Technology Roundtable: Wellbore Cleanout
Why is an effective wellbore cleanout program essential when looking at the production and run life of a well?
Schlumberger: Movement of sand and accumulation of debris can have a considerable impact on fluid flow. On the surface, a river can deposit so much silt that it blocks its own flow, changing its course and perhaps threatening farmland and communities. Similarly, downhole in a well, influx of sand and debris can impair or stop the flow of oil or gas from a reservoir.
An effective wellbore cleanout is a critical step to restoring the production of a well, and enabling access to the wellbore and reservoir for subsequent evaluations or treatments that are a crucial part of the wells lifecycle.
Baker Hughes: Wellbore cleanout programs provide insurance to completion, workovers and production by basically reducing risks and NPT. The data has shown that more than 30% of NPT is the result of debris in the wellbore. This downhole debris can lead to many completion and workover problems such as a packer prematurely setting, screens getting blanked, safety valves malfunctioning, liner hanger not running to depth, etc. These problems can further affect production and reduce the life of the well.
Halliburton: First of all, any well loading with different type of deposits (sand, scale, wax, biofilm, corrosion byproducts, etc.) or any liquid loading in gas wells could result in flowing bottomhole pressure (FBHP) increase, decreasing production. The deposits can also damage perforations and filtration properties of wellbore area. All mentioned above could be a reason for a production decrease, intermittent production or even total well shut-down.
Any intrusion into the formation has potential for wellbore formation damage. Drilling and completion operations can leave drilling mud, fines, and water damage in normal operations. Any workover operation can also leave damage, such as rigid film emulsions after acid jobs in heavy oil, cooling of the formation from workover fluids to cause paraffin to deposit, CO2 flooding causing asphaltene deposits, swelling and scale from incompatible water use, and other problems. Fines can deposit in the wellbore area over time, reducing near wellbore permeability. Reduction of pressures and disturbances in fluid stability during production at the wellbore can cause scale, iron sulfide, biofilm, corrosion byproducts, and other damage, all leading to loss in production rates. Any of these can cause premature loss of production or water injection in the well.
Is wellbore cleanout adopted in both newly completed and mature wells across Russia?
Schlumberger: Accumulation of sand and solids in wellbores significantly impairs oil and gas production, regardless if it is a newly completed or mature well. However accumulation of sand/debris is more likely in a mature well, and hence the tendency is higher for a wellbore cleanout. In Russia it is also common to cleanout a newly completed well after a hydraulic fracturing operation has been performed.
Baker Hughes: In Russia, more and more operators have realized the importance of wellbore cleanout operations and have started to evaluate the risk vs. cost. We have seen increasing numbers of new wells using wellbore cleanout operations, especially in high cost wells. However, the cleanout operation is still very limited in mature wells in Russia.
Halliburton: It is difficult to say for the whole of Russia. It could vary from company to company. It is normal practice for a just-completed well to have a clean wellbore area. The problems in mature wells often are connected with not properly managed operations in the field.
In a new well, how can you measure the cost verses effectiveness of a cleanout program?
Schlumberger: The effectiveness of a cleanout can be measured by comparing the production gain following a cleanout against the well’s true production potential (typically obtained from reservoir studies and recent well test results). The cost of the intervention is essentially the cost of the intervention service including all human resources, tools and fluids required to perform the cleanout. An economic analysis can then be performed to determine the pay back period to achieve the incremental production gain following the cleanout.
Baker Hughes: The operators need to evaluate the potential risks and NPT involved if the wellbore is not cleaned out. The risks can include prematurely set packers, failed screens, malfunctioning of downhole or surface equipment, etc. The risk and NPT related costs should be compared to the wellbore cleanout operations cost. The decision should be also be made considering the complexity and cost of the operations. In a low cost and simple completion operation, it may make sense to complete the well without a wellbore cleanout operation; however, in a complicated and high end well, the risk and cost of completion or workovers with debris in hole will be too high, and a wellbore cleanout operation is the best choice. In short, wellbore cleanout is the insurance premium paid to increase the life of the well and ultimately production.
