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 Sedimentation rates vary by eleven Orders of magnitude and the physical scale of depositional units varies by fourteen orders of magnitude. These variations suggest a hierarchical ordering of depositional units in clastic sedimentary deposits. A tentative grouping of architectural units has been constructed, based primaril on the recurrence interval of the depositional events: Group 1 deposits are the product of events taking tens of seconds to a few minutes, such as the burst-and-sweep activitiy of a fluid boundary layer. Group 2 deposits are those formed in a few minutes to a few hours, and include ripples and dune depositional increaments. Group 3 deposits are those forming in a few hours to a day or two, including diurnal tidal bundles. Group 4 deposits form in days to a few months, and include such processes as neap-spring tidal cycles:group 4 deposits also encompasse the spacing of many storm events. Group 5 deposits represent one to a few years, such as seasonal events (spring runoff, glacial varves), and occasional violent storrms. Group 6 is for sedimentary processes of a hundred to thousands of years duration, including the evolution of fluvial macroforms, eolian dunes and tidal sand-wave fields. Group 7 represents longterm geomorphic processes, over thousands to tens of thousands of years, such as channel and draa migration. Group 8 processes extend over tens to hundreds of thousands of years, and represent such depositional elements as channel belts, ergs and sand-ridge fields. Fifth-order stratigraphic sequences, many generated by Milankovitch causes, are also of this rank. Group 9 processes are of hundreds of thousands to a few million years duration, such as fourth-order stratigraphic cycles (e.g., major cyclothems, shelf coarsening-upward cycles driven by thrust-loading events, etc). Deposits assigned to group 10 are those taking a few millions to tens of millions of years, including third-order stratigraphic cycles. Instantaneous sedimentation rates are of a similar order of magnitude within each group, ranging from 10 5 m/ka for the smallest scale of deposit, to 10 -1 m/ka for groups 9 and 10. Deposits of each group may be defined, in some cases, by enclosing bounding surfaces. Hierarchiesof such surfaces have been erected for fluvial and eolian deposits and for some suites of estuarine and shelf bedforms. Investigations of each group require different techniques. Deposits up to group 7 and possibly 8 may be documented in expectionalyy good outcrop. Studies of moderm deposits of groups 6 to 8 may be carried out using high-resolution geophysical techniques. Groups 7 to 10 require investigation and reconstructio using basin-mapping techniques based on careful correlation. Subsurface well and seimic data may be employed. Abstract An enormous mobile-oil resource (35 Bbbl in Texas and 80–100 Bbbl in the United States) is trapped in inefficiently drained, mature reservoirs. Much of this oil can be recovered at low cost through conventional infield exploration and development strategies that target untapped compartments in these reservoirs. Three-dimensional facies architecture exerts the primary control over the distribution and continuity of reservoir compartments. Reservoirs with complex internal architecture contain large volumes of remaining mobile oil; those with a simpler internal architecture are efficiently drained. Three Texas reservoirs, representing differences in internal architecture, illustrate variations in reservoir-pay continuity: barrier-island (41-A reservoir in West Ranch field in south-central Texas), fluvial (Jim Wells and Brooks reservoirs in La Gloria field in South Texas), and submarine fan (reservoirs in the Spraberry Trend in the Midland Basin). Methods of estimating pay continuity based on facies geometry and variations in permeability between wells can be used to describe reservoir heterogeneity and indicate areas for infield exploration in each of these reservoirs. Although most barrier-island reservoirs are considered to be relatively homogeneous, the 41-A barrier-island reservoir in West Ranch field contains wide, dip-oriented belts of lenticular tidal-inlet facies that disrupt reservoir continuity in the main barrier-core facies. Additionally, the tidal-inlet facies are internally less continuous than the barrier-core facies. Other reservoir compartments that exhibit low continuity in the 41-A reservoir occur in flood-tidal-delta sandstones partly encased in lagoonal mudstones updip of the barrier core. Infill wells drilled into the lower-continuity facies in the 41 - A reservoir at well spacings less than the conventional 20-acre spacing can contact additional oil, resulting in substantial reserve additions. Fluvial reservoirs have a higher degree of internal complexity than do barrier-island reservoirs, and they exhibit significant heterogeneity in the form of numerous