Variations In Water Saturation Research Articles

3D model of water saturation, effective porosity and volume of shale in upper Assam Shelf, India using multi-attribute regression and cascade-probabilistic neural network

Quantitative interpretation of geophysical data for reservoir identification to study the vertical and horizontal variation of lithofacies, involves integration of multiple disparate datasets. We use a 3D seismic data and two wells (Km and Te) to predict a petrophysical model within the Paleocene to Oligocene formations, and the Precambrian basement in the upper Assam Shelf. The conventional well data were examined in each well to identify reservoirs within the formations. This is followed by a model based seismic inversion of 3D post-stack seismic data resulting in a 3D impedance model. Next, the cascade-probabilistic neural network (CPNN) was trained using the well log derived attributes (target label data) at the collocated seismic observations (observed features). We were able to successfully train the network to predict water saturation, effective porosity, and volume of shale from the inverted seismic traces with the cross-correlation of range 0.96, 0.97, 0.97, respectively. The optimum set of multi-attributes at well-seismic tie locations are extracted from the seismic data and the selected optimum set of attributes are used at all locations in the application of CPNN. CPNN is found to train the target data better than probabilistic neural network and multi-layer feedforward neural network. Hydrocarbon reservoirs are found in shaly sandstones within the Kopili and Sylhet formations of Eocene and Paleocene ages, and Precambrian basement. The hydrocarbon reservoir shows the variation in water saturation 20% to 50%, with the volume of shale of range 40% to 60%, and the effective porosity of range 8% to 30% respectively.

Water contact mapping and saturation estimation using simultaneous inversion of time-lapse seismic data constrained by fluid substitution and Leverett J-function analysis

The integration of a Leverett J-function analysis with the Gassmann and mass-balance equations allows the time-lapse change of seismic reflectivity to be expressed explicitly in terms of the change of the free water-contact (WC) level, reservoir porosity, and initial water saturation. Given the initial 3D distribution of water saturation and porosity and a well-log derived height-saturation-porosity function as a hard inversion constraint, synthetic modeling suggests that time-lapse seismic data can potentially be directly inverted for the change in free-water level, and time-lapse changes in the spatial variation of water saturation can thus be predicted. This integrated inversion approach is applied to a real time-lapse seismic difference volume from the Maui-B field in the Taranaki Basin, New Zealand, where the change of WC level from a baseline model is the only free parameter to be inverted and is obtained by searching for the global error minimum between tmodeled and real time-lapse seismic differences as the modeled WC level is varied. The method correctly predicts the gas depletion and a measurable rise of the water contact on the southern flank of the field.

Study on the Viscosity Optimization of Polymer Solutions in a Heavy Oil Reservoir Based on Process Simulation

Polymer flooding has been proved by many scholars for use in heavy oil reservoirs. However, due to mobility control effects and injectivity, selecting the appropriate solution viscosity is essential. It is difficult to form a deep understanding of the effect and mechanism of polymer flooding using conventional experimental methods with oil recovery as the reference standard, so it is necessary to conduct further study with the aid of simulation methods. In this study, a one-dimensional displacement mathematical model based on the Buckley–Leverett theory was established, and in the range of water–oil viscosity ratio from 0.1 to 0.6, the variation of water saturation along the flow caused by polymer solution was studied. The research results showed that under the action of a polymer solution, compared with water flooding, there was a decreasing region of water saturation along the flow due to oil phase accumulation. The larger the water–oil viscosity ratio, the larger the area of water saturation decline and the greater the degree of water saturation decline, resulting in a better the displacement effect. However, under the condition of oil–phase viscosity of 70 mPa·s, when the water–oil viscosity ratio reached 0.4, the range and degree of water saturation decline along the way no longer changed, all the crude oil that could be swept had been displaced, and the outlet end was close to producing only water, not oil; therefore, further increasing the water–oil viscosity ratio could not increase the oil recovery. At the same time, the increase in pressure had not changed, that is, the increase in pressure had not resulted in the same increase in oil recovery. When the viscosity of oil phase increased to 140 mPa·s, the same rule was displayed, the appropriate water–oil viscosity ratio was also 0.4. The paper analyzed the action mechanism of polymer solution through process description, and the results provided a clear selection method for selecting reasonable polymer solution concentration, as well as a reference for polymer solution range under different crude oil viscosity conditions.

