1,720,987 research outputs found
In-depth water simulation strategies
No full textIn-depth water diversion is a chemical EOR method that has been winning acceptance over the last years because of several reasons. One of them is the fact that sodium silicate, active component, is considered a green chemical. Moreover, this component has shown the ability to generate thermally activated plugs at far away distances from the wellbore improving oil recovery. This work aims to give further understanding of how to approach the simulation of silica gelation kinetics, by integrating experimental data to a novel simulation approach for this process and how it can be applied to industry needs. The simulations are performed using a thermal-compositional reactive formulation in Stanford’s Automatic Differentiation General Purpose Research Simulator (ADG- PRS) based on a fully implicit approach. The motivations for selecting this method is the strong coupling between chemical and flow variables linked to drastic changes in permeability profile and the absence of methods in literature addressing this subject consistently. The implementation of the silicates reaction assumes an oligomerization reaction through a fourth-order reaction rate describing the deposition of solid silicate along the reservoir. The methodology followed in this document is structured in three chapters: calibration and study of kinetics, comparison with a previous study and field applications. Validation of the model displays a match between core experiments and simulations. Results from this section suggest a strong dependence on upscaling of the reaction rate constant and encourage further research on this topic. Study of kinetics, from a simulation perspective, reveals that the process timescales and local domain play a major role in resolution. Numerical convergence of the solution was achieved for a two-meter grid along the flow direction and simulation timesteps below 1 day. Results from comparison with previous works show great differences in the formation of the in-depth silicate plug. The prescription of the equation as a solids deposition proposes more realistic results in terms of plug distribution and activation. Moreover, cumulative oil production improvements rounding 7% over a fields file, account for realistic figures. The application on channeled subsurface confirms the possibility of implementing the process on more realistic subsurface. A clear optimization of the water sweep around the plugged zones is evidently leading to improvements, rounding the percentage mentioned above. Contrary to expectations, after introducing a blockage, no major variation in flow towards producer’s perpendicular to the main channel are observed. In the geothermal applications, the generation of a plug helps to increase the thermal breakthrough time, extending the geothermal doublet lifetime. The overall process has proved to be sensitive to parameters such as silicate concentration in solution, the volume of a pre-flush batch and the volumes of silicate solution injected. These factors give room for optimization of the process for future studies
The effect of impurity of CO2 stream on enhanced gas dissolution
No full textOne of the methods of reducing the amount of CO2 in the air is CO2 sequestration by dissolving the gas underground in an aquifer. In practice,there will be impurity gases in the injected CO2 stream or in the aquifer, which influence the dissolution rate of the CO2 stream. This research aims at finding a method to evaluate and calculate this influence. We focused on H2S and CH4. We found that given the specific circumstances underground and with added impurity gases, it is advisable to use an Equation of State, for which we chose Peng-Robinson. For the first simulation with a large aquifer model, we were able to see the difference between a stream of pure CO2 and mixtures of CO2 with H2S and CH4 respectively. We observed that the gas stream with CH4 moved considerably faster along the aquifer than the streams of pure CO2 or CO2 mixed with H2S. On the other hand, we found that the dissolution rate was higher when H2S was present in the mixture. In the dissolution process, we see a large influence of instabilities on the dissolution rate as a result of density differences in the aquifer. However, the resolution of the large aquifer model did not allow to evaluate this influence sufficiently. In two consequent steps, we adapted our simulation model. First, we used a small scale model using only a fraction of the large aquifer model, thus considerably reducing the calculation time. Next, we increase the resolution of the small scale model. This higher resolution gave considerably more accurate results, reflecting the differences between the three cases and the influence of the instabilities in the aquifer. We concluded that the simulation based on the small scale and high resolution model yields accurate and reliable results. However, the calculated outcomes have to be corrected for the difference in boundary conditions between the large and small scale models.<br/
Multiphase flow in tight formations
