Exploration Significance of Unconformity Structures on Subtle Pools Kongyou Wu, Ph. D Associate...

Exploration Significance of Unconformity Structures on Subtle Pools

Kongyou Wu, Ph. D

Associate Professor

[email protected]

China University of Petroleum (Huadong)College of Geo-Resources and Information

Add:66 Changjiangxi Rd., Economic & Tech. Development District, Qingdao, Shandong Province, 266555, P. R. China


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



Using the interpreting results of seismic and logging data, b

ased on the core and outcrop observation, the structures of

unconformity can be divided into three layers vertically:

①rock above the unconformity surface

（ including transgressive sandstones and basal conglomerate ）

②weathered clay

③leached rock

First


Outcrop

a-leached rock ；b-weathered clay ；c-transgressive sand

stones ；d-basal conglomerat

e a

b

d

c

b

a

a

First

(1)

(2)

(3)

(4)


First

Core Z18 Z28

dc

b b

a a

b

a

d QG3

a-leached rock ； b-weathered clay ；c-transgressive sandstones ； d-basal conglomerate


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 Logging response Logging response Logging responseLitho-logy

Litho-logy

Litho-logy

Conglo-merate Sand Mud Coal

Clay

Conglo-merate Sand Mud Lime-

stone

Dolomite Granite Metamorfic

rock

Lack


First

Tectonic movement, ancient landform, arid climate and

exposed period were the key factors to control the types of

rock above the unconformity surface.


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






Outline


Second


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. T

his lithologic difference causes different fluid transporting ca

pacity. It also determines whether a trap can be formed or n

ot, 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


Second

( )Ⅰ

( )Ⅱ ( )Ⅲ

Silty mudstone

Silty mudstone

mudstone

mudstone






Outline


Third


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 overlyi

ng sediments. Thus, it is a strata with good sealing capability 。

y = 0. 8007e0. 0016x

0

5

10

15

20

25

30

0 500 1000 1500 2000 2500深度（m）

突破

压力

（MP

a）

Depth

Bre

akth

rou

gh

Pre

ssu

re

Horizontal axis

Ver

tica

l ax

is


Third

3.2 Conduction of vertical structures of unconformity

When the unconformity surface was gentle, the d

eposited transgressive sands or basal conglomerates w

ould connect with each other, thus a migration channel

would be formed.


Third

3.3 Trap of vertical structure of unconformity

When the unconformity surface was in a slope-break zone d

uring the early transgression, the deposited sands would be c

overed by the lateral mudstones, thus a trap of the stratigra

phic overlap or a lithologic pinch would be formed.






Outline


Fourth


Simulation experiments showed that the oil migration along the unconformity

was controlled by the petrophysical parameters and the angles of slope. The t

raps above the unconformity surfaces were more favorable than the traps bel

ow the unconformity surfaces to entrap oil and gas.

Acknowledgements

National Natural Science Foundation of China

(No.40772081) , 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.

THANK YOUTHANK YOU ！！

Exploration Significance of Unconformity Structures on Subtle Pools Kongyou Wu, Ph. D Associate...

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