Introduction

New England Research, Inc. (NER) offers a range of apparatuses to measure the effects of temperature, pressure, and rock-fluid interaction on deformation and the elastic, electrical, and flow properties of rock.  Each apparatus supports standard ASTM and ISRM rock mechanics tests as well as diverse measurements over complex loading trajectories at reservoir pore pressures, confining pressures, and temperatures.  NER’s systems are the result of years of experience on a wide variety research and client directed projects on the behavior of rocks at in situ conditions. Progressive improvements in technique, analysis software, and hardware are incorporated into the design of each unit. Since each product we offer is used at NER, qualified technical support is constantly available.

For over thirty-five years, NER has supplied AutoLab systems to universities, national laboratories, national oil companies, and major oil and gas companies worldwide. Many of these systems have been customized to meet specific research needs and other unique requirements of our customers.  It is not surprising therefore to see a significant number of refereed publications in international journals mentioning NER’s AutoLab systems. As of May 2025, Google Scholars finds two hundred thirty-eight (238) peer reviewed journal articles referencing our AutoLab apparatuses supporting their work since 2004. These data are shown graphically.

AutoLab Design

Dual Coaxial Chamber Vessel

What is different in NER’s approach?  A distinguishing feature NER’s AutoLab triaxial series is the design. The AutoLab uses high pressure servo hydraulic intensifiers to control the axial load (or axial displacement) and confining pressure in a pressure vessel divided into two coaxial chambers as illustrated in the schematic below. An instrumented sample is sealed in the lower chamber which is independently pressurized to simulate the overburden (confining pressure). High pressure fluid is injected into the space between the top closure nut and the top of the piston to generate force on the sample. A sealing bushing divides the upper and lower chambers and guides the axial loading piston.  The coaxial design results in precise, parallel loading of the sample. It also eliminates the need for a large (two or four post) test frame which primarily supports a large hydraulic cylinder in conventional systems.

The feedbacks for axial loading are:

• the pressure in the upper chamber (axial pressure).
• an internal load cell positioned at the bottom of the sample assembly that gets converted to axial stress using the sample diameter.
• the displacement transducer mounted on top of the test frame.
• virtual channels defined by the user.

The feedbacks for confining pressure are:

• the pressure in the lower chamber (confining pressure).
• virtual channels defined by the user.

Advanced Protocol Demonstration: Uniaxial Stress Loading to Post-failure

In this section we provide one example protocol that benefits from NER’s equipment design. The compactness of the system gives rise to its inherent stiffness. For example, the stiffness of the AutoLab is 20 MN/mm. The stiffness allows the systems to bring many rock types stably through failure into the post failure regime.  Uniaxial stress loading of a dry sample of Berea sandstone is shown below. Axial displacement and stress difference are plotted as a function of time. The test was conducted in displacement feedback. As the sample reaches peak stress difference of 171 MPa, it fails with an attendant drop in stress. The stress continued to decrease and plateaued at 116 MPa; the duration of this process is 17.5 minutes. During the entire test (25.5 minutes), the sample was loaded at a constant displacement rate of 8 x 10^-4 mm s^-1.

The smooth transition into the post failure regime allows investigators to study the failure process. While these results were obtained on a sandstone, other rock types such as low porosity, fine grained brittle rocks may not exhibit the same characteristics. Machine stiffness is not the sole controlling factor for the stabilization of failure; pore pressure, permeability, porosity, loading rate, and axial load feedback influence the failure process.

AutoLab Vessel Sizes

For the triaxial systems, we offer three standard vessel bore diameters rated for confining and pore pressures of 200 MPa and a temperature of 200^oC. Each apparatus is customizable for higher pressures and temperatures. A key determinator is the sample size, which correlates directly with the diameter of the pressure vessel, and the force that the unit generates. These values are given below.

Other Noteworthy Design Features and Options for the AutoLab Series

High Pressure, High Temperature.  To address the increasing need for measurements at elevated temperatures, NER developed a unique option for our triaxial systems, the AutoLab 3000. The triaxial vessel and pore pressure intensifiers are housed in an oven which heats the entire system to 150^oC. This configuration ensures that the pore fluids entering pressure vessel are at the same temperature as the rock sample.

Output Volumes for Pore Pressure Intensifier.  Standard configurations range from 59 cm³ (3.6 in³) to 482 cm³ (29.5 in³). Other output volumes are possible depending on the system configuration. Each intensifier can be configured for automatic recycling, an important feature for fluid substitution and continuous flow experiments.

