Mineralogical and geochemical tests were conducted on bentonitic samples obtained from Imo shale and the Ameki-Bende formations in Anambra basin of southeastern Nigeria, in order to evaluate the potential for use in drilling mud formulation. Fifty samples were collected and screened based on composition, grain size, degree of alteration, and filtration conditions. Four of the samples namely SP1, SP2, SP3 and SP4 that meet the API specification for drilling mud and Wyoming bentonite were subjected to X-ray diffraction (XRD), X-ray fluorescence (XRF) and scanning electron microscopy (SEM) analyses. SP1 is predominantly kaolinite while SP2, SP3 and SP4 are smectite type. The XRF results showed high Fe in some of the samples. The predominant mineral containing Fe that could be present from XRD and SEM data is Nontronite; whereas more Fe may be present in an amorphous phase. Palygorskite and basanite are also present in some of the samples. The smectite clays (SP2, SP3 and SP4) display high Fe/Al ratio and are rich in Ca-Smectite, which differ significantly from the commercial types. Based on these results, the basic criteria for the formulation of drilling fluid, using mineralogical and chemical compositions could be achieved. In comparison with the commercial clays, the study has identified some of the deficient minerals in the local clay and therefore appropriate additives may be necessary to obtain similar mineral composition.

Keywords: Clay, API specification, Smectite, Kaolinites, Imo shale, Nigeria