Halliburton: The main factor of effectiveness and cost of a cleanout program is the time required for the cleanout operation. Controlling this parameter can give us the possibility of reducing costs and increasing the effectiveness of the technology selected for cleanouts. Again, each new well has to have a clean wellbore area in order to provide the best possible production.
Cost effectiveness is measured by ROI of the treatment and achieving predicted well production. If a new well is not producing at the expected rate then wellbore damage from drilling and completion operations should be investigated. Wellbore cleanout cost (chemical, application, and production lost cost) should be determined and compared to expected production to decide on the treatment and also compared to the resulting production change after treatment to decide if the treatments are worthwhile.
How do you know when it is time for a wellbore cleanout in a mature well? Should it be a regular & ongoing process or it is not necessary?
Schlumberger: When the wells production beings to drop, and it is confirmed that the production drop is as a result of solids/sand/scale accumulation in the wellbore, an economic analysis needs to be performed to compare the cost of a cleanout and the production gain to be achieved from the cleanout to determine the timing of a cleanout. In order to avoid the initial production drop and maximize the production from the well, cleanouts should be done regularly particularly if they are from scale build up or debris accumulation.
Baker Hughes: In a mature well, wellbore cleanout is often performed before, during or after any workover operations if it makes sense economically. The examples include cleanout the debris off a safety valve to ensure the proper function of the valve, removing the debris when retrieving or milling a packer or plug, casing ID preparation before a casing exit or plug setting operations.
Halliburton: To identify the wells that need cleanouts, we have to continuously watch production figures. For instance, the following factors are important:
» Look for anomalous and steepening decline rates that do not fit predicted production rates.
» One test could be a pressure fall off survey to determine skin value.
» Look for wells that are acidized often.
» Look for wells that require periodic maintenance.
» Routine asphaltene and paraffin cleanouts can indicate a problem especially if hot oiling has been done downhole.
» Are fluid levels as expected in the well (shoot fluid levels to determine).
Wells can be filled with scale, iron sulfide, salt, sand, or other solids which can be determined by running a simple sinker bar – these wells are cleanout and/or acidization candidates. GIS results could be very helpful in identifying the problem.
What types of wellbore cleanout solutions do you have?
Schlumberger: Schlumberger has many different wellbore cleanout solutions in its arsenal that are fit for purpose, comprising of mainly mechanical tools for milling and scraping, hydraulic tools for jetting and flow back, as well as chemical fluid systems for an effective cleanout through dissolution or viscous solids carrying capabilities. Integration of all these different solutions with a state of the art wellbore cleanout design software and real-time monitoring of key downhole parameters (differential pressure, temperature, casing collar locator (CCL), gamma ray (GR), downhole load) with the ACTive* fiber optic enabled coiled tubing (CT) system, enables the confidence to achieve efficient and optimized wellbore cleanouts.
Baker Hughes: Baker Hughes provides complete wellbore cleanout and displacement solutions, including mechanical tools, chemicals and engineering services. Baker Hughes X-Treme CleanTM mechanical wellbore cleanup and displacement system provides the most complete wellbore cleanout tools in the industry; it includes Riser and BoP cleanout tools, casing ID cleanout tools, junk removal tools, circulation tools, and etc for different applications from land to deepwater. VACS is one of Baker Hughes leading technology. It effectively collects debris downhole, especially in difficult or extreme well conditions. We also provide chemical solutions that are fit for purpose, have outstanding performance and meet the environmental requirements. The displacement fluids include MICRO-PRIMETM, BAKER CLEANTM and WELL WASHTM. By deploying the advanced analysis and simulation tools, such as DISPLEXTM, Torque and Drag, VACSPredictorTM we can further assist the customers to ensure the success of any wellbore cleanup and displacement job.
Halliburton: Halliburton’s Multi-Chem business line can provide a complete customized wellbore cleanout service with a combination of chemicals and equipment. This includes:
» Scale removals
» Wax and asphaltene removals
» Foamers for cleanout operations
» Biocides to remove biofilms
» AcroClear iron sulfide removal
» Foamers to unload gas wells
» Surfactants
» Chemical package for acid job operations, etc.
