Steam-Over-Solvent Injection In Fractured Reservoirs Research Articles

Solvent Selection Criteria and Optimal Application Conditions for Heavy-Oil/Bitumen Recovery at Elevated Temperatures: A Review and Comparative Analysis

Sole thermal or solvent methods for heavy-oil recovery are not effective enough to deliver cost efficient processes. Hybrid applications of those two techniques have been proposed to take advantage of each and a wide range of investigations have been recently performed focusing on extreme conditions such as bitumen containing sands and carbonates, deep reservoirs, and oil-wet fractured carbonates. What is critically important in these applications is to determine the best performing solvent for a particular application and optimal application conditions for a given solvent at high temperature conditions. In this study, the results from various reported works on the hybrid applications of thermal (mainly steam) and solvent methods were complied, analyzed, and compared. Attention was given to a comparative analysis of steam-over-solvent injection in fractured reservoirs (SOS-FR) method. Steam/solvent methods show a promising outcome in general, while specific modifications must be taken into account for different application situations. These were discussed and specified, especially from proper solvent type and optimal application conditions for alternate injection of steam and solvent in different reservoir types.

Experimental Analysis of Heavy-Oil Recovery by Alternate Injection of Steam and Solvent (Hydrocarbon/CO2) in Unconsolidated Sand Reservoirs

Summary This work examines the steam-over-solvent injection in fractured reservoirs (SOS-FR) method--which was originally suggested for heavy-oil/bitumen recovery from oil-wet fractured reservoirs—for unconsolidated sands containing heavy oil. One possible application of the method in such media is the post-cold-heavy-oil-production- with-sands (post-CHOPS) enhanced oil recovery (EOR) considering that the wormholes represent the high-permeability (“fractures”) medium while the unproduced original part of the reservoir is the matrix containing the essential portion of the oil. The methodology used in the experiments and the observations will also provide an insight into the applicability of this method in “homogeneous” oil sands producing under gravity drainage during the alternate injection of solvent and steam (or hot water). The SOS-FR method was initially proposed and tested using high-carbon-number (heptane and above) hydrocarbons for solvent at ambient pressure and temperatures lower than 90ºC for oil-wet consolidated sandstones and carbonates (Al-Bahlani and Babadagli 2008, 2009a; Naderi et al. 2013). Later, lower-carbon number (propane and butane) hydrocarbons were tested at higher pressures and temperatures for consolidated water-wet and oilwet sandstones and carbonates (Naderi and Babadagli 2012a). This study focuses on the unconsolidated sands (water-wet nature) and tests three different types of gases as solvent [propane, butane, and carbon dioxide (CO2)] at high-pressure and-temperature conditions (compatible with a typical heavy-oil-sand deposit in Canada). The use of CO2 as a solvent in this type of process was considered as a lower-cost alternative to more-expensive hydrocarbons and for its permanent-storage potential. Several issues are highly critical in this process. Like other hydrocarbon solvents used under nonisothermal conditions, the recovery process is highly sensitive to pressure and temperature because they determine the miscibility level. Also important is the capability of CO2 to extract matrix oil. Our earlier studies with light oil showed that heavier ends can be extracted if enough time is allowed for CO2 to interact with matrix oil (Trivedi and Babadagli 2009a, 2010). The same needs to be investigated for heavy oils. Another challenge is the inverse proportionality of CO2 solubility with temperature. Steam (or heating) is required to condition oil and decrease its viscosity before CO2 injection, but the temperature should be adjusted critically in order not to sacrifice the CO2 solubility of the oil. To clarify all these points and to determine the optimal application conditions (the duration of each cycle and the CO2 soaking time), we conducted a series of experiments by first soaking core samples saturated with heavy oil in steam, followed by CO2. In the third cycle, steam (or hot water) was injected again to produce upgraded oil in the matrix. The experiments were performed under static conditions (soaking sandpack samples in steam or CO2 chambers) at different temperatures and pressures to determine the optimal application conditions. A similar experimental protocol was followed using propane and butane, and the recovery potential of these hydrocarbon solvents was compared with that of CO2.

