Retrograde Condensation Research Articles

Application of expert systems for accurate determination of dew-point pressure of gas condensate reservoirs

Dew-point pressure is a parameter that has a key role in development of gas condensate reservoirs. Dropping of reservoir pressure below the dew-point pressure results in a decrease in production because of near wellbore blockage. In addition, due to separation of liquids, the produced gas has fewer valuable components. This study tries to develop a dependable method based on machine learning to adequately predict this important parameter. The intelligent system used in this work is Radial Basis Function (RBF) network that is a very flexible tool for pattern recognition. This model was developed and tested using a total set of 562 experimental data point acquired from different retrograde gas condensate fluids covering a wide range of variables. To optimize the tuning parameters of the proposed model, genetic algorithm was incorporated. This study also presents a detailed comparison between the results predicted by the proposed RBF model and those of other universal empirical correlations and intelligent systems for estimation dew-point pressure. The results showed that the presented model is superior to the pervious classic correlations and also intelligent systems.

Towards complete phase diagrams of a holographic p-wave superconductor model

We study in detail the phase structure of a holographic p-wave superconductor model in a five dimensional Einstein-Maxwell-complex vector field theory with a negative cosmological constant. To construct complete phase diagrams of the model, we consider both the soliton and black hole backgrounds. In both two cases, there exist second order, first order and zeroth order phase transitions, and the so-called "retrograde condensation" also happens. In particular, in the soliton case with the mass of the vector field being beyond a certain critical value, we find a series of phase transitions happen such as "insulator/superconductor/insulator/superconductor", as the chemical potential continuously increases. We construct complete phase diagrams in terms of temperature and chemical potential and find some new phase boundaries.

Evolving predictive model to determine condensate-to-gas ratio in retrograded condensate gas reservoirs

Added values to project economy from condensate sales and gas deliverability loss due to condensate blockage are the distinctive differences between gas condensate and dry gas reservoirs. To estimate the added value, one needs to obtain condensate to gas ratio (CGR); however, this needs special pressure–volume–temperature (PVT) experimental study and field tests. In the absence of experimental studies during early period of field exploration, techniques which correlate such a parameter would be of interest for engineers. In this work, the developed model inspired from a new intelligent scheme known as “least square support vector machine (LSSVM)” to monitor condensate gas ratio (CGR) in retrograde condensate gas reservoirs. The proposed approach is conducted to the laboratorial data from Iranian oil fields and reported in literature has been implemented to mature and test this approach. The generated results from the LSSVM model were compared to the addressed real data and generated results of conventional correlation and fuzzy logic models. Making judgements between the generated outcomes of our model and the another course of action proves that the least square support vector machine model estimate condensate gas ratio more accurately in comparison with the conventional applied approaches. It worth mentioning that, least square support vector machine do not have any conceptual errors like as over-fitting issue while artificial neural networks suffer from many local minima solutions. Outcomes of this research could couple with the commercial production softwares for condensate gas reservoirs for different goals such as production optimization and facilitate design.

The Effect of Gas Injection on the Enhancement of Condensate Recovery in Gas Condensate Reservoirs: A Comparison Between a Synthetic Model and PVT Cell Results

Gas condensate reservoirs have complicated fluid flow and thermodynamic processes. As reservoir pressure decreased, the gas condensate system exhibits a dew point. As pressure is reduced, liquid condenses from the gas to form free liquid in the reservoir. This liquid phase develops with pressure reduction and the composition of gas phase is changing due to pressure reduction. The condensate is deposited at such low liquid saturation that is usually trapped by surface tension forces, is therefore immobile, and cannot be produced. Condensate liquid builds up near wellbore causing a reduction in gas permeability and gas productivity. In order to prevent the condensate formation in reservoir, different scenarios have been proposed in which the most important method is gas injection to maintain the pressure or to revaporize the condensed liquid. In other words, the injection of dry gas into a retrograde gas condensate reservoir helps in vaporizing the condensate and increases its dew point. This study prepared a comparison between gas injection scenarios in cells (PVT studies) and a synthetic model of the reservoir. The main goal of this work is to investigate the lean gas recycling into the PVT cell and the synthetic model to enhance condensate recovery. In this work, these subjects were studied: the effect of CO2, separator gas, and N2 on condensate recovery enhancement and comparison of these scenarios with CO2, separator gas, and N2 injection and discussion on why the results are different in these two approaches. This study shows that when CO2, separator gas, and N2 are injected in PVT cell, deduction of condensed liquid during the pressure reduction of simulated constant volume depletion test at different injection volumes related to CO2 is more than separator gas and separator gas scenario is more than N2. In other words CO2 is the most effective and N2 is the least effective scenarios in reduction of condensate in the simulated constant volume depletion. But in the synthetic model, the results are completely different with the simulated PVT cell. In the synthetic model, deduction of condensed liquid during the different injection volumes related to N2 is more than separator gas and separator gas scenario is more than CO2. In other words N2 is the most effective and CO2 is the least effective scenarios in reduction of condensate in the synthetic model. Based on the type of condensate deduction mechanism, the three mentioned gases presented different results. N2 acts as the best gas when the decrease of liquid dropout is aimed to evaporate existing since at the same injection rate for all injected gases, N2 has increased the reservoir pressure more than the other gases and this reservoir pressure increase causes more re-vaporization at the synthetic model. In fact, the injection gas affects the decrease of liquid dropout formation indirectly. But if the injection gas affects directly on the reservoir fluid, CO2 acts as the best injection gas regarding the reservoir composition change. In this mechanism, the injection gas affects the liquid dropout formation directly.

