Richard Nolen-Hoeksema

The squirt-flow mechanism; macroscopic description

We introduce a poroelasticity model that incorporates the two most important mechanisms of solid/fluid interaction in rocks: the Biot mechanism and the squirt-flow mechanism. This combined Biot/squirt (BISQ) model relates compressional velocity and attenuation to the elastic constants of the drained skeleton and of the solid phase, porosity, permeability, saturation, fluid viscosity and compressibility, and the characteristic squirt-flow length. Squirt-flow length is a fundamental rock property that does not depend on frequency, fluid viscosity, or compressibility and is determined experimentally. We find that the viscoelastic response of many sandstones is dominated by the squirt-flow component of the BISQ mechanism and that the viscoelastic properties of these rocks can be expressed through a single dimensionless parameter omega R 2 /kappa , where omega is angular frequency, R is the characteristic squirt-flow length, and kappa is hydraulic diffusivity. The Biot mechanism alone does not give an adequate explanation of the observed velocity dispersion and attenuation, and the viscoelastic behavior of many sandstones.

High-resolution crosswell imaging of a West Texas carbonate reservoir; Part 1, Project summary and interpretation

A carbon dioxide flood pilot is being conducted in a section of Chevron’s McElroy field in Crane County, west Texas. Prior to CO2 injection, two high‐frequency crosswell seismic profiles were recorded to investigate the use of seismic profiling for high‐resolution reservoir delineation and CO2 monitoring. These preinjection profiles provide the baseline for time‐lapse monitoring. Profile #1 was recorded between an injector well and an offset observation well at a nominal well‐to‐well distance of 184 ft (56 m). Profile #2 was recorded between a producing well and the observation well at a nominal distance of 600 ft (183 m). The combination of traveltime tomography and stacked CDP reflection amplitudes demonstrates how high‐frequency crosswell seismic data can be used to image both large and small scale heterogeneity between wells: Transmission traveltime tomography is used to image the large scale velocity variations; CDP reflection imaging is then used to image smaller scale impedance heterogeneities. The...

Estimating seismic velocities at ultrasonic frequencies in partially saturated rocks

Seismic velocities in rocks at ultrasonic frequencies depend not only on the degree of saturation but also on the distribution of the fluid phase at various scales within the pore space. Two scales of saturation heterogeneity are important: (1) saturation differences between thin compliant pores and larger stiffer pores, and (2) differences between saturated patches and undersaturated patches at a scale much larger than any pore. We propose a formalism for predicting the range of velocities in partially saturated rocks that avoids assuming idealized pore shapes by using measured dry rock velocity versus pressure and dry rock porosity versus pressure. The pressure dependence contains all of the necessary information about the distribution of pore compliances for estimating effects of saturation at the finest scales where small amounts of fluid in the thinnest, most compliant parts of the pore space stiffen the rock in both compression and shear (increasing both P‐ and S‐wave velocities) in approximately th...

Modulus—porosity relations, Gassmann’s equations, and the low‐frequency elastic‐wave response to fluids

Gassmann’s equations relate the low‐frequency drained and undrained elastic‐wave response to fluids. This tutorial explores how different modulus—porosity relationships affect predictions of the low‐frequency elastic‐wave response to fluids based on Gassmann’s equations. I take different modulus—porosity relations and substitute them into Gassmann’s equations through the framework moduli. The results illustrate the range of responses to fluids and can be summarized in a nomograph of the effective fluid coefficient, which quantifies the change in the pore‐space modulus (∂Kpore/Kpore) in response to a change in fluid modulus (∂Kfluid/Kfluid). Two ratios control the effective fluid coefficient: the ratio of the fluid modulus to the solid‐grain modulus ( Kfluid/Ksolid) and the ratio of the Biot coefficient to porosity (αK/ϕ). The effective fluid coefficient nomograph is a convenient tool for estimating how low‐frequency elastic‐wave properties will respond to changes in reservoir fluids.

