bluuebunny/crossref_metadata_2025 huggingface dataset:
Contributions to the Empowerment of Women in the Oil Industry
Authors: Hosnia Hashim S. , Capello Maria A.
Published: September 2013

The Society of Petroleum Engineers has taken bold and specific steps in promoting the skills, empowerment and network of female engineers, with several important initiatives, events and activities that position this Society as a pioneer in this area. The paper summarizes the initiatives of SPE in this area, being the first and most important professional society in the Oil and Gas sector to create opportunities for the networking, discussion and motivation of women with professional roles and responsibilities in the industry to move towards higher standards, conditions and leadership positions.

Three key concepts were identified in all SPE activities related to the empowerment of women that deserve a special mention: (1) the concept of inclusion, retention and empowerment of women in the workforce being a clear business necessity, (2) the recognition of the need to train the male counterparts to embrace the increased presence of women in the workforce, and (3) the implementation of guidelines for the implementation of recruitment, succession plans and promotion strategies with a gender-balanced strategy and focus.

An analysis of the characteristics of the current situation of the SPE actions in relation to the female component of the membership shows how the common denominator was found to be the industry's interest to promote the effective progression and retention of the female component towards the highest levels in technical and managerial careers, as one effective and immediate remedial action to overcome the workforce shortage and crew change challenges.
Real-Time Dynamic Surveillance of Deepwater Slope Systems in Block-14, Angola
Authors: Rivera Nestor A. , Drinkwater Nick , Charles Dawari D.
Published: September 2013

Optimal development of deepwater slope system reservoirs in Block-14, Angola, requires proper determination of Original Oil in Place, reservoir connectivity, and lateral heterogeneity. The uncertainty on these parameters can be reduced significantly by using high frequency pressure and production data and pressure versus depth profiles acquired while drilling to augment and calibrate pre-existing interpretation from seismic, cores and logs. The Block-14 Tombua-Landana Drilling and Production Platform was built to develop 8 channelized reservoirs, which have different degrees of heterogeneity and net-to-gross ratios. This variability was recognized early during the development program and resulted in a wide range of initial production rates and declines. In response to this, producers were designed with permanent downhole gauges to improve reservoir surveillance capabilities for better determination of well count and optimal placement of producers and injectors. In addition, real time data integration tools were implemented to facilitate performing real-time dynamic modeling.

Once started operating, downhole and wellhead well-data are transmitted and stored in a data repository. This information is integrated with well-tests and used to calibrate reservoir-to-surface wellbore models and generate real-time production profiles. The workflows capture planned and unplanned shut-ins, are used to perform pressure-transient analysis and determine static pressure. By performing material balance and reservoir simulation modeling, we have been able to determine oil in place, quantify the degree of support from offset injectors, assess interwell connectivity, calibrate and update specific aspects of the geological model and optimize the development plan for each reservoir. These workflows also contributed to predicting well events such as scaling, sand production, and water breakthrough.

This paper describes examples of surveillance and dynamic modeling for wells in the Tombua-Landana (T-L) fields and describe how permanent downhole data has improved reservoir management.
Prevention of Pulsations Caused by Flexible Risers
Authors: Belfroid S. P. , Golliard J. , Korst H. J.
Published: September 2013

In the last few decades, flexible risers have increasingly been used in the offshore oil and gas industry. In gas applications these risers can generate high amplitude tonal pressure fluctuations when the gas velocity reaches a threshold value. The resulting pressure fluctuations can then cause high vibration and cyclic stress levels in the associated topside and subsea pipe work. On a number of platforms, riser pulsations have led to serious limitations of the production capability and in at least one case to the fatigue failure of two small bore side branches, resulting into a shutdown of the platform for five months.

An acoustic assessment is performed to determine the risks of a flexible riser to be a source of Flow-Induced Pulsations (FIP) within its intended operating envelope. This assessment is based on models and methods to predict the onset velocity, pulsation frequency and amplitude and is based on actual field measurements on five different platforms and on research performed in collaboration with multiple operators and universities. Relevant inputs include the riser carcass geometry, operating conditions and the reflective characteristics of the topside and subsea piping. The outcome of the assessment allows for the implementation of corrective measures during the design phase of a project and mitigation strategies for already existing risers.
Inducing Earthquake By Injecting Water In A Gas Field: Water-weakening Effect
Authors: Bois Axel-Pierre , Mohajerani Mehrdokht , Dousi Niek , Harms Stijn
Published: September 2013

On November 26, 2009 a 2.8-magnitude earthquake occurred in southwestern Friesland in the Netherlands at an approximate depth of 2 km. This relatively shallow depth indicated that the event was induced, instead of being natural. Closest mining activities were supposed to be the Weststellingwerf field with well WSF-01 and the exploration well DHV-01. The event was named De Hoeve. However, production from DHV-01 started after the event was occurred. Thus, a study was required to determine the origin of the tremor, evaluate if it could be followed by other tremors in the future, and estimate its magnitude. The objective of this paper is to present the study that was conducted in order to identify whether the gas production and water injection in well WSF-01 could have caused the so-called Weststellingwerf fault to slip leading to the earthquake as observed in November 2009.

