Downhole Steam Generation for Green Heavy Oil Recovery

The ultimate target of heavy oil recovery is to enhance oil mobility by transferring steam's thermal energy to the oil phase, incrementing its temperature, and reducing heavy oil's viscosity. While the various types of steam floods such as Cyclic Steam Injection (CSI) and Steam-Assisted Gravity Drainage (SAGD) are widely used worldwide, they have certain limitations that need further improvements. Notably, in surface steam generation systems, downhole steam quality is around 70% which means that 30% of latent heat is lost while steam travels from the surface to the pre-determined downhole location. Downhole steam generation (DHSG) can be a viable alternative for the surface steam injection in which steam will be generated downhole instead of on the surface. The asserted method presents significant benefits such as preventing steam quality loss, decreasing the environmental effects, and enhancing the heavy oil recovery by co-injecting the flue gas products such as CO2, and consequently, the economic outcomes will be increased. In this research, a comprehensive techno-economic case study has been conducted on a heavy oil reservoir to evaluate the economic and technical advantages of DHSG compared to surface steam generation. Various technical expenses and revenues such as investment costs, operating costs, royalties, and taxes have been considered in a simulation model in MATLAB. This DHSG feasibility assessment has been performed using data of a heavy oil reserve currently under steam flood. Results showed that DHSG could increase up to 50% economic and technical interest than conventional steam injection projects. One of the outstanding benefits of DHSG is the reduction of heat loss. Since steam is produced in-situ, either downhole or in the reservoir, no waste of heat occurs. Typically, most heat losses happen on surface lines and wellbore during steam injection from the surface, which accounts for approximately 32%. Thus, this issue is excluded using the DHSG method. The results of the recent effort fit well into the current industry's requirements. DHSG can (1) increase the rate of heavy oil production, (2) decrease the extra expenses, and (3) dwindle the environmental side effects of CO2 emission of surface steam generation. Compared with conventional thermal methods, in DHSG, the steam to oil ratio remains constant with depth change while the desired steam quality can be achieved at any location. The asserted benefits can ultimately optimize the steam injection with a significant reduction in UTC, hence, improved profitability.

A Dual-Directional Flow Control Device for Cyclic Steam Stimulation Applications

Summary Cyclic steam stimulation (CSS) is one the most effective thermal recovery methods. It is widely used as the primary thermal recovery method to recover heavy oil fields in the Middle East, the Asia-Pacific region, and North and South America. In this paper, a novel dual-directional flow control device (FCD) will be introduced. This FCD technology can allocate accurate steam outflow into the reservoir formation and improve steam quality during the steam injection period and can mitigate steam breakthrough from the neighboring wells during the production period. In the first section, we give a brief introduction on CSS and the main issues encountered in the field operation. A multidirectional flow control nozzle specifically designed for CSS application will be presented. Design philosophy in thermodynamics and hydrodynamics of the nozzle will be discussed in detail. Field performance results, computational fluid dynamics (CFD), and flow loop testing data will be shown to evaluate the performance of the technology. The application of the technology in steam-assisted thermal applications will be introduced. Well-known issues such as erosion and scaling on the FCD tools will be studied in the end.