No full textGiven the substantial growth of the shale industry over the last decade, understanding flow in confined spaces will play a primordial role in the future of the upstream petroleum sector. Most compositional simulators are designed for standard (unconfined) reservoirs. Additional physical phenomena occurring in confined spaces such as capillary pressure, diffusion and adsorption are not taken into account. Moreover, most studies conducted on this topic only focus on shale gas, without regards to the presence of a liquid phase. This thesis focuses on the effects of capillary pressure on a multiphase flow and describes the modified production profiles.Recent studies have shown that elevated capillary pressure in confined spaces modifies the phase behavior of the hydrocarbon mixture, namely causing a reduction of the bubble point, which in turn affects the oil density and viscosity. These modifications will alter well produc- tion dynamics.Standard compositional simulators couple a mass balance equation with conservation laws and thermodynamic equilibrium, which comes in the form of a nonlinear constraint describ- ing the equality of chemical potentials. This research work replaces the last condition with a modified K-value constraint. The K-value is simply the ratio of a component’s composition in its vapor phase to its liquid phase. The latter is specific to the pressure, temperature and the hydrocarbon sample’s molar composition; and is derived from equations of state (EOS) which are employed to describe the phase behavior of a system. Capillarity is introduced in the K-value by adding the Parachor model, which determines the interfacial tension and the Laplace equation to the EOS derivation.The modified K-values are incorporated into Stanford’s Automatic Differentiation General Purpose Research Simulator (ADGPRS) based on a fully implicit approach. Other necessary modifications were made to include the effects of heterogeneity in the system. Simulations were ran in both simple one-dimensional reservoirs and more complex fractured models de- picting fractured shale reservoirs and compared to the production results generated by stan- dard compositional model
Multiscale Reconstruction of Compositional Transport
No full textDesigning strategies for efficient oil production from reservoirs rely heavily on reservoir simulation studies, which in-turn is based on various nonlinear formulations. It is therefore very important to develop a robust simulation model that captures the flow of various components present in different phases and the associated thermodynamic and chemical interactions. A compositional formulation is a reliable option for understanding these complex subsurface processes. However, this type of model has a great computational cost, since the number of equations (nc) that needs to be solved in each grid block increases proportionally with the number of components employed.The solution of the multicomponent multiphase flow problem is obtained by solving the associated nonlinear governing equation describing the conservation of mass, thereby determining the pressure (P) and compositional changes (Z) of the system. On the other hand, an Equation of state (EoS) model is employed to describe the phase behavior of the system, which in turn is accomplished in two stages: Phase stability test - to identify the existence of number of phase in a particular grid cell, and Flash calculation - to determine the split fraction of components amongst the phases present. The aforesaid procedure is referred as the standard EoS based approach to solve compositional problem and they are generally arduous.In previous works, a compositional-space parameterization approach was proposed to speed up the phase-behavior calculations by replacing the flash calculation with interpolations in the parameter space of the problem. The phase behavior of gas-injection processes is predominantly controlled by the properties of the two key tie-lines that extend through the initial and the injection compositions, and hence it is convenient to parameterize the problem based on these two tie-lines. It has also been proven that the projection of composition solution onto the full tie-line space is invariant to the hydrodynamic property of the compositional system.Here we utilize this technique to develop a multiscale reconstruction of compositional transport. Two types of prolongation operators are defined based on the local saturation history, with each having different computational complexities. In the first stage, a fine scale prolongation operator is implemented on a modified conservation equation with the objective of reconstructing the leading and trailing shock positions in space. Once the position of shocks are identified, the solution lying in the regions outside the shock can be solved on a coarse-scale mesh, since the structure of the transport solution outside of the two-phase region is relatively simple. Later, the fine scale projection of this coarse solution is carried out using the constant prolongation operator. The solution for nc components lying in between leading and trailing shocks is reconstructed by solving just two equations. The proposed reconstruction strategy results in coarsening of the compositional problem, both in space and representation. By this way, the simulation time is appreciably reduced by several folds without significant loss in accuracy of the results. Also, the proposed multiscale technique is evaluated by comparing them with a suitable upscaling methodology, since they are generally characterized by an affable framework of implementation and one of the most widely sought out ways to enhance computational efficiency.Petroleum Engineering and Geo-science
