection (Huff-n-Puff) in the Sooner Trend Anadarko Canadian Kingfisher (STACK) shale play in Oklahoma. The lab study focuses on characterizing the rock-fluid interactions as well as upscaling key parameters for the field-scale modeling and simulation. A systematic approach was followed in the design of a laboratory program specific to the characteristics of rock/fluid interaction and the proposed injection scheme of a cyclic gas injection pilot. Digital Core Analysis (DCA) incorporating micro CT, SEM and FIB-SEM analyses were performed in order to determine basic petrophysical properties at micro scale, with capillary pressure and relative permeability curves simulated digitally. Porosity and relative permeability end points were also measured on preserved STACK core plugs. Minimum miscibility pressure (MMP) measurements of field separator gas and STACK crude oil was performed with a rising bubble apparatus (RBA). Finally, a huff-n-puff experiment was designed and performed within a custom pressure cell to study the recovery efficiency at the existing core sample scale. Digital Core Analysis (DCA) has been shown to reliably produce petrophysical properties for tight STACK cores. Laboratory miscibility pressure measurements were conducted at reservoir conditions (4,500 psi and 183 °F) using field crude samples and the associated gas composition. Seven injection/production cycles were applied to a re-saturated standard core plug with oil production observed and measured in the effluent. Cyclic injection continued until no further oil could be visually observed in the effluent. A customized 2-stage drawdown was incorporated to provide input for the recovery process. The total recovery after seven cycles reached 82 %OOIP. This work provides the first rock and fluid analysis integrating digital and traditional approaches for assessment of EOR potential in unconventional reservoirs such as those found in the STACK. This systematic approach presents properly designed and executed laboratory experiments without leaving out key formation and fluid variables. This workflow can be applied in similar UCR EOR studies to lay a solid foundation for appraising UCR EOR potential and providing reliable inputs for upscaling to the field level studies.
- Geology > Mineral (0.69)
- Geology > Petroleum Play Type > Unconventional Play (0.34)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Thermal methods (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Gas-injection methods (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Core analysis (1.00)
Performance of Air- Vs. CO2 - Water Injection in a Tight, Light Oil Reservoir: A Laboratory Study
O'Brien, W. J. (Nitec LLC) | Moore, R. G. (Schulich School of Engineering, University of Calgary) | Mehta, S. A. (Schulich School of Engineering, University of Calgary) | Ursenbach, M. G. (Schulich School of Engineering, University of Calgary) | Kuhlman, M. I. (MK Tech Solutions)
Abstract This paper outlines the results of a comparative study of air- and immiscible CO2 - Water injection based Enhanced Oil Recovery (EOR) processes for a 30+ °API tight, light oil reservoir. This was accomplished by embedding multiple low- permeability core plugs in crushed reservoir core material to create a composite core that was contained in a 1.84 m long core holder. The objectives of this unscaled experimental work were: 1) to understand the suitability of each EOR process for a low permeability reservoir, 2) to define process parameters prior to a potential field pilot, and 3) to understand the relative merits of each EOR process to mobilize light oil from a tight matrix to a fracture network. A detailed experimental investigation was conducted at realistic reservoir conditions to evaluate the feasibility of an air injection-based EOR process. The air injection results were compared with those from an immiscible CO2-Water injection EOR experiment using the same experimental setup and reservoir conditions. Both the air- and CO2 - Water coreflood tests were performed at 10.3 MPa (1500 psig) and 99 °C in a 100 mm diameter, 1.84 m long composite core-holder using 38 mm diameter reservoir core plugs (that represented the matrix) and mounted within the crushed reservoir core material (that represented the fracture); inert helium gas was used to pressure up the core-holder to reservoir pressure. Permeability of the core plugs was from 0.3 to 3 millidarcies, while the permeability of the crushed core material was 1 to 3 Darcies. Air injection was performed as a standard combustion tube test with injection of 2.3 pore volumes (PV) of air to burn 71% of the packed core length (including helium, a total of 4.3 PV of gas injected). The CO2-Water coreflood was performed with the injection of 2.86 PV of CO2 followed by an extended soak period, then a second injection of an additional 2.86 PV of CO2, followed by the injection of 2.6 PV of water. The pre- and post-test core plug measurements of oil saturation show that the air injection process removed significantly larger quantities of hydrocarbons than the immiscible CO2-Water injection process. Relative to the initial conditions of the core plugs for the Air-Injection experiment, 95+ percent of the hydrocarbons were removed; noting that some fraction of original oil was consumed as fuel. In the post-test CO2-Water injection core plugs, oil recovery was in the range of 30 to 55 percent of OOIP. These findings suggest, under an appropriate field design, that both processes have the potential to recover incremental oil from tight reservoirs. However, the air-injection may be better suited to mobilize oil, due to thermal expansion, rather than the CO2 - Waterflood process.
