Probabilistic Hydrocarbon Reserves Estimation: A Novel Monte Carlo Approach

Abstract

Abstract Probabilistic reserves estimating using a generalised Monte Carlo Probabilistic reserves estimating using a generalised Monte Carlo approach has many advantages over simpler deterministic or other probabilistic methods. The particular method described deals more probabilistic methods. The particular method described deals more thoroughly with geologic structural dependency and at the same time allows for a high degree of accuracy. Data preparation is kept to a minimum, allowing seismic and other basic data to be used directly in calculations without the need of preparing time consuming area-depth graphs used in more conventional methods. A further advantage is the elimination of certain arbitrary decisions related to extreme structural scenarios based on geological mapping of a very limited number of possible situations. Sensitivities related to uncertainties and errors possible situations. Sensitivities related to uncertainties and errors are handled in an easy manner. The approach related to gross rock volume calculations is different from more conventional probabilistic reserves simulations in that it involves the direct manipulation of all surfaces bounding the most likely rock volume. Such uncertainty, described by statistical distributions (e.g. seismic velocity error) and functional relationships, involves geological horizons bounding individual sands (reservoirs), structural surfaces such as unconformities and faults, and fluid contacts. Introduction Reserves estimating may be based primarily on initial volumetric estimates or at a later stage in field development on performance analysis involving numerical simulation, material balance methods and production decline curve analysis, as was for example recently summarised production decline curve analysis, as was for example recently summarised by Garb. While these so called accepted, deterministic methods are sufficient in many cases, particularly when ample well data exists, it may be necessary in some situations to handle initial volumetrics more appropriately by applying suitable probabilistic methods which make use of all available data, including seismic, and which furthermore give an appreciation for uncertainties and accuracy associated with volume estimates. Such methods are not only more flexible in dealing with uncertainties but are also more advantageous for providing a better basis for investment decisions. It may also be mentioned that at this moment in time Petroleum Engineering lags behind other sectors in industry, notably Mining, in using and generally accepting statistical methods.