Large scale applicability of the steam-over-solvent injection in fractured reservoirs (SOS-FR) method: Optimal operating conditions through numerical simulation

Heavy oil reserves are considered to be the upcoming hydrocarbon resource. Yet, more efficient methods are needed as there are substantial economic and environmental drawbacks to the sole injection of steam and solvents. A combined application of these methods yielded promising results in the laboratory experiments. But optimal application conditions and cost lowering options need to be determined. Steam-over-solvent injection in fractured reservoirs (SOS-FR) is a recently proposed method, which consists of an alternate injection of steam and hydrocarbon solvents to improve oil recovery over steam injection and to accelerate the solvent retrieval rate. This method was suggested to take advantages of sole thermal and solvent recovery methods in a staged technique and also to reduce the drawbacks of such methods using a hybrid one. For simplicity, the initial tests were done for hot-water conditions instead of steam and liquid solvents (Al-Bahlani and Babadagli, 2008, Al-Bahlani and Babadagli, 2009a, Al-Bahlani and Babadagli, 2009b, Al-Bahlani and Babadagli, 2011b). In our modification to this method, we introduced CO2 as an alternative to hydrocarbon solvents for only one pressure and temperature condition (Naderi and Babadagli, 2012a, Naderi and Babadagli, 2012b). The initial results of this study showed a moderate recovery of 50% OOIP on average for unfavorable matrix conditions (oil wet). In the present study, the SOS-FR applications with CO2 were tested at various conditions numerically and with different timings to improve recovery. First, the effect of different parameters was studied to obtain the best match between the simulation and experimental results. This exercise not only provided data for field scale simulations (relative permeability and diffusion coefficients) but also clarified the impact of different rock and fluid properties on the mechanics of the proposed EOR technique. Finally, an optimization scheme was suggested for field scale applications. In this exercise, a field scale numerical model of experiments was performed based on an experimentally validated core scale model and the optimal conditions (solvent type, application pressure and temperature and duration of cycles) were determined to maximize the recovery.

Bitumen Recovery by the Steam-Over-Solvent Injection in Fractured Reservoirs (SOS-FR) Method: An Experimental Study on Grosmont Carbonates

We adapted the previously introduced SOS-FR (Steam-Over-Solvent Injection in Fractured Reservoirs) method and conducted 12 experiments using preserved core samples from the Grosmont formation. The method applied in this study is based on soaking rather than continuous injection. The samples were immersed in hot water (90 °C), first to mimic low-temperature presteaming to condition the reservoir for solvent injection. This was followed by a solvent soaking period under varying conditions (duration, solvent type, etc.). Heptane and the distillate obtained from a heavy oil upgrading facility were used as solvents. Finally, the core samples were soaked in hot water again. Oil recoveries varied between 40% and 90% OOIP, with a mean value of 68%. Asphaltene precipitation, as a percentage of original oil in place (OOIP), was measured between 6.5 wt % and 33 wt %. The oil recovery and asphaltene precipitation depended on the solvent type, the solvent exposure duration, the position of matrix rock (horizontal or vertical), and the duration and number of solvent/hot water cycles. Most importantly, the last phase (hot water immersion) yielded substantial recovery of solvent diffused into matrix oil by applying a temperature value close to the boiling point of the solvent. The solvent retrieval was extremely fast and varied between 62% and 82% of the solvent diffused into the core during solvent exposure. Experimental observations look promising for further applications, as indicated by the high recovery values. The important aspects are that the solvent from readily available distillates used for transportation of heavy oil are very responsive and the temperature requirement for final hot water injection applied to retrieve solvent was <100 °C. Solvent retrieval was extremely quick and reasonably high, which is more likely to make the process economical.

