Estimation of Thermal Conductivity in the North-western Niger Delta Sedimentary Basin, Nigeria, Using Geophysical Well Logs

Abstract

Thermal conductivity estimates are computed from nineteen petroleum wells in the north-western Niger Delta, Nigeria, using a geometric mean model. Sonic and gamma-ray logs were digitised and used in the estimation of in situ conductivity. The Niger Delta is composed of three major diachronous lithostratigraphic units of shaly Akata, shaly-sandstone Agbada and sandy Benin formations, which form the bulk of the deltaic sediments. All the wells used in the study could only penetrate the topmost Benin and the underlying Agbada formations, except Akata that is the last deeply lying formation. Mineralogy, porosity and lithology exert the most important control on the matrix thermal conductivity in the Niger Delta sedimentary basin. There is a decrease of thermal conductivity with increasing shale fraction. The bulk conductivity also show an increase with increasing sandstone fraction. Increase in porosity results in a decrease in bulk conductivity. Thermal conductivity values and variations for a given lithologic unit are reduced at increased porosity, such that thermal conductivity of the topmost continental Benin sandstone Formation vary between 2.39W/m°C and 2.74W/m°C with an average of 2.52W/m°C. Thermal conductivity for the underlying, marine shaly-sandstone Agbada formation varies between 2.16W/m°C and 2.69W/m°C with an average of 2.33W/m°C.