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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: The Milton Field, Harris County, Texas, Produced Before Discovery *
By
*Presented before the Society, May 8, 1961.
The Milton field is located approximately 15 miles northwest of
Houston in northwestern Harris County, Texas. The field was discovered
in November, 1953, and has produced approximately 827,000
barrels of oil and 3600 MMCF of gas to January 1, 1961, from a productive
area of approximately 925 acres and from 20 completed wells.
The field includes some interesting features from a geological and
petroleum engineering standpoint. Oil and gas production from the
Fairbanks sand is from a lenticular buried sand dune or buried offshore
bar. Oil and gas accumulation within the Fairbanks sand of the
Milton field is controlled by the up-to-the-north fault at the south edge
of the field. The Fairbanks reservoir pressure was subnormal at discovery.
It is interpreted that the fault seal
at the south edge of the
field became ineffective after pressure drawdown in sands in juxtaposition
with the Fairbanks sand in the North Houston field to the south.
Drainage across this fault plane occurred prior to discovery of the
field. It is estimated that approximately three and one-half million
barrels of fluids were drained from the Milton field prior to date of
discovery. Pressure drawdown within the Milton field is greater than
warranted by present production and drainage across the fault is believed
to be current. Oil saturation within the Fairbanks sand, approximately 17½ per cent of the pore space, has been noted within the
Fairbanks sand to depths of 23 feet or more below the proved water
level at date of discovery. This zone is considered to have been
drained prior to discovery. Structural maps relative to the problem
were presented of the Milton and North Houston fields as contoured on
top of the Frio sand; on the top of the first Yegua sand or the top of the
"D-Y" sand; on the top of the Fairbanks sand; on the base of the Fairbanks
sand; and on the top of the Look sand. An isopachous map of the
Fairbanks sand lens is presented for the purpose of showing the lenticular
nature of the Fairbanks sand zone. A cross section extending
from north to south across the Milton field and into the North Houston
field and comprising a portion of the Yegua section is presented for the
purpose of showing the juxtaposition of the "D-Y" sand in the North
Houston field to the Fairbanks reservoir in the Milton field and the
apparent relationship of the discovery water level of the Milton Fairbanks
reservoir to the structural position of the top of the "D-Y" sand
in the North Houston field. A bottom hole pressure decline curve of
the Fairbanks sand in the Milton field and a well-head pressure decline
curve of the North Houston field is presented to illustrate some unique
pressure characteristics within the North Houston "D-Y" reservoir
and the apparent date (January, 1950) that the fault
seal
between the
two reservoirs became ineffective. A profile drawn along the fault
plane is presented for the purpose of showing the structural position of
the top and base of the "D-Y" sand on the downthrown side of the fault
in the North Houston field; the structural position of the top and base
End_Page 21-------------------------
of the Fairbanks sand in its upthrown position in the Milton field; the cross sectional areas of the Fairbanks sand occupied by gas, oil and
water in the Milton field at date of discovery; the cross sectional area of the Fairbanks sand in the Milton field as it presumed to have been
drained prior to discovery and the cross sectional area (in excess of two and one-half acres) where the "D-Y"
sand on the downthrown side of the fault is adjacent to and in juxtaposition with the Fairbanks sand
on the upthrown side of the fault. It is the conclusion of the authors that (1) pressure withdrawal in the
"D-Y" sand in the North Houston field due to production from that reservoir broke the effective seal
of
the fault in the Fairbanks reservoir of the Milton field prior to discovery; (2) bottom hole pressures within the Fairbanks sand of the
Milton field declined in excess of 500 pounds prior to date of discovery; (3) approximately three and one-half million barrels of fluids were
drained from the Fairbanks reservoir of the Milton field in the approximate seven year period from date of first production in the North
Houston field to the date of discovery of the Milton field; and (4) based on present pressure decline curves within the Fairbanks reservoir of
the Milton field and governed by reservoir voidage from the oil and gas reservoirs, it appears probable that there is current drainage of fluids
across the fault plane from the Fairbanks reservoir in the Milton field to the
"D-Y" sand in the North Houston field.
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