Vertical Phase Array Acoustic Logging Of Buried Hill Reservoir

Buried hill reservoir is one of the continuous growth points of fossil energy exploration in China,but the strong heterogeneity brings great difficulties to reservoir research.It is urgent to solve the problem of effectiveness discrimination and facies characterization of complex lithology buried hill reservoirs.The array acoustic logging can measure multiple wave trains by using multiple sound sources and multiple receiving acoustic systems.The waveform components of different wave trains are closely related to reservoir parameters such as porosity and permeability.It is one of the commonly used reservoir effectiveness evaluation methods.From the perspective of the sedimentary evolution process of the buried hill,the buried hill is affected by various geological processes such as weathering leaching and tectonic activities during the formation process,and it shows obvious zonality vertically.Using logging data to carry out quantitative characterization of the vertical facies belt of the reservoir can not only accurately identify the facies belt,but also understand the spatial distribution law of the reservoir through multi-well profiles,and predict the dominant exploration zone at the macro level in the study area.Firstly,through the processing of array acoustic logging data(including the extraction of monopole,dipole and frequency domain signals),the response relationship between the pore type and each waveform of the dual-porosity medium reservoir is analyzed.Combined with the productivity test data,the lower limit of the porosity of the effective reservoir is 3 %.On this basis,four acoustic characteristic parameters are extracted based on the principle of waveform fracture detection,and the classification standard of reservoir level in the study area is established.The main spatial types of type I reservoirs are fracture pore type,porosity greater than or equal to 10.8 %,spectral energy attenuation coefficient greater than or equal to 1,Stoneley wave attenuation coefficient greater than or equal to 0.5,dominant frequency offset rate greater than or equal to 8 %,and spectral correlation coefficient less than or equal to 0.64.The main spatial types of type II reservoirs are dissolution fracture type,porosity range is 7.5 %-10.8 %,spectral energy attenuation coefficient range is 0.35-1,Stoneley wave attenuation coefficient range is 0.1-0.5,dominant frequency offset rate range is 4.1 %-8 %,spectral correlation coefficient range is 0.64-0.78;the main spatial types of type III reservoirs are fracture type,porosity range is 3 %-7.5 %,spectral energy attenuation coefficient is less than or equal to 0.35,Stoneley wave attenuation coefficient is less than or equal to 0.1,dominant frequency offset rate is less than or equal to 4.1 %,spectral correlation coefficient is greater than or equal to 0.78.Secondly,in view of the characteristics of vertical zonation of buried hill reservoirs in Xinjiang,South China Sea and other regions,according to the degree of reservoir transformation by geological processes,buried hill reservoirs are vertically divided into three facies belts: strong transformation belt,transformation belt and non-transformation belt.Considering the buried hill development model and sedimentary evolution process,the buried hill reservoir is further subdivided into five sub-zones: weathered fracture zone,vertical connected zone,transition zone,horizontal connected zone and primary zone based on logging.On the basis of summarizing the differences in physical properties,electrical properties and fracture development degree of buried hill reservoirs,the porosity spectrum peak,acoustic fracture and comprehensive characterization coefficient are calculated by using logging information,and the logging characterization method of vertical facies belt is formed.Comparing the buried hills in the two areas,it is found that the dolomite buried hills in the X Basin and the granite buried hills in the Y Basin can be divided into five facies belts vertically,and the characterization coefficients of the porosity spectrum peaks are not much different,indicating that the two buried hills are similar in physical properties.The acoustic fracture characterization coefficient varies greatly.The highest dolomite buried hill is0.25,and the highest granite buried hill is 1.7,indicating that the granite buried hill has a higher degree of fracture development.The application results show that the weathered fracture zone,vertical connected zone and horizontal connected zone are the dominant reservoir development zones.The plane distribution law of the dominant reservoir development zone in the northern X Basin is that the thickness of the weathered fracture zone increases first and then decreases from northeast to southwest,the thickness of the vertical connected zone decreases gradually,and the thickness of the horizontal connected zone increases gradually.This study can serve the prediction of dominant reservoirs in strong heterogeneous reservoirs and expand the application of acoustic logging in the evaluation of buried hill reservoirs.