Co-injection of CO2 or light hydrocarbons with steam in the SAGD process may improve SAGD efficiency and lead to lower greenhouse gas emissions through reduced Steam Oil Ratios (SORs). Various additives are postulated to have differing effects on bitumen recovery, depending on the nature of the reservoir, the operating conditions, and the API gravity of the oil. A PVT study was conducted to investigate the phase behaviour of CO2-, C3-, and C4-bitumen systems at varying concentrations, representing the edge of a SAP steam chamber with the expected temperature range of 70°C to 160°C. A produced and dewatered bitumen sample was collected from the Cenovus Osprey Pilot in the Cold Lake oil sands region and characterized. Constant Composition Expansion (CCE) experiments were conducted on solvent-bitumen systems in the temperature range of 70°C to 160°C. Filtration tests were also conducted at high temperature and reservoir pressure to investigate the effect of solvent type and concentration on asphaltene precipitation. A Peng-Robinson Equation of State (PR-EOS) model was calibrated to measured data for CO2-, C3-, and C4-bitumen systems. Viscosity of the bitumen saturated with CO2, C3, and C4 was measured with an electromagnetic-based viscometer elevated temperatures. Phase equilibrium calculations were performed using the calibrated EOS to predict the solubility of the solvents in bitumen. A correlation was fitted to the measured viscosity data to predict the liquid phase viscosity as a function of solvent solubility and temperature for each solvent. From the CCE tests, two equilibrium phases (i.e., liquid and vapour) were observed for the C3- and CO2-bitumen systems. Three equilibrium phases were observed for the C4-bitumen system at high C4 concentrations. These three phases include a bitumen-rich heavy oil phase, a solvent-rich lighter oil phase, and a vapour phase. Due to the extracting/condensing mechanism and asphaltene precipitation, the bitumen-rich phase formed in C3-bitumen system was lighter than the one in C4-bitumen system. Filtration tests showed more asphaltene precipitation by C3 and C4 dissolution than CO2. Moreover, C3 has more potential for asphaltene precipitation than C4. Viscosity measurements showed that dissolution of C3 and C4 in bitumen resulted in greater viscosity reduction than CO2 dissolution. This difference was more pronounced at lower temperatures. The highest C4 solubility in bitumen and C4 potential for forming a C4-rich liquid phase showed stronger condensing and extracting effect of C4 than C3 and CO2 in solvent-bitumen interactions. Moreover, C4 lead to more bitumen swelling than C3 and CO2. EOS predictions and viscosity measurements indicated that increasing the solvent concentration in a solvent-bitumen system beyond a defined Threshold Solvent Concentration (TSC) has an insignificant effect on solvent solubility and bitumen viscosity reduction.

The SAGD process can be defined to have three sequential phases to its operating mode, namely: startup, SAGD mode and wind-down. The startup phase most commonly has the shortest operating period, yet it has significant influence on the success of the subsequent operating modes. Historically, there are two primary means to achieve startup of a SAGD well pair and are commonly referred to as circulation and bullheading. The circulation process was employed at the Grand Rapids SAGD Pilot on Well Pair 1 and Well Pair 2 in 2010 and 2012 respectively. The circulation process is complex to optimize from a heat transfer perspective. Parameters such as well length, tubular sizing, steam injection rates, steam injection pressures, steam blanketing, and reservoir dynamics all influence the performance of the process. Transient reservoir simulation models with fully coupled well and reservoir grids are required to effectively model the process, relying on key inputs from field data to calibrate models. Typically, the objectives of circulation are to achieve a uniform heating profile along the entire length of the lateral portion of the SAGD well pair and establish fluid transmissibility between the injector and producer. A study on startup methods was conducted with the intent of optimizing temperature conformance, thermal efficiency and circulation time. The study generated several alternative startup designs, many of which employ insulated tubing strings and varied operating conditions to optimize heat exchange and energy efficiency. A field based trial was conducted using the closed circuit startup design (Canadian patent pending) at the Grand Rapids SAGD Pilot in 2015. Results of the study and field trial suggest that the closed circuit design offers several advantages; it is a thermally efficient, able to operate at higher temperatures, can use less steam per well pair, is scalable up to 1,200 meter long laterals, and can achieve excellent thermal conformance during startup. The findings of this field based investigation add to the knowledge base related to startup techniques and well conformance. The closed circuit technology employed at the Grand Rapids SAGD Pilot is an innovative startup design that may be used in other heavy oil and oil sands reservoirs to enhance startup and promote recovery.

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Discover a Career The substantial reduction in global oil prices has put the oil and gas community in a challenging and yet vaguely familiar position. It is once again reminded of the effect oil and gas prices have on companies working to profitably exploit these resources. When there are changes in prices, reserves estimation can dictate the profitability an operator can ultimately obtain. Larry Mizzau, principal for reserves and resources governance at Cenovus Energy reflects on his 30-plus years of experience in the industry and shares his thoughts on how commodity prices impact operators, reserves consultants, and young professionals (YPs) looking to establish a career in reserves estimation. What is reserves estimation? Reserves estimation is a key step in understanding an oil and gas company’s resource base and the opportunities it affords. It is found at the crossroads between asset management and financial stewardship. It involves the estimation of remaining volumes of hydrocarbons economically recoverable from an oil and gas operator’s subsurface assets using current technology. Given that reserves exist deep in the ground, they cannot be determined with absolute certainty and, as such, can only be estimated. To assist investors in understanding this uncertainty, reserves estimates are typically determined at different confidence levels. In Canada and the United States, public operating companies must disclose an updated estimate of their remaining oil and gas reserves on a yearly basis as part of their yearend financial reporting. Specifically in Canada, operators are required to disclose assessments prepared or audited by independent qualified reserves evaluators (IQREs) who can be externally or internally retained by the company.