Make Your Re-Entry & Workover Wells Successful

The Key Issue

A mentor once said that 80 – 90% of workover wells, exceed their time and cost estimate! This post examines why this is so, and how we may avoid the cost over runs.

An existing well was thought to be under-performing, and production from this well needs to be improved. A quick work program was put together to fix the well. Unfortunately, the work has taken more time than estimated, resulting in cost overruns, and worse still, the program has been unsuccessful. Or, to use a real life example, a 15-day workover was planned with a $60,000 per day rig. Close to execution, management, thinking to save cost, considered that using a Hydraulic Workover Unit (HWU) costing $30,000 per day, would save 50% cost of rig rate. Not recognising the difference in the two alternatives. Unfortunately, the HWU completed the work in 109 days, resulting in a huge cost overrun, and the well work still unsuccessful!

Well Objectives:

Before examining some of the reasons for the prevalence of re-entry operations failures, let’s take a look at sample reasons for re-entry/workovers:

1)   High casing annular pressure (CAP) resulting from a damaged production casing, leaking liner lap, parted tubing, failed accessories such as sliding sleeves, Gas Lift Mandrels, or, packer, etc.

2)   Excessive gas/water production due to cusping/coning, wrong perforation placement or wrong horizontal well landing, watered or gassed out perforations/horizontal legs, poor cement jobs behind liner shoe, etc.

3)   A well simply did not deliver after newly completed due to a problem with the well construction, or the expected reserves was never there, in the first place!

4)   Sidetracking a well to target better pay.

5)   Plug and abandon well. Etc.

Re-Entry Work Outline in Simple:

In spite of the myriads of the reasons we re-enter a well, every re-entry work follows a simple outline as follows:

a)   Secure the well

b)   Move rig

c)    Kill the well

d)   De-Complete the well

e)   Carry out diagnostic test/logs, if required

f)    Carry our repairs/sidetrack the well

g)   Prepare the wellbore

h)   Re-Complete the well, and

i)     Handover the well to production.

Issues and Challenges:

Though the outline program for working over a well may appear simple and straightforward, it is rarely so. Each of the outline steps is complicated, requires careful planning and capable of aborting the well operations progress prematurely if appropriate contingencies had not been foreseen and provided, resulting to loss of investment. An experienced colleague, with over 40 years of experience in well work, once asserted that re-entries appear simple and cheap, but they are actually a Pandora’s box – you only know what’s involved after you have commenced the work!

Despite that, the chief reason costs are overrun is the deceptively simple work program. Management often assumes that it is a source of quick and cheap oil, and can be executed with minimal pre-planning. Therefore, not enough front-end planning work is often done. In most cases, risks have not been identified and managed, and contingencies have not been provided.

In remote operations such as those in West Africa (Gulf of Guinea), this is exacerbated by the fact that:

1)   There is limited availability of services or tools options, and long lead times are required to acquire materials.

2)   There is also limited availability of experienced personnel with skills in the outlined program above. Worse still, not recognising this!

3)   Huge language barriers exist. Even in English speaking environments like Nigeria, communication is still a big issue. People will nod ‘yes’ even when they have not understood instructions.

4)   Sometimes local content laws, or nepotism (for that matter) impose incompetent personnel on the team, and this escalates the challenges of carrying out a successful well work.

5)   Complex logistics, and often elaborate security escort arrangements, causing unusual delays in materials delivery.

6)   Sometimes management, in a bid to save costs, do not recognise the risks and complexities involved, and may sanction work without really understanding the complexities involved, perceiving the contingencies as waste of resources.

Solution:

Well planning of re-entry wells is very different from drilling a new wells, and the key success determining factors, are very different. Yet the well planning process is the same: Evaluate the well objectives,

•  Identify options for well repair,
• Carry out a detailed design of the work, identifying risks, mitigation options and contingencies.
• Write the work programme and execute.

The planning work should take a good time, 3 to 6 months typically, so that the execution phase is commenced after every one is satisfied that a high chance of success can be assured.

 In future posts, I hope to discuss case studies and examples of actual re-entry work that were driven to success, to demonstrate the required details in front-end planning.

In conclusion, well re-entry programs are not as simple as the appear. Therefore, it is necessary to ensure that the right materials and personnel with the right experience, are available to plan and execute the work.