At the sub-meter scale, capillary retention occurs when two immiscible phases flow across two het... more At the sub-meter scale, capillary retention occurs when two immiscible phases flow across two heterogeneous media. It happens in the upstream medium, and the phase retained depends on the heterogeneity order and the system wettability. This phenomenon has a major impact on the oil recovery and hence requires comprehension. The analysis of the spatial variation in the phase saturation along the flowing domain is well established. However, the literature lacks the general characteristics of capillary retention caused by such variation at various flowing conditions. The continuum model for the flow of two immiscible phases in porous media at steady-state conditions is examined. The analysis is limited to the medium with a single discontinuity in rock properties. In this examination, the characteristics of the capillary retention upstream of the discontinuity are the primary consideration. Three retention regions related to the flow regime are identified: two plateaus and a transition zone occurring, in general, at intermediate capillary number. The width and location of the transition depend on the fractional flow. The crucial finding is related to the identification of an upper bound for the capillary retention and its dependency on the capillary variable ratio and the form of the Leverett J-curve. Two J-models are investigated, and it is shown that, for a given capillary variable ratio, the upper bound depends on the level of flatness of the J-curve at intermediate saturations. Potential implications of the current analysis to reservoir characterization are also discussed. Article Highlights • Three retention regions related to the ow regime are identified: two plateaus and a transition zone occurring at intermediate capillary numbers. The width and position of the transition depend on the fractional flow. • An upper bound for the capillary retention is derived and its dependency on the heterogeneity ratio and the form of the Leverett-J curve is discussed.. • Potential implication to reservoir characterization: In the case of steeper Leverett-J curves with low to moderate random heterogeneity ratios, the upper bound is minimal regardless of the various lithologies and their congurations. In such conditions, the upper bound can be used to assert the insignicance of the eld-scale capillary retention.
Abstract The 2D governing equations for the immiscible two-phase flow admissible to linear stabil... more Abstract The 2D governing equations for the immiscible two-phase flow admissible to linear stability analysis are inspected. The identification of the term v w s D δ s i D in the generalized Saffman–Taylor criterion is key to the analysis. It can be regarded as a predictor that correlates with observed immiscible instability in terms of the rate of advancement of the viscous pattern, the number of small protrusions, and their roughness in a given heterogeneous domain described by a correlated random field. The predictor is extended, heuristically, for polymer flooding shock-wise and used to characterize the instability of the two shocks. The extension is validated by simulation. The instability of the primary shock is essential when considering the breakthrough recovery. In light of the instability predictor, the geometric interpretations of the fractional flow are essential to understand the stability enhancement of the primary shock over the Buckley–Leverett shock in water flooding. It is also concluded that the end-point mobility ratio does not directly control the immiscible instability. This conclusion was arrived at by fixing the end-point mobility ratios for three sets of relative permeability curves, and yet noticeably different instabilities occur, both in transverse and correlated random fields. The criterion can predict the viscous instability in the laboratory experiments under certain flooding conditions and sample configurations. Concerning the instability in a field scale, the predictor is applicable if the field is regarded as a prototype of a given model experiment.
We introduce a pseudoisation method to upscale polymer flooding in order to capture the flow beha... more We introduce a pseudoisation method to upscale polymer flooding in order to capture the flow behaviour of fine scale models. This method is also designed to improve the predictability of pressure profiles during this process. This method controls the numerical dispersion of coarse grid models so that we are able to reproduce the flow behaviour of the fine scale model. To upscale polymer flooding, three levels of analysis are required such that we need to honour (a) the fractional flow solution, (b) the water and oil mobility and (c) appropriate upscaling of single phase flow. The outcome from this analysis is that a single pseudo relative permeability set that honours the modification that polymer applies to water viscosity modification without explicitly changing it. The shape of relative permeability can be chosen to honour the fractional flow solution of the fine scale using the analytical solution. This can result in a monotonic pseudo relative permeability set and we call it th...
