Comparative Study of Local Cements with Imported Class G Cement at Different Temperatures for Oil Well Cementing Operations in Ghana
The purpose of this research is to determine the suitability of local cements as an alternative to imported class G cement at different temperatures using oil well cement additives. Laboratory investigations on both local and imported cements to determine physical properties such as thickening time, fluid loss, compressive strength, free fluid and rheology were conducted at bottom hole circulating temperature of 27°C (80°F) and 66°C (150°F). The results indicated that locally manufactured cements are compatible with oil well cement additives at 80°F and 150°F and can be used as an alternative to imported class G cement in oil and gas well cementing operations. However, premature gelations of test results were phenomenal at 66°C (150°F) for the entire locally manufactured cements especially sample CEM B. Therefore, for local cements to be used effectively for cementing high temperature operations, stringent quality control during their manufacturing process is imperative.
The Thickening Time of Ferrous Cement Slurry System in High-Pressure and High-Temperature Environment
Experimentally, the aim of this research paper is to investigate the thickening time (TT) of different ferrous cement slurry systems in high-pressure and high-temperature (HPHT) environment. Objectively, the study collected eight (8) samples of groundwater from 8 different boreholes, as mix-water, from the study area, Kolo Creek. These mix-water samples were subjected to water chemistry analysis, based on the American Public Health Association (APHA) drinking water test methods; the results obtained from these tests were benchmarked with the standard values of World Health Organisation (WHO), and Nigeria Standard Drinking Water Quality (NSDWQ) standards. These results reveal that, in each of the tested mix-water samples, ferrous ion (Fe 2+ ) concentration was higher (0.52 to 6.82mg/L); which is greater than 0.3mg/L, and this was the only chemical parameter that was in strong disagreement with the WHO’s and NSDWQ’s Drinking Water Quality standards. Subsequently, each of these ferrous mix-waters were used in the formulation of cement slurries at the water-to-cement ratio of 0.44 in batches; each of these formulated slurries were used, to test for the effects of ferrous ion concentration in mix-water on the TT performances of the slurries. These TT tests were performed using the Chandler model 7322 HPHT Consistometer. These tests were conducted based on the API Specification 10A methods of 1995. Generally, the results obtained reveal that, as the concentration of Fe 2+ increases in the mix-water, the TT of the cement slurry accelerated in the HPHT environment. This means that the cement slurry set faster. Also, this set-fast behaviour of high ferrous ion concentration towards slurry suggested that, high concentration of ferrous ion induced the exothermic reaction of tricalcium aluminate (C3A) during the hydration of the ferrous cement slurry. Therefore, ferrous neat cement slurry is only suitable for cementing shallow oil-well, except retarding additives are added into the slurry.
What is the cementation exponent? A new interpretation
In 2003, 182 billion barrels of oil reserves worth about US $4.5 trillion were discovered worldwide (Johnson et al., 2004). Moreover, between 1950 and 2002 the total volume of reserves discovered has run to more than 1500 billion barrels for oil and 7.5 trillion cubic feet for gas (Bentley, 2002). More than half of these resources have already been produced and have driven the global economy for the last 50 years.