Canada's oil sands are one of the world's largest hydrocarbon resources. The initial volume of crude bitumen in place is estimated to be approximately 260 billion cubic metres with 11 percent or 28 billion cubic metres recoverable under current economic conditions. Continually improving economics, bolstered by recent higher crude oil prices, has resulted in the International recognition of the vast potential of Canada's oil sands. Based on publicly announced development plans through to 2015, over C$60 billion could be invested in numerous projects to develop the oil sands.
Various factors have to be considered to select the proper cement for zonal isolation of thermal recovery heavy-oil wells. First the cement should be flexible enough to withstand the stresses which occur when casing expands during the heating up of the well. To reduce these stresses, the cement thermal expansion coefficient should be similar to the thermal expansion coefficient of the casing. Finally, cement mechanical properties should not degrade during the whole steam injection process, i.e. when it is subjected to extremely high temperatures (up to 350 degC) for extended periods of time.
Specifically in Canada, the majority of the steam injection wells are drilled in shallow sandstone formations. This requires the cement to have high flexibility to resist the stresses. Moreover, during steam injection, a reaction between the sandstone formation and the cement sheath may occur, impacting the cement matrix and hence changing its properties.
This paper describes the application of a new thermally responsive cement for zonal isolation of heavy oil wells in Canada. This system is designed to have excellent strength, flexibility and thermal properties even upon interaction with sandstone formations. It minimizes the mechanical stresses exerted on the cement sheath during steam injection, thus reducing the risk of loss of well integrity. The numerical simulations performed with these long-term material properties (six months of exposure to 350 degC) for typical Canadian heavy oil wells conditions predict reliable and durable zonal isolation under these extreme conditions. These simulation results are confirmed by several field applications in wells which have not leaked after months of steam injection.
Hydrogen sulfide (H2S) generated by aquathermolysis—a high-temperature reaction of condensed steam (water) with sulfur-bearing bitumen in the reservoir rock—may increase the risk of sulfide stress cracking (SSC) in cyclically steam stimulated (CSS) wells. In a given field, H2S levels and wellbore conditions vary significantly among wells and so do their SSC-susceptibility. Identifying the SSC-susceptible wells is important in terms of reducing SSC risk by allocating resources and implementing pro-active intervention measures to the SSC-susceptible wells. A comprehensive research program, with a dedicated instrumented CSS well as the centerpiece, has been undertaken by Imperial Oil Resources with the objectives of characterizing H2S evolution in the wellbore and developing a tool for identifying the SSC-susceptible wells. The research includes laboratory and field tests, and statistical, phase behaviour and kinetic modelling. The SSC-susceptible zone for Cold Lake CSS has been established from Cyclic Slow Strain Rate (CSSR) laboratory tests incorporating CSS fluid chemistry, stress-strain environments, casing metallurgy, and variable temperature and H2S partial pressure. A statistical logistic model matches the experimental CSSR data well. The instrumented well data validate the phase behavior model, which in turn explains the measured H2S profile in the wellbore. An aquathermolysis kinetic model has been developed for the instrumented well and validated with data from nine other CSS wells. The research has led to the development of an engineering tool for identifying the wells at the risk of falling into the SSC-susceptible zone.
This paper proposes a new methodology using condensation model to evaluate the early-period SAGD by interpreting the temperature falloff data in injector or producer obtained from fiber optics or thermal couples after the wells are shut-in. Based on the non-condensation model proposed before, the condensation model also assumes a circular hot-zone shape since in the early stage of SAGD operation, and characterize the system as composed of a steam-zone of steam temperature, a cold-zone of reservoir temperature and a transition-zone in between as the initial temperature distribution. Besides, the condensation model incorporates the effect of steam condensation on the condensation-front. The movement of steam condensation-front is calculated to account for the steam-zone shrinkage. Sensitivity analysis over this models indicates that the sizes of steam-zone, transition-zone and the observing location directly affect the temperature behavior at observation point. Synthetic case study shows that the temperature falloffs from condensation model and from simulation are in good agreement and suggests that condensation model can be used to estimate the chamber size at the early stage of SAGD. As is known, it is important to obtain an even steam chamber distribution along the horizontal wellbore to shorten the ramp-up time so that maximized economics can be achieved. In reality, the reservoir heterogeneity, the wellbore undulation and the operation condition make the steam chamber conformance impossible. Because of the ready-to-use temperature data and the semi-analytic solution, the condensation model proposed in this paper can provide quick and reliable estimation of the steam chamber size to help the engineers to monitor and optimize the chamber development thereafter.