Journal of Petroleum Science and Engineering, 2021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
We investigate the effect of heterogeneous petrophysical properties on Low Salinity Water Floodin... more We investigate the effect of heterogeneous petrophysical properties on Low Salinity Water Flooding (LSWF). We considered reservoir scale models, where the geological properties were obtained from a giant Middle East carbonate reservoir. The results are compared against a typical sandstone model. We simulated low salinity induced wettability changes in field scale models in which the petrophysical properties were randomly distributed with spatial correlation. We examined a wide range of geological realisations which mimic complex geological structures. Sandstone was simulated using a log-linear porosity-permeability relation with fairly good correlation. A carbonate reservoir from the Middle East was simulated where a much less correlated porosity permeability relationship was obtained. The salinity of formation water was set to typically observed values for the sandstone and carbonate cases. A number of simulations were then carried out to assess the flow behaviour. We have found th...
Low salinity waterflooding is an effective technique to accelerate and boost oil recovery. The im... more Low salinity waterflooding is an effective technique to accelerate and boost oil recovery. The impact of this technique has been investigated widely in laboratories for various scales and rock typing, most of which have demonstrated a potential improvement in oil recovery. This improvement has been attributed to several chemical and physical interactions that led to a change in the wettability to become more water-wet, as well as a reduction in the residual oil saturation. Meanwhile, it is rare to find a discussion in the literature about the efficiency of low salinity flooding in naturally fractured reservoirs. Therefore, in this work, we investigate the potential advantages of this method in fractured reservoirs using numerical simulations. A new approach to estimate the weighting factor using a tracer model has been proposed to determine the brine salinity and, hence, its properties in the mixing region. We have also used the relative permeability curves as a proxy for any physic...
The process of post-stack inversion is routinely carried out to obtain acoustic impedance (AI) fr... more The process of post-stack inversion is routinely carried out to obtain acoustic impedance (AI) from seismic data and, hence reservoir properties in the target oil field. In this study, we have been describing characterization of a Mid-Cretaceous reservoir using two seismic inversion techniques which have been applied to the main oil bearing complex reservoir in this giant field. These two methods were implemented as an approach to predict the reservoir properties and the reservoir features such as the complex geometries and connectivity patterns, with focusing on benefits and uncertainties between these two techniques. Analysis of post-stack seismic inversion for various reservoir properties estimation is generally applied for reservoir characterization. The two methods have been interrogated and successfully applied on a heterogeneous carbonate reservoir. Model based inversion has been extensively applied on many case studies and has produced superior results on other techniques. T...
Gravity drainage is one of the essential recovery mechanisms in naturally fractured reservoirs. S... more Gravity drainage is one of the essential recovery mechanisms in naturally fractured reservoirs. Several mathematical formulas have been proposed to simulate the drainage process using the dual-porosity model. Nevertheless, they were varied in their abilities to capture the real saturation profiles and recovery speed in the reservoir. Therefore, understanding each mathematical model can help in deciding the best gravity model that suits each reservoir case. Real field data from a naturally fractured carbonate reservoir from the Middle East have used to examine the performance of various gravity equations. The reservoir represents a gas–oil system and has four decades of production history, which provided the required mean to evaluate the performance of each gravity model. The simulation outcomes demonstrated remarkable differences in the oil and gas saturation profile and in the oil recovery speed from the matrix blocks, which attributed to a different definition of the flow potentia...
Identification of tidal channels fairways is key for predicting behavior of areas at higher risk ... more Identification of tidal channels fairways is key for predicting behavior of areas at higher risk to water breakthrough or otherwise have a significant impact on the development and monitoring of reservoir performance. However, tidal channels in carbonates are not often easily characterized using conventional seismic attributes. It is important to decipher the complexity of the carbonate tidal channel architecture with integrated multisource data and a variety of approaches.In this paper, petrological characteristics and petrographic analysis is conducted on well logs and validated carefully using core data. Then, the second step is to compare the carbonate channel systems with modern analogue in Bahama tidal flat and outcrop scales in Wadi Mi'Aidin (Northern Oman). Thereafter, the supervised probabilistic neural network (PNN) and linear regression method were undertaken to detect an additional channel distribution.The relationship of high porosity with low acoustic impedance app...
