Geotechnical, Physico-Chemical and Mineralogical Evaluation of Black Cotton Soil for Potential Use in Drilling Mud Formulation

Geotechnical and mineralogical properties of black cotton soils obtained from the Accra plains of Ghana were evaluated with the aim of using it as potential component of drilling mud. Samples were collected from Dowhenya, Tsopoli and Prampram, air dried, crushed and subjected to geotechnical, chemical, mineralogical, physico-chemical properties and free swell index laboratory tests. The index properties show that, the black cotton soils have over 70% clay content with very high plasticity. However, the commercial bentonite had over 90% clay with an extremely high plasticity. Chemically and mineralogically, the black cotton soils are similar to the commercial bentonite except that, it contains a lot more of the oxides that have no influence on the desirable properties of the soil as compared to the commercial bentonite. It was also determined from the chemical, mineralogical and physico-chemical properties that, the black cotton soils contain Ca-montmorillonite while the commercial bentonite contained Na-montmorillonite as the dominant clay minerals. However, an addition of 10% Na2CO3 improved the free swell index of the black cotton soils and hence its properties are expected to compare much closely with those of commercial bentonite.