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Abstract: Sequence Stratigraphic and Reservoir Architecture of Middle to Late Miocene Tidal and Fluvially Influenced Lower Delta Plain to Marginal Marine Clastics in Block A-18, Malaysia-Thailand Joint Development Area (MTJDA)

LAWRENCE, DAVID A., (Present addresses: Fina Exploration Norway SCA, GRANT R. GILCHRIST, Carigali-Triton Operating Co. Sdn. Bhd., Malaysia: AND ERLING I. H. SIGGERUD Smedvig Technologies a.s., Z&S Geologi a.s., Norway: (Present addresses: Fina Exploration Norway SCA and Smedvig Technologies a.s.

Summary.

Block A-18, JDA is located in the offshore South China Sea, at the juncture of the southern Gulf of Thailand, and the northern Malay Basin, a contiguous Tertiary extensional basin system. The sedimentary fill comprises a prospective Oligocene to Late Miocene section, of which tidal and fluvially influenced Middle to Late Miocene clastics, the focus of this paper, are the primary, exploration targets. Lower delta plain to marginal marine clastics records a history of repetitive sub-regional transgressive and regressive events developed daring active basinal subsidence, culminating in a regional transgression m the Late Miocene. Repeated delta progradation from the north and northwest took place on a gentle southerly sloping basin axis. High tropical precipitation, shallow water depth, and a narrow basin morphology resulted in reduced overall salinity but periodically strong tidal circulation.

Integration of sedimentary facies, dip interpretation, and ichnofabric analysis of core and high resolution borehole resistivity image logs from 9 wells, with calibration from biostratigraphic data, and seismic attribute analysis has enabled construction of a unified and detailed sequence stratigraphic and reservoir architecture model. Sedimentary dip interpretation of the borehole image log dataset, calibrated with core observations and ichnofabric stacking patterns provides an appropriate resolution to distinguish and detail tidal influence.

The sequence stratigraphic architecture is characterised by third order genetic stratigraphic sequences. These average 1.0 My in duration, and may be subdivided into higher frequency fourth order sequences (or sub-sequences) with an average 0.2 My duration. In addition to flooding surfaces, transgressive, tidal ravinement, wave ravinement and potential fluvial incision surfaces are recognised. Paleoenvironment reconstruction with time suggests that coastal regime, and particularly tidal influence, varies systematically both within genetic sequences, and in response to overall transgression. Basin morphology plays a key role in amplifying tidal activity, especially during the early stages of transgression.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah