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Integrated Reservoir Analysis is a procedure where interpreted stratigraphic and facies frameworks are combined with structural analysis to produce more accurate and appropriate reservoir maps. The result is a three dimensional interpretation of the thickness, shape, lateral extent, and internal distribution of porosity and permeability in individual reservoir units. The principal steps of the procedure are: (1) planning, (2) data gathering, (3) determination of the stratigraphic framework, (4) determination of the facies framework, (5) structural analysis, (6) data manipulation, and (7) mapping.
The stratigraphic framework is developed by combining pattern correlation techniques with knowledge about the influence of specific facies on stratigraphic patterns. A network of cross sections are designed utilizing correlation "grain" and/or depositional strike. Correlations on these sections develop a framework of horizons which ideally will isolate, in a stratigraphic envelope, individual reservoir units resulting from a unique depositional episode.
The facies framework results from environmental facies analysis and the use of electric log facies. The proper identification of reservoir facies is required for the mapping of reservoir geometry and the determination of the internal distribution of porosity and permeability. Facies-biased contouring techniques and the lateral extension of facies relationships along cross sections were used in the planning and design of a waterflood project by Lagoven, S.A., in fluvial-deltaic clastics of the Miocene La Rosa Formation in the LL3 field, Lake Maracaibo, Venezuela. Important clastic reservoir facies recognized in cores were (1) stream-mouth-bar, (2) distributary-channel-fill, and (3) fluvial point-bar deposits. These environmental facies often occurred in various combinations in deltaic obes and displayed the electric log shape of the deltaic couplet. Characteristic electric log shapes of specific reservoir facies were an essential part of the study.
The pilot waterflood was designed to inject into stream-mouth-bar facies and withdraw from centrally located distributary-channel-fill deposits with their better porosity and permeability. Critical to the design and subsequent performance of the waterflood project were (1) the distribution of porosity within the various reservoir facies, and (2) the occurrence, attitude, and lateral distribution of clay laminations within the lower stream-mouth-bar and upper fluvial deposits. The influence of clay laminations in lower stream-mouth-bar facies was particularly critical to waterflood performance. They were deposited on the distal slope of the stream-mouth-bar at a slight angle to the rock unit boundaries and therefore could mask parts of the reservoir from waterflood treatment. The amoun of masking was determined by calculations from facies geometry. After one year's operations, radioactive tracers indicate that the flood is operating as designed only at a reduced rate--probably as a result of the clay laminations.
Integrated Reservoir Analysis can be useful not only to production operations such as waterflood projects, infill drilling, recompletions, and reserve estimates, but a similar procedure could also be applied to exploration activity in mature areas with plentiful log data.
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