An Intelligent Approach For Obtaining True Resistivity (𝑅𝑇) From Rock Acoustic Data : A Laboratory Verification

Rock true resistivity (Rt) is known as more sensitive than compressional-wave velocity (Vp), the principal output of a seismic survey, to variation in water saturation. Therefore, it would be of a great value if there were a way to predict resistivity distribution from seismic signals. This study is essentially an effort to see the possibility of predicting Rt from Vp through a pattern recognition approach. For the purpose, a series of laboratory tests were performed on some Central Sumatran clay-free sandstone samples of various porosity values and at various water saturation levels. For studying the pattern of relationship, artificial neural networks (ANNs) were applied. From the ‘training’ (i.e.pattern recognition) activity performed using the ANNs, it has been show between Vp and Rt in the following ‘blind test’, it has also been shown that the trained relationship can be used to estimate Rt reliably using other data as input. Comparisons between estimated and observed Rt data have indicated good agreement implying the success of the approach taken in the study. This has laid the foundation and justification for further application of the approach on seismic and well-log data.

Enhanced oil recovery by emulsion injection in heterogeneous heavy oil reservoirs: Experiments, modeling and reservoir simulation

Many of western Canada's heavy oil reservoirs are too thin to allow expensive thermal recovery techniques. Therefore, waterflooding is still often employed in heavy oil reservoirs due to its relatively inexpensive and easy manipulation. However, heterogeneity in permeability and/or in water saturation has been widely encountered in heavy oil reservoirs, resulting in very poor oil recovery with excessive water production. In this study, performances of enhanced oil recovery (EOR) by injection of oil-in-water (O/W) emulsions in heterogeneous heavy oil reservoirs were evaluated through experiments, modeling and reservoir simulation. For experiments, each O/W emulsion was firstly characterized via its stability behavior, emulsion quality, oil-water interfacial tension (IFT), oil viscosity, and droplet size distribution. Parallel-sandpack models with two different types of heterogeneities, either in oil saturation or absolute permeability, were applied to simulate the heterogeneity in heavy oil reservoirs. Experimental results show that injection of the emulsions is effective to recover the by-passed oil in the water-unswept sandpack and the EOR performance is strongly dependent on the emulsion characteristics. In order to achieve optimal oil recovery, a conformance in water mobility (outflow percentage ratio of 50%:50%) is found to be effecitve in the parallel-sandpack with heterogeneity in permeability. In parallel-sandpack with variations in water saturation, a strong blockage in high water saturation sandpack with a long penetration distance contributes an optimal oil recovery. An in-house simulator was developed based on an optimized emulsion flow model, for the first time, to be able to describe the physics of emulsion-assisted EOR in heterogeneous porous media. The simulation results show that emulsion injection in parallel-sandpack causes a greater average permeability reduction in the high water mobility sandpack resulted from longer emulsion slug penetration compared to that in the low water mobility sandpack. This leads to an increased water flood rate in the low water mobility sandpack, resulting in more oil production. A case study of emulsion flooding for EOR in a heterogeneous heavy oil reservoir was conducted. Strategies for optimal EOR in heterogeneous heavy oil reservoirs were discussed. Reservoir simulation results show that a greater ratio of emulsion slug in high water mobility zone to that in low water mobility zone is beneficial for EOR with a fixed emulsion plugging strength. For a given emulsion slug, there exists an optimal emulsion plugging strength for a prime EOR which can be designed through the optimized emulsion flow model.