A holographic p-wave superconductor model

We study a holographic p-wave superconductor model in a four dimensional Einstein-Maxwell-complex vector field theory with a negative cosmological constant. The complex vector field is charged under the Maxwell field. We solve the full coupled equations of motion of the system and find black hole solutions with the vector hair. The vector hairy black hole solutions are dual to a thermal state with the U(1) symmetry as well as the spatial rotational symmetry breaking spontaneously. Depending on two parameters, the mass and charge of the vector field, we find a rich phase structure: zeroth order, first order and second order phase transitions can happen in this model. We also find "retrograde condensation" in which the hairy black hole solution exists only for the temperatures above a critical value with the free energy much larger than the black hole without hair. We construct the phase diagram for this system in terms of the temperature and charge of the vector field.

Gas wells chemical stimulation – experimental design and field optimization

Abstract Retrograde condensation in gas reservoirs leads to long-term loss of condensate and short-term liquid blocking, both of which cause a reduction in well productivity. The problem of loss of condensate was recognized long ago, while that of liquid blocking was not rigorously investigated until recently. Recent efforts have led to a better understanding of the liquid-blocking problem, and numerous approaches, with varying degrees of success, have been proposed to mitigate its effects. Based on the results of a large number of experimental measurements and a few reported field trials, near-wellbore chemical stimulation seems a viable solution to the liquid-blocking problem, though more successful field examples need to be reported for this technology to become a well-established and reliable practice for industry. The main characteristic of the treatment is its effectiveness in bonding to the rock surface and permanently altering its wettability toward non-wetting. Many difficulties arise when evaluating the possible chemicals available for this purpose, especially when the final objective is to design a field trial. A considerable number of papers have been published on the topic, but a publication that combines all the details is lacking. It is extremely important to know the physics behind this treatment approach and have a clear understanding of the key parameters profoundly affecting the outcome of evaluation and decision-making. Development of this knowledge will produce a better assessment of results and a thoughtful decision that reduces the risk of failure for field trials. This paper provides a stepwise procedure for correct evaluation and design of chemical treatment, starting with lab measurement designs and followed by simulation and economic optimization, all of which will help save time, effort, and money. Additionally, this paper highlights the necessary details that should be considered at each stage.

Research on a Computational Method for Reservoir Pressure of a Water-Drive Condensate Gas Reservoir

Reservoir pressure of condensate gas reservoir is an indispensable parameter for calculation of gas reserves, gas well productivity evaluation, dynamic analysis, and evaluation of anticondensate. The water-drive condensate gas reservoir is ranked among the most complex types during development. In the development process, reservoir pressure declines, condensate oil dropouts, and content of water vapor in condensate gas increases, while edge water invades continuously, thus accurate calculation and prediction of reservoir pressure is particularly difficult and important. Calculation of retrograde gas condensate influenced by porous media adsorption and capillary pressure, and water vapor content in condensate gas tested under different pressure, according to material balance principle, material balance equation of water-drive condensate gas reservoir is established by consideration of absorption in porous media, capillary pressure and water vapor as well, and finally reservoir pressure at any time during production could be computed by iteration. Case study shows that the reservoir pressure calculated by this method gets much closer to actual reservoir pressure and it finally shrinks the workload in field testing and brings more convenience to scientific research and production management.

