DETERMINATION OF WEATHERING STRUCTURE IN SOUTH-EASTERN AND SOUTH-WESTERN PART OF NIGER DELTA USING SEISMIC REFRACTION

The aim of this research work is to ascertain the thickness of the weathering layer, the velocities associated with weathering and consolidation, and the presence of high statics within the designated area. Drill logs from twenty (20) Uphole locations were meticulously analyzed in conjunction with theoretical interpretations to establish a robust dataset for making informed inferences regarding boundary distinctions. Each Uphole location, drilled to a depth of 66m and logged to 60m, provided essential lithological information, predominantly comprising sand and clay units with varying grain sizes from fine to coarse. The analysis of weathering thickness and velocities across the prospect area revealed noteworthy findings. In the south-western part of the study area, weathering thickness ranged from 2.6m around station 2160 – 5240 to 6.6m at station 2080 – 5080. Conversely, in the south-eastern Niger Delta, the weathering thickness varied from 3.3m around station 2784 – 7672 to 7.7m on station 2728 – 7512. Comprehensive results of Uphole (refraction) surveys, as presented in Tables 4.3 and 4.4 (Pages 33 and 34), indicated a prevalent 2-layer model in the south-western Niger Delta and a 3-layer model in only six locations in the southeastern Niger Delta. The average thickness of the weathering layer to the first refractor consolidated layer in the south-western area was determined to be 4.6 meters, with an average weathering velocity of 541ms-1 and an average refractor consolidated layer velocity of 1709ms-1. In the south-eastern area, the corresponding values were 4.6m and 3.9m (weathering layers 1 and 2), with average weathering velocities of 439ms-1 and 818ms-1, along with an average consolidated layer velocity of 1783ms-1. Elevation data indicated an average elevation of 15.948m in the southwestern area, while the south-eastern area exhibited a higher average elevation of 18.429m, ranging from 5.12m to 32.299m. The observed low weathering thicknesses and velocities in the south-eastern area of the Niger Delta region suggest the prevalence of loose, unconsolidated, and aerated soil materials, particularly clay, which may result in a higher absorption of seismic energy. Furthermore, variations in the velocity of the weathered layer underscore the high degree of inhomogeneity within this layer and signify the potential for smooth static behavior. These findings contribute valuable insights into the geological characteristics of the studied region, aiding in the comprehension of subsurface structures and their implications for seismic survey applications.