Mabruk Reservoir in West Mabruk oil Field , (Sirt Basin, Libya)

Abstract: The Sirt Basin in the north-central part of Libya is one of the youngest sedimentary basins on the African craton. Sedimentation was controlled by tectonic and eustatic influences, locally inducing high sedimentation rates with the distribution of the various lithologies being governed by ridge-and-trough paleotopography. The carbonate intervals of the Heira Formation which including the Mabruk Member, The upper Mabruk unit which represent the main reservoir producing oil in the Mabruk oil field in (Block C17), the main objective of this study was to evaluate the carbonate reservoir member by Petrophysical and geological analysis methods using Techlog and Petrel softwarefor five selected wells (B1-17 , B2-17 , B3-17 , B4-17, B5-17 ) .The upper Mabruk unit with gross thickness is ranging from 70 to 90 feet, while the net pay thickness ranging from 14 to 46 feet. The results reveled good reservoir quality content average porosity ranging from 14 to 23%, average permeability ranging from 19 to 309 MD, and average water saturation variations with some wells reached 34%, and increasing toward south reached 71% which located at the edge of oil water contact. the lateral facies evolution creates Petrophysical variations The heterogeneities is big impact in carbonate reservoir quality, although this study used only five wells with short distances between the wells but clear lateral variation encountered as in well B4-17 and B5-17 , heterogeneities can enhance physical properties such as permeability as it was in B4-17 and B5-17(19 and 191 md) .

Continuous Recording of Viscoelastic Relaxation Processes at a Constant Ultrasonic Frequency Due To Wave‐Induced Fluid Flow in a Microporous Carbonate Rock

In a set of water injection, imbibition and drying tests on the Obourg Chalk, relaxation processes induced by variations in water saturation were continuously recorded at a constant ultrasonic frequency, with a peak in attenuation concomitant to a velocity increase from a lower to an upper bound. This behavior is well described by standard viscoelastic models, considering a continuously changing relaxation frequency which at water saturation above 80% matches the frequency of our ultrasonic pulse generator. Using a patchy saturation model, we show that the heterogeneity in fluid distribution is responsible for this relaxation phenomenon which could be observed at the ultrasonic frequency, thanks to the very fine scale of the rock microstructure combining low permeability and high porosity. We believe that our detailed data set can feed new models or help improve existing ones for a better understanding of wave-induced fluid flow processes in reservoir rocks.

Microscopic imbibition characterization of sandstone reservoirs and theoretical model optimization

Traditional porous media imbibition models deviate from the actual imbibition process in oil and gas reservoirs. Experimental studies on gas–water imbibition in reservoirs were carried out to describe the dynamic profile variation process of wet phase saturation in reservoirs and to further reveal the variation of the imbibition front and the imbibition amount. Optimization and correction methods were established, and experimental verifications were performed. Studies have shown the following: (1) Unlike homogeneous porous media, the water phase imbibition process in oil and gas reservoirs is more complicated, and it is impossible for the maximum saturation of imbibition to reach 100%. (2) Contrary to the theoretical hypothesis, the imbibition of water is not piston-like, and there is a clear transition zone at the imbibition front. This transition zone is the main cause of water saturation variations in the imbibition zone; with the expansion of the imbibition zone, the influence of the transition zone on water saturation weakens. (3) Traditional theoretical models predict a positive correlation between the imbibition amount and the measurements; however, there is a large deviation in the numerical values, which must be corrected. (4) The L-W model was optimized and the parameter group fluid factor F and the reservoir factor R were proposed to characterize the properties of the fluid and the reservoir, respectively. These two parameters have a clear physical significance and are easy to accurately test. After experimental correction, the optimized model is favourably suitable for oil and gas reservoirs.

Dynamic Variation of Water Saturation and Its Effect on Aqueous Phase Trapping Damage During Tight Sandstone Gas Well Production.

Dynamic variation of water saturation near a wellbore may cause serious aqueous phase trapping (APT) damage in gas well production, especially in partly water-saturated tight sandstone gas reservoirs. In this paper, a prognosis model was deduced and used to characterize the dynamic variation of water saturation. In addition, experimental evaluations of APT damage were conducted to reveal the influence of water saturation changes on APT damage. The results showed that the new model used for the prognosis of the water saturation consists of immobile water and a water film and has good reliability. The results obtained from the model and experiments agreed with each other well; the error is very little and only 2.94%. Decrease of drawdown pressure or increase of hydrostatic pressure will result in increasing water saturation, which is positively correlated with APT damage. The chart curve of APT damage degree versus water saturation indicates that the APT damage degree will increases from 23.14 to 68.27 and 91.37% during the middle-later stages of tight sandstone gas well production, respectively. Finally, results of a sensitivity analysis showed that the surface tension and wetting contact angle have a great significant impact on water saturation. The interfacial modifier could effectively enter the reservoir pores in a near-wellbore zone and continuously act on the reduction of surface tension and increase of wetting contact angle, which is very helpful for releasing APT damage.

