The peripheral waterflood in the Main Body 'B' Reservoir located in the Elk Hills Oilfield, Kern County, California, is mature with remaining reserves estimated at 122 MMBO from initial reserves of 212 MMBO.
Pressure maintenance early in the life of the reservoir Pressure maintenance early in the life of the reservoir improved oil recovery. Recent performance data indicate that the MBB Reservoir is layered and has potential for bypassed reserves.
Future geologic, reservoir and production activities will be dominated by defining, correlating and managing the reservoir by layers.
The Elk Hills Oilfield is located in the southern San Joaquin Valley of Central California approximately 20 miles WSW of Bakersfield and 10 miles north of Taft (Figure 1). The Elk Hills Field contributes the majority of the production and reserves of the Naval Petroleum Reserve No. 1 (NPR-1) which also includes small portions of North Coles Levee, Buena Vista, Railroad Gap and Asphal to Fields. NPR-1 was established in 1912 to provide fuel resources to the Navy in the event of a national emergency. The reserve was produced periodically until 1976 when It was opened up to production to provide a steady supply of petroleum during the energy crisis. Since 1976, Elk Hills has produced approximately two thirds of its total production to date - more than 900 million barrels of oil.
Elk Hills has four productive zones: the Dry Gas Zone (San Joaquin), the Shallow Oil Zone, the Stevens Zone (Elk Hills Shale) and deeper zones such as the Carneros and Santos (Figure 2). Of approximately 80,000 barrels of oil produced daily at Elk Hills, more than 50% is currently produced from the Stevens Zone. Of the nearly 65,000 barrels of oil produced from the Stevens each day, nearly one-third is produced from the Main Body 'B' (MOB) Reservoir.
Structurally, the Elk Hills Oilfield is dominated by three anticlines. These anticlines, the 31S, 29R and Northwest Stevens (Figure 3), originated as early as Miocene times as a result of tectonic stresses that created movement along the San Andreas Fault, The San Andreas Fault is about 15 miles west of Elk Hills. Later deformation of the same area during recent times has created a surface anticline with dramatic topographic expression. At its highest point, Elk Hills rises more than 1000 feet above the adjacent valley floor.
The Stevens Oil Zone at Elk Hills is the productive portion of the Elk Hills Shale member of the Miocene Monterey Formation. The Stevens Zone is divided into a number of stratigraphic units, From the top down, those Intervals are the N, A, B, C, D, DD, and PG. These Monterey-type rocks are dominantly clay shales and siliceous shales. At Elk Hills, these lithologies not as substantially fractured as elsewhere in California, and sandstone reservoirs within the shales have provided the bulk of both production to date and proven reserves.
The Monterey Formation at Elk Hills is in many respects similar to the Monterey in areas where sandstone reservoirs do not dominate production. Much of the Stevens at Elk Hills consists of thinly laminated shales. These shales contain a very high percentage of biogenic silica seemingly inconsistent with the occurrence of sand reservoirs several hundred feet thick. The sand reservoirs are turbidity deposits and owe their existence to the proximity of clastic source areas that surrounded the San Joaquin Basin during Miocene times much like the mountains surround in the San Joaquin Valley today (Figure 1).