Steam Assisted Gravity Drainage (SAGD) production is a challenging environment where the economics are driven by optimization of the steam injection and oil production. An accurate metering system coupled with downhole pump information is required as is the reduction in physical intervention and operating expenditures.
Suncor's Firebag team engaged themselves in this challenging endeavor over the last 4 years to build a strategy using multiphase flowmeter (MPFM) to (1) provide a compact and versatile solution for new wells, (2) comply with regulations, and (3) validate the metering performances of the MPFM against the conventional separator.
The goal of this paper is to address the learnings and challenges faced in the MPFM deployment under these high temperature and harsh line conditions. This knowledge sharing is expected to serve as a guideline for future users of this MPFM technology in SAGD applications particularly with Cold Weather Operations, Multiphase Sampling and High H2S environment, also considering Pressure-Volume-Temperature (PVT) Modeling.
From a practical point of view, the qualification, application and benefits of MPFMs in field conditions will be highlighted versus the conventional solution. A particular focus will be placed on the production optimization and reservoir management.
Additionally, the synergy between the downhole pump information and instantaneous MPFM flow rate measurements will be reviewed along with the positive impact on the production optimization. The benefit of the MPFM accuracy and continuous measurement is expected to improve the allocation factors applied to all wells and pads.
The Suffield Caen reservoir contains 17?API heavy oil and the pool has been under waterflooding since 1996 with water cut of 96%. Primary and secondary oil recovery is 15 ? 20% of OOIP. A major problem encountered in waterflood was poor sweep efficiency and high water cut caused by high water/oil mobility ratio, as water quickly broke through the reservoir owing to fingering effects. It is known that sweep efficiency during waterflood can be improved significantly by increasing the viscosity of injected water by use of polymer solution, thus generating a more favorable mobility ratio and enhancing oil recovery. The results of reservoir simulation studies suggested that polymer flood would achieve incremental recovery factor of 7 ? 12%, and coreflood results indicated that 29 ?32% of incremental recovery is achievable by 0.5 pore volume (PV) of polymer injection.
Core floods including polymer, surfactant/polymer(S/P) and alkali/surfactant/polymer (A/S/P) were conducted through lab experiments and eventually polymer flood was selected as a pilot project to improve oil recovery for the Caen reservoir on the basis of polymer, S/P and A/S/P core flood results and project economic evaluation.
Polymer injection started in the reservoir 15 months ago and a very positive response has been seen as oil cut has increased to 10% from 5% and oil production rose to 600 bbl/d from 400 bbl/d. Therefore, the polymer flood pilot project is continually implemented and the polymer flood is planned to extend to similar reservoirs in the Suffield area.
There is a large amount of conventional heavy oil resaves in the West Canada Basin, so far the primary recovery factor is only 10%, there is a big potential to enhance oil recovery by polymer flood. This polymer flood pilot project provides valuable experiences and guidance to field application.
Only 5 - 10% of the oil in Lloydminster heavy oil reservoirs is recovered during cold production with sand (CHOPS). Cyclic solvent injection (CSI) is the most promising post-CHOPS follow-up process. In CSI, a solvent mixture (e.g. methane-propane) is injected and allowed to soak into the reservoir before production begins (Figure 1). CSI has been focused on heavy oil recovery from post-CHOPS reservoirs that are too thin for an economic steam-based process. It has been piloted by NEXEN and by Husky and was a fundamental part of the $40 million Joint Implementation of Vapour Extraction (JIVE) solvent pilot program that ran from 2006-2010.
This paper describes field scale simulations of CSI performed with a comprehensive numerical model that uses "mass transfer?? rate equations to represent non-equilibrium solvent solubility behaviour i.e. there is a delay before the solvent reaches its equilibrium solubility in oil. The model contains mechanisms to consider foaming or to ignore it depending on the field behaviour. It has been used to match laboratory experiments, design CSI operating strategies, and to interpret CSI field pilot results.