The following work plan was devised: 1) Perform seismic interpretation; 2) Construct fit-for-purpose geological model of Weststellingwerf area; 3) Construct reservoir simulation model; 4) History match production data of two wells and record pressure and temperature distribution as a function of time; and 5) Build 2-D geo-mechanical model, feed geological data and structure into model, feed pressure and temperature from dynamic model into geo-mechanical model, assign reasonable geo-mechanical properties, perform stress calculations at critical time steps, and determine potential slip displacement along Weststellingwerf fault.

Five triggering mechanisms were tested: 1) Salt dissolution; 2) Pressure depletion during gas production; 3) Re-pressurization due to water injection; 4) Thermal stresses due to cold water injection; and 5) Fault weakening due to water injection (chemical alteration)

Geo-mechanical simulations showed the causes of the earthquake should be looked for, not in stress variations along Weststellingwerf fault, but instead in a fault weakening upon first contact with water. Two mechanisms can be at the origin of this reduction: fault lubrication or decrease in capillary pressure in the fault gouge material when it was first contacted by water.

The simulations also showed that no earthquake should occur in the section of the fault where displacements occurred during de Hoeve tremor. Sections that did not show any displacement could be at the origin of new earthquakes when first contacted by water, but probably of lower magnitude.
Pressure Pulsing Cyclic Solvent Injection (PP-CSI): A New Way to Enhance the Recovery of Heavy Oil through Solvent-Based Enhanced Oil Recovery Techniques
Authors: Jia Xinfeng , Zeng Fanhua , Gu Yongan
Published: September 2013

Hydrocarbon solvent-based enhanced oil recovery (EOR) techniques, such as vapor extraction (VAPEX) and cyclic solvent injection (CSI), have shown a great potential to recover heavy oil reserves. Solvent dissolution into heavy oil and diluted oil flow are the two main processes of these techniques. VAPEX suffers a low production rate because of the slow mass transfer and inefficient gravity drainage. Although benefited from solution gas drive and foamy oil flow, CSI is bothered with the solvent gas release and viscosity re-increase during the production period, which might seriously slow down the oil production. In this study, it is found that foamy oil flow would generate a foamy oil zone which re-saturated part of the solvent chamber. On the basis of this a phenomenon, this paper proposes a new way to enhance the CSI performance through a three-step pressure control scheme during the production period: first, reduce the model pressure to induce foamy oil flow and foamy oil zone; second, re-increase the model pressure to a preset value; third, maintain a certain pressure difference between injector and producer for gas flooding. This three-step process is called one pressure pulse and it can be consecutively repeated several times during the production period.

A series of laboratory experiments have been conducted with a visual rectangular sand-packed physical model. The sandpack permeability is ∼5 Darcy. Propane is used to recover a heavy oil sample with a viscosity of 5,875 cP. Results show that (1) foamy oil could effectively re-saturate the solvent chamber; (2) more pressure pulses would lead to more oil production, while the oil production decreases with pulse number in one cycle; (3) the oil production rate of PP-CSI is 4.37 times of that of conventional CSI, and the final recovery factor of PP-CSI is 17.9% higher than that of CSI. (4) flooding-induced viscous fingering can accelerate the mass-transfer rate; meanwhile, the viscous fingering will not cause an early breakthrough of the solvent chamber.
Seismic Anisotropy Characterization in Heterogeneous Formations Using Borehole Sonic Data
Authors: Jocker Jeroen , Ferla Maurizio , Pampuri Ferdinanda , Wielemaker Erik
Published: September 2013

Inverting borehole sonic data for anisotropic elastic parameters requires data acquired in, at least, two different orientations. In practice this often means combining acquisitions from two offset wells, which is only straightforward if the encountered formations are laterally continuous. If wells do not tie laterally, or if data acquired at different depths in vertically heterogeneous strata need to be combined, then an inversion strategy is required that explicitly takes heterogeneity into account.

This short note outlines such a strategy on the basis of borehole sonic and conventional petrophysical data, structural information, and well surveys. A new and sophisticated workflow was developed to estimate TI anisotropic parameters from borehole sonic logs, adopting a smart data clustering approach. Among other things, the output consists of elastic properties as a function of independently acquired data such as shale volume and density. In turn, these expressions constitute a model that is driven by measurements instead of assumptions, that can be established also in the presence of lateral and vertical heterogeneity, and that can be applied in neighboring wells where the amount of sonic data are insufficient for a complete inversion.
Standards for Characterization of Rock Properties in Unconventional Reservoirs: Fluid Flow Mechanism, Quality Control, and Uncertainties
Authors: Bertoncello A. , Honarpour M. M.
Published: September 2013

Estimating basic properties of unconventional shale reservoirs—such as permeability and porosity—is critical for reservoir evaluation, formation damage prediction, hydraulic fracture design, and performance forecasting. Several techniques can be used to measure these properties. For instance, the Gas Research Institute (Luffel et al. 1993) uses crushed rock, modeling high-resolution images of micron-sized samples, pulse decay, steady-state techniques to evaluate the permeability, and gas expansion and mercury immersion for porosity of a shale sample. However, the accuracy and reliability of these techniques are not well-established for unconventional reservoir rocks because of concerns about the flow regime, the absence of net confining stress, the sample size, and the imaging technique resolution.