sandstone stringers bounded vertically and laterally by thin mudstone layers. Successful infill wells in La Gloria field contact partly drained reservoir compartments in splay deposits that pinch out laterally into floodplain mudstones. Recompletions in bypassed stringers in La Gloria field contact channel-fill sandstone compartments that are isolated vertically by floodplain mudstones. Mud-rich submarine-fan deposits are extremely heterogeneous and may have the greatest potential for infill drilling to tap isolated compartments in clastic reserviors. The Spraberry Trend in West Texas contains thin, discontinuous reservoir sandstones deposited in a complex midfan channel- and levee-system. Although facies relationships in Spraberry reservoirs are similar to those in fluvial resevoirs in La Gloria field, individual pay stringers are thinner and more completely encased in low-permeability mudstone facies. Abstract Photomosaics can be useful tools for understanding and communicating geologic features expressed on outcrop faces. In order to utilize photomosaics properly, maximum resolution and minimum geometric distortion of the features is necessary. Maximum resolution is best obtained by using quality equipment and by attending to proper technique. In some cases increasing contrast will improve resolution; various methods can be utilized. Sufficient overlap of photographs in the construction of photomosaics will remove distortion in most situations. A common problem is perspective distortion, the convergence of vertical lines. This occurs when the film plane and outcrop face are not parallel and results in curved or "smiling" mosaics. When it is not feasible to obtain parallelism, several methods can be used to help correct this problem. In many situations fitting a 35-mm camera with a perspective control lens is the simplest and most economical strategy for reducing or eliminating the problem.

Abstract An enormous mobile-oil resource (35 Bbbl in Texas and 80–100 Bbbl in the United States) is trapped in inefficiently drained, mature reservoirs. Much of this oil can be recovered at low cost through conventional infield exploration and development strategies that target untapped compartments in these reservoirs. Three-dimensional facies architecture exerts the primary control over the distribution and continuity of reservoir compartments. Reservoirs with complex internal architecture contain large volumes of remaining mobile oil; those with a simpler internal architecture are efficiently drained. Three Texas reservoirs, representing differences in internal architecture, illustrate variations in reservoir-pay continuity: barrier-island (41-A reservoir in West Ranch field in south-central Texas), fluvial (Jim Wells and Brooks reservoirs in La Gloria field in South Texas), and submarine fan (reservoirs in the Spraberry Trend in the Midland Basin). Methods of estimating pay continuity based on facies geometry and variations in permeability between wells can be used to describe reservoir heterogeneity and indicate areas for infield exploration in each of these reservoirs. Although most barrier-island reservoirs are considered to be relatively homogeneous, the 41-A barrier-island reservoir in West Ranch field contains wide, dip-oriented belts of lenticular tidal-inlet facies that disrupt reservoir continuity in the main barrier-core facies. Additionally, the tidal-inlet facies are internally less continuous than the barrier-core facies. Other reservoir compartments that exhibit low continuity in the 41-A reservoir occur in flood-tidal-delta sandstones partly encased in lagoonal mudstones updip of the barrier core. Infill wells drilled into the lower-continuity facies in the 41 - A reservoir at well spacings less than the conventional 20-acre spacing can contact additional oil, resulting in substantial reserve additions. Fluvial reservoirs have a higher degree of internal complexity than do barrier-island reservoirs, and they exhibit significant heterogeneity in the form of numerous sandstone stringers bounded vertically and laterally by thin mudstone layers. Successful infill wells in La Gloria field contact partly drained reservoir compartments in splay deposits that pinch out laterally into floodplain mudstones. Recompletions in bypassed stringers in La Gloria field contact channel-fill sandstone compartments that are isolated vertically by floodplain mudstones. Mud-rich submarine-fan deposits are extremely heterogeneous and may have the greatest potential for infill drilling to tap isolated compartments in clastic reserviors. The Spraberry Trend in West Texas contains thin, discontinuous reservoir sandstones deposited in a complex midfan channel- and levee-system. Although facies relationships in Spraberry reservoirs are similar to those in fluvial resevoirs in La Gloria field, individual pay stringers are thinner and more completely encased in low-permeability mudstone facies.