Shah, Swej Y. (Delft University of Technology) | As Syukri, Herru (Delft University of Technology) | Wolf, Karl-Heinz (Delft University of Technology) | Pilus, Rashidah M. (Universiti Teknologi Petronas) | Rossen, William R. (Delft University of Technology)
Foam reduces gas mobility and can help improve sweep efficiency in an enhanced-oil-recovery (EOR) process. For the latter, long-distance foam propagation is crucial. In porous media, strong foam generation requires that the local pressure gradient exceed a critical value (∇Pmin). Normally, this happens only in the near-well region. Away from wells, these requirements might not be met, and foam propagation is uncertain. It has been shown theoretically that foam can be generated, independent of pressure gradient, during flow across an abrupt increase in permeability (Rossen 1999). The objective of this study is to validate theoretical explanations through experimental evidence and to quantify the effect of fractional flow on this process.
This article is an extension of a recent study (Shah et al. 2018) investigating the effect of permeability contrast on this process. In this study, the effects of fractional flow and total superficial velocity are described. Coreflood experiments were performed in a cylindrical sintered-glass porous medium with two homogeneous layers and a sharp permeability jump in between, representing a lamination or cross lamination. Unlike previous studies of this foam-generation mechanism, in this study, gas and surfactant solution were coinjected at field-like velocities into a medium that was first flooded to steady state with gas/brine coinjection. The pressure gradient is measured across several sections of the core. X-ray computed tomography (CT) is used to generate dynamic phase-saturation maps as foam generates and propagates through the core. We investigate the effects of velocity and injected-gas fractional flow on foam generation and mobilization by systematically changing these variables through multiple experiments. The core is thoroughly cleaned after each experiment to remove any trapped gas and to ensure no hysteresis.
Local pressure measurements and CT-based saturation maps confirm that foam is generated at the permeability transition, and it then propagates downstream to the outlet of the core. A significant reduction in gas mobility is observed, even at low superficial velocities. Foam was generated in all cases, at all the injected conditions tested; however, at the lowest velocity tested, strong foam did not propagate all the way to the outlet of the core. Although foam generation was triggered across the permeability boundary at this velocity, it appeared that, for our system, the limit of foam propagation, in terms of a minimum-driving-force requirement, was reached at this low rate. CT images were used to quantify the accumulation of liquid near the permeability jump, causing local capillary pressure to fall below the critical capillary pressure required for snap-off. This leads to foam generation by snap-off. At the tested fractional flows, no clear trend was observed between foam strength and fg. For a given permeability contrast, foam generation was observed at higher gas fractions than predicted by previous work (Rossen 1999). Significant fluctuations in pressure gradient accompanied the process of foam generation, indicating a degree of intermittency in the generation rate—probably reflecting cycles of foam generation, dryout, imbibition, and then generation. The intermittency of foam generation was found to increase with decreasing injection velocities and increasing fractional flow. Within the range of conditions tested, the onset of foam generation (identified by the rise in ∇P and Sg) occurs after roughly the same amount of surfactant injection, independent of fractional flow or injection rate.
Gas cycling enhanced oil recovery (GCEOR) is under intense investigation. A novel experimental procedure was developed to quantify the parameters that affect GCEOR performance. Porous media, exhibiting in-situ liquid permeability from 200 nD to 2 µD, were evaluated for GCEOR upside. The influence of cycling pressure, injection gas composition, soak time and level of primary depletion before initiation of GCEOR were measured.
The innovative experimental design for core-flow testing permitted the quantification of GCEOR using large lab-scale hydrocarbon pore volumes (HCPV). The unique experimental design allowed nano-darcy media to be tested using a time line comparable to conventional millidarcy media. Two dominant flow regimes were incorporated: matrix mass transfer into the fracture and flow within the fracture. Three mechanisms for EOR are described: extraction, swelling, and reduction of interfacial tension. Full reservoir conditions were reproduced and primary depletion followed by huff and puff GCEOR were evaluated, while changing the design parameters listed above. This work was performed on diverse oil and rock properties.
More than 30 primary depletion tests followed by GCEOR have been conducted. The effects of cycling pressure, injection gas composition, soak time, level of primary depletion before GCEOR, and other parameters were investigated. Due to large HCPV, good mass balance was maintained and sufficient fluids were produced, as a function of cycle number (huff and puff), in order to be able to measure effluent gas and liquid compositions and densities from each cycle along with the recovery of original oil in place (OOIP). All testing was done in order to quantify the relative benefit of huff and puff GCEOR compared to primary depletion recovery. Results indicate that recovery of OOIP can be more than doubled by implementing GCEOR: cycling pressure should be optimized (highest pressure does not necessarily perform the best); soak time/ huff time may compensate for non-optimal pressure operation; injection-gas composition can impact performance; gas utilization values are low compared to conventional continuous gas injection projects; less depletion before GCEOR initiation can accelerate recovery and can access residual oil that was not produced at higher levels of primary depletion.