Optimization of Steam-Over-Solvent Injection in Fractured Reservoirs (SOS-FR) method using hybrid techniques: Testing cyclic injection case

Many processes and techniques have been proposed to improve the heavy oil recovery from fractured reservoirs. Such complex processes require careful design to achieve optimal efficiency with minimal costs and environmental impacts. Steam injection is one of the options for heavy-oil recovery from fractured reservoirs but significant steam requirement for effective matrix heating due to heterogeneous structure poses important challenges in terms of cost, water availability, and environment impacts due to water processing and steam generation. Al-Bahlani and Babadagli, 2008, Al-Bahlani and Babadagli, 2009a proposed a new process called Steam-Over-Solvent in Fractured Reservoirs (SOS-FR) by adding solvent component to minimize the heat needed. The SOS-FR technique consists of a heating phase using steam injection, subsequent solvent injection, and low temperature steam injection for solvent retrieval and additional oil recovery. Optimization of this process is a critical step to determine optimal injection (and soaking) schedules as the heterogeneous structure of this kind of reservoirs may easily yield an inefficient process due to high cost and excessive use of steam and solvent. In this study, we adopted a global optimization scheme, where genetic algorithm is integrated with orthogonal arrays and response surface proxies for better convergence behavior and higher computational efficiency, to optimize the SOS-FR process for cyclic injection option. The results show that one may be able to double the profit obtained with the benchmark model using the optimal injection scheme suggested by our optimization procedure. The results are valid for models with low fracture density; further work should be performed using models with high fracture density and that the fracture orientation is not in the direction of the injector to the producer.

Laboratory scale experimental analysis of Steam-Over-Solvent injection in Fractured Reservoirs (SOS-FR) for heavy-oil recovery

Heavy oil trapped in fractured carbonate reservoirs possesses a great challenge to the petroleum industry due to high oil viscosity, low matrix permeability, and unfavorable wettability of the matrix. Thermal recovery methods (mainly steam injection) show a promising way forward to unlock these reserves. Yet, previous experiences revealed that heating the matrix to drain heavy-oil by gravity is a slow and inefficient process due to low matrix recovery caused by unfavorable matrix properties (oil wetness and low permeability). Acceleration of matrix-fracture interaction by changing the matrix and oil properties could be possible by injecting the proper hydrocarbon solvent alternately with steam as reported in our earlier work. This process, called Steam-Over-Solvent injection in Fractured Reservoirs (SOS-FR), consists of several cycles, each having three phases: (1) steam/hot water injection; (2) solvent injection; and (3) steam/hot water injection.This paper reports a detailed experimental analysis of this new method. Static and dynamic tests were conducted by exposing heavy-oil saturated fractured rocks to hot water and solvent alternately. Oil-wet sandstone and carbonate samples were saturated with heavy-crude oil and tested against different solvents, namely heptane, kerosene, decane and light crude. Fractured cores were tested under dynamic conditions with different solvent injection rates to explore the rate dependency of the process. The physics of the injection rate and the role of asphaltene as a bi-product were examined and discussed. Understanding the physics of this new technique will contribute to the development of an alternative method at field conditions for unlocking trapped heavy matrix oil from oil-wet, fractured, and deep carbonate fields.

Steam-over-Solvent Injection in Fractured Reservoirs (SOS-FR) Technique as a New Approach for Heavy-Oil and Bitumen Recovery: An Overview of the Method

Heavy-oil recovery from tight naturally fractured carbonate reservoirs is a great challenge to the oil industry, yet no well-established recovery technique has been adopted by the oil industry. Steam-over-solvent injection in fractured reservoirs (SOS-FR) is a new technology proposed as an alternative method to the sole injection of steam or solvent, and this paper introduces this method through extensive experimental evidence and analysis. The method consists of three phases: (1) steam (or hot water), (2) solvent, and (3) steam (hot water) injection. Phase 1 produces heavy oil by thermal expansion and conditions the oil for phase 2, which is solvent injection. Phase 3 is applied mainly to retrieve the solvent. Several static experiments were conducted mainly to test four critical parameters: (1) wettability of the matrix, (2) solvent type, (3) initial water saturation, and (4) matrix boundary conditions. This was followed by several dynamic experiments, which were aimed at testing the effect of the solve...