Nonmonotonic traveling waves in an unsaturated medium induced by a solid force and fluid mass sources

The traveling wave responses in an unsaturated medium induced by a solid force and fluid mass sources are derived in 3D Green's functions using the Dirac Delta function decompositions. The wave behaviors are described in pore fluid pressures and solid frame displacement along with fluctuations of capillary pressure in response to time variant fluid injections and solid force loadings. These solutions are numerically calculated and analyzed for unconsolidated sands as a function of water saturation as representative examples. Our results reveal and validate four wave modes, a fast compressional wave (P1), two slow compressional waves (P2 and P3), and a shear wave. The P1 wave and shear wave can be effectively observed. The slow waves with diffusive characters bear low amplitudes and low velocities. The traveling waves in the pore fluid pressures and solid displacement are sensitive to the different sources and the water saturation. The solid force induces the total stress perturbation while the fluid mass sources directly make the volume strains in the fluid phases. This fluid-solid coupling difference causes the distinct traveling wave signature contrasts in the pore-fluid and solid-frame response amplitudes and tendencies with water retention. For the variation of water saturation, the traveling wave shows a nonmonotonic feature. The fluctuation of capillary pressure exhibits a concave upward relationship, which can further interpret the changes of wave amplitude with water saturation. A solid force may enhance the fluctuation. However, for high water saturation, the interactive fluid-solid effect by the solid force may break the fluid contact due to the extremely compressible air.

Pore-scale fluid distributions determined by nuclear magnetic resonance spectra of partially saturated sandstones

The acoustic property and the P-wave velocity of partially saturated rocks depend not only on the water saturation but also on the pore-scale fluid distribution. Here, we analyzed the pore-scale fluid distribution using nuclear magnetic resonance (NMR) [Formula: see text] spectra, which present the variation of porosity components associated with NMR transverse relaxation time [Formula: see text]. Based on the [Formula: see text] spectra, we classified the pore-scale fluid distribution during water imbibition and drainage into three models: a low-saturation model, a patchy distribution model, and a uniform distribution model. We specifically assigned the low-saturation model to deal with the acoustic property of the rocks at the imbibition starting stage and the drainage final stage because cement softening has a nonnegligible effect. We studied the acoustic properties of sandstone rocks with various pore-scale fluid distributions, at the imbibition process and the drainage process. We confirmed that, once the variations in water saturation and pore-scale fluid distribution are taken into account, the P-wave velocity prediction matches well with the laboratory measurement of samples, representing nearly tight sandstone rocks that are partially saturated with distilled water.

Slope monitoring: an application of time-lapse electrical resistivity imaging method in Bukit Antarabangsa, Kuala Lumpur

Slope monitoring study using 2-D electrical resistivity imaging method was conducted on a slope where a massive landslide occurred in December 2008 in Bukit Antarabangsa, Kuala Lumpur, Malaysia. The main objective of the study is to determine the subsurface resistivity distribution of the study area and to map the risk/potential zone of landslide in the future. To detect the changes in the subsurface resistivity distribution due to variation in water saturation in the subsurface, time-lapse electrical resistivity imaging method was applied in this study. Repeated measurements of electrical resistivity over chosen lines at different times were done to monitor the changes in the subsurface resistivity distribution. The results obtained from the time-lapse electrical resistivity shows that there are significant changes in the subsurface resistivity distribution during different periods. Locations of possible slope failure are identified along the slope and are divided into Zone 1 and Zone 2. Weak zones are characterized by the large proportion of high water saturation zones and low resistivity values which are highly affected by the supply of water into the subsurface as well as the properties of the subsurface materials. These particular regions are more susceptible towards slope failure as high water content will ease the movement of soil in the subsurface. Thus, proper mitigation must be done at the problematic zones to prevent the occurrence of slope failure in the future.

