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Carbonate Reservoir Delineation from Seismic Data ­ Examples of Crosswell Seismic

Harris, Paul1 (1) Chevron Energy Technology Company, San Ramon, CA Crosswell seismic tomography provides better reservoir resolution than surface data; therefore there should be value added in reservoir delineation. Examples of crosswell seismic data from two fields illustrate the resolution and some potential applications of this type of data: (1) defining greater geologic detail between wells (heterogeneity of reservoir), (2) recognizing laterally continuous zones for improved development (well positioning, completions, injection), and (3) input for reservoir models (layering and assigning porosity). In the first example, the producing formation is limestone with minor dolomite and shale. 3D seismic and downhole log data suggest lateral discontinuities but details are ambiguous due to the poor resolution. Crosswell data defines the nature of some of the reservoir discontinuity, in that clinoforms which are imaged can potentially isolate reservoir compartments. A comparison with outcrop facies geometries provides some sense of the reservoir facies to be expected between wells. The second example is a diagenetically complex cyclic shelf dolomite. Variations in amplitude on the crosswell data are the most striking lateral features, and nearly every positive-amplitude event coincides with a significant increase in velocity on sonic logs. Both the seismic and log data respond to the same diagenetic overprint and its resulting petrophysical characteristics; therefore log-derived facies relate to the crosswell data better than core lithofacies. Comparing crosswell data with geostatistical porosity models and with analogous outcrops to further analyze the potential imaging of lateral porosity variation suggests lateral changes in porosity are being imaged at the scale of tens of meters.

Seismic Stratigraphy and Geomorphology of Oligocene to Miocene Carbonate Buildups, Offshore Madura, Indonesia

Posamentier, Henry W.1, Priscilla Laurin2, Julie Kupecz3 (1) Anadarko Canada Corporation, Calgary, AB (2) Anadarko Petroleum Corporation, The Woodlands, TX (3) Anadarko, Bellaire, TX A variety of carbonate landscapes have been imaged on 3D seismic data from the offshore area north of Madura Island, Indonesia. Carbonate buildups ranging from small patch reefs to platforms with outliers, and tide influenced elongate large patch reefs are observed within the Kujung 2, Kujung 1, and Wonocolo Formations. Outcrop expression of these carbonate buildups are incorporated into the interpretation of the seismic data. The small patch-reef buildups of the Kujung 2 range in size from less than 120 m up to 500 m diameter. Across the platform these buildups are closely spaced with less than 100 m separating isolated buildups. Each buildup is circular in plan view, with vertical relief of approximately 25-40 m. Hundreds of these features are observed within the 3D seismic volume. Larger-scale patch reefs of the Kujung 1 coalesced to form a northwest-southeast trending platform. Individual build-ups within the platform range from 600 m to 2 km in diameter and from 200-300 m in thickness. Smaller patch reefs ranging from 60-120 m diameter are observed at the tops of these buildups. Large scale build-ups form off the platform and can be up to 400m thick with diameters from 1-6.5 km. The Kujung 1 reefs are circular to elliptical in planform. 200 m deep, 650 m wide anastamosing channels trend normal to the platform buildup and terminate at the buildup margin. The Woncolo carbonate buildups generally are larger than the Kujung buildups and are characterized by internal clinoform architecture. These buildups are circular to elliptical in planform and range in size from 4-10 km wide, and up to 20 km in length. They are separated from each other by 1.2-2.5 km wide tidal channels.

Development of Multiphase Karstification in Central Luconia Carbonates ­ Imaging and Modeling the Unpredictable

