Performance Evaluation of Periwinkle Shell Powder as Alternative to Silica Flour in High Temperature Well Cementing Operation (Published)
The effect of high temperature on cement slurry is a problem in the oil and gas drilling industry. Over the years, silica flour was used to prevent the strength of cement that results from high temperature effect. But the silica flour is imported and not environmentally friendly. Hence, the need for local material that can serve as alternative becomes imperative. Periwinkle shell (Tympanostomus fuscatus) was tested in the laboratory to determine its potential use in place of the synthetic silica flour. The shell was pulverised, calcinated, and subjected to laboratory test following the requirement API RP 10B for cement testing. Cement slurry density of 15ppg at 25%BWOC, 30%BWOC and 35%BWOC concentrations of periwinkle shell powder, and temperature range of 2000C and 2500C were conducted. Rheology test, API fluid loss, compressive strength, equivalent circulating density, and annular pressure loss were examined for its suitability to be used as an additive in cement slurry. The results showed that Periwinkle shell powder gave similar results with the silica flour based on its rheological properties, equivalent circulating density (ECD), and annular pressure loss. In addition, periwinkle shell powder performed better than silica flour in all concentrations, temperatures and curing times. The results of this study showed that periwinkle shell powder is a potential alternative for silica flour as an additive for cement strength retrogression for well cementing operation.
Keywords: Compressive Strength, High temperature, Periwinkle shell powder, rheology, silica flour
Characterisation of Mortar Deterioration in Historic Buildings in Bagamoyo, Tanzania (Published)
Masonry components of Historic building in Bagamoyo, Tanzania have suffered considerable deterioration in a variety of forms, and close examination indicates that the root cause of the deterioration of the structure is mainly due to masonry mortar joint failure because of chemical and physical degradation of the material. This paper examines the colours, physical and mechanical properties as well as chemical composition of the mortar; thus its replacement carefully matches the historic in chemical composition, strength and texture as determined by a laboratory analysis. In terms of colour, the mortars were divided into three groups of colours namely light grey, light brown and light yellowish brown. Point counting by microscopical study indicated that the hard mortar has higher binder content and composed of a homogenous hydraulic matrix and a heterogeneous coarse fraction with moderate voids while the moderate hard mortar contained modest binder and soft and friable lime mortar contained little hydraulic binder. The results of chemical composition indicated that the stones composed of high amount of Calcium Oxide (CaO) while the mortar contained low percentage of CaO indicating that the mortar is not pure hydraulic lime but hydrated lime (air-hardening lime).
Keywords: Absorption Capacity, Bulk Density and Repointing, Compressive Strength, Petrography Examination, X-Ray Diffraction (XRD)