Drilling fluid is a vital element of the drilling process. Any drilling fluid must have common properties that facilitate safe and satisfactory completion of the well.

The main component of water base mud is clay (mostly bentonite). The present consumption of bentonite clay in the drilling operations in Saudi Arabia alone can reach over 100 thousands tons a year and all of it is imported from USA. This trend is expected to continue as drilling activity increases. The large consumption and the high importation cost of this material lead to an attempt to find a local substitute.

Clays in Saudi Arabia are represented by numerous commercial stocks. The use of these local clays in the drilling activities can save a huge amount of hard currency that otherwise would be spent on importing it from abroad.

Several attempts were made to investigate shale outcrop precipitates in the kingdom. This work focuses on the possibility of the utilization of local bentonite clay minerals as a basic material for drilling fluids used to drill oil and gas wells. The only known bentonite outcrop in the kingdom is in Khulays area, 70 km north Jeddah adjacent to Makkah-Madinah road.

API specifications for acceptable drilling mud was the base for evaluating the local bentonite The properties of the local mud can be improved economically by adding some cheep materials to the prepared mud to enhance its viscosity and filtration loss (such as CMC, Drispac polymer, and bentonite extenders). Also shearing speed can be used as an enhancement method to improve the dispersion rate of the clay suspension, and hence increase viscosity and decrease filtration loss. But the used shearing speed should be limited to a practical and economical speed.

The bentonite extender can be either a salt or a polymer, it enhances viscosity buildup by slightly flocculating the bentonite suspension. Sodium carbonate is an example of a salt that can be added as an extender. Soaking raw bentonite with a solution of sodium salt resulted, through ion exchange, in a higher sodium bentonite content. More effective extenders than inorganic salts are the high molecular weight linear polymers.

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