This paper presents the results of a round robin permeability and porosity measurement performed at several commercial and research laboratories. The permeabilities of the evaluated samples vary from 10 nanodarcy to 10 microdarcy, and their porosities vary from 5 to 10%.

A wide range of natural and synthetic material was computed tomography (CT) scanned and microscopically examined. Selected samples were used based on their suitability for the desired range of porosity and permeability. The samples were examined before and after drying in a vacuum oven and then tested under several stress cycles. Gas permeability was measured by use of steady-state, transient pulse decay techniques and derived from mercury injection data. Porosity was measured by use of the gas expansion technique and mercury immersion. Image analysis of focused ion beam-scanning electron microscope (FIB-SEM) was also used to model permeability. Klinkenberg permeability was derived from apparent permeability by use of a range of mean pressures to examine validity of the Darcy flow regime.

The results of the round robin testing of porosity and permeability indicate:

Darcy flow is the predominant flow regime in shales with permeability as low as 10 nano-darcy, based on Klinkenberg characteristics and flow rate-pressure drop criteria. Permeability measurement on 10 nano-darcy to 10 micro-darcy permeability core plugs, under 400 to 5000 psi, is feasible and repeatable with a reasonable uncertainty range, at qualified commercial laboratories. Porosity data showed uncertainties in the range of ±1.0 p.u. for the natural samples. Steady-state method provides similar results from different laboratories, as long as an identical procedure is implemented. Uncertainty in steady-state permeability data from different laboratories could be as high as ±150%. Liquid permeability testing by use of supercritical fluid or laboratory fluid (Decalin) provides a complementary and valuable piece of datum. Rotary sidewall core plugs may provide higher quality core standards for shale material testing because the core plugging takes place under reservoir temperature and stress conditions.
Modifying Van Der Waals Equation of State to Consider Influence of Confinement on Phase Behavior
Authors: Ma Yixin , Jin Luchao , Jamili Ahmad
Published: September 2013

Phase behavior and fluid properties in porous media are governed by not only fluid molecule-fluid molecule interactions but also fluid molecule-pore wall interactions. The current available equations of state consider only fluid molecule-fluid molecule interactions and neglect the interactions between the reservoir fluid molecules and the solid wall of the porous media. For conventional reservoirs, this assumption may be valid because the formation pore sizes are much larger than molecular mean free paths. However, in shale formations that are characterized by nanopores, the fluid molecule-pore wall interactions play such an important role that can change phase behavior and crticial properties of the reservoir fluids. Consequently, the critical temperatures and pressures of multi-component hydrocarbon mixtures under nanopores confinement are influenced strongly by fluid molecule-pore wall interactions.

This work investigates the effect of pore proximity in tight and shale formations on phase behavior and fluid properties of the reservoir fluids by modifying van der Waals equation of state. Effects of both fluid molecule-fluid molecule and fluid molecule-pore wall interactions are included in the newly proposed equation of state. Based on molecular simulation studies, correlations are developed to consider the effect of fluid molecule-pore wall interactions for each component required for phase equilibria calculations under nanopore confinement using the proposed equation of state.

Phase behavior calculations of a mixture of methane, n-butane and n-octane were studied under confinement effects for pore sizes ranging from 10 to 2 nm. In general, with the decrease of pore size, the two-phase region of the fluid mixture tends to shrink, which makes the fluid mixture behave more like a dry gas. The results indicate that bubble point and dew point pressures of the confined fluids are up to 150 psi and 300 psi higher than their correspondent bulk values. Also n-butane and n-octane tend to evaporate more when pore size dereases.

