Chapter 14: Case Studies of Multicomponent Seismic Data for Fracture Characterization: Austin Chalk Examples
Xiang-Yang Li, Michael C. Mueller, 1997. "Case Studies of Multicomponent Seismic Data for Fracture Characterization: Austin Chalk Examples", Carbonate Seismology, Ibrahim Palaz, Kurt J. Marfurt
Download citation file:
Shear wave studies of multicomponent seismic data were done along the Austin Chalk trend in Texas. Six surface seismic lines of four-component shear wave data from Pearsall and Giddings fields and three zero-offset vertical seismic profiles (VSPs) from three sites with different production rates were studied to demonstrate the applications of shear wave splitting for fracture reservoir delineation. The three seismic lines (1–3) from Pearsall field formed a classic experiment for studying shear wave splitting. They have different (line) azimuth with respect to the regional fracture strike (parallel, perpendicular, and at ~40°, respectively), are in areas with different hydrocarbon production, and have different split shear wave behavior. The anisotropy along line 1 is small, which correlates with the absence of nearby commercial production. There is an increasing trend in anisotropy from line 2 to 3, which correlates with line 2 being close to and line 3 being within the producing Austin Chalk acreage. The trend of anisotropy variation along line 3 also correlates with the distribution of producing oil wells along that line. In particular, production from the three horizontal wells (W1–W3) drilled nearby correlates with the variation in shear wave polarization, time delay, and amplitude. Line 4 from Giddings field had a horizontal well drilled on it, and mud logs were obtained for identifying fracture zones. The fracture swarms identified by the mud logs are coincident with the dim spots identified from the section of the slow split shear wave. Lines 5 and 6, also from Giddings field, demonstrate classic S2 dim spot and S1 versus S2 mistie behavior, respectively.
The three VSPs, from three wells with different production rates, show different shear wave responses. VSP 1, from a nonproductive well, shows minimal shear wave time delay and no amplitude anomalies. VSP 2, from a water-producing well, shows some amount of splitting but no anomalies in shear wave attributes. VSP 3, from an oil-producing well, shows clear shear wave splitting and anomalies in shear wave amplitudes. Amplitude corrections are necessary for preserving and recovering shear wave anisotropy information associated with the target, and the linear transform technique (LTT) simplifies the processing sequence for examining anisotropy in shear wave reflection data. Stacked polarization logs can be used for identifying local variations in polarization (often associated with local variations in crack geometry) and for better imaging of subsurface structure, as in line 3.
Figures & Tables
We first collaborated in the area carbonate seismology in 1990 while mapping Cretaceous and Tertiary carbonate reservoir facies from neighboring seismic data surveys gathered in the Pelagic Sea of Tunisia and Malta. Both areas, one shallow water (<50 m) and one deep water (>500 m), were plagued by a “penetration” problem through shallow carbonates and by a resolution problem of low-relief stratigraphic targets at depth. While the geologists on our teams had an ample supply of up-to-date sources devoted to the details of carbonate sedimentology and sequence stratigraphy, those of us working on the seismic data were left to our own devices. With considerable effort, we were able to come up with a handful of technical papers, some good notes from continuing education courses, and a thick pile of expanded abstracts from diverse sources to help us understand the seismic expression of carbonates. We augmented this sparse material with expert advice from our Amoco colleagues, our contractors, and our partners.
It was at this point when we first saw the need for an integrated reference book on carbonate seismology, and we vowed that once we were finished with our assignments, we would attempt to put such a book together. The years of 1992–1994 were tumultuous in the petroleum industry, with most of the major oil companies downsizing and the competing service companies consolidating. During this period, we saw many of our experienced colleagues who had provided us with expert advice leave the oil industry. With this additional lack of available “folk” wisdom in the area of carbonate seismology, we found it more imperative than ever to capture the current state-of-the-art before it was lost to posterity.
Our goal was to produce a book that would integrate the principles of carbonate geology with its seismic expression and would be readily understandable to the practicing geologists, geophysicists, and engineers that form the exploration and exploitation teams in the petroleum industry. The result is a single integrated volume, written in plain language by acknowledged experts in their fields, that illustrates the interrelationships of carbonate geology, petrology, sequence stratigraphy, rock properties, seismic data acquisition, seismic data processing, and integrated interpretation.
We have taken care in the editing process to ensure that every concept is explained clearly and concisely without getting lost in domain-specific terminology. Our hope is that this volume will sit dog-eared on the desk of every practicing geoscientist, to help the seismic data processor determine parameters to enhance the fidelity of carbonate images, to help the seismic interpreter better recognize the expression of sequence stratigraphy, to help the engineer understand patterns of permeability and fractures, and to help the carbonate geologist understand the expression of the rock record at the seismic scale and differentiate it from common seismic acquisition and processing artifacts.
We have provided ample examples on the application of carbonate AVO and acoustic logging. Tying acoustic logs to seismic is a common theme throughout the book. We have included two chapters by Fischer et al. and by D’Angelo et al. that show how, with the aid of careful seismic modeling, AVO can be calibrated and used to map porosity in carbonate rocks.
We wish to thank all the contributing authors for their hard work, perseverance, and patience. We also want to thank those authors who had hoped to contribute to this volume and did much of the work but, through the turmoil in the oil industry, found themselves severed from their data and ultimately unable to contribute.
Kurt J. Marfurt