The relationships between density and velocity are important in many geological analyses that involve rock property parameters. However, the accuracy of the results is often limited when there is a verbatim application of generalized rock property relationships. Many studies in the Niger Delta Basin suffer from this limitation. As a way forward, well logs in the Niger Delta were used to derive lithology-specific coefficients that can be applied in density-velocity transforms that make use of the Gardner equation. Whereas the default coefficient (a) and exponent (b) in the original Gardner equation are 0.31 and 0.25, respectively, fitting the Gardner curve to local data results in a coefficient value of 0.33 and 0.29 for shales and sands, respectively, when the exponent is kept at the default value. Comparing measured density data with estimates obtained from sonic velocities using the original Gardner equation gives a regional mean absolute deviation of 0.13 g/cc while those of the newly derived local coefficients do not exceed 0.05 g/cc giving an improvement of over 60% in the accuracy of estimated rock properties.
The rocks underlying many parts of Southeastern Nigeria had undergone extensive alterations to form considerable clay deposits. The mineralogical compositions of some of these clay deposits were evaluated with the X-Ray Diffraction (XRD) method to ascertain the suitability of the deposits as raw materials. Results of the analyses indicated that kaolinite (Al 2 Si 2 O 5 (OH) 4 ) is the dominant clay mineral. Traces of bentonite and dickite were also observed, while the identified non-clay minerals were quartz and iron. Chemical analysis of the clays revealed the predominance of SiO 2 , Al 2 O 3 , Fe 2 O 3 and TiO with values ranging from 31.70 to 56.45%, 19.30 to 29.30%, 3.11 to 29.42% and 2.21 to 7.04%, respectively, while the compositions of CaO, MgO, Na 2 O, and MnO in the analyzed samples were relatively lower with values ranging from 0.19 to 0.29%, 0.13 to 0.19%, 0.11 to 0.70% and 0.01 to 0.03%, respectively. The Al 2 O 3 /TiO 2 ratio (3.7 to 13.5) of the studied clays indicated a mafic to intermediate igneous rock origin. Binary plots of TiO 2 versus Al 2 O 3 to distinguish between granitic and basaltic sourced clays indicated basalt-rhyolite/granite provenances. The high chemical index of alteration (95.8%), chemical index of weathering (98.3%) and low contents of alkali and alkali earth elements (averaging 0.11%) of the clayrich sediments, is indicative of a relatively intense weathering source area. The SiO 2 -K 2 O/Na 2 O plots suggested that the sediments in the study area were deposited between passive and active continental margins. In comparison with other reference clays and standard specifications, the clay deposits in the study area possess characteristics satisfactory for economic and some engineering purposes.
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