Evaluation of Petrophysical and Geomechanical Analysis of Subsurface Geological Information for Sustainable Groundwater and Engineering Development in Parts of Anaocha Local Government, Anambra State, Nigeria

Abstract

A well log is the recording of the measurement of a geophysical parameter plotted continuously against depth in the well bore. It is used to identify and correlate underground rocks, determine their lithology, generate their physical properties and the nature of the fluids they contain. The study aimed to conduct a geophysical evaluation of geologic formations for sustainable groundwater and engineering development. Electrical resistivity logging was carried out on the existing wells at Anoacha to evaluate the geological formation of the subsurface and well efficiency. The study area is positioned within the geographical coordinates of 6° 12' 25''N latitude and 7° 04' 04''E longitude. In the study area Aguluzibo location showed resistivity range from top to 40 m sandstone, 40 m – 60 m shaly sand and 60 m – 180 m is sandstone, the resistivity signal became irregular in ranges at the depth of 162 m – 180 m, this reflects the negative deflection of Spontaneous Potential (SP) long. At Awkaeze location, the lithology from the resistivity log revealed shaly sandstone at a depth of 50 m, sandstone at 50 m – 135 m, shale at a depth range of 135 m – 152 m and at terminal depth 152 m – 204 m of the drilled well is sandstone. In this location, the SP log shale baseline showed at two occurrences beds of 20 m – 75 m and 135 m – 204 m, respectively. The existing well at the Amatutu Agulu location revealed irregular deflection of SP long. The range of negative and positive deflection depicts the presence of salinity, and the resistivity value shows the predominant formation of shaly sand and sandstone. The results revealed the geological constituents of the study area. For the shaly sandstone reservoir, the presence of both top and bottom seals, along with the resistivity characteristics, helps in identifying it as a potential reservoir zone. However, the infrastructural and structural integrity concerns due to the presence of shale and the variation in resistivity with depth necessitate careful planning and advanced engineering solutions to ensure successful development and production.