Hierarchical constraint geological modelling method for carbonate paleokarst caves: A case study of Ordovician fracture-cavern unit in Tahe Oilfield

Abstract

The characteristics of carbonate paleokarst cave and filling have always been the difficulty of characterization and modelling. Based on the seismic, geological and logging data, this paper puts forward the idea of three-level progressive modelling of karst cave complex, single karst cave and karst cave internal filling. The karst cave complex is a large-scale geological body, which can be identified by seismic in most cases. The truncated Gaussian simulation method is used to establish the karst cave complex model; the single karst cave belongs to the medium-scale geological body, and which is difficult to beidentified by seismic. Based on a large number of outcrops measured data, the single karst cave distribution model is established by using the target based indicative point process simulation method; the internal filling of karst cave is small.It is barely recognizable by seismic waves at current resolutions. The multi-point geostatistics method is applied to establish a single karst cave internal filling structure model. The "three-step" modeling idea of hierarchical constraint can gradually reduce the uncertainty of geological model, improve the accuracy of geological modelling.The new idea was tested by a case study in a fracture-cavity unit in Tahe Oilfield, and the related issues and study directions of the new idea were discussed. The test results indicate that the "three-step" modeling idea karst cave reservoir, and the implementation effect is remarkable.

Keywords

• geological modelling
• paleokarst cave
• cave filling
• multipoint geostatistics
• carbonate