The confinement effects can cause the fluid mixture to behave similar to dry gas, which results in reduction in condensate banking and less near-wellbore permeability impairment in comparison to conventional reservoirs. This has several implications for reservoir and well performances. One is that we can observe increased gas rates and enhanced recoveries over the life of the field by modeling these effects in a numerical reservoir simulation package.
Use of Co-Solvents to Improve Alkaline-Polymer Flooding
Authors: Fortenberry Robert P. , Kim Do Hoon , Nizamidin Nabijan , Stephanie S. Adkins , Pinnawala Arachchilage Gayani W. , Koh Heesong , Weerasooriya Upali , Pope Gary A.
Published: September 2013

We have found that the addition of low concentrations of certain inexpensive light co-solvents to alkaline-polymer solutions dramatically improves the performance of alkaline-polymer (AP) corefloods in two important ways. Firstly, addition of co-solvent promotes the formation of low viscosity microemulsions rather than viscous macroemulsions. Secondly, these light co-solvents greatly improve the phase behavior in a way that can be tailored to a particular oil, temperature and salinity. This new chemical EOR technology uses polymer for mobility control and has been termed Alkali-Co-solvent-Polymer (ACP) flooding. ACP corefloods perform as well as ASP corefloods while being simpler and more robust. We report 12 successful ACP corefloods using four different crude oils ranging from 12 to 24 °API. The ACP process shows special promise for heavy oils, which tend to have large fractions of soap-forming acidic components, but is applicable across a wide range of oil gravity.
Delivering Key WITSML Measured and Interpreted Well Information Through RESQML V2 for Reservoir Characterization and Flow Simulation
Authors: Henri-Bally Raphaele C. , Rainaud Jean-François , Deny Laurent , Legg Chris A. , King Michael J. , Verney Philippe , Schey Jana
Published: September 2013

It is now possible to integrate WITSML rig-issued well data, such as trajectory and associated raw measurements, and well analysis results stored in other data formats, including PPDM, into the RESQML set of data-objects that comprise the description of a reservoir or "Earth Model". It is now also possible to update the model as it is refined, through the life of a field.

To develop this integration, the RESQML and WITSML Special Interest Groups (SIG) of Energistics formed a Wells sub-group for the current RESQML version 2 (V2) development cycle. The sub-group is focusing on using the current WITSML V1.4.1.1 data model to abstract a simplified WITSML well consisting of three fundamental objects: its trajectory, either in depth and/or in time; a"WellboreFrame", which is used to reference the WITSML log data; and its extension to reference WITSML marker data. These objects reference WITSML but now exist in the RESQML data model, which allows them to access existing RESQML capabilities. Through this unified vision, the RESQML V2 data standard will allow drillers and production engineers to seamlessly access reservoir characterization and simulation results, and allow the reservoir engineers to benefit from the entire range of well-based drilling, petrophysical, and production data within an integrated team.

This paper presents how the RESQML V2 design allows association of WITSML and RESQML dedicated objects, and how to establish the relationships between these new objects and the structural, stratigraphic, and reservoir elements inside a RESQML model. In part, this integration has been enabled by the new Energistics Open Packaging Conventions (EPC), which allows multiple data standards (not only RESQML and WITSML) to be recognized and managed consistently.

This integration provides the foundation for future RESQML work, including plans to integrate the WITSML Completion data-object, and seismic data (represented in either time or space), both in the reservoir and at the wells.
Integration of Static and Dynamic Data for Enhanced Reservoir Characterization, Geological Modeling and Well Performance Studies
Authors: Ma S. M. , Zeybek M. , Kuchuk F. J.
Published: September 2013

A new methodology is presented for reservoir characterization, geological modeling, and well performance prediction by integrating a complete suite of petrophysical and pressure transient test data to build a detailed geological reservoir model with anisotropy. Data used includes cores, openhole logs, wireline formation tester (WFT) pretests, and vertical interference tests (VIT), production logs, and downhole pressure buildup and injection falloff tests. Core data is first integrated with openhole logs and WFT pretests to build a detailed geological model. Vertical and horizontal permeabilities derived from the VITs were then integrated to have a geological model with anisotropy. With the model, a single-well numerical pressure transient analysis was performed by simultaneously history matching the packer and the probe pressures as well as pressure derivatives to identify the presence of tight reservoir streaks and quantify reservoir layer permeability ranges. The model is further refined and validated by comparing with dynamic data derived from production logs and downhole pressure build-up and injection fall off tests. This validated reservoir model was used in single well reservoir simulation studies to predict well performance and inferring insitu reservoir scale reservoir condition petrophysical properties such as relative permeability and capillary pressure.
Mapping CO2 in Real Time in Hydrocarbon Reservoirs with Downhole Fluid Analysis: First Successful Experience in the East Irish Sea, UK Continental Shelf
Authors: Quayle B. , James S. , Quine M. , De Santo I. , Jeffreys P. , Y. Zuo Julian
Published: September 2013

This paper describes the first successful attempt in the UK Continental Shelf (UKCS) to map CO2 in real time while logging during Centrica's recently concluded four well drilling campaign in the East Irish Sea, offshore north-west England. The East Irish Sea basin is characterised by a range of source rock types, prolonged history of hydrocarbon generation, and Tertiary igneous intrusion. As a result, reservoirs contain varying proportions of carbon dioxide (CO2), nitrogen (N2), and hydrogen sulfide (H2S) in addition to oil and methane. Two of these wells will develop the Rhyl gas field that was discovered in 2009 and found to contain high concentration of methane and CO2 and some N2. An early and accurate understanding of gas composition and variation in such newly discovered fields is critical to reserves estimates, and scheduling and optimizing gas processing at the onshore North Morecambe Terminal.