High-resolution crosswell imaging of a West Texas carbonate reservoir; Part 5, Core analysis

We conducted a core analysis program to provide supporting data to a series of crosswell field experiments being carried out in McElroy Field by Stanford University’s Seismic Tomography Project. The objective of these experiments is to demonstrate the use of crosswell seismic profiling for reservoir characterization and for monitoring CO2 flooding. For these west Texas carbonates, we estimate that CO2 saturation causes P‐wave velocity to change by −1.9% (pooled average, range = −6.3 to +0.1%), S‐wave velocity by +0.6% (range = 0 to 2.7%), and the P‐to‐S velocity ratio by −2.4% (range = −6.4 to −0.3%). When we compare these results to the precisions we can expect from traveltime tomography (about ±1% for P‐ and S‐wave velocity and about ±2% for the P‐to‐S velocity ratio), we conclude that time‐lapse traveltime tomography is sensitive enough to resolve changes in the P‐wave velocity, S‐wave velocity, and P‐to‐S velocity ratio that result from CO2 saturation. We concentrated here on the potential for CO2 sat...

High-resolution shallow geophysics and geology in the Hudson-Raritan Estuary Ecosystem Restoration, New Jersey

The Hudson-Raritan Estuary of New York and New Jersey is one of the largest estuaries on the East Coast of the United States. It includes part of the New York City metropolitan area and includes the Port of New York and New Jersey. The estuary is an important economic, environmental, and recreational resource and asset for the region. Fresh water enters the estuary from the Hudson, Hackensack, Passaic, and Raritan rivers. Since the 17th century, the estuary has experienced industrialization and residential growth that have profoundly altered the estuary and surrounding land from its precolonial state.

The future role of geophysics in reservoir engineering

Reservoir engineers seek to obtain the highest possible economic hydrocarbon recovery from petroleum reservoirs. During primary production, their goal is to position wells at the correct locations for maximum recovery. During secondary and enhanced recovery, their concern is to maximize the volume of hydrocarbon contacted by injected fluids; that is, to achieve maximum volumetric sweep efficiency. To minimize cost and risk, engineers attempt to predict reservoir performance—for both planning and evaluation of hydrocarbon recovery projects. Correct predictions of reservoir performance hinge on how well the reservoir is understood and has been described in the models used for fluid‐flow simulation. Today, 40 years after Muskat wrote the words prefacing this paper, reservoir characterization (especially in terms of reservoir architecture, flow paths, and fluid‐flow parameters) continues to be the key to good reservoir engineering. The premise that underlies this paper is that geophysical methods will play a ...

Thinking possible in Pittsburgh: The 2015 ISEF

The theme for the 2015 International Science and Engineering Fair (ISEF) was “Think Possible.” The 2015 SEG award and honorable-mention winners tackled problems related to calculating horizons for unmanned aerial vehicles, measuring a sidereal day, simulating gas flow in fractures, generating electricity from wave motion, explaining polar-vortex weakening, modeling the El Nino Southern Oscillation, and designing filters for road runoff.

Bright minds shine in Los Angeles: The 2014 ISEF

The theme for the 2014 International Science and Engineering Fair (ISEF) was “Bright Minds Shine.” The 2014 SEG award and honorable-mention winners tackled problems related to transforming data to sound, identifying species using Bayes’ theorem, attenuating tsunami waves, extracting signal from noisy data, placing wind turbines in urban areas, and measuring water waves caused by partial coalescence cascades.

Mentoring global innovation in San Jose: The 2010 ISEF

The theme for the 2010 International Science and Engineering Fair (ISEF) was “Mentoring global innovation.” This year, Agilent Technologies introduced the Agilent Teacher Awards for teachers of ISEF finalists to support their professional development in the sciences, further their mentoring, and support students in independent research. The first awards went to four teachers who mentored projects in the categories Cellular and Molecular Biology, Computer Science, Earth Sciences, and Electrical and Mechanical Engineering.