The use of water based fluids replacing oil based drilling fluids has been increasingly being applied in the Petroleum Industry in order to mainly accomplish environmental legislation.

A challenge when using water based drilling fluids in highly reactive shales is to overcome problems such as wellbore instability, torque and drag and environmental requirements. This was the case in the Orito oil field in Colombia.

The Orito field is located to the south of the country and has been operated by Petrominerales Colombia Ltd. During years of exploitation, the Orito wells were drilled with oil base muds in order to address wellbore instability problems related to the highly reactive shales of the Villeta formation, which is drilled in the 311 mm (12 ¼") hole and is about 300 m (1000 ft) long.

Some years ago, different water based mud systems have been used in the area; however, it has not achieved the high performance expected by the operator to successfully drill the troublesome Villeta formation. Thus, in order to drill the two last development wells in the Orito field, it was proposed that an Amine/PHPA system to be evaluated. The Amine/PHPA system has been developed by Q'Max Solutions in Canada and has also been used in Ecuador with very good results.

According to own experiences in the field, the Amine/PHPA system was formulated to achieve the right concentration of each mud product to satisfy the necessity of a system that provides at the same time good inhibition, adequate rheology properties and lubricantion during the angle build section.

Capillary Suction Test (CST) were carried out to determine the right concentration of amine and PHPA to provide inhibition for the highly reactive Villeta shales. Historical cases of hydraulics and operational performance were studied to find out xanthan gum concentrations to reach adequate yield point values that secure hole cleaning during the most critical deviated section of the interval and lubricant concentration was also determined to reduce torque and drag in the water based system.

This paper is intended to present the performance of the Amine/PHPA system and environmental achievements in an environmentally sensitive area. Laboratory and field data obtained during the project is also presented.

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