» Mutual solvents for fines displacement and wettability control
» Clay swelling control products
» Monitoring Service for results
» Coiled tubing for application (Boots & Coots)
– Hydra-Blast for cleanouts
– Pulsonix TFA for cleanout
– CoilSweep for cleanouts
– DeepReach for application
– Monitoring for services
– Pinpoint placement of application
» Pumping services
» Frac services as needed
How do the solutions on the market differ in terms of the key issues they solve?
Schlumberger: Efficiency is essential in optimizing production from aging oil fields and reservoirs that are difficult to produce. By understanding the interrelationships and potential synergies in process elements, new technologies emerge, helping operators return wells to production faster. As non productive time decreases, costs decrease and field output increases.
Understanding key process elements is not always straightforward, and often requires the insights of experts from diverse disciplines. For example, chemists generally develop cleanout fluids, while mechanical engineers and fluid mechanics specialists develop nozzle technology; the Schlumberger ACTive service with integrated wellbore cleanout system exemplifies this type of multidisciplinary collaboration. Schlumberger engineers have the tools and computing support to quickly model, perform multiple iterations and optimize cleanout system performance for most wellbore conditions and requirements, all in real-time while intervening in the wellbore – where it matters the most! This solution allows operators to perform cleanouts in underbalanced conditions, large wellbores, or wells that are highly deviated or horizontal.
Baker Hughes: Most operators and service providers share the basic wellbore cleanout concepts and practice. Mechanical tools and chemicals are combined to provide the best results. However, there are differences in tool and chemical designs and functions, and detailed operation procedures among difference companies. For example, many service providers, including Baker Hughes, believe in non-rotation (the scraper blades or brushes that have direct contact with the casing ID do not rotate with the casing string) wellbore cleanup tool design to avoid any damage to casing ID, while others use rotational design. In general, there is increasing focus on wellbore cleanout operations in the industry, and the operators and service companies have been working together to drive the most effective cleanout products and services to reduce the costs and NPT.
Halliburton: The solutions for wellbore cleanout are different in respect to the chemicals and fluids from which solvents are made. Both hydraulic and chemical cleanouts are accomplished by circulating fluids in the well but the choice of chemical reagents depends on the problem to be solved. So, we prepare individual cleanout programs for each well. In many cases, the chemical solution could be the only possible or the most cost efficient way to fix the problem.
Solutions should be customized to the problem to be solved. In that view it is important to determine the causes of the well problems. Use of the wrong treatment may create more damage (hot oil, acid), fail to correct the problem, treat the wrong problem, or be either excessive or un-needed, all causing lost time, production, and money. Not understanding root causes of the problem can result in not solving the problem by use of continuous remedial actions (i.e., multiple scale removals in a well not considering a scale inhibitor squeeze to prevent the scale problem) or repeating the cause of the damage (hot oil or acidizing). For example, use of acid to increase production, although successful, may not be addressing the real issue. Analysis of the returning fluids form the acid job would indicate if scale was being dissolved (increase in calcium and loss of acid). If this calcium increase and loss of acid was not happening then perhaps just fines were being displaced from the wellbore and the use of acid (or acid concentration) would not be needed.
What are the key differences between a cased and open well cleanout?
Schlumberger: One key difference between the two is the level of potential risk. Open hole cleanouts are riskier than cased hole cleanouts due to the increased likelihood of fluid loss resulting in less efficient solids lifting capabilities. There is also a well integrity risk in open hole by the introduction of different chemicals or mechanical jetting tools required for an effective cleanout, resulting in a potential collapse of the open hole section resulting in stuck pipe. As a result of these risks, open hole cleanouts require extensive pre-job planning and measurements to ensure an effective and safe operation.
Baker Hughes: In an open-hole cleanout, the consideration is to minimize the damage to the formation and filter cake while effectively removing the debris. Mechanical tools that have direct contact with the hole ID, such as the scraper and brush, are typically not used in an open hole cleanout operation. The open hole cleanout is achieved mainly through chemical treatment and effective circulation. In cased hole cleanout, the mechanical tools, combined with chemicals, are the main methods to achieve the casing and hole cleanout. The tools are typically rotated at a relatively high speed to assist the cased hole cleanout, especially in deep and deviated well applications; while in an open hole cleanout, the rotation of the tool string needs to be avoided or controlled at a very low speed.
