Annotation
Technological and procedural advances in inflow and reservoir management have increased the design life of the field and, as a result, increased the use of field equipment. In order to protect structural integrity, it is increasingly important to properly maintain wellhead equipment to ensure that well integrity is at optimal levels and to ensure that the surface barrier against hydrocarbon leakage can be relied upon in an emergency.
Continuous high quality and efficient production can lead to satisfaction with wellhead integrity issues and insufficient attention to routine maintenance - but what if a catastrophic failure occurs that requires an emergency shutdown?
The lack of maintenance of critical components and the impact of various kinds on the elements can affect the equipment as a whole, increasing the likelihood of production downtime caused by equipment failure.
These very real risks can be mitigated through a planned and effectively managed well maintenance program, including valve maintenance, pressure testing, functional testing, and monitoring of the overall wellhead condition and operational dynamics. These measures will lead to more efficient production and longer equipment life, while reducing equipment overhaul costs.
Our company details the most important mechanisms for wellhead assembly failures and describes the benefits of a typical long term externally controlled well maintenance program, and provides complete traceability and integrity assurance for the operator.
Introduction
Oil exploration and production have played a significant role in the financial success of the Central Asia region since the early 1990s. The large size of oil discoveries often meant that the fields continued to produce commercially viable volumes of oil beyond the expected life of the field. While this is very beneficial from a financial point of view, it is important that operators are aware of the implications for the integrity of the well equipment and the safe operation of the field. Environmental conditions in the Central Asian region, combined with the corrosive and erosive properties of hydrocarbons, lead to accelerated wear of the wellhead and borehole assemblies, as well as wear of the casing strings.
Combined with general wear and tear on mechanical components and additional unforeseen equipment damage, it is critical that field operators have the appropriate programs for routine well maintenance to quickly and efficiently identify and address problem areas. This greatly reduces the risk of catastrophic failures and the need to shut-in the well to replace worn out or gripping mechanical parts - operations with significant financial losses. Regular maintenance is much more cost effective than waiting and responding to problems.
The most common mechanisms of failure and how to fix them
The structural integrity of the wellhead and wellbore depends on various external influences, and the reasons for deterioration or failure are often not immediately obvious. Investigation of a small fracture or seepage can quickly develop into a more serious problem in the well structure that requires immediate attention. Regular inspection and maintenance will keep the wellhead running safely and efficiently even after its original production life has been passed.
The most common failure mechanisms found during the checks and related remedies are detailed below:
Mechanical Assemblies - Main valves and diverter valves are usually the primary point of flow control on the wellhead and wellhead assembly. Valves and actuators are a common component prone to seizure and breakage caused by lack of proper lubrication and long periods of inactivity. While galling can often be eliminated with flushing lubricant, this approach is not 100% effective. Stuck or stuck valves usually require replacement, resulting in costly well shut-in operations.
Situations like this can be complicated if the valve is stuck in a closed or partially closed position. When this occurs, the valve must be hot tapped to reopen the wellbore while maintaining pressure control prior to plugging using a polished stem lubricator and replacing the valve assembly. Preventive maintenance is key to ensuring that the valves remain operational - monitoring and recording the number of revolutions to open and close the valve, look for signs of valve body damage and seal leaks, and respond to early signs of sticking.
The wellhead and wellbore are constantly subject to corrosion and erosion due to the external environment, when the wellheads are exposed to windblown sand, and nearshore surface wellheads are in aggressive salt water, as well as hydrocarbons that destroy the internal casing / tubing strings during a certain period of time. The gradual softening of metal structures caused by these corrosive environments will ultimately lead to cracks or holes through which hydrocarbons or gas will flow, causing fouling and further accelerating the destruction of wellhead materials.
While it is difficult to determine the structural integrity of the casing at any given time, regular monitoring of the wellbore pressure and casing annulus can reveal flow dynamics. Changes in pressure over time can indicate fluid transfer between the rings and therefore possible malfunction. In extreme cases, hydrocarbons can penetrate the outer casing, in which case immediate action is required to locate the breach in order to clearly identify the leak from the inner pipe and identify the area needed for workover to ensure the structural integrity of the wellhead. This poses additional challenges for onshore wells where excavation of near-surface fractures requires excavation to determine the source of the leak. However, if the breach is deep within the well, the operator's only option is to perform a full repair.
Corrosion caused by the environment and weather conditions can be dealt with cheaply and effectively by removing and reapplying coatings and paint to protect bare metal. This is a basic requirement for wellhead maintenance and is the recommended action every time you visit the wellsite for preventive or routine maintenance.
Seals and Gaskets - Similar to erosion and corrosion detection described above. Pressure monitoring and regular visual inspections are key to ensure the integrity of the wellhead seals. This is critical for elastomeric seals that are prone to prolonged wear and must be replaced after they have exceeded their design life. Regular thermal cycling of wellhead materials also leads to deformation of metal-to-metal seals and subsequent opening of leakage channels. This can be corrected by introducing sealants. In more severe circumstances, when sealants are ineffective, it becomes necessary to dismantle the wellhead assembly and replace the necessary seals.
