Abstract
This paper discusses the integration of dip data from dipmeters and openhole logs. It addresses the relationship between these two types of data and introduces a new methodology using a horizontal well to produce a two-dimensional (2-D) model.
Borehole images provide valuable information about the borehole wall and can be extended to construct a structural cross-section. The software used in this study focuses on dip data and cannot integrate openhole logs directly into the cross-section. However, the log data were integrated by populating the lithofacies obtained from the logs along the bed boundaries identified using other software programs. The generated model did not always reflect the true structures surrounding the well, as accuracy depended on the direction of the cross-section. Computing and displaying different structural zones helped resolve this issue.
In this case study, 2-D seismic data revealed a graben and horst system with a single structural trend-oriented NE-SW. At the time of logging, 3-D seismic data were being processed and later used to validate the model. During the drilling of the 1,820-ft horizontal section, which included 260 ft of cap rock, a logging-while-drilling (LWD) gamma ray log was obtained. The Cretaceous carbonate reservoir section was directly beneath the cap rock, composed of a thick layer of calcareous shales. To address the challenges of drilling through the calcareous shales and to better understand the structure and geology of the reservoir, borehole images and openhole logs were acquired.
The model identified six different structural zones, including a fold, and seven reverse faults. It also defined a structural trap with potential for further development. A newly processed 3-D seismic survey confirmed the 2-D model and revealed four additional reverse faults. This case study demonstrates that a 2-D geological model is crucial for accurate structural and geological definition of the wellbore environment, especially during early exploration stages when data are limited, and uncertainties are high. The procedures developed can be applied to both deviated and vertical wells.