Toward a predictive model for estimating dew point pressure in gas condensate systems

Dew-point pressure is one of the most important quantities for characterizing and successful prediction of the future performance of gas condensate reservoirs. The objective of this study is to present a reliable, computer-based predictive model for prediction of dew-point pressure in gas condensate reservoirs. An intelligent approach based on least square support vector machine (LSSVM) modeling was developed for this purpose. To this end, the model was developed and tested using a total set of 562 experimental data points from different retrograde gas condensate fluids covering a wide range of variables. Coupled simulated annealing (CSA) was employed for optimization of hyper-parameters of the model. The results showed that the developed model significantly outperforms all the existing methods and provide predictions in acceptable agreement with experimental data. In addition, it is shown that the proposed model is capable of simulating the actual physical trend of the dew-point pressure versus temperature for a constant composition fluid on the phase envelope.

Methanol treatment in gas condensate reservoirs: A modeling and experimental study

Well productivity in gas condensate reservoirs is reduced by condensate blockage when the bottom-hole pressure drops below dew point pressure. The present experimental study on limestone cores shows that the relative permeability of gas decreases due to liquid blockage; furthermore, methanol has proven effective in the removal of condensate and restoration of gas relative permeability. In this research, the decrease in gas relative permeability caused by condensate banking and the effect of methanol treatment on condensate-blocked rocks was simulated using the cubic-plus-association (CPA) equation of state. The CPA equation of state was applied to the modeling of two-phase flows through cores for methanol–hydrocarbon mixtures due to charge transfer and hydrogen bonding, both of which may strongly affect the thermodynamic properties of such mixtures. Differential equations were solved by means of the orthogonal collocation method, a method particularly attractive for solving nonlinear problems. The modeling results confirm the experimental results, and both methods indicate that significant productivity loss can occur in retrograde gas condensate reservoirs when the flowing bottom-hole pressure falls below dew point pressure. Moreover, the results show that methanol treatment can improve gas relative permeability by a factor of about 1.3–1.6. These results may help reservoir engineers and specialists to restore the lost productivity of gas condensate.

A Dew Point Pressure Model for Gas Condensate Reservoirs Based on an Artificial Neural Network

Dew point pressure (DPP) is one of the most important parameters to characterize gas condensate reservoirs. Experimental determination of DPP in a window pressure-volume-temperature cell is often difficult especially in case of lean retrograde gas condensate. Therefore, searching for fast and robust algorithms for determination of DPP is usually needed. This paper presents a new approach based on artificial neural network (ANN) to determine DPP. The back-propagation learning algorithms were used in the network as the best approach. Then equations for DPP prediction by using weights of the network were generated. With the obtained correlation, the user may use such results without a running the ANN software. Consequently, this new model is compared with results obtained using other conventional models to make evaluation among different techniques. The results show that the neural model can be applied effectively and afford high accuracy and dependability for DPP forecasting for the wide range of gas properties and reservoir temperatures.

Thermodynamic Behavior of Hydrogen Binary Systems with Critical Curve Divergence and Retrograde Condensation

In binary systems of hydrogen and hydrocarbons, the fluid-phase thermodynamic behavior is unique in having the divergence of the critical curves to a high pressure region. The thermodynamic properties of the binary systems including hydrogen with methane, ethane, propane, and carbon dioxide were calculated from a Peng-Robinson equation of state (PR EOS). The mixing parameter of the present EOS has a functional form of temperature generalized by the critical temperatures of the hydrocarbons and carbon dioxide. Based on the corresponding states principle, the coefficients of the parameter were determined with a non-linear least squares fitting to the experimental critical points of the mixtures. The developed PR EOS shows good agreement with the experimental data of not only the critical points but also the phase equilibria. In the hydrogen binary systems, retrograde condensation is expected. The volumetric and enthalpy changes in this process were simulated for a hydrogen + carbon dioxide mixture of 0.55 mole fraction using the PR EOS at 270 K.

Case Studies Examine Exploitation Strategies for Development of Mature Gas and Oil Fields