Pore Fluid Compatibility for Pore Pressure Intensifier.  Commonly utilized fluids include brine, CO₂, gas, and oil. Titanium is primarily used for the intensifier body.  For applications, using acids or other corrosive fluids the pore pressure intensifier bodies are constructed with C276 Hastelloy. Ceramic pistons are standard on all AutoLab pore pressure intensifiers to ensure smooth operation, corrosion resistance, and long seal life.

Electrical Feed Thus.  A large number of high-pressure electrical feed thrus are incorporated into the base plug to facilitate a variety of experimental set ups such as transverse velocity or collecting and locating acoustic emissions (AE). For example, thirty-two (32) feed thru’s are standard in the AutoLab 1500.  Although there are initial constraints incorporated into the initial design, the final number is determined by the customer’s experimental requirements.

Electronics Console.  The AutoLab electronics console, standard on all NER systems can be expanded to incorporate a large number of temperature, velocity, and resistivity measurements. This flexibility in system design, software development, and electronics support ensures that the system is readily adaptable to meet immediate research needs and to provide an opportunity for future development as research projects evolve.

Uniaxial Stress Test Frame.  Since it is inconvenient and cumbersome to carry out unconfined rock mechanics experiments inside a pressure vessel, a dedicated uniaxial test frame is often supplied as an option to facilitate these measurements.  The uniaxial stress test frame is a four-post servo hydraulically controlled apparatus for measuring unconfined compressive strength, elastic constants, fracture toughness, and Brazil indirect tensile strength. The system can also accommodate odometers for testing unconsolidated materials.  The system operates in either force or displacement feedback.

The uniaxial test frame operates using the same electronics console and data acquisition system at the triaxial apparatus, consequently both components of the apparatus cannot be operated simultaneously.  The LVDT and load cell have both full-scale and a high resolution amplification to accommodate a full complement of unconfined tests.

AutoLab Series Software

The latest software release for our AutoLab series Autolab v6 builds on years of experience developing and running computer-driven laboratory protocols for unique client needs. This section highlights some key components that comprise Autolab v6.

Building a Protocol

Autolab v6 has a built-in que system that allows the user to graphically put together an advanced protocol in minutes. There is a script that is automatically generated in Python from the user’s graphical inputs that can be saved and loaded again for future use. The scripts are editable with a large array of built-in functions allowing the user flexibility in designing customized protocols with minimal effort.

Data Storage

Data is stored in a Postgres database with full querying functionality. There are predefined experimental types for the user to quickly navigate through sample measurements. All the support information relevant to the experiment is linked to the experimental type such as calibration parameters, velocity endcaps, etc., minimizing the chance for human error in post-processing. Data can be easily queried and output in standard file formats for further analysis.

Automated Analyses and Reporting

A report can be generated for a given experimental type that processes the data with Python code. Charts and graphs can be automatically created and applied to all similar experimental types through the Postgres database for consistent reporting and immediate feedback on how an experiment went.

For more in-depth insights into an experiment we can help users develop a module that processes data and produces charts and graphs as an experiment is running or provides graphical user interfaces for post-processing. We use modules internally with our standard protocols to quickly identify instrumentation issues or other problems with experiments. Modules can be used to recognize faulty strain gauges, hide measurements from analyses and calculations, and create quality control plots to assess an experiment as it is still running.

Experiment-Specific Modules

For many experimental types, we have developed processing software that is included in AutoLab v6. Notable advanced processing suites are our velocity module that expedites accurate velocity picks and our permeability module that helps the user assess errors in transient permeability methods on the fly.

High Temperature-High Pressure Versions of the AutoLab Series

There has been an increasing demand for rock properties measurements at higher temperatures and pressures.  University research on crustal processes requires temperatures to 350^oC at pressures greater than 300 MPa for geothermal programs, rock-fluid interactions at mid-crustal depths, frictional properties for studies of intermediate depth earthquakes, etc.  The oil and gas companies are drilling deeper wells into high temperature formations in both conventional and unconventional plays.  These efforts demand high quality data on at in situ conditions over realistic stress and thermal paths.

To address these needs, NER modified the AutoLab series to operate at higher temperatures and pressures while maintaining the complete option selection at temperatures below 200^oC.  Since the vessel design is coaxial and unencumbered by a large thermally conductive support frame, the logical choice was to increase the maximum operating temperature to 350^oC by adding internal heaters and modifying the pressure vessel dimensions.  The system continues to support to support NER’s standard measurement options of velocity, permeability, and deformation at the maximum temperature and pressure conditions.  For velocity measurements, compressional (or longitudinal) and torsional (shear) waves are propagated through waveguides at each end of the sample.  A schematic of the vessel detailing the velocity transducer and sample waveforms are shown below. At temperatures above 200^oC, the samples are primarily jacketed in seamless copper.