- North America > United States > Texas (1.00)
- Asia (0.67)
- North America > United States > Alaska > North Slope Borough (0.28)
- Europe > United Kingdom > North Sea > Central North Sea (0.24)
- Geology > Petroleum Play Type > Unconventional Play (0.67)
- Geology > Geological Subdiscipline > Economic Geology > Petroleum Geology (0.60)
- Water & Waste Management > Water Management > Lifecycle > Disposal/Injection (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- North America > United States > Texas > Permian Basin > Wolfcamp Formation (0.99)
- (29 more...)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Waterflooding (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Gas-injection methods (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Core analysis (1.00)
Core Scale Simulation of Spontaneous Solvent Imbibition from HPAM Gel
Andersen, Pål Østebø (Dept. of Energy Resources, University of Stavanger) | Lohne, Arild (The National IOR Centre of Norway, University of Stavanger) | Stavland, Arne (The National IOR Centre of Norway, University of Stavanger) | Hiorth, Aksel (Dept. of Energy Resources, University of Stavanger) | Brattekås, Bergit (Dept. of Energy Resources, University of Stavanger)
Abstract Capillary spontaneous imbibition of solvent (brine bound in gel) from formed polymer gel into an adjacent, oil-saturated porous medium was recently observed in laboratory experiments. Loss of solvent from the gel by spontaneous imbibition may influence the blocking capacity of the gel residing in a fracture, by decreasing the gel volume, and may contribute to gel failure, often observed in water-wet oil fields. Formed gel cannot enter significantly into porous rock, which has important implications for spontaneous imbibition: the gel particle network itself is not imbibed, and remains close to the rock matrix surface, while gel solvent can leave the gel and progress into the matrix due to capillary forces. Polymer gel is an inherently complex fluid and modelling of its behavior is, as such, complicated. Accurate description and quantification of gel properties and behaviour on the laboratory scale is, however, necessary to predict the performance of gel placed in an oil field, particularly in fractured formations. In this work, we present an original modelling approach, to simulate and interpret spontaneous solvent imbibition from Cr(III)-Acetate HPAM gel into oil-saturated chalk core plugs. A theory describing solvent flow within a gel network is detailed, and was implemented into an in-house simulator. Simulations of spontaneous imbibition from gel was performed, and compared to free spontaneous imbibition of water. A good overall match was achieved between experiments and simulations on the core scale, which validates the proposed gel model. All Faces Open (AFO) and Two Ends Open - Free Spontaneous Imbibition (TEOFSI) boundary conditions were used in the experiments, and formed the basis for simulation. Spontaneous imbibition occurs at the core end faces that are open to flow and exposed to gel (different for the two boundary conditions). The gel surrounding the core was discretized and included as a part of the total grid to capture transient behavior. The surrounding gel is treated as a compressible porous medium where the gel's polymer structure constitutes the matrix having constant solid volume while the gel porosity is a function of pore pressure. The gel permeability is modelled as function of gel porosity using a Kozeny-Carman approach. The flow equations for the gel and core domains were solved simultaneously by implementing the proposed description into the core scale simulator IORCoreSim. Two properties were identified to control the transport of water from gel into the adjacent matrix: the permeability and compressibility of the gel. The flow of water from the gel was observed in simulations to occur in a transient manner, driven by the coupled gradients in gel fluid pressure and gel porosity, where the gel porosity initially decreases in a layer close to the core surface due to reduced aqueous pressure. Gel porosity continued to decrease in layers away from the core surface; the propagation rate was controlled by two main gel parameters: (i) Gel compressibility controlled the pressure gradient within the gel network, and the amount of water transported from the outer part of the gel towards the core surface to balance the pore pressure. (ii) Gel permeability limited how fast water could flow within the gel at a given pressure gradient, thus increasing the time scale of the overall imbibition process.
