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Hein, Frances J., 2013, Overview of heavy Previous HitoilNext Hit, seeps, and Previous HitoilNext Hit (tar) sands, California, in F. J. Hein, D. Leckie, S. Larter, and J. R. Suter, eds., Heavy-Previous HitoilNext Hit and Previous HitoilNext Hit-sand petroleum systems in Alberta and beyond: AAPG Studies in Geology 64, p. 407435.


Copyright copy2013 by The American Association of Petroleum Geologists.

Overview of Heavy Previous HitOilNext Hit, Seeps, and Previous HitOilNext Hit (Tar) Sands, California

Frances J. Hein1

1Energy Resources Conservation Board, Suite 1000, 250-5th St. SW, Calgary, Alberta, T2P 0R4, Canada (e-mail: [email protected])


The Energy Resources Conservation Board, Calgary, provided technical assistance and support. I thank Kevin Parks, Doug Boyler, Jon Schwalbach, and Daniel Schwartz for helpful suggestions to improve the manuscript and Dan Magee for digital graphics. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the author or the Alberta Government.


California has one of the largest reserves for heavy Previous HitoilNext Hit in the world, second only to Venezuela. Recent declines in conventional resources and reserves during the last decade have prompted other jurisdictions to examine their prospective unconventional resources, such as heavy Previous HitoilNext Hit and Previous HitoilNext Hit sands, in a more favorable technological and economic setting. However, this has not been done universally in the United States, where thermal enhanced Previous HitoilNext Hit-recovery technologies (mostly used to produce heavy Previous HitoilNext Hit) have experienced a decline in production, concomitant with the downturn in conventional production.

In California, the seep and Previous HitoilNext Hit-sand deposits are mostly unconsolidated sands bound together by biodegraded bitumen. Source rocks for both modern seeps and Previous HitoilNext Hit sands and ancient heavy-Previous HitoilNext Hit deposits are mainly the Miocene Monterey diatomites and equivalent diatomaceous mudstones and organic shales. In California, most of the seeps and Previous HitoilNext Hit sands overlie or are updip from underlying heavy-Previous HitoilNext Hit reservoirs. The seep and Previous HitoilNext Hit-sand deposits occur in areas where cap-rock integrity was compromised for the underlying heavy-Previous HitoilNext Hit reservoirs, breeched mainly by faults or fractures. Hydrocarbons migrated updip into basin-marginal settings or in structural areas of compromised cap rock and then pooled to form the seeps, later hardening into Previous HitoilNext Hit-sand deposits. Hydrocarbons accumulated in a wide variety of depositional environments from deep-sea fans, lobes, and submarine channels to fluvial-lacustrine deltas and incised valleys and every other sedimentary environment in between. This makes it difficult to identify type examples for the California accumulations, although case examples are given.

In the past, steam-flood, condensed water drive, cyclic steam stimulation (CSS), and fire-flood were used to produce the California heavy-Previous HitoilNext Hit reservoirs. Currently, significant California CSS projects underway include Belridge, Cymric, and northern Midway Sunset fields to stimulate intermediate-gravity hydrocarbons in the Monterey, Reef Ridge, and Etchegoin diatomite lithologies. Elsewhere, for example, in Canada, in-situ bitumen and extra-heavy-Previous HitoilNext Hit sands are commonly developed using CSS or steam-assisted gravity drainage (SAGD). Combined application of CSS along with SAGD from horizontal wells may recover bypassed pay in heavy-Previous HitoilNext Hit reservoirs and may be used to recover bitumen from associated Previous HitoilNext Hit sands, and multistage multifracing technologies may recover Previous HitoilNext Hit from the deeper unconventional (Monterey) source rocks.

These technological developments, along with improved computing techniques (i.e., three-dimensional [3-D] geologic modeling/visualization), allow for real-time exploration and development of unconventional reservoirs. A significant effort exists in California to improve recovery from Pleistocene, Pliocene, and Miocene heavy-Previous HitoilNext Hit deposits; for example, at present, 70 to 80% recovery from heavy-Previous HitoilNext Hit steam drives is seen in Pleistocene Tulare Formation fluvial and alluvial sands. Full 3-D models anchored by extensive coring and logging programs have reaped benefits in many older Previous HitoilNext Hit fields (e.g., South Belridge, Midway Sunset, Cymric, Lost Hills, Kern River). Bypassed pay and new production from associated shallow Previous HitoilNext Hit sands and deeper source rocks may ultimately be a key to attainment of increases in secure unconventional energy reserves in North America. In the future, full integration of new technologies, along with technology sequencing, may be applied to old California Previous HitoilNext Hit fields for production of bypassed pay in heavy-Previous HitoilTop fields.

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