Wang, Kun (Department of Chemical and Petroleum Engineering, University of Calgary) | Liu, Hui (Department of Chemical and Petroleum Engineering, University of Calgary) | Luo, Jia (Department of Chemical and Petroleum Engineering, University of Calgary) | Chen, Zhangxin (Department of Chemical and Petroleum Engineering, University of Calgary)
Unconventional petroleum reservoirs, such as shale gas and tight oil reservoirs, have changed the entire energy equation in the world. An accurate and efficient reservoir simulator is essential for the development and management of these reservoirs and the optimization of their production schedules. However, the gas storage and transport mechanisms in ultra-tight matrix, including gas adsorption/desorption, non-Darcy flow, and surface diffusion, are different from those in conventional petroleum reservoirs. In addition, hydraulic fracturing techniques are often required to achieve their economical production, which leads to existence of complex fracture networks in the unconventional reservoirs. These features of unconventional reservoirs make their accurate numerical simulations a big challenge. In this paper, we develop a simulator for fractured unconventional reservoirs, which takes the specific gas storage and transport mechanisms into consideration, employs a multiple interacting continua (MINC) model to handle well connected natural fractures, utilizes an embedded discrete fracture model to simulate large-scale disconnected hydraulic fractures, and uses a coupled model to efficiently describe multi-scale fractures with irregular geometries. To reduce the computational time, parallel computing techniques are also employed, with which large-scale reservoir simulation cases can be finished in practical time. From the numerical experiments, we can see that reasonable physical phenomena is captured and accurate predictions are performed by this simulator.
Yang, Min (University of Calgary) | Harding, Thomas G. (Nexen Energy ULC) | Chen, Zhangxin (University of Calgary) | Yu, Kuizheng (University of Calgary) | Liu, Hui (University of Calgary) | Yang, Bo (University of Calgary) | He, Ruijian (University of Calgary)
Steam injection is a widely used thermal technology to recover heavy oil and oil sands resources, while high operating costs have made it vulnerable to low crude oil prices. In-Situ Combustion (ISC) provides an alternative to steam injection with the advantage of low operating costs and high energy efficiency. Hybrid steam and ISC has great potential in oil sands recovery because it combines the advantages of both steam injection and ISC. Before design of this hybrid process, it is important to understand the displacement mechanisms during this hybrid process.
In this study, numerical simulation has been performed to investigate the performance of co-injection of an air and steam process at the experimental scale. A three-dimensional radial numerical model has been developed using CMG STARS to simulate a steam flood test and a combustion tube test. The co-injection of enriched air and steam was performed after a period of hot water flooding in the combustion tube test. Simulated temperature profiles and combustion front velocities were matched with experimental measured results, indicating that the high temeprautre oxidation (HTO) reactions were captured in the simulation. In order to understand displacement mechnisms, simulation results obtained from both tests have been compared and analyzed, including temperature profiles, a steam front velocity, residual oil saturation, and oil recovery.
It is found that co-injection of steam and enriched air has the potential to improve oil recovery. An ultimate recovery factor of around 90% is achieved for the co-injection of the steam and enriched air process, while the recovery factor is around 60% for the steam flooding test. This is because ISC is able to recover residual oil left behind by the steam flooding. However, steam still plays a dominant role in displacement of bitumen. The steam front propagates faster than the combustion front. Also, the steam front travels faster with the presence of the combustion front, indicating that the combustion front behaves as a heat source for steam front propagation. This work greatly increases the understanding of displacement mechanisms in a hybrid steam and combustion process.
Liu, Hui (University of Calgary) | Wang, Kun (University of Calgary) | Yang, Bo (University of Calgary) | Yang, Min (University of Calgary) | He, Ruijian (University of Calgary) | Shen, Lihua (University of Calgary) | Zhong, He (University of Calgary) | Chen, Zhangxin (University of Calgary)
New reservoir simulators designed for parallel computers enable us to overcome performance limitations of workstations and personal computers and to simulate large-scale reservoir models with billions of grid cells. With development of parallel reservoir simulators, more complex physics and detailed models can be studied. The key to design efficient parallel reservoir simulators is not to improve the performance of individual CPUs drastically but to utilize the aggregation of computing power of all requested nodes through high speed networks. An ideal scenario is that when the number of MPI processors is doubled, the running time of parallel reservoir simulators is reduced by half. In real simulation, numerical difficulties and performance problems appear when the number of MPI processors grows due to the deteriorating linear solver efficiency and increasing communication overhead, which are determined by a grid distribution.
The goal of load balancing (grid partitioning) is to minimize overall computations and to make sure that all MPI processors have a similar workload. Geometric methods divide a grid by using a location of cells while topological methods work with connectivity of cells, which is generally described as a graph. The geometric methods are much faster than the topological methods. This paper introduces a Hilbert space-filling curve method. A space-filling curve is a continuous curve and defines a map between a onedimensional space and a multi-dimensional space. A Hilbert space-filling curve is one special space-filling curve discovered by Hilbert and has many useful characteristics, such as good locality, which means that two objects that are close to each other in a multi-dimensional space are also close to each other in a one dimensional space. This property can model communications in grid-based parallel applications. The idea of the Hilbert space-filling curve method is to map a computational domain into a one-dimensional space, partition the one-dimensional space to certain intervals, and assign all cells in a same interval to a MPI processor. To implement a dynamic load balancing method, we need a mapping kernel that converts high-dimensional coordinates to a scalar value, and an efficient one-dimensional partitioning module that divides a one-dimensional space and makes sure that all intervals have a similar workload.
