The use of coiled tubing to perform fill clean outs or to remove scale build-up or any other type of restriction inside the wells is becoming one of the most common field applications in Saudi Arabia. In fact, based on the increasing scale tendency in the gas wells, Coiled Tubing scale cleanout represent one of the biggest challenges for Coiled Tubing service activities, especially in gas wells. The trend towards more complex well trajectories, lower bottom hole pressures because of reservoir pressure decline, heavier and harder scale materials and high H2S contents, impose operational constraints on this essential service; making the selection of the cleanout fluid an important component of the design criteria.

Inefficient wellbore cleaning is the main source of costly problems such as stuck CT pipe. A well-known solution to solve the problem is to increase the velocity of the cleanout fluid in the annulus, which will decrease debris concentration in the annular space. The increment of the annular fluid velocity is limited because of the CT friction and surface equipment. Under this scenario, the fluid with proper viscosity to transport the solids is required, even in low annulus velocity scenarios.

Foam was selected as the cleanout fluid for this particular type of wells because of its ability to keep the debris in suspension and transport it out of the well and to control the reservoir pressure to perform the cleanout operation in near balance or slightly overbalanced conditions.

This paper describes some field experiences using foam as a fluid to transport the removed material out of gas wells, independently of well deviation, using coiled tubing. It describes the technical details behind this approach as well as the operational results and best practices for field applications.

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