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In chemistry, pH is a measure of the concentration of hydrogen ions in an aqueous solution. pH is measured on a scale from 0 to 14. A pH of less than 7 indicates an acidic solution, while solutions above 7 are considered alkaline. A pH of 7 is neutral, as in the case of pure water.

pH analysis is fundamental to drilling fluid control. The pH of the fluid affects clay dispersion and the solubility and effectiveness of chemical additives. A change in pH while drilling often indicates contamination by substances such as cement, gypsum, or carbon dioxide. Effective corrosion control and treatment depends upon the proper pH adjustment.

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Alkalinity is one of the most important chemical properties of drilling fluids. But what it is? And how does it affect drilling fluid performance?

Alkalinity is the acid neutralizing power of a fluid. In drilling fluid testing, alkalinity can be measured on either whole mud (designated with a subscript "df") or on the filtrate (designated with a subscript "f"), as collected with a filter press. The data collected from the alkalinity test can also be used to estimate the concentrations of hydroxyl (OH-), carbonate (CO3-2) and bicarbonate (HCO3-) ions in the drilling fluid.

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Cement slurries that are placed in gas bearing formations as part of the well completion process are at risk of gas migration under the right conditions. Gas migration refers to the annular flow of natural gas from the formation up through the cement column. As the gas moves through the cement matrix, it carves a channel that becomes permanent once the cement sets. This permanent channel becomes a conduit that allows for natural gas to continuously bleed from the formation.

After cement placement operations have stopped, the cement slurry begins to develop gel strength under static conditions. The amount of gel strength development and the speed at which it occurs are two of the main factors that describe a cement slurry’s ability to resist gas intrusion. Generally, gas intrusion begins when cement slurries develop 100 lbf/100 ft2 (48 Pa). Gas intrusion ends when the cement develops 500 lbf/100 ft2 (240 Pa). The transition time is defined as the time it takes the slurry to go from 100 lbf/100 ft2 (48 Pa) to 500 lbf/100 ft2 (240 Pa). The shorter the transition time is, the less risk there is for the cement sheath to lose well control.

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