Summary Low-salinity waterflooding (LSWF) is a promising process that could lead to increased oil... more Summary Low-salinity waterflooding (LSWF) is a promising process that could lead to increased oil recovery. To date, the greatest attention has been paid to the complex oil/water/rock chemical reactions that might explain the mechanisms of LSWF, and it is generally accepted that these result in behavior equivalent to changing oil and water mobility. This behavior is modeled using an effective salinity range and weighting function to gradually switch from high- to low-salinity relative permeability curves. There has been limited attention on physical transport of fluids during LSWF, particularly at large scale. We focus on how the salinity profile interacts with water fronts through the effective salinity range and dispersion to alter the transport behavior and change the flow velocities, particularly for the salinity profile. We examined a numerical simulation of LSWF at the reservoir scale. Various representations of the effective salinity range and weighting function were also exa...
As an enhanced oil recovery method (EOR), chemical flooding has been implemented intensively for ... more As an enhanced oil recovery method (EOR), chemical flooding has been implemented intensively for some years. Low Salinity WaterFlooding (LSWF) is a method that has become increasingly attractive. The prediction of reservoir behaviour can be made through numerical simulations and greatly helps with field management decisions. Simulations can be costly to run however and also incur numerical errors. Historically, analytical solutions were developed for the flow equations for waterflooding conditions, particularly for non-communicating strata. These have not yet been extended to chemical flooding which we do here, particularly for LSWF. Dispersion effects within layers also affect these solutions and we include these in this work.Using fractional flow theory, we derive a mathematical solution to the flow equations for a set of layers to predict fluid flow and solute transport. Analytical solutions tell us the location of the lead (formation) waterfront in each layer. Previously, we dev...
SPE Middle East Oil and Gas Show and Conference, 2019
The objective of this work is to characterize the porosity distribution and the types of carbonat... more The objective of this work is to characterize the porosity distribution and the types of carbonate facies in the Mishrif reservoir in the West Qurna/1 Oil Field using seismic inversion results, well log data, rock physics model and core data analysis. Identification of the pore system and the spatial distribution of lithology are keys for constructing Mishrif reservoir model, which have a great impact on the development of the most prolific reservoir in the field Mishrif reservoir. Seismic inversion process is transforming of seismic response into a quantitative elastic properties of the reservoir rocks. It enables the modeling of porosity and lithology distribution in 3D space away from well control. In order to achieve the aim of the work, a step wise approach will be taken. First of all, the vertical distribution of porosity based on well log data and its relationship with elastic properties was undertaken. A model-based seismic inversion guided by rock physic analysis modeling w...
Schemes for automatic history matching of reservoir modeling are studied for the Nelson oilfield ... more Schemes for automatic history matching of reservoir modeling are studied for the Nelson oilfield in the Central North Sea. A complete workflow of automatic history matching involves selection of reservoir variables that require modification and parameter updating schemes, automatic history matching, data analysis, and combination of the best results to obtain an ensemble of best reservoir models. Automatic history matching of Nelson field is conducted using production and time-lapse seismic data, with global single-variable approach, regional multi-variable approach and local multi-variable approach as updating schemes, net to gross, horizontal and vertical permeability as updating parameters. It is revealed that local multi-variable approach can effectively improve history matched results by reducing the number of simulation models, saving computing time and increasing the simulation precision. Global single-variable approach is only a suitable parameter updating scheme for cases where the history matching parameters are independent. Regional multi-variable approach is suitable for the cases where there is strong dependency between properties chosen for updating, and there are wells very close together with strong interaction. Local multi-variable approach is very useful when the history matching parameters are dependent but each selected region for updating is independent of others.
Automatic history matching may be used to condition reservoir simulation models by including time... more Automatic history matching may be used to condition reservoir simulation models by including time-lapse seismic data. Stochastic optimization algorithms are used to ensure a good search of the parameter space to ensure proper determination of the best models. These approaches can require many thousands of simulations for large dimensional problems. Divide and conquer is an assisted history matching approach that enables deconvolution of the parameters so that they can be searched more efficiently and also leads to better uncertainty analysis. We present an application of this approach on the Nelson field. Nine years of production history data are used along with baseline and monitor surveys. Localised variations were made to permeability and net:gross. The reservoir was divided into separate parameter regions by combining experimental design and proxy model analysis. The former enabled insignificant parameters to be discarded while the latter showed that each region could be treated...
