NGWA Conference on Characterization of Deep Groundwater: Alphabetical Content Listing

General Discussion 1

William Alley, Ph.D.

General Discussion 2

Mike Wireman

Hydrologic Characterization of Deep Aquifers

Andrew Manning, Ph.D.

Characterization of Deep Hydrogeology for Borehole Disposal of High-Level Radioactive Waste

Bill Arnold, Ph.D.
Deep borehole disposal of high-level radioactive waste and spent nuclear fuel is being considered as a potential alternative to shallower mined geologic repositories.  The basic concept of deep borehole disposal consists of drilling a borehole to a depth of about 5,000 m into crystalline basement rocks, emplacement of waste canisters in the lower 2,000 m, and sealing the upper 3,000 m of the borehole.  Preliminary evaluations indicate that deep borehole disposal of radioactive waste would be viable, safe, and cost effective.  Several factors, including high-salinity fluids at depth, low average permeability, geochemically reducing conditions in deep crystalline rocks, and long transport lengths to shallow fresh groundwater resources, suggest long-term isolation of radionuclides from the biosphere.  Deep hydrogeological conditions favorable to waste isolation likely exist over broad regions in North America, particularly in the geologically stable continental interior. 

Hydrogeological characterization for deep borehole disposal should be focused on those aspects of the groundwater system most important to disposal safety, including the following.  Saline groundwater residence time is an important indicator of long-term isolation of the deep hydrogeological system and can be interrogated using a number of natural isotopic tracers.  Salinity stratification of deep fluids would oppose thermally driven circulation of fluids from waste heat.  Overpressured conditions at depth would be unfavorable to waste isolation.  Permeability of the host rock must be evaluated and is expected to have a low average value; although, individual fracture zones may have significantly higher permeability, even at great depth.  Deep geochemical conditions have important implications for radionuclide mobility, with reducing conditions causing lower solubility and greater sorption for many radionuclides.  Differential horizontal stress may impact borehole stability and the disturbed rock zone permeability in deep boreholes.  Chemical and mineralogical interactions with borehole seals may affect long-term seals integrity.

Deep Groundwater Exploration and Characterization in Alberta, Canada

Alexander Haluszka, M.Sc., P.Geol.
Alberta contains the bulk of the Western Canadian Sedimentary Basin, which is host to the Athabasca Oil Sands in the northeast and several tight gas targets, including the Montney and Duvernay Formations, closer to the Rocky Mountain front in the northwest. These unconventional projects have intensive water requirements. Steam Assisted Gravity Drainage is used for extracting in-situ oil sands and slick-water hydraulic fracturing for tight gas resources. Alberta’s Water Allocation and Allocation Guideline for Oilfield Injection requires operators to investigate saline water sources prior to making an application to use fresh water for an industrial project. In Alberta, saline groundwater is defined as >4000 TDS mg/L by the provincial Water Act. The base of groundwater protection (BGWP) is the depth at which groundwater exceeding 4000 TDS mg/L is encountered. Across the province, the BGWP exceeds 1000 m (3300 ft) near the Rocky Mountains to as shallow as 300 m (1000 ft) at the updip part of the basin where the oil sands occur. This regulatory framework and geologic setting requires hydrogeologists working in Alberta to be well versed in deep groundwater exploration methods. Fortunately, Alberta is data-rich in terms of data sets to use for these purposes. All oil and gas wells drilled in the province must be geophysically logged, including running a gamma ray and neutron-porosity tool to ground surface through casing. These logs, along with water chemistry and pressure data (i.e., drill stem tests), must be submitted to the Alberta Energy Regulator and made public after a confidentiality period. Various mapping software has been developed to streamline access to these datasets. We will discuss how this data is used to explore for deep groundwater, using some examples from projects that Matrix has been involved with.

Deep Injection Wells Injection Capacity Evaluation for Disposal of RO Concentrate and Facility Process Wastewater

Richard Walther, P.G.
Two deep injection wells have been constructed and tested in Polk County, Florida to dispose of reverse osmosis concentrate from the treatment of regional reclaimed water and process wastewater flows. The injection wells are completed in Cretaceous aged formations to a total depth of 8000 feet below land surface and are the deepest injection wells in the state of Florida. Based on injection capacity evaluations, each injection well will have an anticipated maximum operational injection rate of approximately 1.3 million gallons per day (900 gallons per minute).