The paper summarizes the impact on simulation predictions of post-CHOPS reservoir characterizations where the wormhole region was represented by one of the following five configurations: (1) an effective high permeability zone, (2) a dual permeability zone, (3) a dilated zone around the well, (4) wormholes (20 cm diameter spokes) extending from the well without branching, (5) wormholes extending from the well with branching from the main wormholes,. The different post-CHOPS configurations lead to dramatically different reservoir access for solvent and to different predictions of CSI performance.
The impacts of grid size, upscaling, well inflow parameter, solvent dissolution and exsolution rate constants, and injection strategy were examined. The assumption of instant equilibrium solubility resulted in a 23% reduction in oil production compared to when a delay in solvent dissolution and exsolution was allowed for. Increasing the grid block size by a factor of 9 reduced the predicted oil production five-fold. Assuming isothermal behaviour in the simulations decreased predicted oil production by 17%.
Ghoodjani, Eshragh (Sharif University of Technology) | Kharrat, Riaz (Petroleum University of Technology) | Vossoughi, Manouchehr (Sharif University of Technology) | Bolouri, Seyed Hamed (U Of Shahid Bahonar Kerman)
Heavy oil in Middle East fractured carbonate reservoirs account for 25-30% of the total oil in place in the region. Production of heavy oil from such reservoirs is thought to play an important role in the future of the ever-growing world's energy consumption in which Iran's recoverable heavy oil is more than 85 billion barrels. The offshore Ferdows field in Iran is reportedly on the order of 30 billion barrels of oil and holds perhaps the greatest promise to add significant future carbonate heavy oil production within the region.
With depletion of conventional petroleum reserves and increase of hydrocarbon fuel demand, there is no doubt that there will be a tremendous demand on the development of heavy oil reservoirs in the coming decades. Despite its strategic importance, recovery of heavy crude from fractured carbonate reservoirs has found limited applications due to the complexity of such reservoirs. As most of the oil is stored in matrix due to its higher storage capacity than fracture network, reservoir development plans will aim at maximizing the matrix oil recovery. For reservoirs with high recovery factor, minimizing matrix residual oil saturation is a critical issue to extend the life of the reservoir. For reservoirs with low recovery factor, accelerating the production rate is more vital. For each of these reservoir types, different Enhanced Oil Recovery (EOR) methods should be considered and implemented accordingly.
In this study, a comprehensive review is conducted to figure out the feasibility of heavy oil recovery from fractured carbonate reservoirs by use of Cyclic Steam Stimulation (CSS), Steam injection, In-Situ Combustion (ISC), Steam Assisted Gravity Drainage (SAGD), Vapor Extraction (VAPEX) and Expanding Solvent-Steam Assisted Gravity Drainage (ES-SAGD).
Carbonate reservoirs introduce great challenges due to their complex fabric nature (low matrix permeability, poor effective porosity, fractures) and unfavorable wettability. These challenges are further displayed when combined with increased depth and low grade oil (high density and viscosity). A huge amount of oil is contained in such reservoirs without any technological breakthrough for improving the recovery efficiently (Briggs et al. 1992).
Until recently, heavy oil reserves did not attract much interest. The lowest oil profitability, the low price of the oil barrel in the international market, the difficulties involved in its extraction and its refining, and the large amount of light and medium oils to be explored could not justify the investments. Maturity of light and medium oil fields and the significant increase in oil price placed that source of energy under a new perspective. It is possible to increase heavy oil recovery in some of these reservoirs with the help of enhanced oil recovery processes, thus enhancing oil field productivity and profitability. Screening criteria have been proposed for all enhanced oil recovery (EOR) methods by SPE (Taber et al. 1997) for conventional reservoirs.
The most proven approach to produce heavy-oil reservoirs is through thermal methods, specifically speaking steam injection. Yet, the typical reservoir engineering approach is based on mobility reduction by reducing oil viscosity through effective heating, and by producing oil through viscous and gravity displacement. In carbonate systems, which are fractured in general, introduce rock complexity at different scales, i.e., faults, fissures, micro fractures, vugs, poorly interconnected matrix pore structure, and unfavorable wettability are combined with high oil viscosity. Thus oil recovery from this type of reservoir becomes a real challenge and classic thermal application theories fail to define the process. Main drive mechanisms in fractured reservoirs are shown in Figure 1 (Taber et al. 1997, Farouq and Meldau 1983).