Proceedings of EUROPEC/EAGE Conference and Exhibition, 2007
In seismic history matching, we perform a computer assisted history match to conventional product... more In seismic history matching, we perform a computer assisted history match to conventional production data but also include the spatio-temporal information offered by time-lapse (4D) seismic to further constrain the model. Good predictive models can only be found with a suitable search of the space of uncertain parameters such as permeability, porosity, net:gross and fault transmissibility. We present a method of history matching that speeds up the search process. By using streamlines in place of a finite difference simulator, a factor ten speed up in simulation can be obtained. The model accuracy is slightly diminished affecting both the predicted well data along with saturations and pressures that are used to predict the 4D signal. We show how to reduce any bias effects by calibrating the model error and including it in the misfit calculation. The method has been applied to the UKCS Nelson field using six years of production history and two seismic surveys. The field is maintained above bubble point and is ideal for streamline simulation. We compare the use of the finite difference simulator with the streamline method in history matching when we change net:gross and vertical permeability properties. By addressing the mismatch in seismic data together with production, we improve our predictive capability. A proper parameter search increases the reliability of predictions made using simulations, and has great benefits for reservoir management. Decisions regarding water and gas handling, well maintenance and optimisation of production can be made with greater confidence and new wells can be planned with reduced risk.
A 2014, 'Improved normalization of time-lapse seismic data using normalized root mean square repe... more A 2014, 'Improved normalization of time-lapse seismic data using normalized root mean square repeatability data to improve automatic production and seismic history matching in the Nelson field',
Journal of Chemical and Petroleum Engineering, 2018
History matching is used to constrain flow simulations and reduce uncertainty in forecasts. In th... more History matching is used to constrain flow simulations and reduce uncertainty in forecasts. In this work, we revisited some fundamental engineering tools for predicting waterflooding behavior to better understand the flaws in our simulation and thus find some models which are more accurate with better matching. The Craig-Geffen-Morse (CGM) analytical method was used to predict recovery performance calculations and it was simple enough which can be applied in a spreadsheet. In this study, the analytical approach of history matching was applied to a layered reservoir from a shallow marine deposit which was composed of different facies includes lower shoreface facies (LSF), middle shoreface facies (MSF) and upper shoreface facies (USF). Truncated Gaussian Simulation (TGS) is often used to stochastically distribute the facies in the geological model around a deterministic mean representation. The actual distribution is often hard to determine. Starting with the deterministic element of ...
Summary Time-lapse (or 4D) seismic is increasingly being used as a qualitative description of res... more Summary Time-lapse (or 4D) seismic is increasingly being used as a qualitative description of reservoir behavior for management and decision-making purposes. When combined quantitatively with geological and flow modeling as part of history matching, improved ...
Intra-reservoir, sub-seismic shale beds with a thickness range from 1-10 m are present in most cl... more Intra-reservoir, sub-seismic shale beds with a thickness range from 1-10 m are present in most clastic reservoirs. They are often studied to investigate their effect on fluid flow and reservoir performance. Here, it is found that shales with such thicknesses can also strongly affect the effective elastic wave behaviour of the composite reservoir, particularly when observed with frequent time-lapse surveys. More specifically, for reservoirs experiencing pressure depletion, the effective impedance of the reservoir interval is usually expected to harden, however our results indicate that shales can reduce this hardening effect or perhaps unexpectedly soften the overall impedance. The overall in situ stress sensitivity of the reservoir is reduced below that predicted from taking laboratory core plug measurements of sand stress sensitivity alone. These predictions are based on a combination of geomechanical and pressure diffusion phenomena that are in turn controlled by the shale thickness, permeability and the mechanical properties. As sub-seismic shale layers of approximately 1 m thickness take less than three months to pressure equilibrate whilst thicker shale layers of 10 m can take over 20 years, in the context of repeated seismic surveying our predictions require accurate knowledge of the shale properties and statistics and hence a good description of the sedimentology. Based on our default property values, it appears that reduced or anomalous stress sensitivity is likely to be more important for 4D projects with frequent acquisitions of 3-12 months but is of less concern when seismic is repeated on conventional time periods of every 5-10 years. The critical set of parameters required to carry out accurate calibration of these predictions is not yet fully available from published literature.