The injection zone is composed of moderately permeable limestone along with sequences of low permeability limestone and dolostone beneath a 1100-foot-thick anhydrite sequence. The injection zone has extremely high salinity, with total dissolved solids concentrations greater than 200,000 mg/L. The high salinity of the injection zone significantly increases the density of the formation fluids and presented unique challenges to performing pump tests, analyzing formation pressures resulting from injection testing, and assessing the portion of the open borehole available for injection.

A significant amount of data has been collected and analyzed within the injection zone from packer tests, coring, geophysics, and short-term step injection tests to acquire a better understanding of how the well and formations will respond to operational use. The short-term testing data indicates that the injectate is primarily utilizing the formation above 5000 feet below land surface; however, long-term operation will likely utilize all permeability in the borehole. Since this well will be receiving a combined waste stream, a plugging and precipitation study is being conducted to evaluate the risks and potential pretreatment to minimize geochemical issues.

Deep Regional Groundwater Flow in the Northern Great Plains

Klaus Udo Weyer, Ph.D., PG, PHG
Deep regional groundwater flow is often seen as a long distance transmission process from high elevation outcrop areas of aquifer systems to their low lying outcrop areas. In this concept, aquitards are considered to be impermeable. Such long-range groundwater flow systems have been postulated in the literature, as for example from Montana to beyond the Manitoba/Pembina escarpment with about 1100 km length, or from Montana to northern Alberta with about 1600 km length. Although groundwater dynamic considerations had previously put doubt on their existence, nevertheless they have been postulated and adopted in determining residence times at the Weyburn CO2 sequestration site in Saskatchewan and the fate of injected wastewater at the Athabasca oil sands in northeastern Alberta, etc.

Contrary to widespread belief, aquitards are an integral part and also a reason for deep regional groundwater flow systems due to the thermodynamic principle that the total energy consumption in the groundwater force field and the dependent flow field is minimized. Accordingly, deep groundwater flow systems at the Athabasca oil sands (Birch Mountains), the Weyburn test site for CO2 sequestration (Moose Mountain, Missouri Coteau), and at the Manitoba escarpment (Riding Mountain and Turtle Mountain) penetrate many hundreds of meters of aquitard into the underlying aquifer systems as shown by a comparison of head values at the groundwater table and within various aquifers. The results confirm that the postulated long-range deep groundwater flow systems do not exist with groundwater flow from recharge areas in Montana to discharge areas more than a thousand kilometers away.

Saline Contamination Pathway Assessment Using Spatial Variations in Groundwater Salinity, Baton Rouge Fault, Southeast Louisiana

Frances Colleen Wendeborn, M.S., P. Geol.
There has been considerable interest in the role of faults as barriers and conduits for fluid flow. The Baton Rouge fault is a listric fault that cuts a thick siliciclastic sequence of complexly interbedded fluvial sands and mudstones in southeast Louisiana. Aquifer sands north of the fault, to a depth of 1000 m, are the principal supply of fresh water to the metropolitan and industrial Baton Rouge area. Sands near the fault have been increasingly contaminated by brackish water. The vertical migration up the fault of saline waters produced by the dissolution of deep salt has been proposed as the source of contamination of shallow aquifer sands. An alternative hypothesis is that the source of saline contamination is south of Baton Rouge and that saline waters have migrated laterally across the fault.

A detailed study has been done of the spatial variations in salinity as calculated from wire line logs for wells on either side of the Baton Rouge fault. Most of the logs were run in the 1960s, and the information provides a snapshot of the salinity structure prior to significant groundwater contamination. The spatial variations in salinity across the fault are consistent with natural lateral interfingering of fresh waters derived from the north, and brackish waters from the south. A 2004-2005 study of chloride concentrations in the groundwater showed that the highest chloride concentrations occurred at mid-depth in the aquifer system rather than the base, as might be expected if salt transport were up the fault. The most likely source of the saline contamination lies to the south, where dissolution of salt domes has produced saline plumes which extend upward all the way to the ground surface. Conduits for upward transport of salty water appear to be faults associated with the domes rather than regional listric faults.

Hydrologic Characterization of Deep Aquifers (cont.)

Andrew Manning, Ph.D.

Deep Groundwater Administration in New Mexico

Michael S. Johnson, PG
New Mexico aquifers may contain as much as one billion acre-feet of brackish groundwater.  Largely unutilized but long recognized as an important resource, this groundwater is receiving increased attention.  Since 1967 nonpotable water in deep aquifers has been legally excluded from groundwater basins administered by the State Engineer.  These are defined in statute as any aquifer the top of which is at least 2500 feet below ground surface and which contains nonpotable water (total dissolved solids content greater than 1000 parts per million). 