How to Space SAGD Well Pairs for Optimal Performance

Steam-Assisted Gravity Drainage (SAGD) is a remarkably successful process for the tar sands (oil sands). Two closely spaced parallel horizontal wells, injector above the producer, form a SAGD well pair. Steam is injected to provide heat to the reservoir oil and mobilize it. The low viscosity oil drains down to the producer under the gravity effect. Parallel well pairs 1000 m long are utilized in the process, spaced 100 m apart horizontally almost in all projects. In this work, an analytical model for the SAGD process is introduced by coupling heat and fluid flow and constitutive equations. A moving boundary, counter-current flow approach is used for the steam chamber rise and subsequent sideways expansion. The model is unique because it assumes the steam injection rate is constant and it permits modeling of the late phase of SAGD when adjacent well pair interference occurs. This leads to a reduction in heat loss to the overburden and a decline in oil production rate. This study examines the question of optimal well pair spacing in relation to the formation thickness and in-place oil. The effect of other variables on SAGD performance is investigated. A case study was performed using Christina Lake oil sand properties to show how the project performance varies under different senerios involving well pair spacing, reservoir thickness, steam injection rate, and steam quality. Results show that, in evaluating a SAGD pad performance, as the spacing is increased, the cumulative oil production decreases, with a simultanous increase in the cumulative steam-oil ratio at the same steam injection rate. However, a smaller portion of injected heat is lost to the overburden. It is concluded that a smaller well spacing requires more wells to deplete the whole pad area. On the other hand, a larger pattern well spacing affects oil recovery and heat consumption. Different conclusions are derived for the same pattern well spacing value using a single well pair model and pattern well pair configuration. Results also show that SAGD well pair spacing can be increased with an increase in formation thickness. The computational procedure is simple and makes it possible to examine a series of options for well spacing for a given set of conditions. This study presents for the first time an analytical relation between SAGD pattern well pair spacing and oil recovery.

Efficient Water Softening for Avoidance of Scales in Heavy Oil Steam Floods

Pigging of Once Through Steam Generators (OTSGs) indicated various types of scales, the most predominant of these being silicates of hardness causing ions. It was noted that scaling propensity can potentially go up with higher Steam Quality (SQ) as the reject stream gets concentrated with ions. However, models suggested that there are benefits of higher SQ in enhancing fuel savings (8%) and electricity savings (2%) when SQ was increased by 20%. The challenges of higher SQ were noted in terms of increased scaling tendency and therefore the need for improved softening. In Field D, the service cycle, the backwash cycle, and the brining cycle were optimized leading to a gain in throughput and reduction in salt consumption. Service cycle improvement gained 30 % to 130 % in throughput between two regenerations, backwash cycle improvement by fluidizing the bed to nearly 35% helped gain 10% in throughput, and reduction of brining cycle from 75 minutes to 48 minutes helped reduce salt consumption by 56% without impacting the throughput. In Field B, a six month pilot revealed that shallow shell resins where ion-exchange is more efficient due to inert core (better intra particle diffusion control) can enhance the throughput by 30% - 80% and simultaneously reduce the number of regenerations by 15 – 30%. Resin fouling is still a major challenge to contend with as oil can foul the resin and throughput can decline by 0.5 – 3 folds. In a plant operation, where there are multiple softener and brine vessels, there is a need to optimize them as a system. Reliability, Availability, and Maintainability (RAM) Models are used in Field C to a) Address equipment configuration optimization with impact on capital capacity expansion project scope b) Understand how net softwater delivery capacity was affected by increases in inlet hardness and c) Assess through a comparison scenario, if the large cost of addressing the valve issue in an upstream nutshell filter was worth the lost production opportunity related to unplanned downtime.

A Dual-Directional Flow Control Device for Cyclic Steam Stimulation CSS Applications

Cyclic steam stimulation (CSS) is one the most effective thermal recovery methods. It is widely used as the primary thermal recovery method to recovery heavy oil fields in Middle East, Asia Pacific, North and South America. In this paper, a novel dual-directional flow control device (FCD) will be introduced. This FCD technology can allocate accurate steam outflow into the reservoir formation and improve steam quality during steam injection period and can mitigate steam breakthrough from the neighboring wells during production period. In the first section, we will give a brief introduction on CSS and the main issues encountered in the field operation. A multi-directional flow control nozzle specifically designed for CSS application will be presented. Design philosophy in thermodynamics and hydrodynamics of the nozzle will be discussed in detail. Field performance results, Computational Fluid Dynamics (CFD) and flow loop testing data will be shown to evaluate the performance of the technology. The application of the technology in steam assisted thermal applications will be introduced. Well-known issues such as erosion and scaling on the FCD tools will be studied in the end.

