Abstract

The field size distribution method, such as the Pareto model, is commonly used in hydrocarbon resource assessment in China. It has the advantage of predicting not only the total resources but also the individual field sizes. However, the method has a large uncertainty range in the model parameter estimates. A multi-parameter-constrained Pareto model is proposed to improve parameter estimations. The constraints introduced include: a) total resource estimate from other methods (e.g. genetic method); b) the largest size of undiscovered fields from an empirical relationship between play resources and the largest field sizes in well explored basins; and c) the number of undiscovered fields constrained by the number of untested traps (including subtle traps). By introducing the three constraints, the method provides realistic results with less uncertainty and is consistent with petroleum system models derived from hydrocarbon exploration. The application of this proposed method to Bozhong Sag in the Bohai Bay Basin suggests a total resource of 4130×10⁶ m³ in 48 fields, of which 1165×10⁶ m³ are in 27 discovered fields and 2965×10⁶ m³ are in the remaining 21 undiscovered fields. The largest discovered field is 369×10⁶ m³ and the largest remaining field expected is 853×10⁶ m³. The results of the application appear to be consistent with the current exploration status and geological understanding of the study area.