1. Traps: Anticlinal
Most of the world's known oil deposits are trapped in
anticlines. (About 80%)
Origin of Folds:
1. Igneous Intrusions may arch overlying rock. An unusually
symmetrical dome, thought to be the result of laccolithic
intrusion.

2. 2. Settling or subsidence may produce folds, providing that it
is differential in character.
3. When soluble rocks occur in the section, leaching
followed by slumping may produce sagging in the
overlying strata, with arching over the blocks that have
not collapsed.
4. Residual structural highs may also possibly result from the
plastic flow of salt.
5. Horizontal movements are at their maximum in orogenic
belts where the earth's crust is under compression.
Pseudo-Folds, so called because they look like folds but
are not the result of any movement, are formed by
deposition parallel to an uneven ocean floor. If the
deposition is from suspension, and the slopes are not
steeper than the angle of repose of the unconsolidated
sediment, the layers may be deposited with initial dips
which conform to the topography of the submerged
surface.
Anticlines come in all sizes. The length varies from less
than a mile to many miles and the amount of closure
ranges from tens of feet to thousands of feet. As a general
rule, the larger anticlines do not carry oil the entire length.
Instead, the superimposed domes or nodes are oil-bearing
and the intervening saddles contain only water. The larger
anticlines are also less likely to be filled with hydrocarbons
to the spill point.

3. Trap Case Study
1-San Pedro field, Argentina.
Location: In Salta Province in northern Argentina.
Type: (Elongate Anticline) It occurs along the crest of a
partly eroded, tightly folded anticline which makes a ridge
in the San Antonio range.
Beginning: 1921 Discovery well: 1928
Commercial production: 1930
2-Ghawar Oil Field, Saudi Arabia.
It is one of the largest oil fields in the world. It is the result
of the merger of five oil fields along a great anticlinal arch.
Type: Elongate Anticline.

5. 3-Cumberland Oil Field, Oklahoma,
U.S.A.
Location: Lies on the south flank of the Arbuckle
Mountain system in southern Oklahoma.
Type: (Anticline) A closed faulted anticline which lies
within a down-faulted block of sedimentary rock.
Discovery well: 1940
4-Cymric Oil Field, California, U.S.A.
Location: Lies in Kern County, California, on the west side
of the San Joaquin Valley.
Type: (Anticline) it is elliptical in plan and unusually
symmetrical.
Discovery well: 1916
5-Rangely Field, Colorado.
Location: Lies in northwestern Colorado on the
northeastern edge of the Unita basin.
Type: (Anticline) Asymmetrical.
Beginning: 1878 Discovery well: 1902
6-Augusta Field, Kansas, U.S.A.
Location: Lies in Butler County, Kansas, extending from 3
miles north of the city of Augusta to 7 miles south of it.

6. Type: (Anticline) divided by a saddle into the north
Augusta and south Augusta.
First well: 1914
7-Bahrain Field, Bahrain.
Location: Lies in the central part of Bahrain Island, which
lies at the mouth of the bay between Qatar Peninsula and
the mainland of Saudi Arabia.
Type: (Anticline) Elliptical in plan.
Size: 12 miles long and 4 miles wide.
Production: 32000 barrels a day during 1957
Commercial production: 1932
8-Santa Fe Springs Oil Field, California,
U.S.A.
Location: Lies in Los Angeles County, about 12 miles
southeast of the center of the city of Los Angeles.
Type: (Dome) an unusually elliptical dome.
Area: 1500 acres.

7. Discovery well: 1919
9-Big Lake Pool, Texas, U.S.A.
Location: Lies in the southwestern corner of Regan
County, in west Texas.
Type: (Dome)
Discovery well: 1923
10- San Joaquin Field, Venezuela.
Location: Lies in the central part of the state of
Anzoátegui, in eastern Venezuela.
Type: (Dome)
Beginning: 1934 Discovery well: 1936
Commercial production: 1939
11- Burgan Field, Kuwait.
It, along with the adjoining Magwa and Ahmadi fields, has
for some years been the largest source of petroleum in
the world, with a daily output of over one million barrels.
Type: (Dome) Faulted elliptical dome with the major axis
trending almost north-south.
Size: 15 miles long and 10 miles wide.
Beginning: 1932 Discovery well: 1938
Commercial production: 1945