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WHITEPAPERS & RESEARCH ARTICLES

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Jul 27,2015 On Fingering of Steam Chambers in Steam-Assisted Heavy Oil Recovery Oil sands reservoirs in Western Canada are among the largest petroleum accumulations in the world. Given the high viscosity of the oil, typically in the hundreds of thousands to millions of cP, these oils are recovered from the reservoir by using steam, which heats the oil to between 180 and 250°C that lowers its viscosity to less than 10 cP. The key issue faced by these recovery processes is steam conformance and its consequent their thermal efficiency and greenhouse gas emissions and water use. The worse the non-uniformities of the steam chamber, the greater the greenhouse gas emissions and water use per unit oil volume produced and the lower the economic viability of the recovery process itself. Ultimately, non-uniformities arise from instabilities of fluids in the porous media and the thermal efficiency is controlled by the efficiency of heat transfer at the steam-oil interface at the edge of the steam chamber. The fingering phenomenon seen at the edge of steam chamber has long been explained as the penetration of steam (water vapor) phase into the oil layer. Here, simulation results reveal that fingering taking place in the gas phase beyond the edge of the hot steam chamber in the gas zone is created due to solution gas exsolution. The results also suggest that non-ideal steam conformance may occur in perfectly homogeneous reservoirs.

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Jul 27,2015 Prediction of Steam to Oil Ratio of Steam-Assisted Gravity Drainage from Reservoir Characteristics Forecasts suggest that production of bitumen from oil sands reservoirs will increase by a factor of at least 2.5 times over roughly the next 15 years. Although a significant economic benefactor to the Canadian economy, there are challenges faced by oil sands operators with respect to greenhouse gas emissions and water consumption. For the Athabasca deposit, the current oil recovery process of choice is the Steam-Assisted Gravity Drainage (SAGD) method where high temperature and high pressure steam is injected into the oil sands formation. At present, there are more than ten SAGD operators in Alberta, Canada and results to date reveal that the geology of the reservoir impacts SAGD performance. Given the growth of the SAGD industry in Alberta, forecasting tools are required that can predict performance versus reservoir characteristics. Here, we present a neural network-based model to predict SOR in oil sands reservoirs by using log and core data to characterize the reservoir porosity, permeability, oil saturation, depth and thickness. Our analysis confirms that the lower the porosity, permeability, and oil saturation of the reservoir, the worse the performance of the operation. In other words, the lower the quality of the reservoir, the lower the oil rate, and the higher the steamto-oil ratio (SOR). Our analysis also shows that well performance (i.e., SOR), is predictable with a relatively high degree of accuracy (R2~0.80) using log and core data via a neural network model. These results imply that the depth of the reservoir, gamma ray readings, and permeability are the most important determinants of the variation in SOR.

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Jul 24,2015 Evaluation of Thermal Efficiency of the Pre-Heat Period in the SAGD Process for Different Completion Methods

In the Steam Assisted Gravity Drainage (SAGD) process, the pre-heat is a very important step in the successful development of the steam chamber. The pre-heat period lasts months and is deemed complete when the temperature between the injector and producer is high enough to establish hydraulic communication. A uniform pre-heat along the wellbore is crucial to achieve steam chamber conformance throughout the life of the well pair. The efficiency of the pre-heat can be affected by several factors, with completion type being one of the most important among them. The objective of this study is to evaluate the impact of this factor on thermal efficiency during the pre-heat phase of the SAGD process.

In this study, the completion practices in five major SAGD projects in Alberta, Canada (Suncor's Firebag and Mckay River, Cenovus' Christina Lake and Foster Creek, and ConocoPhillip's Surmont) were evaluated. The critical factor used to determine the efficiency of any completion type in the pre-heat process is the heat loss and heat exchange along the producer and injector wellbores and the completion components. This variation in thermal efficiency results from factors such as concentric versus eccentric dual tubing completion, and tubular size, length and configuration.

The results of the study provide a comparison of different completion practices in the five major SAGD operations in Canada. The simulation modeling of the process, along with field experience and observations, helped to understand the impact of counter-current heat exchange and heat loss in concentric versus eccentric completions. Also, the results were used to quantitatively evaluate the impact that vacuum insulated tubing has on delivering energy to the reservoir and its associated thermal efficiency during the pre-heat process.

This paper is aimed at providing a better understanding of the impact of different completion methods on thermal efficiency during the pre-heat period in the SAGD process. The study also incorporated actual field performance of the 5 major SAGD projects available in the public domain and AER reports.

Jul 24,2015 Design and Optimization of Orifice based Flow Control Devices in Steam Assisted Gravity Drainage: A Case Study

The classical SAGD (Steam Assisted Gravity Drainage) involves drilling wells in parallel horizontal pairs. Steam is injected into the upper well (injector) to heat the reservoir and mobilize bitumen/heavy oil so that it drains to the lower well (producer) and can be lifted to the surface. In this process, steam distribution in the injector and a sustainable liquid level above the producer are key to achieve steam chamber conformance. The completion designs of these wells are critical in order to achieve optimal bitumen/heavy oil recovery and steam chamber development1.

Orifice based Flow Control Devices (FCDs) are being used in the SAGD wells. The FCDs in the injector (Steam Splitters) are used to customize steam distribution along the well. The FCDs in the producer (Inflow Control Devices) are used to develop a uniform inflow along the horizontal wellbore.

In this paper, a method will be presented for determining the size and position of Steam Splitters and Inflow Control Devices. This method can be used for both simple and complex reservoirs containing geological heterogeneity, hydraulic barriers and baffles. The validation of the design by field data in a Case Study will also be presented. It is shown that using FCDs in the wellbores helps to improve conformance and performance of SAGD well pairs significantly.

Jul 20,2015 A New Approach for Designing Steam Splitters and Inflow Control Devices in Steam Assisted Gravity Drainage

The classical SAGD involves drilling wells in parallel horizontal pairs. Steam is injected into the upper well (injector) to heat the reservoir and mobilize bitumen so that it drains to the lower well (producer) and can be lifted to the surface. In this process, steam distribution in the injector and a sustainable liquid level above the producer are key to achieve steam chamber conformance. The completion designs of these wells are critical in order to achieve optimal bitumen recovery and steam chamber development.

Two common tools in SAGD wellbore completions are Steam Splitters and Inflow Control Devices. The Steam splitters are used to customize steam distribution in the injector. The Inflow Control Devices are used in the producer to develop a uniform inflow along the horizontal wellbore.

This paper presents a method for determining the size and position of Steam Splitters and Inflow Control Devices. This method can be used for both simple and complex reservoirs containing heterogeneous geology and hydraulic barriers and baffles.
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