VISUALISATION OF A FLUVIAL CHANNEL RESERVOIR ANALOGUE FROM THE BIRKHEAD FORMATION, MERRIMELIA, MERANJI AND PELICAN FIELDS, EROMANGA BASIN

The effective production of hydrocarbons from the Birkhead Formation, Eromanga Basin, relies heavily on understanding the complex distribution of reservoir and seal rocks deposited in a fluvial environment. To visualise this complexity, sequence stratigraphic concepts applied to non-marine basins were combined with 3D seismic data visualisation in a study of the Birkhead interval over the Merrimelia, Meranji and Pelican fields.Fluvial channel, crevasse splay channel, floodplaincrevasse splay complex and floodplain facies were recognised from the well log motifs in the Birkhead Formation. The interval is interpreted as an alluvial transgressive systems tract bounded by flooding surfaces consisting of shaly or coaly intervals. Lateral discontinuity of the fluvial system can be demonstrated between these surfaces. Seismic amplitude distributions in the 3D seismic data in the upper part of this transgressive systems tract illustrate well developed meandering fluvial channels. Combining the spatial distributions of sedimentary facies from the well logs and the seismic amplitudes results in the interpretation of a fluvial meandering channel belt that includes point bars and abandoned channels.The point bar sandstones in the channel belt should make good reservoirs and the juxtaposition of the point bar and abandoned channel facies can result in a stratigraphic trap component to the reservoir rocks within the channel belt. Although the point bars are known to be wet in the study area, it is still useful to consider their capacity as oil reservoirs, since they may serve as analogues for similar untested point bars elsewhere. Multiple realisations of the distribution of sandstone thickness of the point bars were generated by conditional simulation, using seismic amplitudes to control extrapolation of the well data. This gave a potential reserves distribution with a mean value of 18.8 million bbl in place. The complexity of the fluvial channel systems in the Birkhead Formation described in this paper should aid understanding of the reservoir and seal distribution and help optimise production from this interval in other fields.

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TOWARDS AN EFFICIENT EXPLORATION FRONTIER: CONSTRUCTING A PORTFOLIO OF STRATIGRAPHIC TRAPS IN FLUVIAL-LACUSTRINE SUCCESSIONS, COOPER-EROMANGA BASIN

The APPEA Journal ◽

10.1071/aj01008 ◽

2002 ◽

Vol 42 (1) ◽

pp. 131

Author(s):

T. Nakanishi ◽

S.C. Lang

Keyword(s):

Net Present Value ◽

Spatial Arrangement ◽

Mean Value ◽

Seismic Survey ◽

3D Seismic ◽

Sequence Stratigraphic ◽

Depositional Systems ◽

Efficient Exploration ◽

3D Seismic Data ◽

Eromanga Basin

In the Cooper-Eromanga Basin, the future of exploration lies in identifying an appropriate exploration portfolio consisting of stratigraphic traps in structurally low or flank areas. A variety of stratigraphic trap prospects in the Moorari and Pondrinie 3D seismic survey areas are identified in the Patchawarra, Epsilon, Toolachee and Poolowanna formations. To identify the stratigraphic traps, an integration of sequence stratigraphic concepts applied to non-marine basins and advanced 3D seismic data visualisation was employed. This paper focusses on estimating the chance of geologic success and the probabilistic reserves size for each prospect within its sequence stratigraphic context (lowstand, transgressive or highstand systems tracts). The geologic chance factors for an effective stratigraphic trap include reservoir, top seal, lateral seal and bottom seal within each depositional systems tract, the seal effectiveness of the adjacent depositional systems tracts and the appropriate spatial arrangement of these factors. The confidence values for the existence of geologic chance factors were estimated according to the distributions of the possible reservoir and seal rocks within each genetic-stratigraphic interval and the chance of geologic success of each prospect was calculated. For probabilistic reserves estimation, geologically reasonable ranges were estimated for each parameter employing Monte Carlo simulation to calculate the reserves distribution. When a series of possible exploration portfolios, including single or multiple prospects from the prospect inventory are plotted in terms of the chance of geologic success vs. the mean value of the reserves estimate, an efficient exploration frontier emerges. The portfolio candidates on the efficient exploration frontier were assessed with regard to chance of economic success and expected net present value (ENPV) using a simple cash flow model. The results indicate that appropriate portfolios include multiple prospect exploration especially with lowstand systems tract plays using single or multiple exploration wells. The portfolio construction approach for stratigraphic trap exploration should ultimately be made consistent with conventional play types, to enable an assessment of all exploration opportunities.

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