Subsurface Lithostratigraphic Characterization Using Integrated Log and Cross-Plot Analysis: Re-evaluation of a Borehole in Chirirbandar, Dinajpur, Bangladesh

Abstract

This research represents a detailed Litho-stratigraphic characterization of Precambrian basement complex by integrating geophysical log and drilling data of GDH-76 from technical reports of the Geological Survey of Bangladesh (GSB). It is a re-evaluation of a Borehole data by interpreting drilling parameter and interval-averaged geophysical log data. A high-resolution petro-physical “fingerprint” of the Northwestern Bangladesh basement complex is identified by integrated cross-plot analysis. This study delineates a six subsurface zones by correlated Rate of Penetration (ROP), Percentage of Core Recovery, Magnetic Susceptibility, Gamma-Resistivity signatures. The Result shows a distinct 6 meter weathered transition zone (200-206 m) characterized by low core recovery (45%) and moderate ROP (1.02 m/hr). The basement entry at 206 m is marked by moderate to high (0.46 to 1.1 m/hr) in ROP and moderate resistivity (72.5 ohm-m) indicating weathered condition. Notable feature include a 15-meter thick magnetic anomaly zone (295-310 m), identified with a peak susceptibility of 1130 cgs unit, suggesting a mineralization zone. Moreover, a high-gamma unit (318-336 m) exhibiting a value of 375 cps (peak value) with extremely low ROP (0.132 m/hr) indicates a high strength potassium-rich felsic lithology. Furthermore, the research also pinpointed the F39 fault boundary between two boreholes.