Seismic attribute analysis in recent decades has been an instrumental tool in improving the quality of reservoir characterization for hydrocarbon identification. Coherency and curvature are geometric seismic attributes which measure seismic continuity and are particularly useful in mapping the structure and shape of geological features of interest, such as faults, channels and fractures. As these geologic features are prevalent in carbonate fields and heavily influence the productivity of reservoirs in these fields, accurate fault/fracture description employing coherence and curvature analysis is advantageous from a prospecting and production standpoint. It is these attributes that are most useful in fault and fracture characterization in carbonates, and are thus the focus of my investigation.
With a 3D dataset and well data from the Huabei Field in North China, a carbonate reservoir is identified and interpreted through the field. We use the reservoir top depth to narrow our window of investigation of coherence and curvature values through the dataset. Cross-correlation, variance, and eigenstructure-driven coherence as well as volumetric curvature are calculated through the dataset in order to map the regional and small-scale faulting.
Results show that eigenstructure-based coherence analysis generally produces the best general fault analysis for our data, which is attributed to the eigenstructure calculation's separation of waveform and amplitude into mathematically independent measures which are evaluated separately and then analyzed together.
Analyzing the results of cross-correlation, variance/ant-tracking, and eigenstructure-coherence, we are able to observe general faulting and channel behavior, as well as some smaller-scale fault detail when the data volumes are preconditioned with dip-estimates. Used together with volumetric curvature analysis, which identifies small faults and possible fractures in greater detail, we are able to identify the areas in our reservoir with smaller faults and thus highest probability of fractures, which are strong hydrocarbon indicators in carbonates.
This study demonstrates the capacity of seismic coherence and curvature to delineate faults and fractures in complex carbonate fields, enhances our understanding of how to apply the optimal coherence/curvature methods and their respective parameters to identify different geologic features, and enables us to apply these attribute analysis findings towards prospect identification and production planning in carbonate fields.
- Sun, Yuefeng Mollie B. & Richard A. Williford Professor