This article, written by Editorial Manager Adam Wilson, contains highlights of paper OTC 23373, ’Exploitation Strategy in the Development of Mature Gas and Oil Fields: Case Study,’ by Gina Vega Riveros, Reservoir Consultant, and Emad Yehya, Smoothwell Oil Services, prepared for the 2012 Offshore Technology Conference, Houston, 30 April-3 May. The paper has not been peer reviewed. Copyright 2012 Offshore Technology Conference. Reproduced by permission. Two case studies examine the creation of strategies for the development of mature gas/condensate and oil fields. For the gas/condensate field, the integration of geologic, seismic, production, and reservoir data identified new opportunities for drilling. For the oilfield case study, it is clear that the strategy of exploitation can be improved. According to study results, the oil and gas condensate in place have been increased by 9% and 22%, respectively, compared with the official reserves estimates. Gas/Condensate Case Study Geologic Framework. The gas/condensate reservoirs are in the Roble, San Joaquin, and Guario fields, approximately 11 km southwest of Anaco, Venezuela. The geological model in the Guario 3 reservoir allowed for the integration of four reservoirs as a unique hydraulic unit (Fig. 1). Geologically, the study area is within the greater Oficina area, on the south flank of the Eastern Venezuela basin. The Merecure formation is Oligocene to early Miocene and was deposited in a transitional environment, yielding sandstones with good lateral extension. Petrophysics. In Guario 3, ME-G and ME-H sands have an average effective porosity of 14%. Permeability ranges from 20 md to more than 70 md. The water resistivity of 0.1 Ω·m, cementation exponent of 2.00, saturation exponent of 2.00, and shale volume cutoff of 40% were obtained from field data. Both ME-G and ME-H sands showed similar petrophysical properties. Reservoir Properties. The northwest-ern crest of the Guario 3 reservoir is defined as gas/condensate crude. The eastern part contains a volatile zone of medium gravity with a high concentration of paraffin. The integrated static and dynamic models validated the existence of an areal and vertical communication of four reservoirs into a unique reservoir named Guario 3 (G-3). Geochemical Study. To verify vertical and lateral reservoir communication between ME-G and ME-H sands, gas chromatographic correlations of samples from wells in different reservoirs were used to establish a clear vision about fluid communication. Correlations for Predicting Gas/ Condensate Reservoirs. Many empirical correlations have been reviewed in the literature, and they take into account retrograde condensate. The average ranges for applying the correlations and the equations used can be found in the complete paper. Using the correlations, the original gas condensate in place was 1226.84 billion scf, which was considered satisfactory in comparison with the volumetric method of 1267.37 billion scf.

Energy Control in the Depletion of Gas Condensate Reservoirs with Different Permeabilities

Energy control (i. e. pressure control) has an obvious effect on development effect in the depletion of gas condensate reservoir. Phase change behavior and characteristics of the relative pemeability in gas condensate reservoirs were displayed in this paper, then pressure and condensate distribution were showed through reservoir simulation. Finally, the influence of the pressure drop on condensate distribution and condensate oil production in gas condensate reservoirs with different permeabilities was studied. Results show that: First, in high / moderate permeability gas condensate reservoirs, the pressure and the condensate blocking will extend to further reservoir, while the pressure and condensate just appear in the vicinity of wellbore in low permeability gas condensate reservoirs. Second, the influence of pressure drop on condensate distribution in high permeability gas condensate reservoirs is obvious, the condensate blocking extends with the increasing of the pressure drop, and condensate extent can be controlled by optimizing a rational pressure drop, while the influence is inconspicuous in low permeability gas condensate reservoirs. Third, the influence of pressure drop on condensate oil production in high / moderate permeability gas condensate reservoirs is conspicuous, a rational pressure drop exists, while the influence is indistinct in low permeability or tight gas condensate reservoirs, before the retrograde condensation, a low pressure drop should be adopted in a long term until the bottom hole flowing pressure drops below the dew point pressure, when the condensate blocking forms, well stimulation is advised before developing by pressure control.

Mathematical Model for Condensate Gas Flow in Porous Media with Phase Change

The retrograde condensation occurs in the condensate gas reservoir when the formation pressure is under dew point. The condensate appears in the formation with phase change in the process of condensate gas flowing in porous media, which change the temperature field and distribution of fluid pressure and affect flow rules of condensate gas in porous media accordingly. New momentum equations are set up, considering Non-Darcy flow effects, the phase change between condensate gas and condensate, phase velocity and fluid character, based on a simple model of three zones. Surface tension and capillary pressure were introduced into the new model. At the same time energy equations are deduced considering latent heat of vaporization and fluid-solid heat coupling. A mathematical model of multiphase flow in porous media with phase change is set up in this paper combining new momentum equations, new equations of energy with equations of mass conservation.

Application of evolutionary Gaussian processes regression by particle swarm optimization for prediction of dew point pressure in gas condensate reservoirs

One of the most critical quantities for characterizing a gas condensate reservoir is dew point pressure. But, accurate determination of dew point pressure is a very challengeable task in reservoir development. Experimental measurement of dew point pressure in PVT (Pressure, Volume, Temperature) cell is often difficult, especially in the case of lean retrograde gas condensate. So, different empirical correlations and equations of state are developed by researchers to calculate this property. Empirical correlations do not have ability to reliably duplicate the temperature behavior of constant composition fluids, and equations of state have convergence problem and need to be tuned against some experimental data. In addition, these approaches are not generalizable to unseen data, and they usually memorize the data used to develop them. In this paper, we develop an intelligent model to predict dew point pressure of gas condensate reservoirs using Gaussian processes optimized by particle swarm optimization. The developed model is generalizable and can estimate unseen data with the same distribution of training data accurately. Results show that the proposed method in this paper outperforms the previous published models and correlations.