At the sub-meter scale, capillary retention occurs when two immiscible phases flow across two het... more At the sub-meter scale, capillary retention occurs when two immiscible phases flow across two heterogeneous media. It happens in the upstream medium, and the phase retained depends on the heterogeneity order and the system wettability. This phenomenon has a major impact on the oil recovery and hence requires comprehension. The analysis of the spatial variation in the phase saturation along the flowing domain is well established. However, the literature lacks the general characteristics of capillary retention caused by such variation at various flowing conditions. The continuum model for the flow of two immiscible phases in porous media at steady-state conditions is examined. The analysis is limited to the medium with a single discontinuity in rock properties. In this examination, the characteristics of the capillary retention upstream of the discontinuity are the primary consideration. Three retention regions related to the flow regime are identified: two plateaus and a transition zone occurring, in general, at intermediate capillary number. The width and location of the transition depend on the fractional flow. The crucial finding is related to the identification of an upper bound for the capillary retention and its dependency on the capillary variable ratio and the form of the Leverett J-curve. Two J-models are investigated, and it is shown that, for a given capillary variable ratio, the upper bound depends on the level of flatness of the J-curve at intermediate saturations. Potential implications of the current analysis to reservoir characterization are also discussed. Article Highlights • Three retention regions related to the ow regime are identified: two plateaus and a transition zone occurring at intermediate capillary numbers. The width and position of the transition depend on the fractional flow. • An upper bound for the capillary retention is derived and its dependency on the heterogeneity ratio and the form of the Leverett-J curve is discussed.. • Potential implication to reservoir characterization: In the case of steeper Leverett-J curves with low to moderate random heterogeneity ratios, the upper bound is minimal regardless of the various lithologies and their congurations. In such conditions, the upper bound can be used to assert the insignicance of the eld-scale capillary retention.
Abstract The 2D governing equations for the immiscible two-phase flow admissible to linear stabil... more Abstract The 2D governing equations for the immiscible two-phase flow admissible to linear stability analysis are inspected. The identification of the term v w s D δ s i D in the generalized Saffman–Taylor criterion is key to the analysis. It can be regarded as a predictor that correlates with observed immiscible instability in terms of the rate of advancement of the viscous pattern, the number of small protrusions, and their roughness in a given heterogeneous domain described by a correlated random field. The predictor is extended, heuristically, for polymer flooding shock-wise and used to characterize the instability of the two shocks. The extension is validated by simulation. The instability of the primary shock is essential when considering the breakthrough recovery. In light of the instability predictor, the geometric interpretations of the fractional flow are essential to understand the stability enhancement of the primary shock over the Buckley–Leverett shock in water flooding. It is also concluded that the end-point mobility ratio does not directly control the immiscible instability. This conclusion was arrived at by fixing the end-point mobility ratios for three sets of relative permeability curves, and yet noticeably different instabilities occur, both in transverse and correlated random fields. The criterion can predict the viscous instability in the laboratory experiments under certain flooding conditions and sample configurations. Concerning the instability in a field scale, the predictor is applicable if the field is regarded as a prototype of a given model experiment.
We introduce a pseudoisation method to upscale polymer flooding in order to capture the flow beha... more We introduce a pseudoisation method to upscale polymer flooding in order to capture the flow behaviour of fine scale models. This method is also designed to improve the predictability of pressure profiles during this process. This method controls the numerical dispersion of coarse grid models so that we are able to reproduce the flow behaviour of the fine scale model. To upscale polymer flooding, three levels of analysis are required such that we need to honour (a) the fractional flow solution, (b) the water and oil mobility and (c) appropriate upscaling of single phase flow. The outcome from this analysis is that a single pseudo relative permeability set that honours the modification that polymer applies to water viscosity modification without explicitly changing it. The shape of relative permeability can be chosen to honour the fractional flow solution of the fine scale using the analytical solution. This can result in a monotonic pseudo relative permeability set and we call it th...