Managing Risks Associated With Turbine First Steam Admission Following Inadequate Boiler Cleaning

Unit 6 of the recently completed six-unit Medupi coal-fired power station was the first unit to go into commercial operation. Synchronisation of the generator to the transmission grid had occurred five months before commercial operation. Prior to the admission of first steam to the turbines, the boiler underwent a three stage cleaning process, which was performed by the boiler contractor, to ensure that debris left over in the boiler from construction was removed and to avoid damage to the turbine when steam was admitted. Steam blowing of the boiler was the penultimate stage of boiler cleaning and contractually the steam would have been deemed clean when the steam cleanliness acceptance criteria were met. The steam cleanliness acceptance criteria, which were set by the turbine contractor, relate to the number and size of indentations caused by particles striking a given area of each target plate situated in the temporary piping downstream of the inlet valves of the high pressure and intermediate pressure turbines. For each target plate, values were prescribed for these variables and for the flow conditions that should prevail in the pipe upstream. The boiler contractor had to meet these requirements. Unfortunately, there was a mismatch between the steam cleanliness requirements set by the turbine contractor and those included in the boiler contract. The less stringent steam cleanliness requirements set for the boiler contractor in the boiler contract meant that the boiler would not be adequately cleaned, from the point of view of the turbine contractor. The boiler contractor designed a temporary pipework system for the steam blow-through process that permitted steam to bypass the turbines and exhaust to the atmosphere through a silencer. During steam blowing, the prescribed pipe flow conditions for accepting the steam were not being met, even after a large number of blows had been conducted. Mathematical modelling of the process revealed that the required pipe flow conditions could not be attained at the intermediate pressure turbine inlet and as such, the steam blow-through pipework was inadequately sized. The solution was to redesign the temporary pipework, and manufacture and install a new system of pipework, all of which would have taken a couple of months. Business needs required an alternative solution, and so a decision had to be taken on the way forward. Engineering judgement, based on operating and maintenance experience with the current fleet, suggested that the steam was sufficiently clean to be admitted to the turbine, with little risk. Of the two feasible options available to the project team, admission of steam after a defined number of blows was accepted. Care had to be exercised to manage the risk that the potential turbine contractor non-compliance to any of the performance guarantee conditions could be blamed on poor steam quality. An analysis of the risks associated with this option was conducted and controls were adopted to mitigate the risks. Eventually, steam was admitted to the turbines. Subsequent inspections and tests conducted on the turbines indicated minimal damage and no loss of performance. This paper describes the Medupi Unit 6 steam blow-through problem and the analytical process that revealed the inadequacy of the blow-through pipework. It describes also the process of analysing the risks associated with admission of first steam to the turboset, the decision processes that were followed to admit the steam, and the process of managing the identified risks through the controls that were put in place.

Test Bench for Characterization and Design Against Steam Turbine Fouling

The fouling phenomenon addressed in this paper is related to the deposition within steam turbines of steam impurities and to the presence of solid debris, coming from upstream plant sections, that can create solid build-ups in stationary and moving parts inside the turbine. As a consequence, fouling causes unit efficiency decline but, in severe cases, it may also lead to sticking of moving components, such as valves, that may be critical in machine control and/or safety. Despite well-studied and well-considered in design and operation of large power utility plants, where steam quality is of primary importance for boilers, super-heaters, turbines and condensers, this subject is often overlooked in small power generation or industrial applications, where efficiency may be less critical but turbine availability is of paramount importance for plant operation (e.g. LNG plants). The steam fouling is a subject that, despite widely studied in the past, has been quite neglected in more recent years. This paper, with the aim of underlining the importance of fouling in the operation of turbines for industrial applications, starts with examples of field evidences of severe fouling. Then the design of a test bench for the experimental characterization of fouling rates and validation of turbine components, exposed to fouling conditions, is presented along with the description of the deposition models that were developed on the basis of the physical phenomena involved in the fouling process. This study addresses the main deposition physical principles and their implications in the thermodynamic design of the test bench, on the basis of the specific physical properties of the impurities of interest. To better match plant real cases, the contaminants tested included those which have been usually identified within the units during maintenance activities and for which specific limits are prescribed by OEMs. In the following section, details relevant to the main deposition mechanisms due to different geometries and flow-fields are discussed. The results obtained are qualitatively in line with literature and internal practices, yet, through the test activities, it has been possible to establish a quantitative relationship between the concentrations of each contaminant at inlet section and the different thermodynamic conditions along the test bench, so capturing the impact of solubility changes along with the steam expansion.