CO2 had been recognised as a risk prior to drilling the Rhyl exploration well due to the relatively low CO2 content in the neighboring North Morecambe field. During logging and testing several qualitative indications of a higher CO2 content were identified: a high gas density measured at the separator and difficulty in sustaining a flare. Traditionally, the presence of CO2 has been assessed and quantified via lab analysis on samples acquired by both wireline formation testing tools and well tests. Reliable quantification of CO2 from reservoir fluid samples can be difficult due to mud filtrate contamination and because it readily dissolves in produced formation water.

In many CO2 rich reservoirs, compositional gradients are observed with higher CO2 concentrations at the base of the gas column. The two Rhyl development wells provide an opportunity to improve our understanding of the CO2 distribution throughout the field. The latest generation of Downhole Fluid Analysis (DFA) technologies was deployed with the Wireline Formation Testing (WFT) tool. Such technology uses a dual spectrometer system (filter and grating) to accurately measure CO2 content downhole, prior to scavenging. A dedicated channel for the CO2 absorption peak is complemented with dual baseline channels on either side to subtract the overlapping spectrum of hydrocarbon and small amounts of water. The DFA sensor was used at each sampling station during the WFT run of the first Rhyl development well measuring an almost constant vertical CO2 distribution. DFA data was complemented by pressure and pressure gradient analysis and integrated with high definition fullbore microresistivity images, allowing a better understanding of the gas composition across the Rhyl field, hence removing a significant project risk.
Prototype Test of an All-Electric Intelligent Completion System for Extreme Reservoir Contact (ERC) Wells
Authors: Bouldin Brett , Verma Chandresh , Bellaci Isidore , Black Michael , Dyer Steve , Algerøy John , Oliveira Thales , Pan Yulin
Published: September 2013

One of the core focus areas in Saudi Aramco's effort to increase hydrocarbon recovery is in the application of extreme reservoir contact (ERC) wells. These wells with upwards of 20km of reservoir contact are needed to ensure fluid off-take points are distributed throughout the reservoir efficiently. Accurate sensing and control are crucial to the efficient sweep of heterogeneous formations. This paper describes a recent multilateral (ML) well trial that validated a number of core technologies and methods required to make ERC a reality:

Well construction and deployment practices to allow electrical umbilicals to be reliably deployed in openhole laterals Deployment and testing of revolutionary low-power, infinitely positioned electric flow control valves (FCV) designed to be deployed in each compartment in an openhole segmented lateral completion Validation of the fully integrated onboard production monitoring system providing direct downhole measurements of pressures, temperatures, flow rates, and water cut for each controlled compartment Integration of the surface acquisition and monitoring system to the production supervisory control and data acquisition (SCADA) system to provide real-time downhole production information, as well as valuable system health status data that can ensure operational integrity during the life cycle of the well.

A multilateral well close to the oil-water contact point was allocated to validate the functionality of two prototype systems installed and has now been providing valuable reservoir data for over a full year of production. The well trial successfully demonstrated the ability to install and retrieve an umbilical completion from a 10,000ft horizontal lateral. The ability to control downhole flow to within a few barrels per day measured at the reservoir face is proving revolutionary to the way the operator will approach future reservoir management. The sensing system will be capable of delivering continuous compartment productivity. The SCADA integration allows for a real-time management function where the compartment can be controlled to a target offtake rate directly, without resorting to the use of traditional well system models for estimating control settings. This paper highlights the objectives, installation, validation, and functional aspects of this new ERC well system, as well as identifying some of the immediate production impacts emerging from this level of visibility and control at the formation face.
Assimilation of Microseismic Data into Coupled Flow and Geomechanical Reservoir Models with Ensemble Kalman Filter
Authors: Tarrahi Mohammadali , Jafarpour Behnam , Ghassemi Ahmad
Published: September 2013

Hydraulic stimulation of tight unconventional and geothermal reservoirs has been observed to trigger microearthquakes (MEQs). Triggering of MEQ events has been linked to pore pressure, temperature, and in-situ stress variations. The resulting clouds of micro-seismic events are believed to carry information about the underlying coupled flow, geomechanics, and thermal processes and, hence, rock hydraulic and mechanical properties. We develop a framework for integrating microseismic events as monitoring data to infer reservoir property distributions. To model the reservoir stimulation and induced microseismicity, we use a fully coupled thermo-poroelastic model with coupled heat transport, fluid flow, and rock deformation capabilities as forward model and apply the ensemble Kalman filter (EnKF) to assimilate MEQ measurements. Because discrete MEQ events are not amenable to continuous estimation methods, we first use a kernel density estimation (KDE) method to convert the observed cloud of MEQ events into a continuous seismicity density map. We then apply a variant of the EnKF to integrate the resulting continuous seismicity density map to estimate heterogeneous hydraulic and geomechanical rock property distributions such as permeability, Young's modulus, tensile strength and Cohesion. We demonstrate that assimilating the large correlated datasets of seismicity density map with the EnKF can result in substantial loss of ensemble spread. To mitigate this issue, we investigate three alternative EnKF implementations: 1) dampening the changes introduced during the update, 2) projecting the microseismic data onto a low-dimensional subspace that is defined by left singular vectors of the perturbed observations matrix, and 3) using coarse-scale continuous representation of the microseismic data. We use numerical experiments to evaluate the performance of these methods.
Joint Inversion of Production and Temperature Data for Identification of Permeability Distribution with Depth in Deep Reservoirs
Authors: Zhang Zhishuai , Jafarpour Behnam
Published: September 2013

