Showing papers by "Jack Dvorkin published in 2012"

Stochastic inversion of facies from seismic data based on sequential simulations and probability perturbation method

Abstract: We presented a new methodology for seismic reservoir characterization that combined advanced geostatistical methods with traditional geophysical models to provide fine-scale reservoir models of facies and reservoir properties, such as porosity and net-to-gross. The methodology we proposed was a stochastic inversion where we simultaneously obtained earth models of facies, rock properties, and elastic attributes. It is based on an iterative process where we generated a set of models of reservoir properties by using sequential simulations, calculated the corresponding elastic attributes through rock-physics relations, computed synthetic seismograms and, finally, compared these synthetic results with the real seismic amplitudes. The optimization is a stochastic technique, the probability perturbation method, that perturbs the probability distribution of the initial realization and allows obtaining a facies model consistent with all available data through a relatively small number of iterations. The pr...

Method and system for integrating logging tool data and digital rock physics to estimate rock formation properties

Abstract: The present invention relates to a method and system for integrating logging tool data and digital rock physics to estimate rock formation properties. A rock sample from a logging tool such as a sidewall plug or large enough cutting can be extracted by the logging tool at approximately the same well bore location that the logging tool measures fluid properties. The rock samples thus obtained is scanned using a CT scanner, scanning electron microscope or other suitable scanning device. The resulting scanned rock image can be segmented and rock properties comprising porosity, absolute permeability, relative permeability, capillary pressure and other relevant rock properties are calculated. The resulting digital calculations are integrated with logging tool data and rock property estimates to improve the accuracy and timeliness of the logging tool data.

Rules of upscaling for rock physics transforms: Composites of randomly and independently drawn elements

Abstract: The tight trends (transforms) between two rock physical properties obtained in the physical or digital laboratory on cm- or mm-sized samples may hold for a composite constructed of these samples. One requirement is that all the elements of the composite obey the same trend. Another requirement is that the composite is spatially uncorrelated and, hence, approximately isotropic. The final requirement is that the underlying elemental transforms are approximately linear. The methods we use to address this exportability of trends for the dynamic elastic moduli (or the elastic-wave impedance) versus porosity, permeability versus porosity, and electrical resistivity versus porosity are, respectively, theoretical elastic bounding, numerical reservoir-scale fluid flow, and electrical current simulations. A practical implication is that if an elastic property of a large volume is determined from remote sensing, be it seismic or cross-well data, its average porosity can be estimated using the transforms established at a much smaller scale. Then, this average porosity can be translated into the hydraulic and electrical properties once again, using the elemental transforms established in the physical or digital laboratory.

Etudes in computational rock physics: Alterations and benchmarking

Abstract: We tested computational benchmarking data for the absolute permeability, electrical formation factor, and elastic moduli based on the Finney pack, a physical dense random pack of identical spheres digitally rendered into a 3D rectangular coordinate system, as the starting digital object. It is altered by (a) changing the radius of each sphere and (b) geometrically inverting these new packs by swapping grains and pores. Porosity, the absolute permeability, electrical formation factor, and elastic moduli are computed for all these alterations. The direct (grain-based) objects are relevant to clastic rock, and the inverse objects are proxies for carbonates with moldic pores. To corroborate these computational results, we matched the permeability versus porosity, formation factor versus porosity, and elastic moduli versus porosity trends they form by established theoretical rock physics models. These trends persisted when we reduced the scale of investigation by subsampling some of the digital objects...

Elastic Properties of Silica-Rich Mudrocks: Woodford Shale, Anadarko Basin, Oklahoma

Abstract: Applications of seismic methods in mudrock exploration are limited due to a lack of well developed rock physics models that can relate mudrock matrix and fluid properties to seismic velocities. We propose a first principle based rock physics modeling method for predicting Pand Swave velocities in mudrocks accounting for silica (quartz), porosity, and free gas. Using sonic and shear-sonic logs we apply the proposed method to estimate silica, porosity, and free gas depth profiles in the Woodford Shale of the Mcneff 2-28 well, Grady County, Anadarko Basin, Oklahoma. Our modeling suggests that silica and free gas decreases (9050% and 90%-85% respectively) and the porosity increases (10–20%) in the Woodford from the top to its base. The estimated silica and porosity depth profiles are validated by comparison with the photoelectric and the density-porosity logs. X-Ray Diffraction analysis of a rock sample from the Upper Woodford in the Cambell 1-34 well located ~1 km to the southeast additionally supports high silica content in the Upper Woodford. This study strongly suggests that the rock physics method, such as that proposed here, can be potentially used as a guide for relating seismically-derived properties of the subsurface to key parameters such as silica, porosity, and gas saturation; the former two especially important for inferring brittleness and fracability and the latter for the production potential.

Effects of fluid changes on seismic reflections: Predicting amplitudes at gas reservoir directly from amplitudes at wet reservoir

Abstract: The equations for fluid substitution in a sample with known porosity and the mineral’s and pore-fluid’s elastic moduli are well-documented. Discussions continue on how to conduct fluid substitution in practical situations where more than one fluid phase is present and the porosity and mineralogy are not precisely defined. We pose a different question: If we agree on a fluid substitution method, and also agree that at partial saturation the bulk modulus of the “effective” pore fluid is the harmonic average of those of the components, can we conduct fluid substitution directly on the seismic reflection amplitude? To address this question, we conducted forward modeling synthetic exercises: We systematically varied the porosity, clay content, and thickness of the reservoir and assumed that the properties of the bounding shale are fixed. Next, we used a velocity-porosity model to compute the elastic properties of the dry-rock frame and applied Gassmann’s equation to compute these properties in wet rock...

Oil Sands: Rock Physics Analysis From Well Data, Alberta, Canada

Abstract: Laboratory ultrasonic velocity measurements have been conducted on pure bitumen samples as well as bitumen sands (e.g., Wolf, 2010). A big challenge in interpreting such measurements for the purpose of seismic interpretation is the dichotomy between the high frequency of laboratory experiments and relatively low frequency of seismic exploration data and well data. To bridge this difference, experiments have been conducted in the laboratory in the seismic range frequencies (e.g., Das and Batzle, 2008).