Equipment And Experimental Methods For Obtaining Laboratory Compression Characteristics Of Reservoir Rocks Under Various Stress And Pressure Conditions
Authors: Newman G.H. , Martin J.C. 
Published: December 2007

Laboratory equipment is described a experimental methods presented for the measurement of the compression characteristics and permeability of reservoir rock under various states of stress, pore pressure and temperature. The equipment is capable of subjecting cylindrical samples to independently varying pore pressure, axial stress, lateral stress, and temperture. Independent measurements are made of the amount of pore fluid expelled from the sample, the axial strain, the lateral strain, the acoustical travel time across the sample, the rate of fluid flow through the sample, and the fluid pressure drop across the sample. These measurements allow the determination of rock parameters including permeability, porosity change, bulk, pore and grain volume porosity change, bulk, pore and grain volume compressibilities; Poisson's ratio; Young's modulus; and compressional wave (P wave) velocity.

Laboratory data are presented of the compressional characteristics of three rocks subjected to two different test conditions. Results are presented of tests on isotropic and anisotropic rock. Results indicate that the past industry practice of calculating bulk and pore volume compressibilities from only axial strain measurements can lead to serious errors if the rock sample is anisotropic.

Introduction

Many investigators have presented laboratory equipment and/or experimental methods for measuring the compression characteristics of reservoir rocks under various states of stress and fluid pressures. In some cases the equipment was either limited to a single stress state or limited to the number of physical quantities that could be measured at a given stress state. In other cases the equipment was limited both in stress level and temperature so that simulated reservoir conditions for many reservoirs were not possible.

This paper describes equipment and experimental methods used for the measurement of compression characteristics of reservoir rocks under various states of stress and fluid pressure at temperatures up to 350 degrees F. The compression characteristics include bulk, pore and grain volume compressibility; porosity; permeability; Poisson's ratio; Young's modulus; Poisson's ratio; Young's modulus; compressive strength; and "P" wave velocity, many of which can be obtained simultaneously.

The stress and pressure capabilities of the compression equipment include uniaxial, hydrostatic and biaxial loading. The hydrostatic and biaxial loading can be obtained under either effective or simulated reservoir stress conditions. The stress and pressure capabilities of the compression equipment include uniaxial loading to 45,000 psi, hydrostatic loading to 10,000 psi, biaxial loading to 45,000 psi axial psi, biaxial loading to 45,000 psi axial stress, and 10,000 psi confining stress with pore fluid pressures to 10,000 psi. Axial and lateral strains of the rock samples are monitored during stress and pressure application and a direct measurement pressure application and a direct measurement of the pore fluid volume changes can be made during the application of effective stress with atmospheric pore fluid pressure. pressure.

THE EQUIPMENT

The basic test equipment is shown schematically in Figures 1 and 2 and photographed in Figure 3. It consists photographed in Figure 3. It consists primarily of a test cell, a hydrostatic primarily of a test cell, a hydrostatic loading frame, a pressure system and a strain monitoring system.