Tight oil production has increased dramatically and contributed to 61% of total US oil production in 2018. However, recovery factors for primary depletion with multistage fractured wells are low, typically less than 10%. Gas huff-n-puff emerges as a promising technique to push the recovery factor beyond 10% in tight oil reservoirs, based on laboratory studies, simulation and field pilot tests. A CO2 huff-n-puff pilot was implemented in the Midland Basin, and data collected demonstrated significant incremental oil recovery, but with higher than expected water-cut rise.
To understand the excessive water production, a compositional model was built. Eight pseudo-components were used to match the PVT lab results of a typical oil sample in the Wolfcamp shale. A lab scale model was established in our simulator to match the results of gas huff-n-puff experiments in cores, where key parameters were identified and tuned. A half-stage model consisting of five fractures was built, where stress-dependent permeability was represented by compaction tables. Then a sensitivity analysis was conducted to understand the roles of different mechanisms behind the abnormal high water-cut phenomenon on this scale. Our simulation results have shown that initial water saturation, IFT-dependent relative permeability, reactivation of water-bearing layers, and re-opening of unpropped hydraulic fractures may all affect water-cut after gas injection. Among them, re-opening of unpropped hydraulic fractures was the most critical one.
Data from a pilot test imply substantial water production after gas injection, which may impede oil production, but the underlying mechanisms are poorly understood. A numerical model is developed to study possible mechanisms for high water-cut pilot results. This study also intends to quantify the impact of high water cut on cyclic gas injection.
The compositional flow simulation model was frequently used to evaluate the miscible water alternating CO2 flooding (CO2-WAG). The uncertainty and sensitivity analysis have to be conducted to examine the parameters mostly affecting the performance of the process. Accordingly, multiple simulation runs require to be constructed which is a time-consuming procedure and finally increase the computational cost. This paper presents a simplistic approach to assess the miscible CO2-WAG flooding in an Iraqi oilfield through developing a statistical proxy model. The Central Composite Design (CCD) was employed to build the proxy model to determine the incremental oil recovery (ΔFOE) as a function of seven reservoir and operating parameters (permeability, porosity, ratio of vertical to horizontal permeability, cyclic length, bottom hole pressure, ratio of CO2 slug size to water slug size, and CO2 slug size). In total, 81 compositional simulation runs were conducted at field-scale to establish the proxy model. The validity of the model was investigated based on statistical tools; the Root Mean Squared Error (RMSE), R-squared statistic and the adjusted R-squared statistic of 0.0095, 0.9723 and 0.9507 confirmed the reliability of the model. The most influential and the optimum values of the parameters that lead to the higher ΔFOE during miscible CO2-WAG process were identified through proxy modeling analysis. The developed model was created based on the Nahr Umr reservoir in Subba oilfield and can be applied to roughly estimate the ΔFOE during the miscible CO2-WAG process at the same geological conditions as Nahr Umr reservoir.
Quintero, Harvey (ChemTerra Innovation) | Abedini, Ali (Interface Fluidics Limited) | Mattucci, Mike (ChemTerra Innovation) | O’Neil, Bill (ChemTerra Innovation) | Wust, Raphael (AGAT Laboratories) | Hawkes, Robert (Trican Well Service LTD) | De Hass, Thomas (Interface Fluidics Limited) | Toor, Am (Interface Fluidics Limited)
For optimizing and enhancing hydrocarbon recovery from unconventional plays, the technological race is currently focused on development and production of state-of-the-art surfactants that reduce interfacial tension to mitigate obstructive capillary forces and thus increase the relative permeability to hydrocarbon (
A heterogeneous dual-porosity dual-permeability microfluidic chip was designed and developed with pore geometries representing shale formations. This micro-chip simulated Wolfcamp shale with two distinct regions: (i) a high-permeability fracture zone (20 µm pore size) interconnected to (ii) a low-permeability nano-network zone (100 nm size). The fluorescent microscopy technique was applied to visualize and quantify the performance of different flowback enhancers during injection and flowback processes.
This study highlights results from the nanofluidic analysis performed on Wolfcamp Formation rock specimens using a microreservoir-on-a-chip, which showed the benefits of the multi-functionalized surfactant (MFS) in terms of enhancing oil/condensate production. Test results obtained at a simulated reservoir temperature of 113°F (45°C) and a testing pressure of 2,176 psi (15 MPa) showed a significant improvement in relative permeability to hydrocarbon (
Measurements using a high-resolution spinning drop tensiometer showed a 40-fold reduction in interfacial tension when the stimulation fluid containing MFS was tested against Wolfcamp crude at 113°F (45°C). Also, MFS outperformed other premium surfactants in Amott spontaneous imbibition analysis when tested with Wolfcamp core samples.
