Coal seam distribution using amplitude versus offset analysis and pre-stack inversion in Blackfoot Field, Canada

Abstract

In the present, the consumption of energy for everyday life increases rapidly. Coal is an energy source that has been continuously produced for a long time and will increase in the future. Surface geological exploration and geologic log are used to find primary coal reserves but sometimes provide insufficient information. Thus, geophysical survey can provide missing information for obtaining more accurate exploration results. The seismic survey is an appropriate method for estimating coal reserves and determining the subsurface structure of the coal zone. The study area is located in the Blackfoot field, Alberta, Canada. The interesting target zone consists of three coal beds interbedded with shale and sandstone. There are two methods in the study, amplitude versus offset (AVO) analysis and pre-stack inversion using 3D pre-stack seismic and nine well log data. AVO analysis is a tool for identifying lithology and predicting fluid in a reservoir, especially hydrocarbon. AVO analysis was used to define AVO class of the coal zone to study the amplitude behavior of seismic wave that reflect at the upper of the target coal zone. The pre-stack seismic data and a well log dataset were used to calculate the pre-stack inversion to generate the inverted volumes such as Vp, Vs and density volumes. The other eight well logs were used as the blind testing to check the accuracy of the inversion result. The relationships of these inverted volumes were used to discriminate the coal zone from the surrounding rocks by crossplot.In conclusion, the coal zone was classified as class 4 AVO. The crossplot between inverted volumes help to predict the coal zone. Especially, Vp/(Vs)2 and density cross plot can be better discriminate the coal zone from surrounding formation in this study area and be helpful to confirm the new coal zone with crossplot of VP/VS and density.