Lithofacies Stochastic Modelling of a Braided River Reservoir: A Case Study of the Linpan Oilfield, Bohaiwan Basin, China

In the direction perpendicular to a braided river, the continuity of the sand body is sub-optimal, so it is difficult to predict its lateral distribution in the reservoir modelling process. In addition, owing to the differences in well patterns in an oilfield, using the same set of variation functions to establish the sand body distribution model for the whole area is often infeasible, as it cannot reflect the planar heterogeneity of the sand body. In view of these shortcomings of the modelling process, this paper presents a method of sandstone–mudstone facies modelling for braided river reservoirs with irregular well patterns. First, according to the well pattern distribution, the study area is divided into different modelling units to regularize and unify the well pattern of each modelling unit as much as possible. Then, the sandstone–mudstone facies model of each unit is determined by the stochastic modelling method, and the variation function suitable for the unit is obtained. According to the well pattern density within each unit, the corresponding weights are set, and the variation functions of all units are weighted and averaged to derive a set of variation functions suitable for the whole area model. These functions are used to establish the lithofacies model of the Linpan oilfield. Finally, two new methods are adopted to test the accuracy of the model. They both confirm that the model has high stability, the variogram has strong adaptability, and it can effectively predict the distribution proportion of sandstone and mudstone in the unknown area between the wells.