This work used a nanofluidic model that appropriately reflected the inherent nanoconfinement of shale/tight formation to resolve the flowback process in hydraulic fracturing, and it is the first of its kind to visualize the mechanism behind this process at nanoscale. This platform also demonstrated a cost-effective alternative to coreflood testing for evaluating the effect of chemical additives on the flowback process. Conventional lab and field data were correlated with the nanofluidic analysis.
Two-phase oil/water relative permeability measurements were conducted at ambient and high temperatures in two different rock-fluid systems; one using a clean Poly-Alpha-Olefin (PAO) oil and the other with Athabasca bitumen. The tests were performed in a clean sand-pack with the confining pressure of 800 psi, using deionized water as the aqueous phase. Both the JBN method and the history match approach were utilized to obtain the relative permeability from the results of isothermal oil displacement tests. The contact angle and IFT measurements were carried out to assess any possible wettability alteration and change in fluid/fluid interaction at higher temperatures.
Results, Observations, Conclusions: The results of the clean system using the viscous PAO oil confirmed that the two-phase oil/water relative permeability in this ultra-clean system is practically insensitive to the temperature. The slight variation in oil endpoint relative permeability, especially at ambient condition, was attributed to variations in the packing of sand. It was found that the history matching derived two-phase relative permeability from the highest temperature test provides reasonably good history matches of the other displacements that were conducted at lower temperatures. In addition, it is shown that the JBN approach based relative permeability curves show larger variations, primarily due to insufficient volume of water injection at lower temperatures, which makes the practical residual oil saturation much higher than the true residual. In contrast with the ultra-clean system, the results obtained with bitumen showed much larger variations in relative permeability with temperature.
Most of the reported studies involving history matching approach treat the low-temperature measurements as the base case and show that changes in relative permeability are needed to history-match the tests at higher temperatures. We have shown that the displacement done at the highest temperature provides a more reliable estimate of the relative permeability and, in some cases, this relative permeability can successfully history match tests done at lower temperatures. In view of the impracticality of injecting sufficient water to reach close to real residual oil saturation at low temperatures, it would be better to obtain relative permeability data at high temperatures for characterizing the two-phase flow behavior of viscous oil systems.
Initial rate and decline are the two main parameters defining the economics of unconventional shale oil development. To improve economics, companies drill longer horizontal wells with more than twenty equidistant stages, different completion strategies and various additives such as surfactants and nano surfactants. This procedure evolves to factory mode in which tasks are optimized in timing and performance without attention to the matrix aspects of improving the recovery. Here, we report the design of a mutual solvent injection pilot in the Vaca Muerta unconventional reservoir during the completion of four unconventional shale oil wells. Reducing
Vaca Muerta has been long regarded as a water wet shale because of the limited water backflow post-fracking job. Alternating water injection was implementing assuming that the well productivity is driven by spontaneous imbibition, but this strategy has been unsuccessful as capillary pressure hysteresis drives this mechanism. We started studying Vaca Muerta from the rock microstructure using energy-dispersive spectrometry and focused gallium Ion Beam ablation FIB SEM images. The microstructure varied widely from millimeters in the same plug which could be expected because in shale rocks millimeters represent more years of deposition than in a conventional reservoir. We identified intercalations of massive water wet zones and strongly oil wet zones in the Vaca Muerta kitchen zone. The oil wet intercalations have high porosity and adsorption isotherm indicating 100 to 1000 times more permeability than the water wet zone. The water wet intercalations are highly saturated with water, and on the contrary, the oil wet intercalations are highly saturated with oil. The pilot designed consisted of four wells in which we will test different injection concentrations but keeping the total mass constant. In this manner, we will estimate the volume contacted by the solvent.
The laboratory protocol indicates a large percentage of macro and meso-pores. We implemented the dimethyl-ether injection which changes the interfacial tension, viscosity and wettability and we obtained the modified relative permeabilities which were the injection of dimethyl ether at 30% concentration along with the hydraulic fracture stimulation stages doubled the initial oil production rate.
The pilot consisted of five wells in which we will test different injection concentrations but keeping the total mass constant. In this manner, using the numerical simulation, we will estimate the volume contacted by the solvent.
Intercalations of high porosity high permeabilities zones in which the injection of a mutual solvent that reduces viscosity and could change wettability in oil wet/water-wet Vaca Muerta improving matrix connectivity.
