The Sacramento Basin, which occupies the north half of the Great...

The Sacramento Basin, which occupies the north half of the Great Valley of California, is an elongate,
northwest-trending structural trough. The trough is filled with as much as 40,000 ft of Jurassic to
Holocene, marine and nonmarine siliciclastic rocks deposited in a convergent margin between late
Mesozoic and early Cenozoic time. The province, which is 210 mi long and 60 mi wide, is bordered on the
west by the Coast Range Thrust, on the north by the Klamath Mountains, on the east by the Cascade
Range and Sierra Nevada, and arbitrarily on the south by the Stanislaus-San Joaquin County line. The
province covers an area of 11,820 sq mi.
The Sacramento Basin is primarily a gas-producing province with only two small oil fields (Brentwood
(8.2 MMBO) and West Brentwood (1.6 MMBO)), located in the southern part of the basin and 73 gas fields
. Major gas fields, with estimated recoverable gas as of January 1991, are Rio Vista (3.5 TCFG), Grimes
(885 BCFG), Willows-Beehive Bend (387 BCFG), Lathrop (359 BCFG), Lindsey Slough (279 BCFG), and
Union Island (261 BCFG). Cumulative production through 1990 is 8.2 TCFG with 13 MMBO.
Exploration in this province started in 1918, and by the end of 1990 almost 2,600 new field wildcats had
been drilled. The most active period of exploration occurred between 1960 and 1980. About 2,300 wells
were drilled to depths that ranged from 3,000 to 10,000 ft, with several wells approaching 20,000 ft. The
dry hole ratio is 35:1 (2,600:75) or a success rate of almost 3 percent (table 9.1). Discovery dates and
volumes for fields are found with the plays assessed in this province.
Based on stratigraphic and geographic occurrence, hydrocarbon composition (Jenden and Kaplan, 1989),
and direction traps filled, two gas systems are identified in this province, the Dobbins-Forbes(?) and the
Winters-Domingene(?). The Northern Forbes-Kione Play (0901) and the Southern Forbes-Kione Play
(0902) correspond to the Dobbins-Forbes(?) system, and the Winters through Domingene Play (0903) to
the Winters-Domingene(?) system. The first two plays are separated by an arcuate line near T. 12N.
which separates the discovered accumulations to the north (play 0901) from the lack of accumulations on
the south (play 0902).
The hydrocarbons for both systems originate from gas-prone source rocks in the area of the "delta
depocenter" (Zieglar and Spotts, 1981), which is suspected to be the Dobbins Shale or Forbes Formation
for the Dobbins-Forbes(?) system and the Winters Shale or Sacramento Shale for the WintersDomingene(?) system. Regional seal rocks that partition the systems are the Prince Canyon fill and Capay
Shale in the north and, in the south, the Sacramento Shale. The burial-history curve of Zieglar and Spotts