Estimation of porosity and water saturation in dual-porosity pyroclastic deposits from joint analysis of compression, shear, and electromagnetic velocities

In situ measurements of porosity and water saturation of pyroclastic deposits have the potential to improve interpretations of geology and hydrology in volcanic regions, and to provide more accurate estimates of dense rock equivalent for volcanic eruptions. However, rock-property models must consider the dual-porosity structure of pyroclastic deposits (i.e., vesicles within pumices and intergranular pores). Vesicularity, intergranular porosity, and water saturation all affect the density, elasticity, and dielectric properties of pyroclastic materials, which control seismic and electromagnetic velocities. The data from active seismic and ground-penetrating radar (GPR) techniques may improve porosity and water saturation estimation if the responses of seismic and electromagnetic velocities to porosity and water saturation variations are complementary in pyroclastic deposits. We developed a dual-porosity petrophysical model to calculate seismic and electromagnetic velocities of pyroclastic deposits with known intergranular porosity, vesicularity, and water saturation, and we tested our ability to estimate porosity and water saturation from field measurements of seismic and electromagnetic velocities in pyroclastic deposits at Mount St. Helens, Washington, USA. Our petrophysical model demonstrates that seismic velocities are more sensitive to intergranular porosity and less sensitive to vesicularity; electromagnetic velocity is primarily controlled by volumetric water content. In a multioffset GPR and active seismic case study, seismic first-arrival traveltime tomography and multichannel analysis of surface waves can resolve high-velocity anomalies caused by porosity reduction. Joint petrophysical inversion of electromagnetic and seismic velocities indicates that although intergranular porosity and water saturation are well-constrained (i.e., standard deviations of approximately 0.05), quantitative estimates of vesicularity remain less certain (i.e., standard deviation of approximately 0.21), due to weak sensitivity.

Correlating Stochastically Distributed Reservoir Heterogeneities with Steam-Assisted Gravity Drainage Production

Application of big data analytics in reservoir engineering has gained wide attention in recent years. However, designing practical data-driven models for correlating petrophysical measurements and Steam-Assisted Gravity Drainage (SAGD) production profiles using actual field data remains difficult. Parameterization of the complex reservoir heterogeneities in these reservoirs is not trivial. In this study, a set of attributes pertinent to characterizing stochastic distributions of shales and lean zones is formulated and used for correlating against a number of production performance measures. A comprehensive investigation of the heterogeneous distribution (continuity, size, proportions, permeability, location, orientation and saturation) of shale barriers and lean zones is presented. First, a series of two-dimensional SAGD models based on typical Athabasca oil reservoir properties and operating conditions are constructed. Geostatistical techniques are applied to stochastically model shale barriers, which are imbedded in a region of degraded rock properties referred to as Low-Quality Sand or LQS, among a background of clean sand. Parameters including correlation lengths, orientation, proportions and permeability anisotropy of the different rock facies are varied. Within each facies, spatial variations in water saturation are modeled probabilistically. In contrast to many previous simulation studies, representative multiphase flow functions and capillarity models are assigned in accordance to individual facies. A set of input attributes based on facies proportions and dimensionless correlation lengths are formulated. Next, to facilitate the assessment of different scenarios, production performance is quantified by numerous dimensionless output attributes defined from recovery factor and steam-to-oil ratio profiles. An additional dimensionless indicator is implemented to capture the production time during which the instantaneous steam-to-oil ratio has exceeded a particular economic threshold. Finally, results of the sensitivity analysis are employed as training and testing datasets in a series of neural network models to correlate the pertinent system attributes and the production performance measures. These models are also used to assess the consequences of ignoring lateral variation of heterogeneities when extracting petrophysical (log) data from vertical delineation wells alone. An important contribution of this work is that it proposes a set of input attributes for correlating reservoir heterogeneity introduced by shale barriers and lean zones to SAGD production performance. It demonstrates that these input attributes, which can be extracted from petrophysical logs, are highly correlated with the ensuing recovery response and heat loss. This work also exemplifies the feasibility and utility of data-driven models in correlating SAGD performance. Furthermore, the proposed set of system variables and modeling approach can be applied directly in field-data analysis and scale-up study of experimental models to assist field-operation design and evaluation.