Optimization Strategies of CO2 Injection for Sequestration and EOR
No full textThe current situation with green gas emission requires the development of low carbon energy solutions. However, a significant part of the modern energy industry still relies on fossil fuels. To combine these two contradictory targets, we investigate a strategy based on a combination of CO2 sequestration with Enhanced Oil Recovery (EOR) in the hydrocarbon reservoirs. In such technology, the development of miscibility is the most attractive strategy from both technological and economic aspects. Modeling of this process involves solving complex nonlinear problem describing compositional flow and transport in highly heterogeneous porous media. An accurate capture of the miscibility development usually requires an extensive number of components to be present in the compositional problem which makes simulation run-time prohibitive for optimization. Here, we apply a multi-scale reconstructing of compositional transport to the optimization of CO2 injection. In this approach, a restriction operator, based on the parametrization of injection and production tie-lines, is constructed following the fractional flow theory. This operator is tabulated as a function of pressure and pseudo-composition which then is used in the Operator-Based Linearization (OBL) framework for simulation. As a result, a pseudo two-component solution of the multidimensional problem will match the position of trailing and leading shocks of the original problem which helps to accurately predict phase distribution. Applying a simple prolongation operator, based on interpolation between injection and production compositions, a compositional solution with the correct reconstruction of two-phase region can be obtained.The reconstructed multicomponent solution can be used then as an effective proxy-model mimicking the behavior of the original multicomponent system. In this study, we use this proxy-model in the optimization procedure which helps to improve the performance of the simulation with the increasing intricacy of the reservoir model. In this work, the nonlinear constrained optimization function is applied to find optimal pressure values for CO2 injection process to acquire a highest Net Present Values (NPV). Starting with the limited number of the controls, the global extrema of the objective function can be determined from both full physics model and proxy model. The result shows that both models can converge to the similar extrema given various initial guesses. It is noting that for multicomponent system, the proxy model can also have salient accuracy to predict the NPV extrema compared with the original full model. As a result, the reconstructed proxy model can be significantly cheaper than a full conventional compositional model. An additional benefit of the proposed methodology is based on the fact that important technological features of CO2 injection process can be captured with lower degrees of freedom which accelerates the optimization process.Applied Earth Science
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Modelling of Near-Well Acidisation
No full textAcidisation is one of the oldest techniques for enhancing oil recovery, going back more than a 100 years ago. The accurate description of this physical and chemical phenomenon is not a straightforward task. The Darcy law, which is commonly used in continuum modelling at the macroscale, fails when the porosity approaches the unity due to a dissolution. In order to accurately capture the acidisation phenomenon, an upscaling of Navier-Stokes equations is done from pore scale to Darcy scale. The resulting equation is called the Darcy-Brinkman-Stokes (DBS) equation and the approach is called hybrid modelling. The hybrid modelling has the advantage of not having to deal with jumps in velocity and pressure as it makes these variables continuous without any jumps at the interfaces. The research presented here models the phenomenon using both the Darcy and DBS approaches to study the differences. A single phase injection model in 1-D is simulated to understand the flow dynamics and the chemical kinetics of a single wormhole in idealistic assumptions. To study different regimes of wormholes formation, the 2-D model, implemented in Stanford's Automatic Differentiation General Purpose Research Simulator (ADGPRS), was employed. The shape of wormholes is studied and is validated against the published results. The wormholes characteristics, obtained in both Darcy and DBS models, are defined as a function of breakthrough parameters and dimensionless variables. A convergence, sensitivity and performance analysis is performed for key parameters to fully describe and understand the differences in the 2-D solutions. Furthermore, the impact of co-injecting a gas phase namely CO_2 is simulated and compared with the single phase injection in both the models.Petroleum Engineering and Geo-science
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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