Kurt T. Nihei

Preferred orientation and elastic anisotropy of illite-rich shale

Shales display significant seismic anisotropy that is attributed in part to preferred orientation of constituent minerals. This orientation pattern has been difficult to quantify because of the poor crystallinity and small grain size of clay minerals. A new method is introduced that uses high-energy synchrotron X-rays to obtain diffraction images in transmission geometry and applies it to an illite-rich shale. The images are analyzed with the crystallographic Rietveld method to obtain quantitative information about phase proportions, crystal structure, grain size, and preferred orientationtexture that is the focus of the study. Textures for illite are extremely strong, with a maximum of 10 multiples of a random distribution for 001 pole figures. From the three-dimensional orientation distribution of crystallites, and single-crystal elastic properties, the intrinsic anisotropic elastic constants of the illite aggregate excluding contribution from aligned micropores can be calculated by appropriate medium averaging. The illitic shale displays roughly transverse isotropy with C11 close to C22 and more than twice as strong as C33. This method will lend itself to investigate complex polymineralic shales and quantify the contribution of preferred orientation to macroscopic anisotropy.

Inverting for reservoir pressure change using time-lapse time strain: Application to Genesis Field, Gulf of Mexico

There are increasing numbers of published examples from around the world in which significant 4D time shifts have been observed in the overburden above producing reservoirs.

Stress-induced velocity anisotropy measurements in unconsolidated sand using a phased-array uniaxial compaction cell

Summary An experimental device for measuring the transverse isotropic (TI) elastic properties of sediments unde r uniaxial strain conditions has been developed. The phased array compaction cell utilizes matched sets of P- and S-wave ultrasonic transducers located along the sides of t he sample and an ultrasonic P-wave phased array source with pinducer receiver on the ends of the sample. The p hased array provides plane P-waves that are used to measu re phase velocities over a range of angles. From thes e measurements, the five elastic constants for TI med ia can be recovered as the sediment is compacted, without the need for sample unloading or reorienting. Descripti ons of the apparatus and data processing and an applicatio n to an unconsolidated sand sample are provided in this pap er. Pwave anisotropy of 20% has been observed in dry sand under an axial stress of 5 MPa.

Inverting for Pressure Using Time-Lapse Time-Strain – Application to a Compacting GOM Reservoir

A028 Inverting Strain – Application for Pressure to Using a Compacting Time-Lapse GOMTime- Reservoir N. L. Duranti Hodgson* (Chevron (Heriot-Watt ETC) J. University) Rickett (Chevron C. MacBeth ETC) (Heriot-Watt & K. Nihei (Chevron University) ETC) SUMMARY Quantitative estimation of dynamic reservoir properties from time-lapse seismic is becoming increasingly widespread. In compacting reservoirs however the 4D seismic signal is complex due to stress and strain redistribution in reservoir and non-reservoir rocks. Several authors have reported observing measurable time-shifts in the overburden on time-lapse seismic data. A method for using these overburden time-lapse time-shifts to invert for reservoir pressure change is presented.

Frequency Response Modeling of Seismic Waves Using Finite Difference Time Domain with Phase Sensitive Detection (TD-PSD)

P322 Frequency Response Modeling of Seismic Waves Using Finite Difference Time Domain with Phase Sensitive Detection (TD-PSD) K.T. Nihei* (Chevron Energy Technology Co.) & X. Li (Lawrence Berkeley National Laborator) SUMMARY We examine an alternative approach for computing the frequency response of a heterogeneous anisotropic viscoelastic medium. The approach consists of running an explicit finite difference time domain (TD) code with a harmonic wave source out to steady-state and then extracting the magnitude and phase from the transient data via phase sensitive detection (PSD). The PSD algorithm requires integration over a single cycle of the waveform to obtain accurate phase

Observation of seismic wave propagation in particulate composite material with various inclusion sizes and concentrations

Two‐phase particulate composite samples with inclusions of varying size and concentration were made with cement and sand or pebbles. The velocities of P‐wave (60‐kHz) and S‐wave (150‐kHz) pulses and the attenuation of S‐wave pulses were examined. The results of the tests suggested that the velocities were consistent with the results of effective media models which were inclusion size independent. However, the frequency‐dependent attenuation of the S wave was strongly affected by the size of the inclusions. For inclusions sized on the order of 1/10 of the wavelength, the waves showed decreasing attenuation with increasing concentration, while for the sizes of about 1/4 and 1/1 of the wavelength, the waves showed maximum attenuation at volumetric concentrations of about 30% and 70%, respectively. Many aspects of the observed wave behavior for moderate concentrations were similar to numerical simulations of 1‐D wave propagation in a layered media, where the matrix and inclusions were represented by alternati...