When lava flows and pyroclastic deposits exhibit sufficient porosity and permeability, extrusive igneous rocks have the potential to host large hydrocarbon accumulations. The porosity in these deposits can come from either vesicular porosity, or from secondary porosity resulted from later fracturing and hydrothermal alteration. Recent studies show that, significant hydrocarbon reserves are contained in volcanic rocks in China which are primarily found in the Songliao Basin, Bohai Bay Basin, and Erlian Basin. These hydrocarbon rich reservoirs range from upper Jurassic to Tertiary in age.

This study applies a three dimensional seismic geomorphology workflow to map a volcanic reservoir in Songliao Basin, Northeast China. Since the volcanic buildup under the study has strong reflectivity and the volcanic conduit relates to the chaotic zone in seismic response, the amplitude attributes and geometric attributes we used present a very good illumination of the volcanic architectural element.

SummarySummary

0.8

1.3

Seismic attribute expression of an igneous reservoir in China

Kui Zhang*, Zhonghong Wan, Kurt J. Marfurt

ConocoPhillips School of Geology & Geophysics, University of Oklahoma

The Songliao basin in northeast China is a large rift basin with an area of 260,000 km2, covering four provinces, and it s one of China’s most prolific hydrocarbon producing areas. During late Jurassic to early Cretaceous age, several rift depressions were developed in the basin, resulting in deposition in the late Jurassic Huoshiling Formation, early Cretaceous Shahezi Formation, Yingcheng, and Denloukou Formations. Strong volcanic activity considerably began during the deposition of early Yingcheng Formation associated with strong structural inversion. The erupted rock fragments and pyroclastic clasts during this period formed the good reservoir quality. Faults bounding rift depressions served as the major conduits for deep magma and CO2. During the upper Cretaceous, a thick organic rich source rocks were deposited in the basin juxtaposed to the volcanic reservoir.

The seismic survey under our study was acquired in the northeastern part of the Songliao Basin (Figure 1) to better delineate the structural element of the volcanic reservoir deposited as part of the Yincheng Formation (figure 2).

Geological settingGeological setting

0 500 km

Russia

Mongolia

South Korea

North Korea

China

Figure 1. Location map, in which red circle marks the location of the seismic survey under study.

Figure 2. Lithologic column from wells X and Y tied to the seismic data. Volcanic rocks are colored in red. The location of line AA’ and well X and Y is shown in figure 5(a).

Figure 3. Seismic section (a) before and (b) after structure-oriented filtering. Arrows indicate discontinuities that have been enhanced.

Figure 4. An inline seismic section (a) and crossline section (b) with the interpreted igneous body.

(a) Seismic amplitude (b) Amplitude difference

(d) Crossline energy gradient

(c) Inline energy gradient

(e) Energy gradient magnitude (f) Energy ratio similarity coherence

(g) Sobel filter coherence (h) Reflection strength (i) Peak spectral magnitude

Figure 6. Horizon slices with (a) time structure map, (b) Sobel filter coherence, (c) most positive curvature, (d) most negative curvature, (e) reflect strength, and (f) peak magnitude. Blocky arrows in (e)-(f) point to possible volcanic deposits.

Figure 7. Color blended horizon slices with (a) most negtive curvature, (b) most positive curvature, (c) Sobel filter coherence, and (d) peak magnitude with time structure map.

Figure 5. Seismic attributes horizon slices (a) – (i) give different illumination of volcanic deposits.

ConclusionsConclusions

AcknowledgementAcknowledgementWe would like to thanks Bureau of Geophysical Prospecting for use of their seismic data. We also extend our appreciation to the industry sponsors of the University of Oklahoma Attributes-Assisted Processing and Interpretation (AASPI) Consortium.

Volcanic reservoir in China, Argentina, and other part of the world serve as hydrocarbon reservoirs. A prominent feature of the volcanic rocks is that, they typically have a strong amplitude in seismic response, thus energy related attributes such as spectral magnitude and reflection strength provide effective means of mapping volcanics. The geometrical attributes like coherence, amplitude difference, curvature also provide convincing results by revealing of the structure and texture of the surface of the igneous body. The work in next step is evaluation of the igneous reservoir properties measured in logs and analyze their correlation with seismic attributes.