Testing and Analysis of the Soil Thermal Conductivity in Tropical Desert and Grassland of West Africa

Abstract

Thermal conductivity is one of the basic thermal properties of soil. For a buried pipeline, the thermal conductivity of the surrounding soil is the most important factor determining the overall heat transfer from the pipeline, and plays an important role in assessing the safety and energy consumption of pipeline operation. For providing reliable basic data for the commissioning and the operation of a waxy crude oil pipeline stretching in southwest Sahara Desert, six phases of thermal conductivity testing were performed along the pipeline route, respectively in February, March, April, May, July and September, 2011. The pipeline is 462.5km long and 323.9mm outside diameter. The pipeline route crosses tropical desert and grassland. Test points are located at roughly equal spaces along the pipeline route, and additional test points are located in seasonal river beds and rugged terrains. The soil temperature and thermal conductivity were tested simultaneously at a depth of about130cm below soil surface, which is also near to the pipeline centerline. The test equipment used was a field thermal needle system FTN01 for thermal conductivity made in Holland. For a given location along the pipeline route, the soil thermal conductivities have different values in dry season and rainy season. The average soil thermal conductivities for the pipeline route between two stations ranges from 0.5 to 1.1W/(m·°C) in rainy season, and from 0.4 to 0.8 W/(m·°C) in dry season. The test results show that the change of soil moisture content has significant impact on soil thermal conductivity. Because other properties of the tested soil along the pipeline route such as soil mineral composition, particle size distribution and density have no significant change, these factors have little effect on soil thermal conductivity.