In-Situ Physical Properties Using Crosswell Acoustic Data
- P.A. Johnson (Los Alamos Natl. Laboratory) | J.N. Albright (Los Alamos Natl. Laboratory)
- Document ID
- Society of Petroleum Engineers
- SPE/DOE Low Permeability Gas Reservoirs Symposium, 19-22 March, Denver, Colorado
- Publication Date
- Document Type
- Conference Paper
- 1985. Society of Petroleum Engineers
- 1.6.9 Coring, Fishing, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 1.2.3 Rock properties, 5.1.6 Near-Well and Vertical Seismic Profiles, 5.5.2 Core Analysis, 7.2.2 Risk Management Systems, 4.3.4 Scale
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Crosswell acoustic surveys enable the insitumeasurements of elastic moduli, Poisson's ratio, porosity,and apparent seismic Q of gas-bearing low-permeability formations representedat the Department of Energy Multi-Well Experiment (MWX) site near Rifle,Colorado. These measurements, except for Q, are compared with laboratorymeasurements on core taken from the same depths at which the crosswellmeasurements are made. Seismic Q determined in situiscompared to average values for sandstone
Porosity was determined from crosswell data using the empirical relationshipbetween acoustic velocity, porosity, and effective pressure developed byDomenico.6 In situporosities aresignificantly greater than the core-derived values. Sources of the discrepancymay arise from (i) the underestimation of porosity that can result when Boyle'sLaw measurements are made on low-permeability core and (ii) the application ofDominco's relationship,6 which is developed for clean sands, to themixed sandstone and shale lithologies represented at the MWX site.
Values for Young's modulus and Poisson's ratio derived from crosswellmeasurements are comparable to values obtained from core. Apparent seismic Qmeasured in situbetween wells is lower than Q measuredon core and clearly shows the heterogeneity of sandstone deposited in a fluvialenvironment.
There are few ways to investigate rock properties beyond several wellboreradii of gas wells. The principal seismic methods include vertical seismicprofiling (VSP), 3-D seismic surveying, and crosswell acoustic measuring. Thefirst two methods are primarily exploration tools useful in characterizing thegross structure of an area; however, crosswell acoustic surveys can measurerock properties between closely spaced wells. The crosswell techniques alsoallow the determination of in situphysical propertiesparallel or subparallel to bedding, which heretofore have been impossible tomeasure.
In this study, crosswell measurements of Young's moduli, Poisson's ratio andporosity are compared with laboratory measurements made on core; whereasseismic Q measurements are compared with average values for sandstone. Thelaboratory core measurements of moduli, Poisson's ratio, and porosity were madeby oil and gas industry support companies under contract to Sandia NationalLaboratories.
Measurements were conducted at the Department of Energy Multi-WellExperiment (MWX) site in the Piceance Basin near Rifle, Colorado. The crosswelldata were acquired in sands deposited within a delta plain coastal environment,part of the Cretaceous Mesa Verde formation. This region of the Mesa Verde is atarget area for hydrofracture stimulation due to the suspected high gascontent, but low permeability, of this sandstone.
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