Halliburton: The main difference between a cased well cleanout and open well cleanout is additional risks in the second case. These risks are associated with additional fluid losses to the formation (risk of formation damage), wellbore sloughing or collapse, and risk that equipment could get stuck. So, for open wellbores, we need to use other technologies and programs for treatment. These approaches may be foam cleanouts or less aggressive cleanouts using additional chemicals to protect formations.
In uncased completions it could be difficult to place the treatment and could result in treatment loss to un-needed zones/formation. This can increase the treatment cost or reduce effectiveness. Uncased completions also reduce the choice of equipment that can be used for clean outs and may increase need for application equipment.
Is there a risk of formation damage by conducting a cleanout operation?
Schlumberger: There is a risk of formation damage during a cleanout operation particularly when the reservoir has sensitive clays, the lost fluid is unconditioned or has high solids content and non-degradable polymer content. The industry has sophisticated models that help us calculate differential pressures during cleanouts, but these models are based on manual inputs that are not always accurate. In order to ensure that a well is under balanced or at balance conditions during a cleanout operation to avoid formation damage risks, differential pressure at the nozzle needs to be monitored in real-time, which is possible with Schlumberger’s ACTive technology. The ability to monitor and adjust key pumping parameters helps the engineer to act confidently and immediately while the coiled tubing and the tools are still in the well. With operating costs being driven down and especially scrutinized in today’s environment, you need to make sure you get the most out of a well intervention.
Baker Hughes: There are always risks when operating in an open hole cleanout operation. However, by utilizing the right technologies and processes, the risk of formation damage is minimized. The fluid used to drill the open-hole reservoir section is designed to form a thin, removable filter cake that protects the formation from damage. When starting open-hole completion operations, it is typically recommended to displace the open-hole section with a clean fluid prior to pulling up into the casing to start the cleanout process. After the completion assembly is run, the filter cake that is protecting the formation is removed in a subsequent step so that it no longer impedes the production of oil or gas.
Halliburton: Yes is the simple answer (also see our response to Question 1). When selecting a chemical solution it is very important to consider the possible risk of formation damage. During cleanout operations there is a risk of getting fluid in the formation where it can react with the mineral composition of the formation resulting in reduced permeability. This issue has to be given special attention when recommending an acid treatment. Another risk, for instance, is the possibility of creating an emulsion in the wellbore area.
Can you outline a successful cleanout you have run in the region?
Schlumberger: In Western Siberia Schlumberger has performed successful proppant clean outs of multi-layered oil formations after AbrasiFRAC* Through Tubing operations on 5 zones. Apart from cleaning out wells completed in layered formations with potential cross flow between zones, an additional challenge is performing an effective cleanout in highly deviated wells with casing sizes of 146 mm OD. To overcome these challenges, the proper CT string design, cleanout procedure and fluid systems are designed with the help of our integrated cleanout software. Field crew experience and operational efficiency has led to many more successful cleanouts in similar conditions, enabling major operators to optimize recovery from their oil fields in Western Siberia through stimulation techniques made possible by advances in wellbore cleanout solutions offered by Schlumberger.
*A mark of Schlumberger
Baker Hughes: In the Russia Caspian region Baker Hughes has extensive experience in running Baker VACS Junk catcher inside Casing. In one of these job’s for a customer in Belarus, we ran the Baker VACS tool in 6-5/8” casing for a MLT (Multilateral technology) Level 4 project and wherein the tool was run to clean out casing after whipstock retrieval in order to set the LEN (Lateral Entry Nipple) with anchor into the ML packer. We have done several such jobs for a customer in East Siberia. Also Baker Hughes have done several jobs with CT cleanout, using 1.69”, 2.13” & 2.88” Motorhead assemblies and required accessories in Komi and Siberia.
Halliburton: Multi-Chem is a new business line of Halliburton and this is the first year of its operations in Russia; however, Multi-Chem is very well-known chemical supplier in the U.S. and Canada. Multi-Chem is involved in a few coiled tubing cleanout and gas well deliquification projects in Russia.
