• Energy Research

Abstract Solvent Aided-Steam Flooding (SA-SF) focuses on maximizing the oil production by reducing the economic and environmental challenges created by steam generation. However, the solvent selection is vital due to the interaction of solvents with asphaltenes. Moreover, the polar nature of asphaltenes also enables asphaltene-steam interaction which may result in emulsion formation. This study investigates solvent-asphaltene-steam interaction during SA-SF with low and high molecular weight asphaltene insoluble solvents. Two different solvents were tested; n-hexane (E1 and E4) and a commercial solvent (CS) (E2 and E5) with four flooding experiments; two miscible flooding (E1 and E2) and two SA-SF (E4 and E5) experiments. Results were compared with steam flooding (E3) experiment. The performance evaluation of different enhanced oil recovery methods was accomplished by comparing the oil recovery rates. The asphaltene content of produced oil samples was determined by standard methods. The asphaltene-steam interaction was analyzed with microscopic images, and the water content of produced oil samples was measured by Thermogravimetric Analysis (TGA). Even though similar cumulative oil productions were obtained by the end of E1 (n-hexane-flooding) and E2 (CS-flooding), the produced oil quality varied due to asphaltene and clay contents. While higher clay content was measured for E1, E2 had a lower quality, due to higher asphaltene contents. This finding is due to the heavy dearomatized hydrocarbons composition of the CS which ranges from C11 up to C16 and enables more asphaltene production. Even though, E5 yielded the highest liquid production among all experiments; the produced liquid was composed of emulsified oil. The solvent aided-steam flooding (SA-SF) experimental results, which have been conducted with n-hexane/steam (E4) and CS/steam (E5) injections, suggest that as the asphaltene content increases in produced oil samples, more hard-to-break emulsions are formed. The unusual stability of these emulsions can be attributed to the nature of the asphaltene present in the produced oil. From the results presented, it is recommended the use of lower carbon number solvents to leave the larger amounts of asphaltenes in the reservoirs. The solvents differed in their interactions with the asphaltenes present in the oil and with the steam that has a direct impact not only on the quantity of oil produced but the quality as well. Hence, the wise selection of the appropriate solvent cannot be ignored during solvent aided-steam flooding processes.

Abstract Solvent- Steam Assisted Gravity Drainage (S-SAGD) processes for bitumen extraction are proposed to reduce the environmental impact of steam injection. S-SAGD processes require more research due to the unknowns of solvent-bitumen interaction and the desire to reduce the cost of steam and solvent utilized. This study investigates propane-SAGD (P-SAGD) and propane-steam flooding (P-SF) performance for the recovery of a Canadian bitumen from Alberta with 9.6 API gravity, 290,500 cP viscosity (at 25 °C), and 21.7 wt% asphaltenes (n-pentane insoluble) content. Three two-dimensional SAGD experiments (one SAGD and two P-SAGD at two different propane doses) and three one-dimensional flooding experiments (propane, steam, and propane-steam) were conducted. By comparing 2D experiments with 1D, we were able to analyze the effect of continuous steam flow and steam chamber development on process performance in microscopic scale. Water and asphaltenes contents of produced oil were measured. It has been observed that the steam chamber development with propane coinjection enhanced the oil production, however, led to delay in oil production compared to the steam flooding case. Thus, we also tested first steam injection until achieving the communication between the injector and producer in SAGD configuration and then, switching to steam-propane coinjection. After allowing the steam-bitumen interaction first, propane injection did not result in severe water-in-oil emulsion formation. Moreover, lesser permeability reduction due to asphaltenes deposition was observed. The application of propane-SAGD as follow up to SAGD improved the process by the mobilization of trapped residual oil and enhanced the quality of produced oil by minimizing the formation of water-in-oil emulsion.

Abstract The numerical evaluation of dielectric heating in a heavy oil containing sand is presented using a shaped dipole antenna under static (no oil production) and dynamic (with oil production) conditions. The electromagnetic simulator AxREMS™ was coupled to the commercial reservoir simulator STARS™ to model RF heating using three different shaped antenna designs (Straight dipole, Concave, and Convex design). The static simulations showed that the Concave design offers more uniform radiation pattern and temperature profile than the Straight and Convex counterparts. A conceptual model with seven sands (over- and under-burden and five oil-containing sands) was utilized for the dynamic simulation of downhole RF dielectric heating. The results indicated that all the RF heating cases had accelerated oil production than that found for the Base Case (cold production). Modeling shows that peak production is increased if RF heating is initiated before the start of production. However, all cases studied converged to approximately equal cumulative incremental oil above the Base Case, after about 700 days after the initiation of RF heating.

