Abstract
Because of the instability of the oil industry, operators must continually investigate new techniques and equipment to reduce operational costs. This paper will discuss four case histories involving an innovative well-intervention technique in which a coiled tubing unit (CTU) was used to deploy and set bridge plugs for plug-and-abandonment operations in geothermal wells. By using specially designed coiled-tubing (CT) tools, operators eliminated rig time and formation cooling time, thus reducing operational costs. When job designers assessed the job requirements and service options, they considered the following factors:
In geothermal fields, pumping into a well to perform a kill operation for plug-and-abandonment techniques (required for conventional rig equipment) can affect the production of neighboring wells.
Bradenhead pumping or pumping from the surface into a well for a kill operation is not always possible unless a kill string or workstring is deployed to a certain depth.
The expense of rig time and production loss can affect operational costs.
Coiled tubing has been widely used in the oilfield industry because of its versatility and economy. When CT was first introduced, its primary advantage was that it could perform operations faster than a rig because of its increased pipe-moving capability. CT is now recognized for its capability to perform services with the wellbore in an underbalanced state. Specific tools that have been developed for CT operations have supported the increased scope of applications and have increased operational safety and reliability.
In the case histories presented, CT was used under live well conditions to deploy and set up 13 ⅜-in. bridge plugs for plug- and-abandonment procedures. Pressure-operated setting tools allowed entry into these geothermal wells under flowing conditions and allowed operators to successfully set drillable packer mandrels that have bridge plugs installed.
This paper will discuss the operation of setting tools, procedures for running the plugs, and obstacles that must be considered for operators to perform a successful plug-and-abandonment operation.
