Quantitive Characterization Of Internal Heterogeneity Of Carbonate Fracture-cavity Units In Tahe Oilfield

Fracture-carvity reservoirs has characteristics of various types of storage space,different scales,different fillings and complex distribution.The characterization is a challenge and different from clastic reservoirs.In this study,we describe the internal heterogeneity of the fracture-cavity unit in architecture description and connectivity analysis,and build a quantitative heterogeneous model on this basis.173 caves in the 129 wells are identified and cave scale integrated of outcrops,cores,logs,seismic and production data,combination fractures and caves,and filling characteristics are revealed and the effect on yield of the internal heterogeneity of fracture-cavity unit.The scale of caves varies greatly with less of large caves and more of small caves,and there is a big difference in different palaeogeomorphology,different karst zones and the distance from the unconformity surface.According to the combination of caves,vugs and fractures,the reservoir space can be divided into six types: single cave reservoir,single vuggy reservoir,single fracture reservoir,fracture-cave reservoir,fracture-vuggy reservoir,cave-fracture-cave reservoir.The distribution of filling types and filling degree in a single cave,in different palaeogeomorphology and in different karst zones are summarized.The internal heterogeneity of the fracture-cavity unit caused a great difference in the yield of single well.The five types of connectivity channel are identified,which are single fracture,multiple fractures,single cave,fracture-cavity complex,and the ratio of the tracer peak to background value is taken as the statistical parameter to distinguish the connectivity of the connectivity channel into three levels.Then,the whole connectivity index of the fracture-cavity unit is evaluated based on fault density of the unit,the cave drilling density,the filling rate and the average oil production capacity of single well,and the four,six and seven area of Tahe oilfield is divided into 7 first level units,15 second level units and 35 third level units.According to the karst development pattern,the three-dimensional model of fracture-cavity reservoirs with different types and scales are established selecting the appropriate algorithm respectively taking S80 unit as an example,and we merged all the models together and obtained the three-dimension heterogenous model of fracture-cavity reservoirs.For small caves seismic data cannot be identified,taking large cave model reflecting different characteristics in different karst zones as training image,and set the ratio of heights between small caves and large caves as conditional parameters,we established the three-dimension model of small caves by using multi-point simulation.Based on the types of internal connection channel,the three-dimensional heterogeneous model of fracture-cavity unit is modified by using object-based stochastic simulation,and this revised model has similar statistical rules with the original model and solved discontinuity problems of modeling in fracture-cavity reservoirs.