Comprehensive Log Evaluation For Carbonate Reservoir Of Ordovician M₅⁵ Sub-member To M₄ Member In Ordos Basin

The coincidence rate between logging evaluation and oil test results has been relatively low due to the serious heterogeneity of carbonate reservoirs in China.Accurate evaluation of the effectiveness of carbonate reservoir has become one of the most important factors restricting the effectiveness of oil and gas exploration,and it is very important to reduce the cost of oil test and the accurate calculation of reserves.This paper analyzes the lithology,properties,reservoir space and the electrical characteristics of Ordovician carbonate reservoirs in the eastern part of the paleo-uplift,the Jingbian-Ansai area,the Yulin-Shenmu area of the Ordos Basin.The three reservoir parameters of porosity,permeability and saturation were studied.The porosity calculation model based on density log curves and the nonlinear porosity calculation model of variable skeleton parameters suitable for fractured cave reservoirs are established.By removing the data points corresponding to the low porosity and high permeability fracture zones and the high porosity and low permeability isolated cavitation holes,the permeability calculation models for three different regions are established.Based on the nuclear magnetic data,a method for calculating the saturation of variable m and n values was established.It is difficult to identify fluids due to their low porosity,complex reservoir space structure,and strong heterogeneity.In this paper,five methods have been established in the process of identifying complex gas and water layers in the study area.The resistivity-porosity plot method based on conventional logging data is only applicable to restricted platforms.The apparent formation water resistivity spectrum method based on image logging data can realize the qualitative identification of gas and water layers.The mean-variance cross plot of apparent formation water resistivity spectrum can be used for quantitative identification.At the same time,the elastic mechanical parameters method based on array sonic logging data and the T2 spectral distribution method based on nuclear magnetic resonance data have also achieved good results in fluid identification in the study area.Based on the above research,the qualitative evaluation of single well reservoir quality and pore structure effectiveness was achieved through the study of electrical imaging porosity spectrum.The fluid movement index based on array sonic logging data can effectively identify the permeability formation in carbonate reservoirs,making up for the lack of conventional logging in the evaluation of the effectiveness of carbonate reservoirs.