For 40 years only a few notices to drill into deep nonpotable aquifers were filed.  From 2006 through 2010, 68 notices proposing 610 deep wells for the appropriation of over 1.7 million acre-feet were filed, in a veritable “gold rush” on New Mexico’s deep groundwater.  In 2010, actual groundwater withdrawals in the state totaled about 1.8 million acre-feet.  Most of these notices were filed for municipal and related uses in the Albuquerque area.  To date (December 2013) 13 deep wells exist, and actual use of the resource has been small.

Amendments in 2009 allow the State Engineer to declare and administer deep basins.  Appropriations from a declared deep basin for most uses would remain subject to the deep nonpotable aquifer statutes, except for drinking water uses, which would require a State Engineer permit.  The amendments also specify that a deep aquifer contain only nonpotable water, limiting the potential for connection to freshwater sources and effects on senior users and interstate streams.  New Mexico appears to be entering a new phase with respect to deep nonpotable groundwater, with active development to supply a proposed mining use in progress.  Within this context the State Engineer is exploring management options for New Mexico’s deep groundwater, including developing an administrative framework that allows resource development while protecting existing water users.

Development of Deep Non-Potable Saline Groundwater for Industrial Use

David Jordan, PE
INTERA is supporting Intercontinental Potash Corp. USA (“ICP”) in its development of a polyhalite mine and processing facility in southeastern New Mexico for production of sulphate of potash (SOP) for use as a high-quality fertilizer.  Given the limited availability of freshwater resources in southeastern New Mexico, ICP chose to pursue non-potable saline water from the Capitan aquifer as a source to supply the mine and processing facility with necessary water for routine functioning.  Under New Mexico water law, water in an aquifer that is below 2500 feet below ground surface and contains more than 1000 parts per million total dissolved solids is available for mining and industrial use without a traditional water right, as long as development of the water will not impact existing freshwater users.  The Capitan aquifer was formed by a horseshoe-shaped limestone deposit surrounding the Delaware Basin in southeastern New Mexico and western Texas referred to as the Capitan Reef Complex. It extends over a distance of approximately 200 miles. Within Lea County, New Mexico the aquifer ranges from 800 to 2200 ft thick and is approximately 12 miles wide near the Eddy and Lea County boundary and 6 miles wide near Jal, New Mexico.  Through a program of exploratory well drilling, aquifer testing, and groundwater flow modeling, we found that the Capitan aquifer will be a viable water supply for the mine over its 50-year lifespan.   Concerns related to depletions to the Pecos River, a stream which is subject to a contentious interstate stream compact and is hydraulically connected to the Capitan aquifer in areas distal from the mine site, were allayed using a detailed MODFLOW model.  Now that the water supply for the project has been established, the project is moving towards construction beginning in 2014.

Occurrence and Geochemistry of the K-rich Brines in Deep-Seated Aquifers in the Sichuan Basin

Xun Zhou
Subsurface K-rich brines (K contents ranging from 1.5 to 53 g/L) are found in deep-seated aquifers in the Sichuan Basin of China. Most of the K-rich brines occur in the marine carbonate rocks of the Middle and Lower Triassic, Middle Cambrian and Sinian, and only small amounts of the K-rich brines are found in the continental Upper Triassic sandstone aquifers. The brine-bearing formations are at depth ranging from 300 to 4650 m and the brines are rich in anticlines and fault zones. The subsurface brines occur under a sealed state and do not receive any recharge. The brines have high TDS ranging from 80 to 388 g/L with relatively high concentrations of Br, I, Li, Sr, Ba, and B. The K-rick brines are mainly of Cl-Na and Cl-Na·Ca type. In particular, the PL4 well tapping the Middle Triassic brine-bearing carbonate rocks in the western part of the basin flows brines having TDS in the ranges of 348.392 to 377.27-387.78 g/L, which are close to those of the Yellow Sea water and the South China Sea water when evaporated to the stage of epsomite precipitation. K contents of the brines in the PL4 well range from 48.95 to 53.267-53.38 g/L and the B contents are as high as 4.994 g/L, which are much higher than those of the evaporated sea water at the stage of epsomite precipitation. Hydrogen and oxygen isotopes of the brines indicate that the K-rick brines in the carbonate rocks are of marine origin and those in the sandstone aquifers are of meteoric origin.