Thermal methods (steam injection or in-situ combustion) and non-thermal methods (VAPEX) may be cited as examples of such processes.
Phase behaviour of C3H8-n-C4H10-heavy oil systems at high pressures and elevated temperatures has been experimentally and theoretically investigated. Experimentally, a versatile pressure-volume-temperature (PVT) system is utilized to determine the liquid-vapour phase boundary (i.e., saturation pressure lines) and swelling factors of C3H8-n-C4H10-heavy oil systems with varying compositions at high pressures up to 5030 kPa and elevated temperatures up to 396.15 K. The viscosities of the
corresponding solvent(s)-saturated heavy oil systems are measured by using a customized-capillary viscometer at 298.85 K. Theoretically, the volume-translated Peng-Robinson equation of state (PR EOS) with a modified alpha function is used to
model the experimental phase behaviour of C3H8-n-C4H10-heavy oil systems. Two binary interaction coefficient (BIP) correlations, respectively developed for the C3H8-heavy oil system and n-C4H10-heavy oil system, are incorporated into the
volume-translated PR EOS model. The two BIP correlations together with the volume-translated PR EOS are found to be capable of predicting the phase behaviour of the C3H8-n-C4H10-heavy oil systems with a good accuracy. In addition, comparison of five commonly used mixing rules indicates that the Lobe's mixing rule is the most appropriate to predict the viscosity of heavy oil diluted by C3H8 and/or n-C4H10.
Mitigation of bitumen and asphaltene accretion to the drillstring and other drilling components has become an important task due to the increasing production of oil sands and heavy oil deposits. When drilling through oil sands or encountering a bituminous zone, numerous problems can occur due to the extreme adhesive nature of the bitumen. Drillstrings and other tubulars can become coated, causing stuck pipe and undesired nonproductive time (NPT). Surface equipment such as shaker screens, can become fouled, resulting in poor drilling fluid properties. Common methods to counter the adhesive nature of bitumen have involved solvation of the bitumen into the drilling fluid. However, these methods not only contaminate the drilling fluid (resulting in disposal concerns), but can also negatively affect the fluid's properties, such as rheology.
This field trial utilizes a water-based mud and examines the effectiveness of a new polymer additive to mitigate the adhesive nature of bitumen, thereby preventing the occurrence of wellbore accretion. The bituminous cuttings are rendered non-adhesive, transported by the drilling fluid to the surface, and separated by conventional solids control equipment. In this fashion, the drilling fluid properties are not altered, and the water-based mud can be disposed of without the environmental issues of a contaminated fluid. Field trials and lab results have shown that small additions of this bitumen stabilization polymer to water-based drilling fluid renders the bitumen non-adhesive. Field trials have been completed in northern Canada and show extremely positive results with this polymer additive. It was shown that when the tar sands interact with the polymer additive, the tar becomes non-adhesive, and remains non-adhesive following contact with aqueous solutions. By preventing the bitumen from solvating or dispersing into the drilling fluid, the bituminous cuttings can easily be surface-separated. Torque and drag issues commonly seen while drilling through oil sands were also alleviated with use of this polymer additive.
4D seismic imaging requires extensive time to setup, implement, and process to provide information on the progress of recovery efforts such as estimates of the size and shape of reservoirs and their internal artifacts. Conventional seismic imaging results in a resolution on the order of tens of meters. As an alternative, white noise reflection processes use sub-noise signals to image reservoirs and can potentially do this at scales below 1 meter.
Both simulations and lab experiments show that reflections from white noise processes can be used advantageously to localize discontinuities and track their movement through media. For example, for steam-based oil sands recovery processes, it is critical to have an understanding of the steam conformance to improve the efficiency of the recovery process. White noise signaling technologies can be used to monitor the spatial distribution of fluids e.g. a steam chamber interface, and objects e.g. shale layers and concretions, at higher frequencies resulting in finer resolution in real-time compared to conventional methods.
The results demonstrate that acquisition and ranging of discontinuities in the laboratory can be achieved at the centimeter scale. The methods are extended to concurrent use of multiple transducers to improve directionality and triangulation of discontinuities.