The Hilbert space-filling curve method is compared with other load balancing methods, such as the K-way method from ParMETIS and other geometric methods from Zoltan. The results show that our Hilbert space-filling curve is much faster than graph methods. It also has good partition quality. This method has been applied to reservoir models with billions of grid cells and linear scalability has been obtained on many parallel computing systems.
Shale gas is a very important energy resource for humans in the 21st century. However, the mechanism underlying the transoport behavior of shale gas in nanopores (typically 1 nm to 100 nm) remains a huge challenge in industries, as well as in research. In this study, we investigated the free gas transport in nanopores of shale rocks by using the real gas equation of state (EOS) and elastic hard-sphere (HS) model. Excellent results were obtained from the validation of the real gas model on the basis of molecular simulation and experimental data. This paper discusses the following: (1) the model efficiently and reasonably describes the known gas transport behavior in nanopores by establishing the relationship among real gas effect, molecular interactions and collisions, and gas transport behavior; (2) the use of real gas HS EOS considers repulsion, which reduces Knudsen diffusion and laminar slip flow conductance. In addition, packing fraction in EOS provides minimum boundaries for Knudsen number and flow regime; (3) the molecule-wall collision is mainly dominated by pore diameter, and the intermolecular collision is mainly dominated by pressure in nanopores. Under 10 MPa, the molecule-wall collision dominates in nanopores. Otherwise, the intermolecular collision dominates; (4) the laminar slip flow conductance increases with the corresponding increase in strength of intermolecular collision. With increased strength in the molecule-wall collision, Knudsen diffusion conductance increases, thereby improving the transport efficiency, as shown by apparent permeability.
In the petroleum industry, accurately estimating wellbore heat loss in thermal recovery processes remains a critical problem. One difficulty lies in simulating heat transfer and fluid dynamics within wellbore annuli. A literature survey shows that the state-of-the-art thermal wellbore simulators use empirical correlations to calculate the heat loss through wellbore annuli. As more sophisticated wells have been drilled, there is a growing need for a more detailed wellbore annulus heat transfer model. In this study, a 2D transient mathematical model is proposed for the conjugate natural convection and radiation within wellbore annuli. The governing equations consist of a continuity equation, a vorticity transfer equation, an energy transport equation and a radiative transfer equation (RTE). A finite volume approach with a second-order upwinding scheme is implemented for discretization. Newton-Raphson iterations are deployed for linearization. The algorithm is validated by consistence in simulation results compared with benchmark numerical solutions with the Rayleigh number up to 107. Parameters such as an aspect ratio, a radius ratio and a conduction-to-radiation coefficient are examined. A case study on vacuum insulated tubing heat transfer using Marlin Well A-6 data demonstrates the merits of the developed program by the consistence of simulation results compared with field measurements.
Steam assisted gravity drainage (SAGD) is recognized as a profitable and stable approach to address the exploitation of heavy oil and oil sand resources. However, the efficiency of SAGD, a close relative of a sufficiently-expanded and uniformly-developed steam chamber, tends to be deteriorated by quick steam movement and high heterogeneity. Chemical additives and foam assisted SAGD (CAFA-SAGD) is a strategy proposed on this account. This study aims to analyze the mechanisms and phenomena involved.
The injection of chemical additives to promote in-situ foam generation reduces gas relative permeability by slow-moving and stagnant bubbles trapping. Also, lamella resists bubbles flow and increases apparent gas viscosity. The restriction of steam mobility thus favors a sufficiently-expanded steam chamber and the nitrogen co-injected to stabilize bubbles works as a separator between steam and overburden to reduce heat loss. Simultaneously, the interfacial tension reduction due to surfactants injection at a water/oil interface may influence phase behavior, which further leads to the solubilisation of residual oil. CAFA-SAGD is thus likely to increase heat efficiency and add oil output.
A homogeneous model is built to analyze CAFA-SAGD considering foam generation by snap-off and leave-behind, foam trapping in a porous medium and foam coalescence due to both the lack of surfactants and capillary suction. Besides, with the analysis of foam wall slip phenomena, a comprehensive foam property model is coupled to analyze shear thinning rheology and calculate lamella viscosity as a function of gas saturation and gas velocity. In addition, the influences generated by surfactant injection should be added. This study also develops an analytical FA-SAGD model based on Butler's finger rising model (1987) to show foam's effects on a steam chamber growth rate and shape. We derive the FA-SAGD model accounting for the retarded steam movement with higher steam viscosity and lower gas relative permeability. The foam viscosity is calculated as a function of gas saturation and a gas rate, and the modification of gas relative permeability is reflected with a higher gas residual saturation according to Bertin et al.'s foam property model (1998). After comparing, validating, and discussing the developed model against the SAGD model, we find that foam injection contributes to high production efficiency with less steam consumption. A lower steam mobility generated by stronger foam is more likely to have a lower SOR (steam-oil ratio).
