Lessons Learned in Horizontal Well Workovers and Sand Cleanouts, in Cerro Negro Field, Venezuela
Authors: Perdomo Lenin , Molina Giancarlo , Mavares Francisco , Limpio Maria , Correa Elio , Anez Marco 
Published: April 2022

The Orinoco Oil Belt in Venezuela contains the largest known deposits of heavy oil in the world, and Cerro Negro is part of the fields in this area. However, the sand production is a major issue which affects the oil production in this field. There are some major issues that stand in the way of the proper cleanout of these wells. These problems include low reservoir pressure, geometry of the wells, and extremely high oil viscosity. Another major problem is the presence of big pieces of progressing cavity pumps (PCP) elastomers, some metallic parts from pressure and temperature sensors configuration, and other metallic parts from previous workover rig operations, encountered during cleanout operations. As a result of these difficulties, some of the past jobs performed in this field were unsuccessful.

After these unssuccessful jobs, a campaign of recent multiple sand cleanout jobs was planned in the Cerro Negro field. Numerous difficulties arose during these jobs. These issues were largely due to the presence of big pieces of PCP elastomers and metallic parts. An additional issue was the low reservoir pressure. Due to the size of the casing/liner and the horizontal section, the annulus fluid velocity obtained was insufficient. Therefore, several techniques were applied to overcome these problems. One of these methods was to use reverse circulation for the sand cleanout in the 9-5/8-in. slanted casing section, while circulation was still possible to obtain a higher fluid velocity. Afterward, once the circulation was lost, a special stroking pump was used alongside a large string of tubing to store large amounts of sand and debris. This tool was also used to recover pieces of PCP elastomers and other metallic parts. This tool uses a piston pump to create a vacuum effect, and fluid circulation is not needed for the cleanout. Without this innovative stroking pump, it would have been almost impossible to recover these large pieces. This was the first time this innovative tool was used in these types of wells. When the open horizontal 7-in. production zone was reached, coiled tubing (CT) was used with the proper proportion of diesel and nitrogen to obtain enough fluid velocity and the proper equivalent density.

In the end, when necessary, a smaller reliner was run depending on the information obtained during the analysis of the grain sizes. Some techniques were applied to run the reliner successfully in an old and worn out casing, where the geometry of the well and high doglegs caused difficulties.

The challenges to complete the cleanout of the well with lost circulation problems included a large annulus area in the highly slanted and horizontal sections, the extremely high oil viscosity, and the presence of large pieces of PCP and metallic parts. These challenges were overcome by using different methods such as the special stroking pump, reverse circulation in the 9.625-in. section, and CT with the proper diesel and nitrogen proportions. Additionally, to keep sand production under control in the cleaned wells, a smaller reliner was run.

Finally, these workover jobs were finalized to bring these wells back into production successfully. The oil production results of these operations are shown in this paper, and demonstrated that it is possible to retrieve the production in the sanded wells of the Orinoco Belt in a profitable way.