Morning Session

Jamie Crawford

An Overview of Geophysical Methods to Characterize Deep Aquifers

John Jansen, P.G., P.Gp., Ph.D.
The development of deep aquifers is often limited by the scarcity of data. Direct data from drilling is generally limited due to cost and complexity of deep boreholes. There are several surface geophysical methods that can be used to image the structure of deep aquifers and estimate the water quality.

Several electrical methods have been developed that can image the structure of an aquifer and estimate water quality. Many of the most common methods are limited to a few hundred feet of penetration. Two methods, Time Domain Electromagnetic Induction (TEM) and magnetotellurics (MT), can image aquifers to depths of several thousand feet. Case histories will be presented that demonstrate how these methods can be used to map aquifers, find faults and fractures, and map saline water to depths of 1000 to 3000 feet. The MT method can be used to even greater depths.

Seismic reflection can be used to image geologic strata to depths of tens of thousands of feet. The attributes of the reflections can also be used to estimate the lithology of the units and detect facies changes within the aquifer. A case history will be presented where seismic reflection was used to map a sandstone aquifer at a depth of about 3000 feet and identified a facies change where the sandstone graded into a shale unit.

Gravity methods can be used to map deep geologic structures and are often used to map the basement of a groundwater basin or the depth to dense aquifer units such as carbonates. A case history will be presented where gravity measurements were used to map a carbonate aquifer in a complex structural basin where the depth to the aquifer varied from less than 1000 feet to more than 8000 feet over distances of a few miles.

Deep Injection in the Western Canada Sedimentary Basin

Grant Ferguson
Injection of wastes into the deep subsurface has become a contentious issue, particularly in emerging regions of oil and gas production. Experience in other regions suggests that injection is an effective waste management practice and that widespread environmental damage is unlikely. Over the past several decades, 23 km3 of water has been injected into the Western Canada Sedimentary Basin (WCSB). The oil and gas industry has injected most of this water, but large amounts of injection are associated with mining activities. The amount of water injected into this basin during the past century is two to three orders of magnitude greater than recharge to deep formations in the WCSB. Despite this large-scale disturbance to the hydrogeological system, there have been few documented cases of environmental problems related to injection wells. Deep injection of waste appears to be a low risk activity based on this experience, but monitoring efforts are insufficient to make definitive statements. Serious uncharacterized legacy issues could be present. Initiating more comprehensive monitoring and research programs on the effects of injection in the WCSB could provide insight into the risks associated with injection in less developed sedimentary basins.

Geohydrology and Water Quality of Three Deep Test Holes in Fractured Bedrock, North-Central Pennsylvania

John H. Williams
During 2012 and 2013, the U. S. Geological Survey, in cooperation with the Pennsylvania Geological Survey, characterized the geohydrology and water quality of three deep test holes in the fractured-bedrock uplands of Bradford, Tioga, and Sullivan Counties, north-central Pennsylvania.  The 1,500-feet deep test holes were drilled as part of the State Survey’s geologic mapping program in this region of extensive Marcellus shale-gas development.

 A suite of geophysical logs was collected from the test holes including nuclear, electric, electromagnetic, and sonic; acoustic and optical televiewer and video; and fluid-resistivity, temperature, and flow under ambient and pumped conditions. Based on interpretation of the geophysical logs, water-quality samples were collected at specific depths with a wireline sampler for analysis of specific conductance, total dissolved solids, major cations and anions, trace metals, and gas isotopes.  The specific conductance and flow rate of the air-lifted discharge was monitored during drilling of the Sullivan County test hole.  A straddle-packer system was also used in this test hole to isolate selected fractured zones for hydraulic measurement of transmissivity and head and collection of water-quality samples. 

The test holes penetrated multiple water-flow zones at bedding-related fractures and, in a few shallower zones, steeply dipping fractures related to regional jointing.   Minimal fracture transmissivity was penetrated below 700 feet as indicated by the depth at which the temperature-log gradients approached the geothermal gradient.  Fractured zones above 300 feet produced very fresh calcium-bicarbonate type water with no detectable methane.  Fractured zones below 900 feet produced very small inflows of saline sodium-chloride type water with thermogenic methane concentrations that ranged up to 120 milligrams per liter.  Intermediate-depth fractured zones produced water that was transitional between that produced by the shallow and deep zones.

