Core Measurement Services :: New England Research, Inc.

Development and Constraint of Physical Models for Geothermal Reservoirs

The development of effective exploitation strategies requires scientifically sound characterization of geothermal reservoirs. Surface geophysical data are potentially the most powerful and cost effective means of exploration and characterization, providing images of the subsurface structures prior to extensive drilling.

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Core Measurement Services

NER offers core measurement services at its facility in White River Junction, Vermont.

To fill a growing need for high quality data, NER maintains eight servo-controlled AutoLab test systems and an AutoScan II core scanner to carry out a variety of rock properties measurements as a function of state-of-stress, pore fluid composition, and temperature. We offer custom core analysis to meet your specific requirements. Contact us for more information.

Compressional and Shear Wave Velocities
Ultrasonic velocities are used to calculate dynamic Young's modulus and Poisson's ratio. With NER's PS2 transducer, one compressional (P) and two orthogonally polarized shear waves (S1 and S2) are recorded. The difference in the shear velocities provides an estimate of rock anisotropy. Benchtop tests are performed at ambient pressure and temperature. Confined tests are conducted at eight effective confining pressures (confining minus pore pressure). The samples are tested dry or saturated with water, brine or oil.

Benchtop

Hydrostatic Pressure: eight effective pressures (ambient temperature one pore pressure)

Options:
Temperatures to 250°F (121°C)
Additional pore pressures to 15,000 psi

Permeability

Liquid Permeability is measured with a complex transient, pulse decay, or steady state method depending on the rock in the range of 10-6 to 0.5 Darcies

Permeability at six (6) effective confining pressures

Low Permeability to 10-8 Darcies

Permeability at hydrostatic pressure with pore pressure depletion

Permeability at a non-hydrostatic state of stress

Permeability over other loading paths and/or instrumentation for strain

Complex Electrical Impedance
Two and four electrode resistivity measurements are carried out as a function of stress, frequency, and temperature. The four-electrode frequency range is 0.02 Hz to 100 kHz. The two-electrode frequency range is 5 Hz to 1 MHz. Each measurement is at 100% saturation.

Resisitivity at six (6) effective confining pressures

Resisitivity at a non hydrostatic state of stress

Resisitivity over other loading paths and/or instrumentation for strain

Combined Permeability and Complex Electrical Impedance
Permeability and complex electrical impedance can be measured simultaneously on the same sample. The same constraints apply as those listed for the tests performed individually.

Combined Permeability/Resisitivity under hydrostatic stress

Combined Permeability/Resisitivity at a non-hydrostatic state of stress

Other loading paths and/or instrumentation for strain

Pore Volume Compressibility
The following tests are used to obtain information on reservoir drive mechanisms, compaction, and subsidence, to make porosity corrections and in some cases estimate rock strength.

Hydrostatic pore volume compressibility:

Constant pore pressure with a changing hydrostatic stress

(Option) with simultaneous velocity measurement

Hydrostatic pore volume compressibility:

Constant hydrostatic stress with a changing pore pressure

(Option) with simultaneous velocity measurements

Uniaxial Stress:

Pore volume compressibility with a changing differential stress and constant pore and confining pressure

(Option) with simultaneous velocity measurements

Uniaxial Strain:

Pore volume compressibility under uniaxial strain and constant pore pressure

(Option) with simultaneous velocity measurements

Pore Pressure Depletion:

Pore volume compressibility under uniaxial stress or strain and changing pore pressure

Strength and Modulus Tests
Most strength and modulus tests involve the measurement of stress as a function of strain under various loading or stress paths. These tests are used to estimate elastic constants and failure properties of the rock. The tests are usually performed on samples with a length to diameter ratio of 2 to 1. The standard sample size is 1.5 inches in diameter by 3 inches in length. However, other samples' sizes can be used in some cases.

Unconfined Compression

(Option) with simultaneous velocity, permeability, and/or resistivity measurements

Confined Compression to Failure

(Option) with simultaneous velocity, permeability, and/or resistivity measurements

Multistage Confined Compression

(Option) with simultaneous velocity, permeability, and/or resistivity measurements

Tensile Strength (Brazil Test):

Tensile strength computed from splitting of a rock cylinder.

Hollow Cylinder Test:

Hydrostatic load to failure of a 1.5 by 3.0 inch rock cylinder with axially drilled hole. Standard hole diameter is 0.5 inch. The results of this test are used to estimate failure strength of boreholes and perforation cavities. Failure is monitored using pore volume strain.

Bulk Compressibility

Change in bulk volume as a function of hydrostatic pressure to 20,000 psi.

(Option) with simultaneous velocity, permeability, and/or resistivity measurements

Hardness: Brinell, Shore, or Schmidt Hammer

Shear Modulus: Torsion Measurement

Coefficient of friction: Torsion Measurement

Special Loading Protocols for Coupled Processes

Many experiments require complex loading and unloading paths with variable boundary conditions. Using NER's AutoLab systems, these parameters are entered into the control software and executed in a servo-controlled apparatus. At any point in the test sequence velocity, permeability, and/or resistivity measurements may be prescribed.

Core Scanning: continuous velocity, conductivity and permeability

Velocity Anisotropy

Attenuation: by low frequency cyclic loading (0.01 to 100 HZ)

Creep and Static Fatigue

Rock-Fluid Interactions

Thermal Expansion:

Axial strain as a function of temperature to 390°F (200°C) and pressure to 7,500 psi.

Bulk Density, Grain Density and Porosity

Sample Sizes and Preparation
Standard Sample Sizes are 1.00 inch and 1.50 inch diameter cylindrical plugs with a length approximately twice the diameter. Other size samples are considered non-standard

Analysis

Mohr Coulomb Failure Envelope

The Mohr-Coulomb failure envelope is computed from multiple triaxial compression tests either on the same rock (multistage) or on separate rock samples (single stage). The envelope determines stable states of shear stress for a given normal stress.

Pore Structure Inversion and Analysis

Using NER's proprietary PSI methodology, core properties data including velocities, permeability, resistivity, capillary pressure, and NMR T2 spectra are combined with thin section and/or SEM image analysis to constrain an inversion for a pore space model of the sample. The analysis results in a statistical description of the pore space which is physically consistent with the measured properties. The analysis package includes thin section analysis and a detailed report presenting inversion results. Constraining core data (resistivity, permeability and velocity tests) is priced separately.