Distribution of Miocene deep-water reservoirs, and factors controlling their deposition and reservoir quality, southern Gulf of Mexico.

  • Author / Creator
    Gutierrez Paredes, Hilda C.
  • The factors controlling the distribution, geometry, and quality of the Miocene reservoirs, in an area located in the southern Gulf of Mexico (in the offshore part of the Tabasco State) were attained through detailed stratigraphic and facies analyses combined with seismic facies and 3D seismic-derived plan-view images. The depositional systems are dominantly represented by submarine fans (channel systems and frontal splays), lobes of debrites and mass-transport complexes. The main depositional processes were related to turbidity current; debris flows were of secondary importance, as was deposition from the fallout of suspended hemipelagic mud particles. A sequence-stratigraphic analysis was performed to identify significant surfaces, systems tracts, and sequences for the Miocene succession. Five genetic sequences and eleven stratigraphic surfaces were correlated throughout the study area. The Miocene succession, from older to younger deposits, consists of: mass-transport deposits and turbidite deposits (lower Miocene); debrite deposits and turbidite deposits (middle Miocene); and debrite deposits and turbidite deposits (upper Miocene). These sedimentation cycles are delineated by regionally extensive maximum flooding surfaces within condensed sections of hemipelagic mudstone which represent starved basin floors. These maximum flooding surfaces are the key surfaces for the construction of the Miocene stratigraphic framework. The falling-stage system tracts form the bulk of the Miocene sequences. Individual sequence geometry and thickness were controlled by tectonics, halokinesis and large-scale sedimentation patterns. The Tortonian (upper Miocene) sequence includes sandy deposits, whereas the overlying Messinian sequence includes sandy facies at the base and muddy facies at the top; this trend reflects the change from slope to shelf settings. The Miocene depositional elements were deposited in an irregular paleotopography strongly affected by regional and local tectonics. As a result, the recorded deformational events (contraction and extension) together with the halokinesis played an important role in the sedimentation of the area. Such interaction occurred in two ways; the structural elements modified the paleotopography of the basin creating accommodation space for clastic deposition and controlled the entry of sediments to the basin. During the Oligocene to early Miocene, the main depocenter was bounded by diapirs, salt sheets and structural highs formed by older salt anticlines; on the other hand, for the middle Miocene the depocenters were confined by the presence of shortened diapirs and salt sheets in the periphery and structural highs in the south of the study area. The formation of these depocenters provided the accommodation space for sediments deposition; as a result, during the early to middle Miocene, the deposits were confined to these depocenters forming ponded lobes. At the end of the middle Miocene, these depocenters were filled and channel-levee systems and frontal splay complexes predominated in an unconfined setting. During the late Miocene the depocenter’s formation was controlled by an extensional event, which provided the accommodation space for sediment deposition in half grabens, frontal splays and channel-levee systems being the most important depositional elements. All these structural elements had significant implications for the architecture and internal organization of the turbidite systems. Finally, establishing the link between the sequence stratigraphic framework, depositional facies, and diagenetic alterations was critical to determine the main factors controlling the reservoir quality of the Miocene sandstones. The Miocene deep-marine sandstones were attributed to the falling-stage and lowstand system tracts. The middle Miocene falling-stage systems tracts included medium- to very fine-grained, and structureless sandstones deposited in channels and frontal splays, and muddy sandstones, and sandy debrites deposited in lobes. The lowstand system tracts consist of medium- to very fine-grained massive and normally graded sandstones deposited in frontal splay complexes. The upper Miocene falling-stage systems tract includes medium- to coarse-grained, structureless sandstones deposited in channel systems and frontal splays, as well as lobes of debrites composed of grain flows and hybrid-flow deposits. The lowstand systems tracts include fine-grained sandstones deposited in overbank deposits. The results reveal that the depositional elements with the best reservoir quality are the frontal splays deposited during the falling-stage system tracts. The reservoir quality of the Miocene sandstones was controlled by a combination of depositional facies, sand composition and diagenetic factors (mainly compaction and calcite cementation). Sandstone texture controlled primarily by depositional facies appears to be more important in comparison to sandstone composition when determining reservoir quality; and compaction was more important than cementation to porosity destruction, which only stopped when complete calcite cementation occurred.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Doctor of Philosophy
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