Open Discussion

Mike Wireman

Using Drill Stem Test Data to Construct Regional Scale Potentiometric Surface in Deep Aquifers

Tiraz Birdie
Ordovician and older age formations are being targeted for storage of carbon dioxide as a climate change mitigation strategy. These deep aquifers are selected as they not only are separated from shallower potable aquifers by shaley confining zones, but because at depths exceeding 2500 feet, the temperature and pressure conditions are such that CO2 exists in the (dense) supercritical state which maximizes storage.

The volumetric quantities involved in commercial CO2 capture and storage are quite large. The average emission from a power plant in the U.S. is approximately a million tons per year. Injecting such large quantities of CO2 from multiple sources for periods of decades can result in elevated subsurface pore pressures at distances exceeding several hundred miles. In order to simulate the induced pressures and predict the eventual fate of CO2, knowledge of the ambient groundwater flow field is essential for calibrating simulation models and specifying boundary conditions. However, due to the high cost of constructing deep observation wells, the potentiometric surface of deep aquifers is generally not known with certainty. As part of the (U.S. DOE sponsored) initiative to characterize the CO2 storage capacity in Kansas, drill stem test data was used to construct a potentiometric surface map of the Cambrian-Ordovician Arbuckle aquifer in Kansas, which is being evaluated for widespread commercial-scale CO2 storage. The results are highly encouraging, and have been verified with known hydraulic data, which validates the (incremental DST-pressure based) technical approach developed to construct region-wide potentiometric surfaces at multi-state scale. The findings are being used for constructing multiphase models to simulate the effect of commercial scale injection in Kansas.

Morning Session (cont.)

William Alley, Ph.D.

Exploration and Groundwater Development from the DEEP Regional Carbonate Aquifer (RDCA) of Southeastern Nevada

Greg Bushner, RG
All of the tools at hand were used to explore and develop the groundwater resources of several basins in southeastern Nevada by the Lincoln County Water District and Vidler Water Co. (Lincoln/Vidler). The groundwater basins of interest that were explored extensively included the Tule Desert, Kane Springs Valley, Clover Valley, and Dry Lake Valley. Exploration tools used included the drilling and testing of monitor wells and test wells that ranged in depths from 815 feet below land surface (bls) to more than 3800 feet bls. Production wells range in depths from 1810 to 2732 feet bls that yield from 600 up to 2000 gallons per minute (gpm) on a sustainable basis. To gain knowledge of aquifer characteristics, lithologic samples were collected along with down-hole geophysics. Water quality sampling was completed in all wells during aquifer testing, and in some cases zonal water quality sampling was conducted. Water sampled was analyzed for cations, anions, total dissolved solids, Oxygen-18, Deuterium, Carbon-13 and -14, as well as field parameters. Test pumps used included a lineshaft vertical turbine driven pump with bowls set to a depth of 1200 feet bls, to a submersible pump set at a depth of 1800 feet bls for a production rate of approximately 2000 gpm.

Other exploration techniques used included Natural Source Audio-Frequency Magnetotulluric (NSAMT) and Controlled Source Audio-Frequency Magnetotulluric (CSAMT) geophysical surveys that were used in combination with the down-hole geophysical data from each well to better understand the subsurface geology for siting new wells and understanding the RDCA in each basin. All of this information was used to develop a conceptual model and a numerical groundwater flow model in support of new groundwater appropriations from these basins. Efforts by Lincoln/Vidler to develop these water resources are entirely on federal lands with approvals for groundwater appropriations under the purview of the Nevada State Engineer.

Methodology for Characterizing Deep Groundwater Resources Using Studies from the Alberta and Williston Basins

Dan Palombi
Regional hydrogeology studies that have mapped and characterized deep groundwater resources in the Alberta and Williston basins have been undertaken for decades. Understanding regional groundwater flow in these basins has been recognized as essential, given the diverse range of natural resources (oil, gas, and fresh and saline water) and in evaluating the various uses of deep groundwater. There is an increasing demand for both fresh and saline groundwater in Alberta to supply domestic, municipal, and agricultural use in addition to natural resource development. Hence, the characterization of deep aquifers, and inherently the advancement of existing methodologies where needed, are currently a focus of the Alberta Energy Regulator (AER). The assessment of deep aquifers for their potential use as water sources in shale oil and gas, geothermal energy, and for geological storage must involve an inventory and characterization of the available and potential competing uses of groundwater resources.