Coca, Spencer1, Laurent Bourdon2, Laurent Alessio3 (1) Sarawak Shell Berhad, Miri, Malaysia (2) Woodside Energy Ltd, Perth, Australia (3) CS Mutiara Petroleum Co, Kuala Lumpur, Malaysia Three major karstification events associated with the TB 3.1, 3.2, and 3.4 sequence boundaries have been identified in Central Luconia carbonate build-ups. Extensive karstification characterised by development of dendritic cave systems stands testimony to periods of prolonged subaerial exposures that affected dozens of gas bearing carbonate platforms. Since presence of intra-reservoir Karst has an important impact on field development and well placement its identification and realistic modelling becomes crucial. Advanced seismic volume interpretation techniques consisting of spectral decomposition, acoustic impedance opacity rendering, and structurally oriented semblance filtering were used to image the complex palaeo-cave networks in some of the major producing gas fields offshore Sarawak. Subsequently, imaged Karst networks were extracted from seismic by means of bodychecking and imported as geocellular bodies in a reservoir modelling package, where full field dual property models were generated. These models were then used on a field scale for well planning and reservoir management purposes, but were also merged into a regional 3D-Karst model that facilitated regional sequence stratigraphic understanding. Geometrical analysis of modelled Karst shows a close resemblance to modern day analogues in the Bahamas with a core area in the centre of the platform and dendritic drainage towards the margins where mapped palaeo-mixing zones are indicative of former shorelines. In the inter-tidal realm blue holes that are connected to peri-platform Neptunian Dykes could be extracted from seismic.

Canyon Formation on Clinoform Foresets of a Prograding Eocene-Miocene Carbonate Shelf, Offshore Northwest Australia

Reuning, Lars1, Peter Kukla1, Stefan Back2 (1) RWTH Aachen University, Aachen, Germany (2) RWTH Aachen, Aachen, Seismic data from the western part of the Browse Basin, North West Shelf, Australia, reveal the internal geometry and depositional history of a progradational Eocene-Miocene carbonate shelf. The prograding slope system is superbly

imaged by two adjacent, three-dimensional multichannel seismic volumes embedded in a two-dimensional multichannel seismic grid. Based on this data, the 3-D stratal architecture of prograding clinoforms can be mapped throughout an area of ~ 1000 km2. The Eocene-Miocene slope system can be divided into an Eocene clinoform succession strongly prograding towards the northwest, and an Oligocene to Late Miocene progradational to aggradational clinoform sequence. The prograding clinoforms of the Eocene succession progressively develop highly dissected, gullied foresets. In contrast, the Oligocene to Late Miocene system is characterized by relatively smooth foresets that lack major incisions. This change in downslope erosion is accompanied by a transition in platform morphology from an unrimmed heterozoan carbonate shelf in the Eocene to a carbonate platform dominated by coral buildups in the Oligocene and Miocene. The spatial control provided by the 3-D seismic volume supports a detailed analysis of the relationship between the overall morphology of carbonate systems and the erosion mechanisms on their foresets. A better knowledge of the Tertiary succession will further help to optimize seismic velocity models for the study area.

(Palaeo)-Geomorphology of Carbonate Platform Slopes and Deepwater Coral Reefs

Massaferro, Jose Luis1, Gregor P. Eberli2, Karina Miguel Arrieche1, Ana Sanz1, Mark Grasmueck3, Thiago Correa2 (1) Repsol YPF Exploration and Production, Madrid, Spain (2) University of Miami, Miami, FL (3) University of Miami, RSMAS, Miami, FL The deep water surrounding modern carbonate platforms hides the morphology of their slope and adjacent basin. New multibeam data documents geometries of the lower slope and the adjacent basin with unprecedented accuracy. Likewise 3-D seismic data is capable of displaying these morphologies with a resolution that makes a direct comparison possible. Combined they document the platform basin transition that typically consists of a near-vertical wall and a steep cemented upper slope. Below the slope is dissected by channels that widen down slope and are perpendicular to the margin. Slope failure occurs on all portions of the slope, producing scars and debris flow deposits at the toe-of-slope. In water depths of 450 ­ 650 m, deep water coral mounds occur in many places. These ahermatypic coral reefs reach impressive heights of 70 m and width of over 500 m. Along the margin they are typically aligned with the slope channels. Farther basinward they colonize drift deposits and their distribution seems to be mostly influenced by the underlying sand wave pattern. Seismic attributes display the geometry of the channelized lower slope and the orientation of its deposits at the toe-ofslope from an older platform. Deep-water coral reefs are seismically imaged at the present-day sea bottom showing a decrease in abundance as water depth increases. Body checking performed within the Oligocene shows seismic bodies that can be interpreted as deep water coral mounds. Modern and ancient geometries are similar, indicating that slopebasin transition has not changed through the Tertiary.

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