The results agree well with the published high-temperature steam foam experiments and pilot tests. Strong bubbles accumulate along the boundary of a steam chamber to restrict steam movement, while weak foam fills inside the chamber to enhance steam trap, contributing to a higher oil recovery factor and lower SOR.
Zhong, He (Dept. of Chemical and Petroleum Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB) | Liu, Hui (Dept. of Chemical and Petroleum Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB) | Cui, Tao (State Key Laboratory of Scientific and Engineering Computing, Academy of Mathematics and Systems Science, Chinese Academy of Sciences) | Wang, Kun (Dept. of Chemical and Petroleum Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB) | Yang, Bo (Dept. of Chemical and Petroleum Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB) | Yang, Min (Dept. of Chemical and Petroleum Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB) | Chen, Zhangxin (Dept. of Chemical and Petroleum Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB)
This paper describes the algorithms and implementation of a parallel thermal reservoir simulator designed for heavy oil simulation using distributed-memory supercomputers that can solve prohibitive problems efficiently. The thermal simulator inherits the features of a sequential thermal simulator. The performance of supercomputers is proportional to the number of CPUs. As a result, thermal problems can be solved thousands of times faster using supercomputers. This parallel simulator is based on our in-house platform, which provides grid management, data management, linear solvers and a visualization module. The exchange of information between CPUs is achieved by using the message passing interface standard, MPI. Results indicate that this simulator exhibits excellent scalability on the IBM Blue Gene/Q system and is thousands of times faster than serial simulators on a workstation. The simulator is also capable of simulating models with billions of grid blocks and fine resolution results can be obtained.
Cui, Tao (State Key Laboratory of Scientific and Engineering Computing, Academy of Mathematics and Systems Science, Chinese Academy of Sciences) | Wang, Kun (University of Calgary) | Liu, Hui (University of Calgary) | Luo, Jia (University of Calgary) | Chen, Zhangxin (University of Calgary)
In this paper, the multi-stage preconditioners are modified and applied to dual-porosity/permeability (DPDK) model problems. Employed as the first step of the multi-stage preconditioning processes, two modified decoupling processes for DPDK problems are developed. In a DPDK model, mass transfer both between fractures and between matrices is allowed, which means that the pressure both in fractures and matrix behaves as an elliptic property, so it is natural to employ two preconditioning stages solving the fracture pressure system and the matrix pressure, respectively, which draws the first type of a multi-stage preconditioner in this paper. Since the transmisibility between fracture blocks is much higher than that between matrices, the elliptic property of the fracture pressure is much stronger. Hence, we remove the stage of solving the matrix pressure system in the second type of a multi-stage preconditioner. Moreover, an extra stage of the ILU preconditioning process is added to the above multi-stage preconditioners in order to improve their efficiency, which results in another two multi-stage preconditioners. Combination of the modified decoupling processes and four new multi-stage preconditioners are studied and compared by large-scale reservoir simulation problems. Based on these numerical experiments, the optimal method to solve the DPDK model problems is concluded.
Microseismic data are typically characterized as low S/N. The noise suppression or S/N enhancement is often desired to enhance the waveform quality for better processing results. We apply time-frequency denoising using a combination of an S transform and a continuous wavelet transform. A thresholding function is used to suppress the noise energy in the transform domain and the filtered waveforms are reconstructed. We show waveform examples for a set of downhole microseismic data from China. We find that with good S/N data, the used workflow suppresses the background noise efficiently while preserving the vector fidelity of signal waveform. However, when the S/N becomes very low (~1), part of the signal also gets suppressed along with noise energy.
Presentation Date: Tuesday, October 18, 2016
Start Time: 2:15:00 PM
Location: Lobby D/C
Presentation Type: POSTER
Wu, Keliu (University of Calgary) | Chen, Zhangxin (University of Calgary) | Xu, Jinze (University of Calgary) | Hu, Yuan (University of Calgary) | Li, Jing (China University of Petroleum) | Dong, Xiaohu (China University of Petroleum) | Liu, Yuxuan (Southwest Petroleum University) | Chen, Mingjun (Southwest Petroleum University)
Understanding and controlling flow of the water confined in nanopores has tremendous implications in theoretical studies and industrial applications. Here we propose a universal model for the confined water flow based on a conception of effective slip, which is linear sum of true slip, only depending on wettability, and apparent slip, caused by the spatial variation of the confined water viscosity as a function of wettability as well as nanopores dimension. Results by the model show that the flow capacity of the confined water is 10-1~107 times of those calculated by no slip Hagen-Poiseuille equation for nanopores with various wettability, in agreement with 47 different cases from the literature. This work may shed light on the controversy over the increase or decrease in flow capacity from the MD simulations and experiments, and guide to tailor the nanopores structure for modulating the confined water flow in many engineering fields, including nanomedicine, water purification, energy storage as well as the flowback of fracture fluid in petroleum industry.