An Experimental Phase Diagram of a Gas Condensate Reservoir

Most condensate gas reservoirs discovered in Iran are rich in intermediate components. The phase diagram of these fluids is essential for reservoir management. The available commercial reservoir fluid simulators are not able to find the critical point of some of these condensate gas reservoirs to obtain the phase diagram quality lines. The quality lines of these reservoir's samples can be obtained experimentally using the constant mass expansion test data. The authors present experimental development of gas condensate phase diagram along with retrograde condensation and revaporization characterization during the reservoir depletion process of one Iranian condensate gas reservoir.

Holographic superconductors in a cohesive phase. The retrograde condensate paid back

We consider a four-dimensional N=2 gauged supergravity coupled to matter fields. The model is obtained by a U(1) gauging of a charged hypermultiplet and therefore it is suitable for the study of holographic superconductivity. The potential has a topologically flat direction and the parameter running on this "moduli space" labels the new superconducting black holes. Zero temperature solutions are constructed and the phase diagram of the theory is studied. The model has rich dynamics. The retrograde condensate is just a special case in the new class of black holes. The calculation of the entanglement entropy makes manifest the properties of a generic solution and the superconductor at zero temperature is in a confined cohesive phase. The parameter running on the topologically flat direction is a marginal coupling in the dual field theory. We prove this statement by considering the way double trace deformations are treated in the AdS/CFT correspondence. Finally, we comment on a possible connection, in the context of gauge/gravity dualities, between the geometry of the scalar manifold in N=2 supergravity models and the space of marginal deformations of the dual field theory.

A simulation study of the enhancement of condensate recovery from one of the Iranian naturally fractured condensate reservoirs

The structure and analysis of naturally fractured reservoirs (NFRs) is more complicated than the conventional reservoirs because of their double medium nature containing matrix (high porosity and low permeability) and fracture network (low porosity and high permeability). There is an essential need for more study and further understanding of fractured reservoirs characteristics due to the fact that the majority of the world's petroleum reserves, particularly in the Middle East, are in NFRs.The situation is more complicated in gas condensate reservoirs in which the liquid drop-out and condensate blockage phenomena typically occur. In a retrograde gas condensate reservoir, the condensate accumulation in the fractures prevents the fractures to maintain their fundamental role as the most permeable conduit for the gas flow.This article deals mainly with the specific phenomena that occur in the gas condensate fractured reservoirs related to condensate banking and the existence of double porosity media for instance decrease of Gas Oil Ratio (GOR), lower horizontal pressure, uniform condensate properties throughout the reservoir, significant difference in production history, and elimination of transition zones.The results of this study demonstrate the importance of double porosity/dual permeability model in the simulation of gas condensate fractured reservoirs. Also, the physical properties of fractures such as capillary pressure and relative permeability are of great importance in simulation studies such that the use of linear relative permeability curves inside fracture could lead into wrong predictions.

Holographic superconductors from gauged supergravity

We consider minimal setups arising from different truncations of \( \mathcal{N} = 8 \) five-dimensional SO(6) gauged supergravity to study phase transitions involving spontaneous breaking of any of the U(1) symmetries in U(1) × U(1) × U(1) ⊂ SO(6). These truncations only keep the three relevant vector fields, four complex scalar fields carrying U(1) charges, plus two neutral scalar fields required by consistency. By considering thermal ensembles with different fixed U(1) charge densities and solving the complete equations including the full back-reaction, in some cases we find instabilities towards the formation of hairy black holes, which lead to second order transitions, resulting from a thermodynamical competition between different sectors. We argue that these should be the dominant thermodynamical instabilities in the full ten-dimensional type IIB theory. In other cases we find unstable branches of hairy black holes that extend to temperatures above a critical temperature (“retrograde condensation”). The results can be used as a first step to understand new aspects of the phase diagram of large N \( \mathcal{N} = 4 \) SU(N) super Yang-Mills theory with fixed charge densities.

Effect of the wave action on the hydrocarbon filtration flow in gas condensate strata in the presence of retrograde condensation

The effect of the wave action of the filtration flow of a hydrocarbon mixture in a porous medium in the presence of retrograde condensation is considered. It is shown that the wave action on a stratum allows a significant increase in the integral mean output rate of gas-condensate mixture components. The output rate increases with the oscillation amplitude or frequency.