Abstract Development of the 330-billion-bairel oil resource remaining in United States reservoirs after conventional primary and secondary recovery will be dependent on the advanced understanding of facies relations and compartmentalization inherent in reservoir depositional systems. Style of deposition, as reflected in internal reservoir architecture, defines flow units that determine how a reservoir drains, where hydrocarbons remain unrecovered at the interwell (macroscopic) scale, and what approaches will be effective in accessing unrecovered oil. A substantial part of the unrecovered oil resource is nonresidual oil that, although mobile in the reservoir, remains unrecovered owing to poor contact by existing wells and vertical or areal bypassing by the waterflood front. Because heterogeneity style is a product of depositional system, it is predictable and can be characterized in terms from low to high in a lateral and vertical sense. For sandstones, the wave-dominated deltas, barrier cores, and sand-rich strand plains show a low degree of heterogeneity in both dimensions, whereas the highly aggradational backbarrier fans, fluvially dominated deltas, and fine-grained meander belts show a higher intensity of heterogeneity. Other systems can be similarly classified. The resulting matrix leads to delineation of targeted approaches to incremental oil recovery specifically tailored to the distribution of remaining oil saturation. Such approaches, optimized to the character of the depositional system, may include geologically targeted infill drilling, selective recompletion, horizontal drilling, and strategic cross-reservoir flooding involving flood redesign and profile modification. Such techniques are herein termed Advanced Secondary Recovery (ASR) and represent advancements in technology that will lead to near- and mid-term improvements in efficiency that set the stage for later approaches to Enhanced Oil Recovery (EOR).

Abstract Major blanket-geometry, low-permeability gas sandstones in Texas include the Cotton Valley sandstone, the Travis Peak Formation, the Cleveland formation, and the Olmos Formation. The Cotton Valley (Upper Jurassic) and the Travis Peak (Lower Cretaceous) are widespread, sand-rich units within the East Texas basin that contain marginal marine deltaic, barrier-strandplain, and fan-delta facies. Gas production from the Cotton Valley is more extensively developed than from the Travis Peak, in part because today’s hydraulic fracturing technology was either developed or improved during completion of Cotton Valley tight gas reservoirs. The Pennsylvanian Cleveland sandstone of the Anadarko basin is in a mixed gas and oil to somewhat gas-prone province wherein the Cleveland produces gas from thin, distal deltaic facies or prodelta sediments reworked by shelf processes. Clay is abundant in the fine to very fine sandstone of the Cleveland. The Upper Cretaceous Olmos Formation contains gas within broadly lenticular delta-front deposits of the Maverick basin. The Olmos contains fine-grained to very-finegrained silty sandstones within massive shales. In 1980 tight gas sandstones accounted for 28% of gas wells completed in the 5,000- to 15,000-ft-depth range in Texas. Most of the completions in blanket-geometry hydropressured sandstones were within the formations reviewed herein.