Summary Physical and numerical simulations of subsurface upgrading by use of solvent deasphalting (SSU-SDA) at laboratory conditions will be presented with a heavy crude oil and propane as a solvent. In this work, 1D propane-flood experiments were performed in a live-crude-oil-saturated (8.8°API) sand at 120°F and 1,000 psi (7.58 MPa). The results showed oil recovery of 85 wt%, with increases of °API value up to 14°API for the produced crude oil. By use of laboratory-characterization data, a new asphaltene-precipitation model was developed that involves four pseudocomponents (deasphalted oil, heavy fraction, and soluble and solid asphaltenes) and three pseudochemical reactions to numerically simulate the laboratory experiments. [In this text, asphaltenes are the fraction of the crude oil that precipitates in paraffins (propane or heptane) and are soluble in aromatics or chlorine-containing solvents (CH2Cl2)]. History match showed very good agreement between the experimental and calculated oil and gas rates and cumulative oil. Also, reasonably good match between laboratory and theoretical °API value of the produced oils was found throughout the propane-flood experiments. By use of this model, a field-scale well pair in steam-assisted-gravity-drainage (SAGD) configuration was simulated for steam only and two steam/propane cases [10:1- and 1:1-vol% ratio, as measured by liquid volume of solvent per cold water equivalent (CWE) of steam] in a typical heavy-crude-oil reservoir. Results showed accelerated oil production and higher °API values of crude in the presence of propane in comparison with the steam-only case. For the 1:1 steam/propane case, the model predicted that the oil quality improved enough to make the oil transportable through a pipeline. This work finds that SSU-SDA continues to show promise as a viable oil-recovery and -upgrading process when the complex downhole physics is modeled. It is predicted that higher propane/steam ratios are needed during SSU-SDA compared with historical solvent-based enhanced-oil-recovery field pilots to capture both the oil-recovery and -upgrading benefits of this process.

Abstract An extra-heavy crude oil underground upgrading process is described which involves the downhole addition of a hydrogen donor additive under steam injection conditions (280–315°C and residence times of at least 24-h). Laboratory experiments showed a 4° increase in the API gravity (from 9 to 12°) of the upgraded product, a two-fold reduction in the viscosity and, an approximately 8% decrease in the asphaltene content with respect to the original crude. Further increases on the temperature led to products with improved properties reaching 15°API at 315°C. It was found that the presence of the natural formation (catalysts) and methane (natural gas) is necessary to enhance the properties of the upgraded crude oil. From GC and GC-MS results a reaction pathway is proposed that involves hydrogen transfers from tetralin to the extra-heavy crude oil resulting in the formation of 1,2-dihydronaphthalene. This compound is then transformed into naphthalene, further upgrading of crude oil through hydrogen donat...

Abstract The goal of solvent-steam-flooding is enhancing bitumen recovery by the simultaneous development of miscibility and reduction of oil viscosity. Though this strategy reduces greenhouse gas emissions, solvents are expensive. Additionally, bitumen recovery performance is affected by oil/solvent/clay/asphaltene interactions on pore-scale. The solvent dose and type must be optimized to maximize recovery, while minimizing environmental impacts and operational costs. To investigate the performance of solvent-steam processes, six core flooding experiments were conducted on a Canadian bitumen sample with 8.8°API and 54,000 cP. Propane-steam flooding was tested and compared to steam-flooding. The effect of reservoir clays is studied by repeating experiments without clay addition. Three propane flowrates were tested to examine the impact of solvent dosages. After the experiments, asphaltene, clay, viscosity, and water content in produced oil were measured. Propane-steam flooding increased recovery factors, accelerated production, and had higher quality oil than steam-flooding. The lowest propane flowrate (1:9 vol/vol) improved oil recovery by 23%, indicating that higher solvent concentration may not be needed. This work reveals that bitumen microscopic displacement efficiency is enhanced by up to 88% with the addition of solvent to steam flooding. It is proposed that pore-scale interactions, solvent flowrate, and clays also highly influence produced oil quality and oil recovery rates.

Abstract The goal of solvent-steam-flooding is enhancing bitumen displacement by the simultaneous development of solvent miscibility and reduction of oil viscosity. Though this strategy reduces greenhouse gas emissions, solvents are generally expensive. Additionally, bitumen recovery performance is affected by oil/solvent/clay/asphaltene interactions on the pore-scale level. Therefore, solvent dosage and type must be optimized to maximize recovery, while minimizing environmental impacts and operational costs. To investigate the performance of solvent-steam processes, six-core flooding experiments were conducted on a Canadian bitumen sample with 8.8°API and 54,000 cP at room temperature. Propane-steam flooding was tested and compared to steam-flooding. The effect of reservoir clays is studied by carrying out experiments in the presence and absent of clays. Three propane flow rates were tested to examine the impact of solvent dosages. After the experiments, asphaltene, clay, viscosity, and water contents in produced oil were measured. The results indicated that propane-steam flooding increased recovery factors, accelerated production, and had higher quality oil than steam-flooding. The lowest propane flow rate (1:9 v/v) improved oil recovery by 23%, indicating that higher solvent concentration may not be needed. This work reveals that bitumen microscopic displacement efficiency is enhanced by the addition of solvent to steam flooding. It is proposed that pore-scale interactions, solvent flow rate, and clays also highly influence produced oil quality and oil recovery rates.

Abstract An extra-heavy crude oil underground upgrading process is described which involves the downhole addition of a hydrogen donor additive (tetralin) under steam injection conditions. Using a batch laboratory reactor or a continuous bench scale plant (280-315°C and residence times between 24-64 h), physical simulation experiments showed an increase of at least 3° in API gravity of the treated Extra-Heavy Crude Oil, three-fold viscosity reduction and, approximately, 8% decrease in the asphaltene content with respect to the original crude. It was found that the presence of the natural formation (catalyst) and methane (natural gas) is necessary to enhance the properties of the upgraded crude oil. Compositional-thermal numerical simulations were carried out and the results showed a good match between the calculated and experimental °API gravities of the upgraded crude oil (average relative error 1-4%) for all conditions studied. Similar results were obtained with the asphaltene contents (14-23%), percentage of conversion of the >500°C fraction (12%) and tetralin (16-23%).