Oil & Natural Gas Projects
Exploration and Production Technologies
Anisotropic Properties of Compacted Clay-Rich Rocks
The principal objective of this work is to characterize the elastic anisotropic
properties of clay-rich rocks for consolidation conditions simulating compaction
at depths of 0-2 km in young sedimentary basins of interest for hydrocarbon
exploration. To realize this objective, researchers will develop an entirely
new laboratory apparatus capable of directly measuring the anisotropic properties
of clay-rich rocks subjected to stress states simulating confinement at depth.
The ultrasonic phased-array compaction cell that will be designed and fabricated
at Lawrence Berkeley National Laboratory (LBNL) will employ a P-wave ultrasonic
phased-array and a series of resonant P- and broadband S-wave transducers to
recover the five transverse isotropic (TI) elastic constants of clay-rich rocks
during compaction, without the need for sample unloading, recoring, or reorienting.
Lawrence Berkeley National Laboratory
This project has successfully developed a state-of-the-art laboratory device
for measuring the anisotropic elastic constants of clay-rich rocks during compaction.
This device employs an ultrasonic compressional wave phased-array and resonant
P-wave and broadband shear wave transducers. The project performers have used
this device to measure the evolution of transverse anisotropy in compacting
clay-rich sediments provided by industry partners from reservoirs in West Africa.
In the final year of the project, additional anisotropy measurements will be
collected on clay-rich core provided by Chevron and BP. This data will be used
to develop a stress-dependent effective medium model that describes the evolution
of transverse anisotropy in clay-rich rocks for use in seismic imaging and AVO
The financial impact of properly incorporating anisotropy in seismic imaging
and analysis can be measured as the cost of a dry hole versus the value of a
discovery well. With the typical cost of a well at $5-10 million, knowledge
of the anisotropic properties of the overburden required for proper time-to-depth
conversion can be significant, particularly in sedimentary basins. This project
represents a collaborative effort between LBNL and the oil and gas industry
to quantify the magnitude and character of the anisotropy of clay-rich rocks
at depths of 0-2 km. This effort will utilize expertise in laboratory rock physics
and ultrasonic phased-arrays that resides at LBNL to develop a new laboratory
technology anisotropy measurement and to apply this technology to develop a
new data set quantifying the stress-dependent anisotropic properties of clay-rich
There is a growing concern that anisotropy in the overlying reservoir strata,
when left uncorrected for, can hinder efforts to image reservoir structure and
estimate reservoir properties using seismic methods. While clay-rich rocks are
estimated to comprise 75% of sedimentary basins, only a limited number of experimental
anisotropy studies have been performed on such rocks, especially for higher
porosity clay-rich sediments/rocks encountered in the first two kilometers of
depth. New data on the stress-dependent anisotropic properties of compacted
clay-rich rocks (i.e., c11, c33, c55, c66, c13 or can be used directly to achieve
proper focusing in anisotropic imaging and to provide amplitude corrections
for AVO and may provide valuable information on overpressure that can be used
in borehole stability analysis.
Despite the growing data set on shale anisotropy present in the literature,
anisotropy data for less-consolidated and diagenetically altered clay-rich rocks
(25-45% porosity, 0-2 km depth) is presently sparse (especially ). The project
performers will use the ultrasonic phased-array compaction cell to fill this
gap by developing a new data set describing the magnitude and character of the
anisotropy of shallow (0-2 km depth) clay-rich rocks from sedimentary basins
that are of interest for hydrocarbon exploration. Using the knowledge gained
from these experiments and microstructural analysis of the compacted samples
(from X-ray diffraction, SEM, and possibly neutron diffraction), the researchers
propose to develop stress-dependent effective-medium models describing the influence
of compaction-induced texture on the anisotropic properties of clay-rich rocks.
Current Status (August 2006)
- Developed and tested a new apparatus (phased array compaction cell) for measuring the transverse isotropic elastic constants of a compacting clay-rich sediment.
- Completed anisotropy measurements on compacting clay-rich geochemical cores provided by our Industry partners.
- Obtained new data on the evolution of Thomsen parameters with (one-dimensional) consolidation.
- Initiated technology transfer to Industry.
- Demonstrated that the phased array compaction cell can be used to measure stress induced anisotropy in unconsolidated sands.
The project is nearing completion. Data collection and processing is complete. A draft of the paper describing the phased array compaction cell and its utility for measuring the anisotropic properties of soft sediments (to be submitted to Geophysics for publication) is finished. Technology transfer of this device and the findings of this research to Industry (Chevron) are complete.
Project Start: May 27, 2002
Project End: April 6, 2006
Anticipated DOE Contribution: $721,000
Performer Contribution: $0
NETL – Jim Barnes (firstname.lastname@example.org or 918-699-2076)
LBNL- Seiji Nakagawa (email@example.com or 510-486-7894)
A cross section of the ultrasonic phased-array compaction cell showing the locations
of the P-wave phased array and pinducer.
The fully operational ultrasonic phased-array compaction cell.
Two journal submissions are in preparation: one describing the ultrasonic phased-array
compaction cell, and a second presenting the anisotropy measurements and analyses
on marine sediments provided by industry partners.