- Europe (1.00)
- North America > United States (0.93)
- Research Report > New Finding (0.46)
- Research Report > Experimental Study (0.46)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Abstract The wettability of tight reservoir rock plays a critical role in affecting relative permeability and in turn oil recovery. However, the link between wettability and its effects on oil recovery remains poorly understood, and the potential to boost oil recovery by varying the wettability has not been fully explored. This work was an attempt to conduct a systematic experimental study to improve our understanding of wettability of tight oil reservoirs and the mechanisms of its alteration on oil recovery improvement. Contact angles of individual rock-forming minerals and reservoir rock samples were first measured in brines with different salinities. Then the minerals were aged separately with a medium crude oil with sufficient polar components to investigate their tendency for wettability alteration. As well, oil and water distributions inside tight core samples were scanned by a synchrotron-based computed tomography scanner. Contact angle measurements for all minerals and reservoir rocks showed initial water-wetting behavior. After aging with crude oil for over two months, polar components from the oil adsorbed onto the solid surfaces to alter their wettability to less water wet. Consequently, this wettability alteration contributed to oil and water redistribution and saturation change in reservoir cores. The experimental findings suggested that the wettability in tight reservoirs is a strong function of rock mineralogy, formation fluid properties, and saturation history. Preliminary numerical simulation revealed how rock wettability alteration could contribute to improved oil recovery through waterflooding.
- North America > Canada > Saskatchewan (0.95)
- North America > United States > North Dakota (0.94)
- Research Report > New Finding (0.88)
- Research Report > Experimental Study (0.54)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Waterflooding (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Core analysis (1.00)
Abstract To speed up coreflood experiments, we have developed a state of the art experimental setup (CAL-X) designed for high throughput coreflood experimentation. The setup is composed of an X-ray radiography facility, a fully instrumented multi-fluid injection platform and a dedicated X-ray transparent core holder. The equipment was designed to handle small samples of 10 mm in diameter and 20 mm in length, and can be operated at up to 150 bar and 150 °C. The X-ray facility consists of a high power X-ray tube and a high speed-low noise detector allowing real-time radiography acquisition and offering sufficient density resolution to use dopant-free fluids. The injection platform is fully automated and allows the control and monitoring of different parameters (pressure, temperature, flow rate…). 1-D and 2-D saturation profiles are followed in real-time, allowing a precise determination of the recovery curve, reducing thus drastically time-consuming effluent measurements. Using this setup, a typical coreflood experiment can be run in less than a day. To validate the setup we have run a series of experiments on water-wet sandstone samples to determine capillary desaturation curve, steady-state relative permeabilities and recovery factor for a formulation designed for high temperature conditions (110°C). The results show good repeatability as well as good agreement when compared to standard coreflood experiments. In the recovery factor experiment, during surfactant injection, the formation and displacement of an oil bank was observed, yielding a recovery factor of 92% OOIP.
Boosting Oil Recovery in Unconventional Resources Utilizing Wettability Altering Agents: Successful Translation from Laboratory to Field
Kazempour, Mahdi (Nalco-Champion, an Ecolab Company) | Kiani, Mojtaba (Nalco-Champion, an Ecolab Company) | Nguyen, Duy (Nalco-Champion, an Ecolab Company) | Salehi, Mehdi (Nalco-Champion, an Ecolab Company) | Bidhendi, Mehrnoosh Moradi (Nalco-Champion, an Ecolab Company) | Lantz, Mike (Nalco-Champion, an Ecolab Company)
Abstract In recent years, the United States (US) has experienced a resurrection in hydrocarbon recovery owing to the extraction of oil and gas from unconventional resources. Due to the ultra-low permeability nature of these reservoirs and their oil-wet characteristics, oil production declines are steep and oil recoveries remain very low (< 12% of OOIP). This challenge endures even with the assistance of hydraulic fracturing advancements and well spacing optimizations. The billions of barrels of remaining oil is a good target for chemical enhanced oil recovery (EOR) technologies. In this study, after comprehensive laboratory testing, a series of customized chemical formulations was developed to improve oil recovery under the challenging conditions of the Middle Bakken and Niobrara formations (temperature >110 °C, salinity>220,000 ppm, and hardness>15,000 ppm). To examine the performance of the selected formulation in the field-scale, a single well enhancement trial was carried out. A detailed review of the lab and field data (pre-and post- treatment) is discussed in this study. Oil rate decline analysis and numerical simulations were used to obtain more insight about the true effectiveness of the chemical treatments. The results of this field trial reveal that injecting a proper wettability altering agent can improve oil recovery from shale oil reservoirs by up to 25% of the estimated ultimate recovery (EUR). The results of numerical simulations also show that the additional oil recovered in this field trial cannot be achieved by either well shut-in or straight water injection. The lessons learned from this study provide practical information to optimize similar field trial designs leading to more profitable projects. The concepts and information here can be also translated to other unconventional basins and gas condensate or wet/dry gas reservoirs.