The AER’s Alberta Geological Survey has a history of conducting hydrogeological mapping and continues to undertake regional scale projects in assessing both shallow and deep groundwater resources. This presentation will provide an overview of the methodologies that are currently being used to characterize deep aquifers. Moreover, an outline of the approach being taken to inventory our groundwater resources, construct regional groundwater flow models, and provide scientific results to regulators making decisions on water authorizations will be provided. Studies from the Alberta and Williston basins will be used to show methods and results in geological and hydrogeological modelling, mapping distributions of groundwater flow and chemistry, correcting for density-dependent flow, and also techniques to identify the effects of production/injection on data and pressure regimes.

Open Discussion

William Alley, Ph.D., William Alley, Ph.D.

Permeability Versus Depth in Earth’s Upper Crust: An Overview

Andrew Manning, Ph.D.
Permeability is a key parameter controlling the transport of water, heat, and solutes in Earth’s upper crust, and is thus an important factor in several fundamental earth processes. Crustal permeability is highly heterogeneous, determined by multiple widely-varying geologic features such as lithology, fracture intensity, local stress state, etc. However, overall, permeability decreases with depth due to increasing lithostatic pressure and the resulting reduction of porosity and fracture apertures. Studies published within the past 15 years that compile available permeability estimates at various depths have discovered fairly uniform broad-scale relationships between depth and permeability for both lower-permeability crystalline rocks and higher-permeability sedimentary rocks (sandstones and limestones). Depletion and degradation of shallow groundwater resources in the face of a growing population and warming climate are driving a new interest in the prospect of finding deep groundwater resources. Modern hydrologic science has focused almost exclusively on groundwater flow at shallow depths (<1 km), and our understanding of deeper groundwater flow systems remains limited. Usable aquifers must have sufficiently high permeability to allow both high rates of extraction and active groundwater flow (flushing that reduces salinity) enabled by a hydraulic connection to the surface. This talk reviews published depth versus permeability relationships, along with the few available deep groundwater modeling studies, and makes a first-order attempt to address the basic question: How deep in the crust should we expect to find usable aquifers?

Reassessment of the Nation's Saline Groundwater Resources

Jennifer S. Stanton
Declines in the amount of groundwater in storage as a result of groundwater development have led to concerns about the future availability of freshwater to meet drinking water, agricultural, industrial, and environmental needs. Industry and public drinking-water suppliers have increasingly turned to deeper, saline groundwater to supplement or replace the use of freshwater, leading to a 300% increase in the use of saline groundwater between 1995 and 2005. Recent advances in treatment technology have reduced the cost and energy requirements of desalination, making saline groundwater a more viable option for drinking water supplies. Despite the growing demand for alternative water sources, the most recent map showing the occurrence of saline groundwater across the United States was published almost 50 years ago.

The USGS Groundwater Resources Program recognizes the need for a better understanding of saline groundwater resources to support sustainable develop­ment of the resource and to provide reliable science for associated regulatory and policy issues as well as for advancing treatment technologies. To address this need, three pilot studies were conducted (2010-2012) to assess saline groundwater resources at regional scales. The goals of the pilot studies were to determine the availability of data for assessing the distribution and character of saline groundwater and test and develop methodologies for assessing the resource. The recently initiated (2012) National Brackish Groundwater Assessment, which is part of the USGS Water Census, will build upon knowledge gained from the three pilot studies and use a consistent approach across the nation to provide an updated national map of moderately saline, or brackish, groundwater resources less than 3000 feet below land surface, as well as critical information about the physical and chemical properties of the resource.

Tools, Techniques and Methods

Grant Ferguson

Design and Evaluation of Saline Groundwater Wells for Shale Oil Development, Texas Gulf Coast

Jeffrey Henke, PG
Eagle Ford Shale (EFS) oil development in the Gulf Coast of Texas has placed a high demand on water resources of the region. Oilfield demands for hydraulic fracturing make-up water compete with agricultural, municipal, and domestic uses of water in moderate to low-population areas. Producers are evaluating alternate water sources in areas where surface water rights are fully assigned and competition for fresh, shallow groundwater competition is high. One alternative includes exploitation of deeper groundwater aquifers near a known base of freshwater as well as saline water wells below the lowest depth of usable groundwater.