Journal of Petroleum Science and Engineering, 2021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
We investigate the effect of heterogeneous petrophysical properties on Low Salinity Water Floodin... more We investigate the effect of heterogeneous petrophysical properties on Low Salinity Water Flooding (LSWF). We considered reservoir scale models, where the geological properties were obtained from a giant Middle East carbonate reservoir. The results are compared against a typical sandstone model. We simulated low salinity induced wettability changes in field scale models in which the petrophysical properties were randomly distributed with spatial correlation. We examined a wide range of geological realisations which mimic complex geological structures. Sandstone was simulated using a log-linear porosity-permeability relation with fairly good correlation. A carbonate reservoir from the Middle East was simulated where a much less correlated porosity permeability relationship was obtained. The salinity of formation water was set to typically observed values for the sandstone and carbonate cases. A number of simulations were then carried out to assess the flow behaviour. We have found th...
Low salinity waterflooding is an effective technique to accelerate and boost oil recovery. The im... more Low salinity waterflooding is an effective technique to accelerate and boost oil recovery. The impact of this technique has been investigated widely in laboratories for various scales and rock typing, most of which have demonstrated a potential improvement in oil recovery. This improvement has been attributed to several chemical and physical interactions that led to a change in the wettability to become more water-wet, as well as a reduction in the residual oil saturation. Meanwhile, it is rare to find a discussion in the literature about the efficiency of low salinity flooding in naturally fractured reservoirs. Therefore, in this work, we investigate the potential advantages of this method in fractured reservoirs using numerical simulations. A new approach to estimate the weighting factor using a tracer model has been proposed to determine the brine salinity and, hence, its properties in the mixing region. We have also used the relative permeability curves as a proxy for any physic...
The process of post-stack inversion is routinely carried out to obtain acoustic impedance (AI) fr... more The process of post-stack inversion is routinely carried out to obtain acoustic impedance (AI) from seismic data and, hence reservoir properties in the target oil field. In this study, we have been describing characterization of a Mid-Cretaceous reservoir using two seismic inversion techniques which have been applied to the main oil bearing complex reservoir in this giant field. These two methods were implemented as an approach to predict the reservoir properties and the reservoir features such as the complex geometries and connectivity patterns, with focusing on benefits and uncertainties between these two techniques. Analysis of post-stack seismic inversion for various reservoir properties estimation is generally applied for reservoir characterization. The two methods have been interrogated and successfully applied on a heterogeneous carbonate reservoir. Model based inversion has been extensively applied on many case studies and has produced superior results on other techniques. T...
Gravity drainage is one of the essential recovery mechanisms in naturally fractured reservoirs. S... more Gravity drainage is one of the essential recovery mechanisms in naturally fractured reservoirs. Several mathematical formulas have been proposed to simulate the drainage process using the dual-porosity model. Nevertheless, they were varied in their abilities to capture the real saturation profiles and recovery speed in the reservoir. Therefore, understanding each mathematical model can help in deciding the best gravity model that suits each reservoir case. Real field data from a naturally fractured carbonate reservoir from the Middle East have used to examine the performance of various gravity equations. The reservoir represents a gas–oil system and has four decades of production history, which provided the required mean to evaluate the performance of each gravity model. The simulation outcomes demonstrated remarkable differences in the oil and gas saturation profile and in the oil recovery speed from the matrix blocks, which attributed to a different definition of the flow potentia...
Identification of tidal channels fairways is key for predicting behavior of areas at higher risk ... more Identification of tidal channels fairways is key for predicting behavior of areas at higher risk to water breakthrough or otherwise have a significant impact on the development and monitoring of reservoir performance. However, tidal channels in carbonates are not often easily characterized using conventional seismic attributes. It is important to decipher the complexity of the carbonate tidal channel architecture with integrated multisource data and a variety of approaches.In this paper, petrological characteristics and petrographic analysis is conducted on well logs and validated carefully using core data. Then, the second step is to compare the carbonate channel systems with modern analogue in Bahama tidal flat and outcrop scales in Wadi Mi'Aidin (Northern Oman). Thereafter, the supervised probabilistic neural network (PNN) and linear regression method were undertaken to detect an additional channel distribution.The relationship of high porosity with low acoustic impedance app...