Three-dimensional inversion of in-line resistivity data for monitoring a groundwater recharge experiment in a pyroclastic plateau

An artificial groundwater recharge experiment was conducted in a pyroclastic plateau in Kagoshima Prefecture in Japan, and time-lapse electrical resistivity data were collected to monitor the recharge process. In the experiment, time-efficient in-line resistivity surveys were performed along four intersecting lines, because a large amount of water was released from two recharge areas and a relatively fast migration of water into the vadose zone was expected. The migration of recharged water may be estimated from changes in electrical resistivity because resistivity in the vadose zone is largely controlled by water saturation variations there. The geological setting at the experiment site was interpreted from the resistivity distribution inverted from the in-line survey data, which were obtained before the recharge experiment. The resistivity distribution showed an approximately layered structure, which could be correlated with four borehole logs in the area. Three-dimensional (3D) distributions of the resistivity change ratio were derived through constrained nonlinear ratio inversion. Three-dimensional inversion of the in-line resistivity data was more suitable than two-dimensional inversion to describe the 3D phenomena associated with groundwater recharge. During the recharge experiment, the zones of decreased resistivity shifted with time, indicating non-uniform penetration of water from the recharge areas into the ground and a horizontal flow of the recharged water, especially in the secondary Shirasu layer, which comprises lacustrine or marine sediments of pyroclastic origin. These interpretations agree with the variation in water content observed in a borehole.

Small‐Scale Seismic Monitoring of Varying Water Levels in Granular Media

Core Ideas We tested the sensitivity of seismic measurements to water saturation variations. We used ultrasonic techniques to reproduce a small‐scale seismic acquisition setup. Measurements were performed on glass bead layers with varying water levels. Results of 3D numerical modelling were used to validate data at the dry state. Data difference trends between the dry and wet models match with the water level. Physical properties of soils in the vadose zone, and especially their water content, are characterized by strong spatial and temporal variations mostly driven by weather and anthropogenic activities. To understand this variability and help water resource management, seismic methods have been recently suggested as a complement to electrical and electromagnetic techniques. The simultaneous in situ estimation of pressure (P) and shear (S) wave velocities (VP and VS, respectively) and their ratio (VP/VS) offers novel perspectives for the monitoring of space and time variations of vadose zone mechanical properties. However, the seismic response in partially saturated and unconsolidated soils remains complex and deserves to be studied both theoretically and experimentally. In this study, we tested the sensitivity of seismic measurements (i.e., P‐wave travel times and surface‐wave phase velocities) to water saturation variations using controlled physical models at the laboratory scale. Ultrasonic techniques were used to reproduce a small‐scale seismic acquisition setup at the surface of glass bead layers with varying water levels. Travel times and phase velocity measurements obtained at the dry state were validated with both theoretical models and numerical simulations and serve as reference datasets. The increasing water level clearly affected the recorded wave field in both its phase and amplitude. In these cases, the collected data cannot yet be inverted in the absence of a comprehensive theoretical model for such partially saturated granular media. The differences in travel time and phase velocity observed between the dry and wet models show patterns that interestingly match the observed water level and depth of the capillary fringe, thus offering attractive perspectives for studying soil water content variations.

An Iterative Implicit Scheme for Nanoparticles Transport with Two-Phase Flow in Porous Media

In this paper, we introduce a mathematical model to describe the nanoparticles transport carried by a two-phase flow in a porous medium including gravity, capillary forces and Brownian diffusion. Nonlinear iterative IMPES scheme is used to solve the flow equation, and saturation and pressure are calculated at the current iteration step and then the transport equation is solved implicitly. Therefore, once the nanoparticles concentration is computed, the two equations of volume of the nanoparticles available on the pore surfaces and the volume of the nanoparticles entrapped in pore throats are solved implicitly. The porosity and the permeability variations are updated at each time step after each iteration loop. Numerical example for regular heterogenous permeability is considered. We monitor the changing of the fluid and solid properties due to adding the nanoparticles. Variation of water saturation, water pressure, nanoparticles concentration and porosity are presented graphically.