A deep, fresh water well was completed in unconsolidated Eocene Jackson Group strata in northern Lavaca County, Texas to obtain fresh to slightly saline water for multi-stage hydraulic fracturing of multiple horizontal EFS oil wells. The well was installed as part of a water delivery and management system designed to supply make-up water over an approximated 25 square mile area. The well was designed using borehole geophysical logs and core samples from several adjacent oil well locations and installed using a combination of traditional water well and oil well completion technology. Testing of the well after installation and development indicated fresh to slightly saline water quality, substantial potential yield, and the presence of elevated dissolved methane in the produced groundwater. This presentation will describe aquifer evaluation; well design, installation, and development; well yield; and production issues surrounding use of the well for the intended purpose.

Exploring Deep Groundwater Resources Using the Reverse Circulation (RC) Drilling Method

Steve Schneider, MGWC
Several drilling methods are currently being used for deep water supply well construction. This presentation will discuss the application of reverse circulation (RC) for these wells, including the pros and cons of RC drilling as compared to other commonly used drilling methods. Tooling, equipment, and techniques applicable to deep RC drilling and for deep groundwater supply well construction and maintenance will be included in the discussion.

Integrating Modern Suite of Geophysical Logs, Geochemistry, and Seismic Data for Characterizing Deep Aquifers

W. Lynn Watney, Ph.D.
The 5000 ft deep, 1000 ft thick Lower Ordovician Arbuckle Group aquifer in Kansas has been evaluated as a suitable medium for large scale Carbon Capture and Storage (CSS). The petrophysical properties governing flow and transport in this carbonate aquifer are extremely variable due to the presence of complex interbeds of fractured, vuggy dolomite and shale. The extent of the CO2 plume needs to be demonstrated to the EPA every six months and shown to be in compliance with modeled projections in order to continue injection. Therefore, detailed and accurate characterization of the injection and confining zones is vital.

Spectral Gamma Ray, Triple combo log suite, Magnetic Resonance Image (MRI), and Dipole Sonic were used to characterize pore volume, distribution, and connectedness, and also to identify potential sources of drinking water. The MRI data was used with a new (patent pending) Flow Zone Interval method to estimate permeabilities. The confining potential of the caprock was estimated using MRI based pore throat data to calculate entry pressure. The Extended Range Micro Imager log and Computed Tomography (CT) scan were used to characterize fractures.

The stratification and delineation of hydrostratigraphic units derived from geophysical logs was validated by formation geochemistry, and ionic and isotopic analyses. Geochemical logs and thin sections were analyzed for mineralogy and soil characterization to enable reaction kinetics modeling and determining potential for plugging pore space due to mineral precipitation.

Drill stem and injectivity tests were conducted to determine the relationship between laboratory, log, and field scale estimates of permeability. 3-D seismic data was collected to map formation structures and characterize the geologic fabric regionally. The entire set of data was finally integrated into a 3-D reservoir model using Schlumberger’s (geocellular) Petrel Geology/ Modeling software.

Multi-Frequency Oscillating Flow Tests—Making the Best Use of a Few Boreholes

Michael Cardiff, Ph.D.
Characterization of the deep subsurface for flow properties represents an enormous challenge, for several reasons. Surface-based geophysical methods represent a promising approach to aquifer characterization that have been applied at many near-surface aquifers, but such methods (e.g., reflection GPR, and ERT) are not able to obtain good resolution at significant depths. Similarly, the cost of installing deep boreholes and the inability to utilize direct push equipment means that direct access to the subsurface materials may be limited to a few boreholes.

In this work, I discuss Multi-frequency Oscillatory Hydraulic Testing (M-OHT), in which pumping tests of various frequencies are performed, and the response of the aquifer to these oscillations is monitored. The ability to stress an aquifer at multiple frequencies is extremely useful, since the period of oscillation represents an additional testing parameter that can be changed in order to collect different information about the subsurface. In contrast, traditional testing strategies such as (constant rate) pumping tests and slug tests have only one parameter that can be changed—i.e., the rate of pumping, or the height of the slug test—and test response is often insensitive to changes in these testing parameters.

I discuss the theory behind M-OHT and first show some example numerical experiments demonstrating the added information content from multiple-frequency aquifer stimulations. I then present laboratory and field examples of this testing (along with analysis strategies), and discuss the practical implementation issues for carrying out such tests to characterize deep aquifers.