Summary Low-salinity waterflooding (LSWF) is a promising process that could lead to increased oil... more Summary Low-salinity waterflooding (LSWF) is a promising process that could lead to increased oil recovery. To date, the greatest attention has been paid to the complex oil/water/rock chemical reactions that might explain the mechanisms of LSWF, and it is generally accepted that these result in behavior equivalent to changing oil and water mobility. This behavior is modeled using an effective salinity range and weighting function to gradually switch from high- to low-salinity relative permeability curves. There has been limited attention on physical transport of fluids during LSWF, particularly at large scale. We focus on how the salinity profile interacts with water fronts through the effective salinity range and dispersion to alter the transport behavior and change the flow velocities, particularly for the salinity profile. We examined a numerical simulation of LSWF at the reservoir scale. Various representations of the effective salinity range and weighting function were also exa...
As an enhanced oil recovery method (EOR), chemical flooding has been implemented intensively for ... more As an enhanced oil recovery method (EOR), chemical flooding has been implemented intensively for some years. Low Salinity WaterFlooding (LSWF) is a method that has become increasingly attractive. The prediction of reservoir behaviour can be made through numerical simulations and greatly helps with field management decisions. Simulations can be costly to run however and also incur numerical errors. Historically, analytical solutions were developed for the flow equations for waterflooding conditions, particularly for non-communicating strata. These have not yet been extended to chemical flooding which we do here, particularly for LSWF. Dispersion effects within layers also affect these solutions and we include these in this work.Using fractional flow theory, we derive a mathematical solution to the flow equations for a set of layers to predict fluid flow and solute transport. Analytical solutions tell us the location of the lead (formation) waterfront in each layer. Previously, we dev...
SPE Middle East Oil and Gas Show and Conference, 2019
The objective of this work is to characterize the porosity distribution and the types of carbonat... more The objective of this work is to characterize the porosity distribution and the types of carbonate facies in the Mishrif reservoir in the West Qurna/1 Oil Field using seismic inversion results, well log data, rock physics model and core data analysis. Identification of the pore system and the spatial distribution of lithology are keys for constructing Mishrif reservoir model, which have a great impact on the development of the most prolific reservoir in the field Mishrif reservoir. Seismic inversion process is transforming of seismic response into a quantitative elastic properties of the reservoir rocks. It enables the modeling of porosity and lithology distribution in 3D space away from well control. In order to achieve the aim of the work, a step wise approach will be taken. First of all, the vertical distribution of porosity based on well log data and its relationship with elastic properties was undertaken. A model-based seismic inversion guided by rock physic analysis modeling w...
Schemes for automatic history matching of reservoir modeling are studied for the Nelson oilfield ... more Schemes for automatic history matching of reservoir modeling are studied for the Nelson oilfield in the Central North Sea. A complete workflow of automatic history matching involves selection of reservoir variables that require modification and parameter updating schemes, automatic history matching, data analysis, and combination of the best results to obtain an ensemble of best reservoir models. Automatic history matching of Nelson field is conducted using production and time-lapse seismic data, with global single-variable approach, regional multi-variable approach and local multi-variable approach as updating schemes, net to gross, horizontal and vertical permeability as updating parameters. It is revealed that local multi-variable approach can effectively improve history matched results by reducing the number of simulation models, saving computing time and increasing the simulation precision. Global single-variable approach is only a suitable parameter updating scheme for cases where the history matching parameters are independent. Regional multi-variable approach is suitable for the cases where there is strong dependency between properties chosen for updating, and there are wells very close together with strong interaction. Local multi-variable approach is very useful when the history matching parameters are dependent but each selected region for updating is independent of others.
Automatic history matching may be used to condition reservoir simulation models by including time... more Automatic history matching may be used to condition reservoir simulation models by including time-lapse seismic data. Stochastic optimization algorithms are used to ensure a good search of the parameter space to ensure proper determination of the best models. These approaches can require many thousands of simulations for large dimensional problems. Divide and conquer is an assisted history matching approach that enables deconvolution of the parameters so that they can be searched more efficiently and also leads to better uncertainty analysis. We present an application of this approach on the Nelson field. Nine years of production history data are used along with baseline and monitor surveys. Localised variations were made to permeability and net:gross. The reservoir was divided into separate parameter regions by combining experimental design and proxy model analysis. The former enabled insignificant parameters to be discarded while the latter showed that each region could be treated...
