When planning a well intervention, there are many factors that need to be taken into consideration prior to the execution of the operation. Designed guidelines are critical to the success of the milling operations in terms of saving rig time and successful downhole milling operations. These guidelines should include a structured pre-job information questionnaire, provide a more accurate picture of the problem, and also allow for a more detailed and auditable fit-for-purpose solution to the problem in terms of equipment selection, job procedures, and well programming. However without a set of stringent guidelines to assist in detailing the correct tools required for each application, the success of each intervention may not be realized. Through case histories this paper will show that utilizing structured guidelines, appropriate technology and tool designs lead to successful through-tubing intervention milling operations in cases when removing multiple composite bridge plugs. Discussion will involve the pertinent information required prior to equipment selection and job engineering and how that information relates to the equipment's performance and overall success or failure of the objectives of the intervention.


Performing a through-tubing live-well intervention saves time, reduces risk and improves economics over conventional intervention operations that typically require killing the well and removing the completion equipment. However, in order to yield maximum value, through-tubing intervention operations must be approached strategically and executed flawlessly. Significant strides have been taken in the area of improving the success rate and perceptions for through-tubing, live-well intervention operations. "It is essential that both operators and service companies work together so that systems can be put in place to reduce the chances of multiple tool runs and/or uneconomical failures. These systems include:

  1. A set of guidelines that allow the operator to chart the course of the planning phase of a through-tubing intervention;

  2. A structured questionnaire to obtain correct and pertinent information from the operator and to elicit any further information required from other relevant parties (coiled tubing, electric wireline, chemical providers, etc.);

  3. A set of guidelines to engineer a detailed and relevant solution to the operator's problems; and

  4. A system that allows the field technician to check the information and confirm it is correct prior to the deployment of any tools into the well."1

With the correct use of the above principles and information, case histories will show the use of through-tubing equipment as a viable, reliable, and cost effective intervention method which to allows the operator to economically achieve significant reward for minimal outlay.

Leveraging on Success

"It can be seen that significant strides are being taken in the area of increasing the success rate and perceptions of the use of inflatable tools for through-tubing live-well interventions."1 Following a structured plan for through-tubing intervention utilizing inflatable, remedial equipment has lead to not only the success of inflatable technology since the mid 1980s, but also to a vast database of applications from which both service companies and operators benefit from. Building from the development of information gathering techniques and the compulation of data from the last 20 years of inflatable technology creates the successful planning and execution of through-tubing applications. Both inflatable and fishing/milling applications benefit from these guidelines because of their many consistant variables within the through-tubing environment. Some of the characteristics these applications have in common are bottom hole assemblies, running procedures, and service/operating companies. Taking the same philosophies that have been instituted for the successful through-tubing inflatable arena, through-tubing milling operations will take full advantage of said philosophies and become even more successful while at the same time leveraging advancements in technology.

Inflatable Applications Best Practice Techniques

The following is a description of procedures utilized for through-tubing inflatable applications taken from SPE 54476, "Through-Tubing Inflatables: Isolation Planning and Guidelines for Coiled Tubing Applications," by Gordon R.J. Mackenzie and Mark E. Plante.

Design Guidelines

Planning guidelines were developed for the representative of the operating company coordinating a particular through-tubing intervention. These guidelines help the operating company representative provide a structured plan to approach the intervention section of the program. This not only highlights a logical sequence of events in the planning stage, but also documents the requirement to keep service personnel and associated services in the planning loop. By following such guidelines, many problems can be negated before they cause operational failures.

Operator and service company representatives should meet as early as possible to collect well data that provide an accurate picture of the problem the through -tubing intervention is required to solve; chart the course for the intervention operation, and develop a structured plan for a detailed and auditable solution based on equipment selection, engineering considerations, job procedures, and well programming. Specific pre-planning steps should include:

  1. Confirming that the candidate well requires the specialized service of a through-tubing intervention tool,

  2. Arranging an initial meeting between operator and intervention service provider representatives,

  3. Gathering pertinent candidate well data and inputting it into a comprehensive pre-job information database,

  4. Discussing well suitability, equipment selection, engineering considerations, timings, and other details of the proposed intervention,

  5. Providing wellbore schematics, deviation surveys, and other relevant well information that may not have been immediately available,

  6. Preparing and disseminating the proposal

  7. Performing an objective risk and reward analysis,

  8. Constructing the draft well intervention program and issuing it to all relevant parties, including the service provider,

  9. Arranging a follow-up meeting with all major contributing participants to review the draft program and well objectives,

  10. Producing the updated, final program and distributing to all relevant participants, and

  11. Ensuring that any well information that has changed is conveyed to all company representatives and that the program is appropriately re-evaluated prior to executing the intervention.

Pre-Job Information

For service company personnel, a pre-job information request is required to maintain structure throughout the planning process and provides an auditable tool to record the relevant information for the service company's desk engineer and field technician. It is also a quantifiable piece of information for the customer to authenticate. With this information request correctly filled out, the service company can research any further information required (coiled tubing OD, tapers, limitations etc.) and more accurately engineer a viable solution for the customer.

Execution of the Intervention

The success of a through-tubing well intervention is closely linked to the amount of information about the candidate well that is made available to the service provider prior to planning the intervention. For this reason, service company personnel should require the operator to complete an extensive pre-job information form. The recorded information provides an auditable tool for the service provider's engineers and field technicians, establishes the structure around which the intervention will be planned, and serves as the basis for evaluating products and analyzing risk. The service company uses the information in the audit to research coiled tubing OD, tapers, limitations and other additional information needed to more accurately engineer a viable solution for the operator. It is also a quantifiable piece of information for the operator to authenticate.

These techniques listed above describe the steps relating to the success of through-tubing inflatable technology and can be utilized for coiled tubing milling applications because of the similar environments in which these operations (inflatable and milling) are engaged.

Selection of Technology

Coupling the advancement of coiled tubing milling technology and utilizing the guidelines for coiled tubing applications in the field of inflatables for through-tubing milling will lead to the same benefits seen in the past for inflatable applications and technology. The primary enabling technologies for successful through-tubing milling operations are workover motors and cutting structures. Deploying the appropriate, application-based technology is essential to saving rig time and ensuring the success of the operation.

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