Stephenson, Tim (Flotek Industries) | Oswald, Darin (Flotek Industries) | Dwyer, Pat (Flotek Industries) | Brown, Derek (Flotek Industries) | Ndefo, Emeka (Flotek Industries) | Kiran, Sumit (Crescent Point Energy) | Smith, Jeff (Crescent Point Energy) | Gaffney, Breandan (Crescent Point Energy)
Application of chemistries for waterflooding has traditionally required a significant upfront investment in core flood testing. Investments of this sort equate to money and time spent on a reservoir screening tool which does not guarantee an accurate translation into pilots. The aim of this paper is to explore core flood results in conjunction with pilot results for conventional and unconventional reservoirs where microemulsions are deployed in order to enhance oil recovery.
Microemulsions act as a delivery platform for solvent (terpene) and surfactant mixtures throughout a given rock volume. Their ability to alleviate damage and change the energetics of surfaces is believed to enhance mobilization of oil. They’re optimized for a given reservoir in the laboratory based on fluid-fluid and fluid-rock interactions. This includes adsorption (persistency), asphaltene wash-off, demulsification, drop size, and interfacial tension testing. We in turn label changes in injectivity of water as well as increases in oil production as indicators of success in core floods and pilots.
The above strategy has led to microemulsion optimization in Taylorton Bakken (which is more conventional) and Lower Shaunavon (which is more unconventional) in SE and SW Saskatchewan, Canada. These are characterized by changes in permeability, temperature, mineralogy (quartz vs calcite), oil (paraffinic vs asphaltenic) and water (high vs low salinity). This study demonstrates a beneficial core flood and pilot response in conventional reservoirs using microemulsions. What’s however interesting and noteworthy is that the core flood response is negligible in unconventionals (<5% incremental oil recovery) due in part to asphaltenes plating out on the core’s exterior surface during restoration of wettability, whereas the pilot response is quite positive.
The major highlight of this work is the need to address the discrepancy in core flood testing and pilot results in unconventional reservoirs. This is required before core flood testing can be used as a reliable screening tool for unconventional reservoirs. We’ve furthermore demonstrated the beneficial impact of microemulsions in both conventional and unconventional reservoirs as well as the need for optimization based on fluid-fluid and fluid-rock interactions.
We present a CT coreflood study of foam flow with two representative oils: hexadecane C16 (benign to foam) and a mixture of 80 wt% C16 and 20 wt% oleic acid (OA) (very harmful to foam). The purpose is to understand the transient dynamics of foam, both generated in-situ and pre-generated, as a function of oil saturation and type. Foam dynamics with oil (generation and propagation) are quantified through sectional pressure-drop measurements. Dual-energy CT imaging monitors phase saturation distributions during the corefloods. With C16, injection with and without pre-generation of foam exhibits similar transient behavior: strong foam moves quickly from upstream to downstream and creates an oil bank. In contrast, with 20 wt% OA, pre-generation of foam gives very different results from co-injection, suggesting that harmful oils affect foam generation and propagation differently. Without pre-generation, initial strong-foam generation is very difficult even at residual oil saturation about 0.1; the generation finally starts from the outlet (a likely result of the capillary-end effect). This strong-foam state propagates backwards against flow and very slowly. The cause of backward propagation is unclear yet. However, pre-generated foam shows two stages of propagation, both from the inlet to outlet. First, weak foam displaces most of the oil, followed by a propagation of stronger foam at lower oil saturation. Implicit-texture foam models for enhanced oil recovery cannot distinguish the different results between the two types of foam injection with very harmful oils. This is because these models do not distinguish between pre-generation and co-injection of gas and surfactant solution.
The simulation of the In Situ Combustion (ISC) process is a very challenging process due to the complexity and nonlinear nature of the problem. In this work, we propose an efficient technique to simulate experimental procedures for the ISC process including heterogeneity. The effects of permeability on mass flow and heat transfer were studied through a series of numerical frameworks. Different approaches to model the reactions occurring during combustion were attempted and simulation results were validated using experimental results. We focus on two different key areas: the integration of chemical reaction kinetics obtained through kinetic cell experiments, and the analysis of efficient simulations of combustion tube experiments that account for the flow element. After establishing a robust framework that accurately matches lab-scale results, combustion tube simulation results using a commercial simulator were analyzed to corroborate conclusions. Through observing the propagation of the combustion front and the oil bank in heterogeneous zones, assessments around the effects of permeability on the ISC process were performed. This work provides valuable information that would be instrumental in understanding experimental behavior of in-situ combustion and upgrading results to field scale after matching numerical results with experimental data collected in our future work.