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The Dirkala Field is located in the southern Murta Block of PEL's 5 and 6 in the southern Cooper and Eromanga Basins. Excellent oil produc­tion from a single reservoir sandstone in the Juras­sic Birkhead Formation in Dirkala-1 had indicated a potentially larger resource than could be mapped volumetrically. The hypothesis that the resource was stratigraphically trapped led to the need to define the fluvial sand reservoir seismically and thereby prepare for future development.A small (16 km2) 3D seismic survey was acquired over the area in December 1992. The project was designed not only to evaluate the limits of the Birkhead sand but also to evaluate the cost effi­ciency of recording such small 3D surveys in the basin.Interpretation of the data set integrated with seismic modelling and seismic attribute analysis delineated a thin Birkhead fluvial channel sand reservoir. Geological pay mapping matched volu­metric estimates from production performance data. Structural mapping showed Dirkala-1 to be opti­mally placed and that no further development drill­ing was justifiable.Seismic characteristics comparable with those of the Dirkala-1 Birkhead reservoir were noted in another area of the survey beyond field limits. This led to the proposal to drill an exploration well, Dirkala South-1, which discovered a new oil pool in the Birkhead Formation. A post-well audit of the pre-drill modelling confirmed that the seismic response could be used to determine the presence of the Birkhead channel sand reservoir.The acquisition of the Dirkala-3D seismic survey demonstrated the feasibility of conducting small 3D seismic surveys to identify subtle stratigraphically trapped Eromanga Basin accumulations at lower cost and risk than appraisal/development drilling based on 2D seismic data.

Business under-performance in the upstream oil and gas industry, and the failure of many decisions to return anticipated results, has led to a growing interest in the past few years in understanding the impacts of decision-making processes and their relationship with decision outcomes. Improving oil and gas decision making is, thus, increasingly seen as reliant on an understanding of the processes of decision making in the real world. There has been significant work carried out within the discipline of cognitive psychology, observing how people actually make decisions; however, little is known as to whether these general observations apply to decision making in the upstream oil and gas industry. This paper is a step towards filling this gap by developing the theme of decision-making process. It documents a theoretical decision-making model and a real-world decision-making model that has been distilled from interviews with many Australian upstream oil and gas professionals. The context of discussion is to review the theoretical model (how people should make decisions) and the real-world model (how people do make decisions). By comparing and contrasting the two models we develop a prescriptive list of how to improve the quality of decisions in practice, specifically as it applies in the upstream oil and gas industry.

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