Proceedings of EUROPEC/EAGE Conference and Exhibition, 2007
In seismic history matching, we perform a computer assisted history match to conventional product... more In seismic history matching, we perform a computer assisted history match to conventional production data but also include the spatio-temporal information offered by time-lapse (4D) seismic to further constrain the model. Good predictive models can only be found with a suitable search of the space of uncertain parameters such as permeability, porosity, net:gross and fault transmissibility. We present a method of history matching that speeds up the search process. By using streamlines in place of a finite difference simulator, a factor ten speed up in simulation can be obtained. The model accuracy is slightly diminished affecting both the predicted well data along with saturations and pressures that are used to predict the 4D signal. We show how to reduce any bias effects by calibrating the model error and including it in the misfit calculation. The method has been applied to the UKCS Nelson field using six years of production history and two seismic surveys. The field is maintained above bubble point and is ideal for streamline simulation. We compare the use of the finite difference simulator with the streamline method in history matching when we change net:gross and vertical permeability properties. By addressing the mismatch in seismic data together with production, we improve our predictive capability. A proper parameter search increases the reliability of predictions made using simulations, and has great benefits for reservoir management. Decisions regarding water and gas handling, well maintenance and optimisation of production can be made with greater confidence and new wells can be planned with reduced risk.
A 2014, 'Improved normalization of time-lapse seismic data using normalized root mean square repe... more A 2014, 'Improved normalization of time-lapse seismic data using normalized root mean square repeatability data to improve automatic production and seismic history matching in the Nelson field',
Journal of Chemical and Petroleum Engineering, 2018
History matching is used to constrain flow simulations and reduce uncertainty in forecasts. In th... more History matching is used to constrain flow simulations and reduce uncertainty in forecasts. In this work, we revisited some fundamental engineering tools for predicting waterflooding behavior to better understand the flaws in our simulation and thus find some models which are more accurate with better matching. The Craig-Geffen-Morse (CGM) analytical method was used to predict recovery performance calculations and it was simple enough which can be applied in a spreadsheet. In this study, the analytical approach of history matching was applied to a layered reservoir from a shallow marine deposit which was composed of different facies includes lower shoreface facies (LSF), middle shoreface facies (MSF) and upper shoreface facies (USF). Truncated Gaussian Simulation (TGS) is often used to stochastically distribute the facies in the geological model around a deterministic mean representation. The actual distribution is often hard to determine. Starting with the deterministic element of ...
Summary Time-lapse (or 4D) seismic is increasingly being used as a qualitative description of res... more Summary Time-lapse (or 4D) seismic is increasingly being used as a qualitative description of reservoir behavior for management and decision-making purposes. When combined quantitatively with geological and flow modeling as part of history matching, improved ...
Intra-reservoir, sub-seismic shale beds with a thickness range from 1-10 m are present in most cl... more Intra-reservoir, sub-seismic shale beds with a thickness range from 1-10 m are present in most clastic reservoirs. They are often studied to investigate their effect on fluid flow and reservoir performance. Here, it is found that shales with such thicknesses can also strongly affect the effective elastic wave behaviour of the composite reservoir, particularly when observed with frequent time-lapse surveys. More specifically, for reservoirs experiencing pressure depletion, the effective impedance of the reservoir interval is usually expected to harden, however our results indicate that shales can reduce this hardening effect or perhaps unexpectedly soften the overall impedance. The overall in situ stress sensitivity of the reservoir is reduced below that predicted from taking laboratory core plug measurements of sand stress sensitivity alone. These predictions are based on a combination of geomechanical and pressure diffusion phenomena that are in turn controlled by the shale thickness, permeability and the mechanical properties. As sub-seismic shale layers of approximately 1 m thickness take less than three months to pressure equilibrate whilst thicker shale layers of 10 m can take over 20 years, in the context of repeated seismic surveying our predictions require accurate knowledge of the shale properties and statistics and hence a good description of the sedimentology. Based on our default property values, it appears that reduced or anomalous stress sensitivity is likely to be more important for 4D projects with frequent acquisitions of 3-12 months but is of less concern when seismic is repeated on conventional time periods of every 5-10 years. The critical set of parameters required to carry out accurate calibration of these predictions is not yet fully available from published literature.
Uploads
Papers by Karl Stephen