Characterization of permeblity variation with depth in compartmentalized deep aquifers, geothermal and hydrocarbon reservoirs is important for prediction of flow and transport in complex subsurface environments and directly affects the development of natural and energy resources. In deep formations, temperature gradient can be significant and temperature data can provide valuable information about fluid displacement and conductivity in the vertical extent of the formation. This paper examines the importance of temperature data in resolving permeability distribution with depth by integrating flow and temperature data jointly and individually. We show that incorporation of temperature data in model calibration of deep aquifers can increase the resolution of permeability distribution profile with depth. To illustrate the importance of temperature measurements, we adopt a coupled heat and fluid flow model as a forward model to predict the heat and fluid transport in an a deep reservoir and perform a series of numerical experiments for integration of flow data alone, temperature data alone, and flow and temperature data jointly. For model calibration, we use the Maximum A-Posteriori (MAP) estimation approach and for uncertainty quantification we apply the Randomized Maximum Likelihood (RML). We develop an adjoint model for the coupled fluid and heat flow system of equations to compute the required gradients for model calibration. Investigation of the sensitivity of temperature and production data to the distribution of permeability shows that while fluid flow rate data can primarily resolve the distribution of permeability in the lateral extent of the reservoir, the fluid temperature data, even when measured at the surface, show sensitivity to permeability variability with depth, allowing for a higher resolution profiling of the permeability map. The results elucidate the value of temperature data in enhancing the resolution of the estimated aquifer permeability maps with depth.
Continuous Flow Method for Rapid Measurement of Soil Hydraulic Properties: I. Experimental Considerations
Authors: Butters G. L. , Duchateau P.
Published: October 2013

Soil hydraulic properties are important in many vadose zone processes, but the measurement of these properties is usually tedious and often difficult. We describe a continuous flow method that allows very rapid and accurate measurement of hydraulic conductivity, K(h), and moisture retention, θ(h), functions including hysteresis. The experimental design described here employs simultaneous tensiometry and water flow measurements that are easily automated. The design provides a highly versatile approach to controlling draining and/or wetting rates. The analysis uses a combination of direct Darcian analysis and numerical inversion of Richards' equation for estimation of the hydraulic properties. This combination allows for estimation of wetting and/or draining K(h) and θ(h) over the entire tensiometer range of measurement, while retaining the physical significance of the hydraulic parameter estimates. Estimation of K(h) and θ(h) to lower soil water pressures can be accomplished by supplying the inverse analysis with an independently measured water content such as θ(1.5 MPa). The key to applying the inverse analysis to variably saturated conditions unambiguously is identification of the air‐entry pressure of the draining soil. We show how the air‐entry pressure can be identified from an inflection in the soil water pressure and changes in drainage flux. The air entry identification is verified by measurement of the soil air pressure. The continuous flow approach is applied successfully to a variety of soil textures and structures. The effects of drainage rate and range of measurement are also demonstrated and discussed.
Electrical Potential Distributions in a Heterogeneous Subsurface in Response to Applied Current: Solution for Circular Inclusions
Authors: Furman Alex , Warrick A. W. , Ferré Ty P. A.
Published: October 2013

An analytic solution to the Laplace equation for potential distribution in response to current flow in a heterogeneous, two‐dimensional semi‐infinite domain is studied. Circular heterogeneities of varying sizes and electrical conductivities are considered. We investigate the response of the stream function, the potential field, and, in particular, the potential at the top boundary relative to the background as a function of the size, location, and electrical conductivity of circular inclusions taken singly or multiply. The analytic solution sets the basis for the application of sensitivity analysis to the electrical resistance tomography (ERT) method, as an initial step toward improving the application of the method to tracking rapid hydrological processes.
The Effect of the Spatial Sensitivity of TDR on Inferring Soil Hydraulic Properties from Water Content Measurements Made during the Advance of a Wetting Front
Authors: Ferré Ty P. A. , Nissen Henrik H. , Šimůnek Jirka
Published: October 2013

