Abstract

Owing to the high cost and high risk inevitably associated with unexplored, or essentially unexplored, basins in frontier areas where adverse environmental conditions often prevail, a method for ranking basins on a relative basis is necessary for the rational allocation of exploration funds and technical effort. To develop a consistent method for evaluating specific basins, both subjective and objective estimates are required; therefore, risk and uncertainty must be quantified.

A method that relies on both the assessment of the basin's source potential and the sedimento-logical-trap type classification of the basin to yield an estimate of total basin reserves and a field-size distribution is described. Then, based on geographic location, operating conditions, probable type of hydrocarbon and economic considerations, probable type of hydrocarbon and economic considerations, the minimum size for a viable field is determined. Finally, the size and number of economic fields and the probability of success are estimated to give the risk-weighted distribution for the economic reserves of the basin.

The use of this procedure to obtain a relative ranking for the basins under considerations is discussed—with emphasis on the recognition of the probablistic nature of the comparison. An example probablistic nature of the comparison. An example is presented to illustrate the use of the prescribed procedure. procedure

Introduction

The recoverable reserves of a sedimentary basin are determined by the amount of hydrocarbon originally generated from the dispersed organic matter indigenous to the basin and the post-generation geological history of the basin. Theoretically, the volume of hydrocarbon formed may be estimated from source-rock quality and the volume of thermally mature source rock that is present; e.g., Tissot and Welte. Part of the present; e.g., Tissot and Welte. Part of the hydrocarbon generated is expelled from the source rock and it is transported to other basin sediments by mechanisms which are not yet clearly defined. Ultimately, some portion of the migrating hydrocarbons is accumulated in a variety of traps within the basin and some fraction of these trapped hydrocarbons is recoverable. If sufficient paleo-temperature lithologic, tetonic, hydrodynamic and other physical-chemical data were available and if the physical-chemical data were available and if the dominant transport mechanisms were understood, the quantity of recoverable hydrocarbons could be estimated and the basin could be evaluated.

Since these requirements for a quantitative evaluation are not generally satisfied—particularly, for relatively unexplored basins, other methods have been suggested. Jones proposed a predictive model for individual areas while Porter and McCrossan proposed an analog method based on a classification according to depositional and structural characteristics of basins. Statistical and probablistic approaches have also been suggested i.e., cluster analysis by Bois, probablistic modeling by Kaufman et al, Monte Carlo simulation by White et al, a statistical search model by Cozzolino and a geochemical model by Bayliss et al.

The approach that will be taken in this paper is one which will, hopefully, combine the best features of all these suggested methods. Hard data will be used whenever possible and consistent, albeit subjective, estimates will be used whenever required.

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