The Application of Oilfield Advanced Borehole Geophysics for Deep Groundwater Investigations

Ned A. Clayton
Advanced borehole geophysical logging is one the primary methods for evaluating oil and gas reservoirs, providing quantitative characterization of important rock matrix, fluid, and fracture properties across a wide range of geology types, subsurface, and borehole conditions. This technology is being used increasingly for deep groundwater investigations because of the ability to efficiently and effectively characterize the subsurface in deep holes and wells where drilling and completion costs are high. The wireline-conveyed tools provide a wide range of in-situ measurements, packer testing, and sampling capabilities, employing magnetic resonance, dipole sonic, nuclear spectroscopy, and other technologies, to evaluate key hydrogeological, geological, geomechanical, and structural properties continuously in depth. Applications of oilfield wireline technology include deep brackish aquifer resource characterization, deep mine hydrogeology investigations, wastewater injection and geologic sequestration of carbon dioxide into deep non-potable aquifers. Several case examples of advanced geophysical logging used for these deep groundwater applications will be provided, as well as an introduction to the technology and measurements employed.

Tools, Techniques and Methods (cont.)

Grant Ferguson

Deep Groundwater Monitoring Challenges and Best Practices After 30 Years of Westbay System Applications Worldwide

David Larssen
Instrumentation of the deep (>2000 ft) groundwater environment for purposes of hydrogeologic testing, in-situ characterization, regional and local characterization and performance monitoring presents formidable challenges. High costs for drilling and completions, difficult access conditions, high ambient pressures and temperatures, difficult in-situ chemistry conditions combined with heightened health and safety concerns make it mandatory to extract the most scientific value from every borehole. These present challenges in selection of appropriate borehole completion technology.

Given the significant investment in borehole drilling and completion there is significantly increased demand for reliable, modular instrumentation suitable for multi-level applications to deliver high-quality, verifiable, defensible measurements from all of the features intersected by the borehole. Nested monitoring wells, typically used in the environmental industry, are cost-prohibitive in such environments and cannot deliver on the requirements for ease of installation, modularity, verification and defensibility.

The Westbay System is a modular borehole completion technology that has been used worldwide on deep groundwater investigations for over 30 years. With a strong background in applications for geologic repository studies involving instrumentation to depths of 4000 ft or more the Westbay System has been accepted internationally as a reliable, high quality technology suitable to meet the performance and flexibility demanded by such high-visibility projects. Other deep groundwater applications include mining projects and hydrogeologic testing and monitoring of deep sub-permafrost environments in Canada's Arctic. From this breadth of experience comes an understanding of industry best practices and the challenges of operation in the deep groundwater environment. This paper describes the Westbay design, typical deep groundwater applications and limitations, and presents example data from several different sites to illustrate how the requirements for high-quality, defensible data are met, and how such data are used in implementation of data gathering and decision-making processes.

Sampling for Multi-Phase Characterization of Deep, Gas-Rich Groundwater Systems

Kevin Krogstad
Groundwater under pressure often contains dissolved gases at significantly elevated concentrations, which can complicate sampling. Water chemistry can be altered as acid gases such as carbon dioxide come out of solution. Aquifer parameters can be impacted as bubbles form in the aquifer framework, “vapor locking” the area around a pumping well. Finally, the dissolved gases may be toxic and/or explosive, which can create a hazard for samplers or pump crew.

Since water chemistry can begin to change immediately upon exsolution of dissolved gases, prompt field chemistry is critical. Alkalinity, pH, and other project-specific parameters should be determined within minutes of depressurization.

Dissolved gas profiles can be very important for flow modeling, as gas exsolution can reduce the effective hydraulic conductivity by 30-50% or more around pumping wells.

Sampling dissolved gases at the surface raises a number of issues. In most cases, the sample has traveled through a significant length of plastic tubing to reach the surface. A flow-through gas separation system may preferentially collect some gases due to faster exsolution rates. In pumping a deep well, gases at the surface may have originated in water that has not yet left the borehole.

In-situ methods remove tubing from the equation, and are generally a better choice for control of pressure. However, some are not completely isolated from atmosphere, and most have small sample volumes.

An innovative sampler design allows a sample to be collected and maintained at reservoir pressures and isolated from the atmosphere until analyzed, minimizing the alteration in water chemistry associated with exsolution of gases. A large sample volume permits more analyses to be performed, and may entirely replace pumping for some applications. Discharge of the sample into an evacuated container allows capture of exsolving gases, which may then be decanted for analysis.