Analysis of 3D poststack seismic attributes can be used to identify areas of high exploration potential within shale resource plays. We integrated seismic attributes and acoustic impedance (AI) with wireline logs to determine total organic carbon (TOC) distribution within the Eagle Ford Shale in South Texas. We computed TOC from wireline logs using the D Log R method and then used seismic attributes to predict TOC and deep-resistivity log distribution, and identify brittle zones within the seismic survey. Our results show that high-TOC and high-resistivity zones are laterally more continuous in the south part of the survey. In the north, continuity of these properties is broken by NE-SW-trending faults having throws ranging from about 10 to 100 ft (3-30 m). High resistivity occurs in high-quality-factor (Q) attribute zones. Although the relationship is nonlinear, resistivity and TOC increase as Q increases. That is, both properties increase with increasing bed resistance suggesting increasing carbonate. Two high-resistivity zones, an upper resistive bed and a lower resistive bed, are identified within the Eagle Ford Shale. Additionally, because a strong positive linear relationship exists between AI and Q, Q can be used to identify brittle zones. Compared to other attributes used in identification of brittle zones, Q is faster and cheaper to compute from 3D poststack seismic data. Therefore, Q could serve as a quicker, alternate method of identifying brittle zones within the Eagle Ford Shale.
We conducted seismic multiattribute analysis by combining seismic data with wireline logs to determine hydrocarbon sweet spots and predict resistivity distribution (using the deep induction log) within the Austin Chalk and Eagle Ford Shale in South Texas. Our investigations found that hydrocarbon sweet spots are characterized by high resistivity, high total organic carbon (TOC), high acoustic impedance (i.e., high brittleness), and low bulk volume water (BVW), suggesting that a combination of these log properties is required to identify sweet spots. Although the lower Austin Chalk and upper and lower Eagle Ford Shale intervals constitute hydrocarbon-sweet-spot zones, resistivity values and TOC concentrations are not evenly distributed; thus, the rock intervals are not productive everywhere. Most productive zones within the lower Austin Chalk are associated with Eagle Ford Shale vertical-subvertical en echelon faults, suggesting hydrocarbon migration from the Eagle Ford Shale. Although the quality factor (Q) was not one of the primary attributes for predicting resistivity, it nevertheless can serve as a good reconnaissance tool for predicting resistivity, brittleness, and BVW-saturated zones. In addition, local hydrocarbon accumulations within the Austin Chalk may be related to Austin TOC-rich zones or to migration from the Eagle Ford Shale through fractures. Some wells have high water production because the water-bearing middle Austin Chalk on the downthrown side of Eagle Ford Shale regional faults constitutes a large section of the horizontal well, as evidenced by the Q attribute. Furthermore, the lower Austin Chalk and upper Eagle Ford Shale together appear to constitute a continuous (unconventional) hydrocarbon play.
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