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.36)
- North America > United States > West Virginia > Appalachian Basin > Marcellus Shale Formation (0.99)
- North America > United States > Virginia > Appalachian Basin > Marcellus Shale Formation (0.99)
- North America > United States > Pennsylvania > Appalachian Basin > Marcellus Shale Formation (0.99)
- (40 more...)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Shale oil (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- (5 more...)
The Onset of Spontaneous Imbibition: How Irregular Fronts Influence Imbibition Rate and Scaling Groups
Føyen, T. L. (Dept. of Physics and Technology, University of Bergen) | Fernø, M. A. (Dept. of Physics and Technology, University of Bergen) | Brattekås, B.. (The National IOR Centre of Norway, Dept. of Energy Resources, University of Stavanger)
Abstract Spontaneous imbibition is a capillary dominated displacement process where a non-wetting fluid is displaced from a porous medium by the inflow of a more-wetting fluid. Spontaneous imbibition strongly impacts waterflood oil recovery in fractured reservoirs and is therefore widely studied, often using core scale experiments for predictions. Decades of core scale experiments have concluded that spontaneous imbibition occurs by a uniformly shaped saturation front and that the rate of imbibition scales with square root of time. We use emerging imaging techniques to study local flow patterns and present new experimental results where spontaneous imbibition deviates from this behavior. The imbibition rate during early stages of spontaneous imbibition (the onset period) was sometimes observed to deviate from the square root of time behavior. The impact of the onset period on the imbibition process is, however, not well understood. In this work, the development of displacement fronts were visualized during the onset period, using twodimensional paperboard models and core plugs imaged using Positron Emission Tomography (PET-CT). The new experimental results provided insight on the dynamics during the initial spontaneous imbibition period. Controlled two-dimensional paperboard experiments demonstrated that restricted wetting phase flow through the surface exposed to water caused irregular saturation fronts and deviation from the square root of time behavior during the onset period. Local restriction of the wetting phase flow was observed during spontaneous imbibition in sandstone core plugs as a result of non-uniform wetting preference. The presence of nonuniform wetting resulted in unpredictable spontaneous imbibition behavior, with induction time (delayed imbibition start) and highly irregular fronts. Without imaging, the development of irregular saturation fronts cannot be observed locally; hence the effect cannot be accounted for, and the development of spontaneous imbibition in the core erroneously interpreted as a corescale wettability effect. This underlines the undeniable need for a homogenous wettability preference through the porous medium when performing laboratory spontaneous imbibition measurements. Our observations of non-uniform wetting preference will affect Darcy-scale wettability measurements, scaling and modeling. We argue that great care must be taken when preparing core plugs for spontaneous imbibition, to avoid experimental artifacts.
- North America > United States (0.46)
- Europe > Norway (0.29)
Abstract Use of foams to control CO2 floods conformance is attracting a renewed interest in recent years due its flexibility and ease of application. This application becomes even more attractive in current times of low oil price, as it can be an inexpensive mean to maximize CO2 utilization efficiency and increase production at no capital expenses. However, it is generally recognized that to maximize chances of success of a pilot application, an appropriate foaming formulation must be designed for a given reservoir and characterized in petrophysics lab. This usually requires an extensive laboratory work that is not always compatible with cost constraints. We present a new cost-effective workflow that focuses on evaluating two formulation performance indicators derived from the population balance model: foam creation (related to foaming power) and resistance to foam destruction (related to foam stabilization against coarsening and coalescence). We assess these two parameters in representative reservoir conditions by measuring foam mobility reduction in porous media and foam lifetimes. Experimental results and simple scaling arguments show that these two measurements, both of importance to the application, are mostly independent. This shed light on a recurring question pertaining to the relevance of bulk foam experiments to predict foam efficiency in porous media. With this in mind, we present a new approach for measuring mobility reduction in porous media with a higher throughput than usual corefloods experiments. This methodology is based on sandpack experiments as well as serial coreflood experiments that allow multiple successive formulations testing. We show that the link between sandpack and coreflood results is far from being straightforward, and depends on static (geometrical) as well as dynamic (flow) parameters. Overall, this work provides new insights on the major performance indicators used to evaluate foam efficiency for gas conformance control in oil reservoirs. We build on this understanding to present a novel approach that can help developing more efficient foam EOR solutions. In particular, it allows tailoring foaming agents properties (such as foaminess and foam stabilization) to specific conditions of a given application (oil saturation, vertical heterogeneity, etc…).
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 375 > Block 34/7 > Snorre Field > Statfjord Group (0.99)
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 375 > Block 34/7 > Snorre Field > Lunde Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 375 > Block 34/4 > Snorre Field > Statfjord Group (0.99)
- (9 more...)