Impact of laminations on physical properties of the Bahariya ormation, Egypt

The type locality of the Bahariya Formation in Egypt is the Bahariya Oasis, which lies about 280 km southwest of Cairo, Egypt. It is composed mainly of sandstones which deposited in fluvio-marine to shallow marine environment. The high grain density values recorded for some parts of the Bahariya Formation is due to the existence of iron oxides and pyrite presented as pore filling and/or cementing materials. The primary sedimentary structures like wavy and zigzag laminations severely affect the majority of rock petrophysical properties. The rock laminations are considered as the main source of reservoir rock anisotropy. The relation between pore specific surface (Spor) and permeability is positively improved in the laminated rock samples rather than in the non-laminated. There is a robust and close relationship between porosity and bulk density for non-laminated samples (R2 = 0.86), while for laminated samples, the relation is very weak due to the presence of iron oxides and pyrite laminas. Permeability anisotropy is highly scattered, but generally it increases with depth. Higher permeability anisotropy supports the horizontal migration of reservoir fluids. Permeability anisotropy is most likely due to the existence of microfractures and/or laminations which are mostly existed in the upper part of the Bahariya Formation. The low values of electrical resistivity are showing by laminated samples in depth more than 3516m. It most likely due to the presence of conductive solids like iron rich cement or matrix and rock pore space architectures. However, the mineral composition of some few laminas is free of iron oxides (depth=3515m). The electrical resistivity anisotropy has high values for laminated samples relative to the non-laminated ones. It increases, in general, with depth as a trend of highly scattering data points. This anisotropy is responding by the magnitude of the magnetic susceptibility anisotropy. The non-laminated samples have low magnetic susceptibility relative to the samples with laminations. The magnetic susceptibility of the Bahariya samples is apparently not related to irreducible water saturation (Swi). The main reason for irreducible water saturation variations is the amount and type of clay minerals inside the rock pore spaces. The clay mode of occurrence is usually pore filling, lining, bridging or grain coating. The displacement pressure (Pd) measured for the Bahariya samples are ranged from 10 up to 5000 Psi. The pore surface area of non-laminated samples shows a close and reliable relationship with displacement pressure (R2 = 0.97), while the pore surface area of the laminated samples has no relation with the displacement pressure (R2 = 0. 09). The samples expose mean hydraulic pore radius (R50 &R35) less than 0.04 µm are considered as bad reservoir or even sealing rocks or permeability barrier irrespective to laminations.

Monitoring managed aquifer recharge with electrical resistivity probes

The use of managed aquifer recharge (MAR) to supplement groundwater resources can mitigate the risks to an aquifer in overdraft. However, limited information on subsurface properties and processes that control groundwater flow may lead to low levels of recapture of infiltrated water, reducing the efficacy of MAR operations. We used long 1D electrical resistivity probes to monitor the subsurface response over one diversion season at five locations beneath an operating recharge pond in northern California. The experiment demonstrated the benefits of integrating geophysical and standard hydrologic measurements. The water table response interpreted from time-lapse electrical resistivity images was in good agreement with traditional pore-pressure transducer measurements at coincident locations. Moreover, the electrical resistivity measurements were able to identify vertical variations in water saturation that would not have appeared in pore-pressure data alone. Changes in saturation estimated from electrical resistivity models indicated large hydraulic gradients at early time and suggested the presence of highly permeable conduits and baffles between the surface and the screened interval of recovery wells. The interpreted structure of these conduits and baffles would contribute to the movement of a large amount of infiltrated water beyond the capture zone of recovery wells before pumping begins, accounting in part for the low recovery rates.

Application of Bayesian decision making tool in detecting oil-water contact in a carbonate reservoir

Defining Oil-Water Contact (OWC) is essential for detail petrophysical evaluations and reservoir volumetric calculations. This paper presents Bayesian decision making tool as a sophisticated technique in OWC detecting from well log data. The proposed method is applied to data related to three wells of an oil field of the Southwestern Iran. The method’s performance is evaluated based on well testing reports and also through comparisons with the results of conventional approach based on permeability prediction. Results indicate that the proposed method is more accurate than conventional approach and may improve the results about 5% on average. In addition, using this method, any variation of water saturation (Sw) log and reservoir fluid types may be detectable.