Many measurement methods are considered to return point values of volumetric water content, water pressure, or other hydrologically relevant properties. However, many methods have spatially distributed measurement sensitivities, averaging a property of interest over some sample volume. In this investigation, we study the effects of the spatially distributed measurement sensitivity of time domain reflectometry (TDR) on the inversion of hydraulic properties from water content measurements. Specifically, a numerical analysis of the water breakthrough curves that would be measured by TDR probes of varying designs during the advance of a wetting front is presented. Numerical inversion of these water breakthrough curves is performed to estimate the soil hydraulic parameters. Time domain reflectometry probes with larger rod separations show less impact on the flow of water at the wetting front. However, these probes have more widely distributed spatial sensitivities, leading to more smoothing of the observed water breakthrough curve. The TDR‐measured wetting front shape is more distorted for vertically emplaced probes than for horizontal probes. The optimal TDR probe configuration for inversion of hydraulic parameters from measurements recorded during the advance of a vertical wetting front has three closely spaced rods that lie in a common horizontal plane. The inversion results using this design show close agreement with known values and very small 95% confidence intervals of the inverted properties. This specific recommendation cannot be adopted generally for all TDR monitoring applications. Rather, we recommend that a similar analysis be performed for each specific monitoring application. While the results presented are specific to TDR responses, the same consideration should be given to all instruments with spatially distributed sensitivities.
The Impact of Climate Change on the Chemical Composition of Deep Vadose Zone Waters
Authors: Glassley William E. , Nitao John J. , Grant Charles W.
Published: October 2013

Chloride mass balance, and stable (deuterium and 18O) and radiogenic (3H, 36Cl) isotope studies of deep vadose zone pore waters have generally concluded that variations in moisture flux can account for the observed variations in abundance of these approximately conservative tracers. It can be inferred, on the basis of these observations and interpretations, that a climate change record is preserved in these vadose zone waters. In arid regions where thick (>100 m) vadose zones persist, it has been concluded that this record may extend back more than 100 000 yr. Consideration of the mechanisms that control reactive transport led to the conclusion that such climate‐driven effects will also be evident as chemical reactions involving dissolution and/or precipitation of mineral phases along the flow pathway. As a result, there should also be variations in the concentrations of nonconservative chemical species that correspond to changes in the concentrations of the conservative tracers. Simulations of this reactive transport, in a regime typical of the arid U.S. Southwest, demonstrate that these changes can modify pore water chemistry by factors of up to 200%, but the changes take place slowly, requiring thousands of years to achieve steady‐state conditions. This suggests that a very rich archive of climate change history is preserved in this type of setting. However, extracting that history is currently hampered by limitations in data and models (e.g., effective mineral reactive surface areas, fluid flow pathways, and quantified models of wetted fracture surface in unsaturated, fractured systems). This challenge may be overcome if coordinated efforts are undertaken that exploit the power of detailed studies of isotope systematics, microscale rock characterization, and high performance computing.
ADVANCES IN TENSIOMETRY FOR LONG‐TERM MONITORING OF SOIL WATER PRESSURES
Authors: Sisson J. B. , Gee G. W. , Hubbell J. M. , Bratton W. L. , Ritter J. C. , Ward A. L. , Caldwell T. G.
Published: October 2013

Soil water pressures, measured over space and time, are needed to predict the direction of water flow and chemical transport in the vadose zone. Advanced tensiometers (ATs), which utilize a water‐filled porous cup connected directly to a pressure transducer, can be installed at almost any location and depth using standard drilling techniques such as auger drilling, but these methods can significantly disturb the site. For sites where minimal disturbance is desired, alternate approaches for tensiometer placement have been sought. To test installation techniques and performance longevity, advanced tensiometers were placed into the ground at a test site near Richland, WA using two different installation methods, auger drilling and a drive‐cone push technique. The tensiometers were subsequently monitored for nearly 2 yr without refilling or recalibration. The data indicated that tensiometers placed by the auger technique took several months to equilibrate, while the cone push units came to equilibrium within 24 h following their installation. Soil water pressures always remained above −90 cm pressure head (−90 mbar) at depths >90 cm. At the greatest depth (730 cm), positive then negative pressures were observed as the water table was lowered and the soil drained. The results suggest that for our test conditions (coarse sandy soil, no vegetation), soil water pressures stay well within the tensiometer range and unit gradient conditions persist, indicating a draining profile. Advanced tensiometers, placed either by auger or cone penetrometer, provide a robust and reliable method for long‐term monitoring of soil water pressure profiles.
A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry
Authors: Robinson D. A. , Jones S. B. , Wraith J. M. , Or D. , Friedman S. P.
Published: October 2013