Effect of Steam Quality on Extra-Heavy Crude Oil Upgrading and Oil Recovery Assisted with PdO and NiO-Functionalized Al2O3 Nanoparticles

This work focuses on evaluating the effect of the steam quality on the upgrading and recovering extra-heavy crude oil in the presence and absence of two nanofluids. The nanofluids AlNi1 and AlNi1Pd1 consist of 500 mg·L−1 of alumina doped with 1.0% in mass fraction of Ni (AlNi1) and alumina doped with 1.0% in mass fraction of Ni and Pd (AlNi1Pd1), respectively, and 1000 mg·L−1 of tween 80 surfactant. Displacement tests are done in different stages, including (i) basic characterization, (ii) waterflooding, (iii) steam injection at 0.5 quality, (iv) steam injection at 1.0 quality, (v) batch injection of nanofluids, and (vi) steam injection after nanofluid injection at 0.5 and 1.0 qualities. The steam injection is realized at 210 °C, the reservoir temperature is fixed at 80 °C, and pore and overburden pressure at 1.03 MPa (150 psi) and 5.51 MPa (800 psi), respectively. After the steam injection at 0.5 and 1.0 quality, oil recovery is increased 3.0% and 7.0%, respectively, regarding the waterflooding stage, and no significant upgrade in crude oil is observed. Then, during the steam injection with nanoparticles, the AlNi1 and AlNi1Pd1 increase the oil recovery by 20.0% and 13.0% at 0.5 steam quality. Meanwhile, when steam is injected at 1.0 quality for both nanoparticles evaluated, no incremental oil is produced. The crude oil is highly upgraded for the AlNi1Pd1 system, reducing oil viscosity 99%, increasing the American Petroleum Institute (API)° from 6.9° to 13.3°, and reducing asphaltene content 50% at 0.5 quality. It is expected that this work will eventually help understand the appropriate conditions in which nanoparticles should be injected in a steam injection process to improve its efficiency in terms of oil recovery and crude oil quality.

Optimization of Cyclic Steam Stimulation Process Using Response Surface Methodology

Heavy oil has characteristics such as API gravity 10-20 and high viscosity (100-10,000 cp) at reservoir temperature. Several methods have been successfully applied to produce these reserves, such as cyclic steam stimulation (CSS). Cyclic steam stimulation is a thermal injection method that aims to heat the oil around production wells. This paper presents the investigation regarding CSS application in heavy oil using Response Surface Methodology. Several scenarios were done by varying the operating conditions to obtain the most realistic results and also evaluating the factors that most influence the success of CSS process. Optimization is performed to find the maximum recovery factor (RF) value and minimum steam oil cumulative ratio (CSOR). The operating parameters used are CSS cycle, steam injection rate, and steam quality. Then statistical modeling is carried out to test the most important parameters affecting RF and CSOR for 10 years. The simulation results show that the CSS cycle, steam injection rate, and steam quality affect the RF and CSOR. The maximum RF results with the minimum CSOR were obtained at 39 cycles, an injection rate of 300 bbl/day, and a steam quality of 0.9 with an RF and CSOR value is 24.102% and 3.5129 respectively.