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A Robust Technique for Resolving Faulting Problems on the Steeply Dipping Flanks of Salt Bodies, Using the Multiple Bischke Plot Analysis (MBPA)
Among the most difficult problems for production geologists and geophysicists is resolving structural and stratigraphic complexities on the steeply dipping flanks of salt domes. Fault blocks can be mismapped and wells mislocated if missing section in well logs is mistakenly attributed to faulting rather than an unconformity. Steeply-dipping beds on the flanks of salt domes, often result in poor seismic data, and the attenuated stratigraphic section make well log correlations difficult. We review the geology and structural geometries applicable to the flanks of salt domes, and demonstrate how to resolve missing section problems using the d/d or Multiple Bischke Plot Analysis (MBPA). Faults and unconformities exhibit different properties with respect to missing section data. Missing section on unconformities varies between wells, whereas with faults the data stabilize about a near constant value, compared to off-structure wells; thereby, faults and unconformities can be distinguished. MBPA plots can differentiate growth-displacement patterns, resolve stratigraphic and salt-related structural problems, distinguish between faults and unconformities, and recognize styles of faulting. Furthermore, if a structurally high well can be established as a reference well, then these methods can provide significant insights as to whether missing section is caused by faults or by unconformities. Relative to a structurally high well, MBPA plots show missing section, attributable to unconformities, as a discontinuity that exhibits an increasing displacement pattern. If an increasing displacement pattern is observed on the same stratigraphic level in several wells, then the missing section is most likely an unconformity, and is not caused by faulting. In contrast, faults occur as discontinuities that exhibit a decreasing displacement pattern on the plots. In this structural environment well log correlations provide the least expensive data available to geoscientists, and we show how better use can be made of the well log data. Indeed, accurate correlations are fundamental to any viable stratigraphic and structural interpretation. The MBPA method is an accurate and robust technique that can help refine any correlation study involving well logs or seismic data. MBPA plots typically provide insights into the most probable correlations and structural interpretations if about ten or more parasequence correlations can be identified on well logs over the area of interest. However, MBPA cannot insure accurate correlations; anomalies on the plots are often the result of miscorrelation. Various displays enhance interpretation. Real Gulf Coast salt flank examples are presented using Stacked MBPA Plots, along with 3D displays.
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