Substantial advances in the measurement of water content and bulk soil electrical conductivity (EC) using time domain reflectometry (TDR) have been made in the last two decades. The key to TDR's success is its ability to accurately measure the permittivity of a material and the fact that there is a good relationship between the permittivity of a material and its water content. A further advantage is the ability to estimate water content and measure bulk soil EC simultaneously using TDR. The aim of this review is to summarize and examine advances that have been made in terms of measuring permittivity and bulk EC. The review examines issues such as the effective frequency of the TDR measurement and waveform analysis in dispersive dielectrics. The growing importance of both waveform simulation and inverse analysis of waveforms is highlighted. Such methods hold great potential for obtaining far more information from TDR waveform analysis. Probe design is considered in some detail and practical guidance is given for probe construction. The importance of TDR measurement sampling volume is considered and the relative energy storage density is modeled for a range of probe designs. Tables are provided that compare some of the different aspects of commercial TDR equipment, and the units are discussed in terms of their performance and their advantages and disadvantages. It is hoped that the review will provide an informative guide to the more technical aspects of permittivity and EC measurement using TDR for the novice and expert alike.
Gas Diffusion Measurement and Modeling in Coarse‐Textured Porous Media
Authors: Jones Scott B. , Or Dani , Bingham Gail E.
Published: October 2013

Conventional gas diffusion measurements in coarse‐textured and aggregated porous media are severely limited due to hydrostatically induced variations in water content and air‐filled porosity. Motivated by the need to measure gas diffusion in coarse‐textured plant growth media designed for use in microgravity (e.g., aboard the International Space Station), our objectives were (i) to develop and test an automated diffusion measurement system on earth with water content adjustment capability and that minimizes hydrostatic effects, and (ii) to model characteristics of gas diffusion in partially saturated aggregated porous media. The horizontally oriented O2 diffusion cell design for reducing the gravitational effect was based on a thin profile rectangular cell. Continuous measurement of O2 in sealed dual‐chamber diffusion cells provided concentration data for fitting diffusion coefficients where water content was controlled volumetrically using a porous membrane with an imposed pressure for incremental addition or removal of water. Gas diffusion was modeled as a function of air‐filled porosity in millimeter‐sized aggregated particles exhibiting a substantial difference between internal and external aggregate pore sizes. For this case, the internal aggregate porosity contribution to diffusion compared with external aggregate pore space was minor as described by a dual‐porosity diffusion model. The measurement approach described can be used in other coarse‐textured and structured porous media.
Laboratory Calibration, In‐Field Validation and Use of a Soil Penetrometer Measuring Cone Resistance and Water Content
Authors: Topp G. C. , Lapen D. R. , Edwards M. J. , Young G. D.
Published: October 2013

Concurrent and coincident measure of penetrometer cone resistance (PR) and water content (WC) were optimized by hourly in‐field validation of data from time domain transmissiometry (TDT) for WC and piezoelectric force sensor for PR. A piezoelectric force sensor coupled to a cone is followed by a helical wrapped TDT sensor on a single penetrometer shaft. Detailed laboratory calibrations, coupled with in‐field validations, were important to assure the quality of data, which facilitated detailed analyses of PR and WC patterns. The piezoelectric sensor relied on a calibrated spring for the in‐field validation. The calibration of the TDT sensor had three stages: a series of fluids of known dielectric constant; soil columns at known, variable water contents; and field soils at a range of ambient conditions. The penetrometer was used to study soil strength and WC behavior in time and space along 300‐m plots. The treatments were conventional and no‐till, each at two levels of traffic. The crop was corn (Zea mays L.), continuous and in rotation with soybean [Glycine max (L.) Merr.] and wheat (Triticum aestivum L.). The PR vs. WC relationships for two depths (0.21 and 0.27 m), below the level of cultivation, were similar to those at the 0.10‐m depth for the nontrafficked no‐till plots. These relationships for the 0.21‐ and 0.27‐m depths were not influenced by tillage, traffic, and corn cropping system treatments. The variable depth of plowing in tilled plots was found to influence the data consistency for the 0.21‐m depth, indicating the penetrometer's high sensitivity to the soil conditions.
A Depth Control Stand for Improved Accuracy with the Neutron Probe
Authors: Evett S. R. , Tolk J. A. , Howell T. A.
Published: October 2013

The neutron thermalization method for soil water content measurement is well established as being accurate for deep soil profile measurements. However, the method has been criticized as inaccurate for shallow measurements (<30 cm). It is in this shallow zone that many plants have the largest root density and water uptake and where infiltration and evaporation typically cause the largest changes in water content. We show how neutron probe depth influences soil water readings in the top 30 cm of soil, and we describe a depth control stand that serves to control probe depth relative to the soil surface so that probes may be accurately calibrated and successfully used in the field for measurements at shallow depths. Using the stand, calibrations for the 10‐cm depth may be obtained routinely with linear regression r2 values >0.98 and RMSE values of calibration <0.01 m3 m−3 The stand is also useful for elevating the gauge high enough above the surface so that standard counts are not influenced by the water content or nature of the surface, thus enhancing accuracy of both the calibration and subsequent water content readings, both of which depend on standard count values. Also, the stand serves to prevent repetitive strain injuries to backs and knees caused by bending and kneeling to place the gauge on top of access tubes, but without additional occupational exposure to radiation.