Field scale applicability and efficiency analysis of Steam-Over-Solvent Injection in Fractured Reservoirs (SOS-FR) method for heavy oil recovery

Heavy oil recovery from fractured carbonates is a real challenge, yet no proven technology exists as an efficient solution. Reservoir heating is generally inevitable and steam injection is the only effective way to heat heavy-matrix oil in such reservoirs using the steam distributed through fracture network. We propose a new method minimizing heat needed for efficient heavy oil recovery from oil-wet fractured rocks by adding solvent component. Efficiency is a critical issue in this process due to potentially high cost of the process. A new technique we proposed previously called Steam-Over-Solvent in Fractured Reservoirs (SOS-FR) consists of a cyclic injection of steam and solvent in the following manner: Phase-1: Steam injection to heat up the matrix and recover oil mainly by thermal expansion, Phase-2: Solvent injection to produce matrix oil through diffusion–imbibition-drainage processes, and Phase-3: Steam injection to retrieve the injected solvent and recover more heavy oil. Laboratory scale static and dynamic experiments had shown that, under very unfavorable conditions (oil-wet matrix, 4000cp crude), oil recovery at the end of Phase-3 was around 85–90% OOIP with 80–85% solvent retrieval (Al-Bahlani and Babadagli, 2008, 2009a). In this paper, the experimental results obtained earlier were matched to a single matrix/single fracture numerical model and parameters needed for field scale simulation (matrix-fracture thermal diffusion, solvent diffusion and dispersion coefficients) were obtained (Al-Bahlani and Babadagli, 2009b). Using the data obtained through matching, field scale simulations were performed for efficiency analysis and to identify the optimal injection schemes (soaking time for cyclic and injection rate for continuous injection) and durations, and surface steam quality. Specific conclusions as to how to apply this technique efficiently in the field considering the cost of the process were reported.

Mechanics and Upscaling of Heavy Oil Bitumen Recovery by Steam-Over-Solvent Injection in Fractured Reservoirs Method

Summary Recently, the steam-over-solvent injection in fractured reservoirs (SOS-FR) method was proposed as a potential solution for efficient heavy-oil/bitumen recovery in oil-wet naturally fractured reservoirs. The method is based on initial injection steam (Phase 1), followed by solvent (Phase 2). In the third cycle (Phase 3), steam is injected again to recover more oil and retrieve the solvent. Solvent retrieval during the third cycle was observed to be fast if the temperature is at approximately the boiling point of the solvent. This process is controlled by efficient matrix recovery and the mechanics of the process need to be clarified to further determine the efficient application conditions for the given matrix and oil characteristics. Single-matrix behaviour during the process was numerically modelled for static conditions and the results were matched with the experimental observations. The physics of the recovery mechanism was analyzed through visual inspection of saturation and concentration profiles in each cycle. The major observation was the substantial effect of gravity in oil recovery when the matrix were exposed to solvent. Special attention was given to the solvent retrieval rate and amount in Phase 3 and the permeability reduction caused by asphaltene precipitation in Phase 2. This phenomenon was modelled using a permeability function changing with spatial coordinates and time (i.e., k =f (x ,y ,z ,t ). It was observed that permeability reduction caused by asphaltene precipitation is significant and needs to be taken into account in the modelling process. After showing the effect of the matrix size on the oil recovery and solvent retrieval, an upscaling analysis was performed. The log-log relationship between the time value to reach ultimate recovery and the matrix size yielded a straight-line relationship with a noninteger exponent less than two for all three phases of the process. The observed straight-line relationship (and the exponent values obtained) is highly encouraging to extend the study to obtain a universal scaling relationship.