Missing Components - Not all wellhead maintenance is the result of damage or wear to surface equipment. Central Asia is home to a number of onshore and offshore drilling sites that have been neglected due to neglect.
It is not uncommon for such fields to be acquired by new operators and plans are drawn up to re-enter the wells. It is subsequently discovered that wellhead assemblies are incomplete due to the fact that parts were borrowed to repair offset wells, or in some cases taken without consent. Through regular equipment inspections and preventive maintenance visits, the likelihood of this is reduced and steps can be taken to ensure wellbore integrity in the event of a critical component being lost. It is generally advisable for new owners to have their fields appraised and surveyed by well maintenance technicians before planning any form of re-commissioning to ensure that the well condition is as expected.
Changes in Reservoir - As the life of the field increases, the quality of the produced hydrocarbons tends to deteriorate with the increase in the amount of BS&W (basic sediment and water) observed at the surface. While these contaminants can be controlled, operators should be aware of the detrimental effects they can have on well equipment and casing. Sand and water can increase the rate of corrosion and erosion of the inner walls of the casing and can affect the integrity of the wellhead and wellbore valves and seals. Changes in hydrocarbon quality affect how regularly the wellhead should be inspected and maintained.
Produced slurry analysis results should be provided to wellhead control personnel to prioritize the structural integrity risks associated with each well and adjust the well maintenance program accordingly.
Changes in company policy or technology - Wellhead integrity management is an area where new practices or procedures are continually being introduced - whether it is the development of wellhead installation technologies or improvements in safety management that lead to a change in the company's operating policies. If these changes result in the operator's decision to make any significant structural changes, it is recommended that these changes be implemented as part of an ongoing well maintenance program. This ensures that improvements are properly recorded as well as scheduling follow-up visits to ensure that changes are being implemented as expected.
Well maintenance planning and implementation
To ensure that well maintenance campaigns follow a structured approach, it is important that sufficient planning is carried out before a maintenance program is carried out, each required activity is prioritized accordingly, and minor activities are timed with planned shutdowns. While this is not always possible, every effort should be made to use the time efficiently.
The first and most important step before forming a well maintenance plan is to conduct field surveys. This makes it possible to accurately catalog the technical and performance characteristics of each well. It is recommended that this information be consolidated into a central database along with drawings, GPS locations, photographs and other relevant data that can be accessed from the operator's office or remotely from the field at any time. This will then form the basis of a well maintenance campaign, giving the operator full traceability to record and further analyze all changes.
Field surveys are usually the most time consuming part of a well servicing campaign. This is partly due to the complexity of the typical onshore / offshore estuary and the number of components that need to be identified and recorded, partly due to the age of many deposits in Central Asia and the lack of accurate historical reference data. Construction drawings are generally missing or impossible to trace, and it is likely that additional work was carried out on certain wells after installation, meaning that individual components identified during the survey are not necessarily the original installed items.
The field survey is also the first opportunity to identify critical service items for a follow-up campaign. Visual inspection and initial wellbore and annulus pressure / temperature readings will instantly show if the wellhead is affected by leaks, damage, component wear, breakage or even missing parts.
After the field survey and filling in the relevant database, the most important elements are identified, which are reported to the operator for verification along with recommendations for further action. These recommendations are usually accompanied by a work package containing a complete step-by-step work procedure for each proposed activity, a risk assessment for each individual task, and a list of required tools and expected timelines.
Onsite maintenance work, which can be performed without removing any components from the wellhead, is generally the least problematic in terms of maintenance planning. Relief of pressure from the annulus, flushing of a stuck valve or ball valve can be performed in the shortest possible time by a qualified specialist of our company.
Original manufacturer components and assemblies are not always available for deposits that have been in production for decades. Many changes have occurred to OE manufacturers in recent years, some have ceased to exist in the market, others have been merged into new companies. Many parts are now obsolete and not all manufacturers have spare parts for old equipment or offer services for making obsolete structures from old drawings. If it is not possible to timely save or restore a worn part, there are two options: find a manufacturer of the part to manufacture, or redesign the part from scratch. Both of these options, while feasible, come with certain risks, as extra care must be taken to ensure that the new part meets the high quality standards of the original and the correct specification. The ability of the supplier / manufacturer to quickly provide quality parts for retrofits when needed is also a significant advantage.
To reduce the financial impact of a wellhead maintenance campaign, the replaced assemblies are kept in stock. By disassembling the assemblies and fully rebuilding each worn component, the element can be rebuilt and used later when that particular element is required for another well. Over time, the volume of remanufactured parts will increase to the point that the operator will have access to a large stock of replacement parts, reducing the need for redesign or purchasing new parts from an external supplier. By analyzing the failure mechanisms of each component, trends can be identified that can be rationally used to create a checklist of frequent failures with different wellhead designs that will become part of routine inspections. Once the priority maintenance work has been completed, a plan should be drawn up to conduct regular maintenance checks and ensure wellhead integrity. This is carried out on a rotational basis with a scheduled visit to each well in turn. Before proceeding, the wellhead maintenance company and operators must agree on operating limits for each wellhead variable. The following are examples of typical variables that are logged and tracked during each site visit: