Exploration Significance of Unconformity Structures on Subtle Pools Kongyou Wu, Ph. D Associate Professor China University of Petroleum (Huadong) College of Geo-Resources and Information Add:66 Changjiangxi Rd., Economic & Tech. Development District, Qingdao, Shandong Province, , P. R. China

Exploration Significance of Unconformity Structures on Subtle Pools 1 Vertical structural characteristics of unconformity 2 Lithologic configuration of unconformity 3 Significance of vertical structures of unconformity to hydrocarbon accumulation 4 Physical simulations of oil migration and accumulation in unconformity Outline

Exploration Significance of Unconformity Structures on Subtle Pools 1 Vertical structural characteristics of unconformity Using the interpreting results of seismic and logging data, based on the core and outcrop observation, the structures of unconformity can be divided into three layers vertically: ① rock above the unconformity surface （ including transgressive sandstones and basal conglomerate ） ② weathered clay ③ leached rock First

Exploration Significance of Unconformity Structures on Subtle Pools Outcrop a-leached rock ； b-weathered clay ； c-transgressive sandstones ； d-basal conglomerate a b d c b a a First (1) (2) (3) (4)

Exploration Significance of Unconformity Structures on Subtle Pools First Core Z18 Z28 d c b b a a b a d QG3 a-leached rock ； b-weathered clay ； c-transgressive sandstones ； d-basal conglomerate

Exploration Significance of Unconformity Structures on Subtle Pools First Logging response Every layer has the different logging response Structures Rock above the uncon- formity surface Weathered clay Leached rock Litho- logy Logging response Litho- logy Litho- logy Litho- logy Conglo- merate Sand Mud Coal Clay Conglo- merate Sand Mud Lime- stone Dolomite Granite Metamorfic rock Lack

Exploration Significance of Unconformity Structures on Subtle Pools First Tectonic movement, ancient landform, arid climate and exposed period were the key factors to control the types of rock above the unconformity surface.

Exploration Significance of Unconformity Structures on Subtle Pools First Rock is subjected to weathering and leaching,when it exposes the earth's surface, resulting in secondary pores, holes and joints. Therefore, the leached rock contains amount of secondary porosity. Scanner Outcrop Feldspar Limestone

Exploration Significance of Unconformity Structures on Subtle Pools 1 Vertical structural characteristics of unconformity 2 Lithologic configuration of unconformity 3 Significance of vertical structures of unconformity to hydrocarbon accumulation 4 Physical simulations of oil migration and accumulation in unconformity Outline

Exploration Significance of Unconformity Structures on Subtle Pools Second 2 Lithologic configuration of unconformity When the weathered clay has a little thickness or limited distribution, the overlying and underlying strata will contact directly, and the lithologic configuration is often different. This lithologic difference causes different fluid transporting capacity. It also determines whether a trap can be formed or not, and what kind of trap can be formed.

Unconformity develops three types of the lithologic configuration vertically: basal conglomerate - weathered clay(or lack) – leached rock type ( Ⅰ ), transgressive sandstone - weathered clay(or lack) – leached rock type ( Ⅱ ), sandy mudstone – leached rock type ( Ⅲ ). Exploration Significance of Unconformity Structures on Subtle Pools Second (Ⅰ)(Ⅰ) (Ⅱ)(Ⅱ) (Ⅲ)(Ⅲ) Silty mudstone mudstone

Exploration Significance of Unconformity Structures on Subtle Pools 1 Vertical structural characteristics of unconformity 2 Lithologic configuration of unconformity 3 Significance of vertical structures of unconformity to hydrocarbon accumulation 4 Physical simulations of oil migration and accumulation in unconformity Outline

Exploration Significance of Unconformity Structures on Subtle Pools Third 3 Significance of vertical structures of unconformity to hydrocarbon accumulation 3.1 Sealing capability of vertical structures of unconformity Weathered clay contains the fine particles residual material formed by weathering, and would become very strong by the compaction of overlying sediments. Thus, it is a strata with good sealing capability 。 Depth Breakthrough Pressure Horizontal axis Vertical axis

Exploration Significance of Unconformity Structures on Subtle Pools Third 3.2 Conduction of vertical structures of unconformity When the unconformity surface was gentle, the deposited transgressive sands or basal conglomerates would connect with each other, thus a migration channel would be formed.

Exploration Significance of Unconformity Structures on Subtle Pools Third 3.3 Trap of vertical structure of unconformity When the unconformity surface was in a slope-break zone during the early transgression, the deposited sands would be covered by the lateral mudstones, thus a trap of the stratigraphic overlap or a lithologic pinch would be formed.

Exploration Significance of Unconformity Structures on Subtle Pools 1 Vertical structural characteristics of unconformity 2 Lithologic configuration of unconformity 3 Significance of vertical structures of unconformity to hydrocarbon accumulation 4 Physical simulations of oil migration and accumulation in unconformity Outline

Exploration Significance of Unconformity Structures on Subtle Pools Fourth 4 Physical simulations of oil migration and accumulation in unconformity Simulation experiments showed that the oil migration along the unconformity was controlled by the petrophysical parameters and the angles of slope. The traps above the unconformity surfaces were more favorable than the traps below the unconformity surfaces to entrap oil and gas.

Acknowledgements National Natural Science Foundation of China (No ), and Provincial Natural Science Foundation of Shandong (No.Y2008E16) provided financial support for this study. We especially thank Xinjiang Oil Field Company of Petro-China for the permission to use their geological and geophysical data.

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