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With an increasing number of wells transitioning to their abandonment stages, associated operational efficiency and cost cutting have become a major focus in the industry. An operator had an objective to permanently abandon an offshore well that was suspended in 2016. The key challenge was to develop a long-term well abandonment solution leaving the completion tubing and gauge cables in the well. All the associated operations had to be completed utilizing a lightweight well intervention vessel.
Traditionally, retrieving the entire 5 ½-in. production tubing during plugging and abandonment operations has added operational complexity and costs and increases the risk of exposure to health, safety, and the environment (HSE) hazards. Alternatively, a sealant technique placing cement through and around the completion tubing with gauge cables in-situ exists. However, this technique is associated with a heightened risk of leak path development over time. Ongoing experimental work suggested that enhancements to the conventional cement sealant systems would be beneficial to improve long-term sealing; thus, an active self-sealing cement system that would seal microannuli or small fissures around the tubing and gauge cables was designed. The set cement sealant characteristics include low Young's modulus to resist failure from wellbore stresses and the ability to regenerate the original seal upon contact with any hydrocarbons that may seep through any isolation defects through the life of the abandoned well. To achieve proper cement placement, advanced fluid simulation software and carefully tailored fluid density and rheology profiles were used.
During the operation, a plug of the self-sealing cement sealant was pumped through the production tubing and squeezed into the perforations to create a permanent barrier across the reservoir section. Next, a mechanical plug was set inside the production tubing to isolate the lower section, and the tubing was perforated to provide access to the A-annulus above; subsequently, a balanced plug of self-sealing cement (SSC) system was spotted above. After 30 hours, the plug passed a 3.4-MPa [500-psi] verification pressure test. The operator estimated the operation saved 2 to 3 days of rig time, valued at approximately GBP 400,000 to 600,000. The operator also avoided the risk of leaving the well on long-term suspension with mechanical plugs while waiting for a rig to complete the isolation, and the operation minimized the number of intervention steps required for abandonment, thereby limiting scope growth.
Operators are constantly looking for ways to increase reliability, improve efficiency, and minimize risks, and therefore, abandonment techniques are evolving. The developed solution is a novel and robust alternative to conventional well abandonment using an advanced cement sealant technology for the first time and an innovative placement technique.
Zhang, Hua (Schumberger-Doll Research) | Ramakrishnan, T. S. (Schumberger-Doll Research) | Elkady, Youssef Magdy (Schumberger-Doll Research) | Feng, Yixuan (Schumberger-Doll Research) | Elias, Quincy Kurleigh (Schumberger-Doll Research)
As an alternative to cement, the feasibility of bismuth-tin (BiSn; contains 58 wt% Bi and 42 wt% Sn, abbreviations are not in stoichiometric ratio) as a low melting-point plug has been tested by Zhang et al. (2020) for rigless plug-and-abandonment (P&A) service of offshore wells. Similar to BiSn, bismuth-silver (BiAg; contains 97.5 wt% Bi and 2.5 wt% Ag, abbreviations are not in stoichiometric ratio) also exhibits desirable properties compared with Portland cement. However, because of its greater melting point, BiAg has potentially a wider application than BiSn, especially in deep formations. In the present study, we investigate the feasibility of BiAg alloy for P&A. The bond quality of the alloy-shale cores is evaluated through shear, tensile, push-out, and permeability tests, and compared with those of BiSn alloy-shale and cement-shale cores. To avoid phase change-induced shale damage at elevated temperature while setting BiAg plugs, water was first extracted with supercritical carbon dioxide (CO2). For shear and tensile tests with pinhole-anchored BiAg, the ultimate strength and modulus were measured as a function of anchor points at different temperatures (21, 80, and 110°C). For the push-out tests, shale samples of smooth, rough, and pinholed surfaces were prepared with the BiAg alloy plug. In general, we find that, without anchors, bond failure precedes shale failure. Results for cement-shale cores are also reported for comparison. We contrast the performance of BiAg and BiSn alloys at 21, 65, 80, and 110°C to determine the crossover temperature for deployment suitability.
In the oil and gas industry, drilling and completions of wellbores have undergone major technological improvements, that ultimately enabled safer exploration and production of fossil fuels. However, the plugging and abandonment (P&A) of wellbores had not attracted the same level of technological advancements. Wellbore plugging in offshore environments is challenging as the consequence of potential hydrocarbon leakage can cause cumulative damage to the fragile ecosystems for a long time before detection. Gas leakages are especially hard to detect and evaluate for appropriate wellbore intervention and mitigation. Preventing wellbore leakage requires a robust sealing material capable of reducing the permeability through wellbore infrastructure and surrounding formation to zero. One proposed way is to use zeolites as additives. Zeolites could act as scaffoldings for cement hydration reactions to take place and since they have crystal and pore structures similar to Calcium Silicate Hydrate (CSH), they have compatibility. This could act as a bridge between the natural formation and cement. Due to the non-hydraulic nature of zeolites, they could retain some pore water which could be released in an event of fracture providing water for secondary hydration of cement resulting in self-healing properties. Also, zeolites show a very strong skeletal structure despite their large reactive areas and pore sites. Hence, one of the ideas to be explored in this paper is to gain a deep understanding of the zeolite properties before adding it to cement in order to create an ideal hydraulic barrier material. By doing so, ultimately the aim is to achieve a barrier material which could mimic shale which is a natural cap rock and find application in wellbore plugging operation. This paper is focused on evaluation of a natural zeolite ferrierite, primarily microstructural characterization and its chemical stability in contact with fluids that resemble potential subsurface formation fluids. The data suggests that there is no major microstructural change in contact with: low pH aqueous solution, high salinity brine, synthetic oil and water, and some change in contact with high pH Calcium Hydroxide (Ca(OH)2) solution, after 7days exposure at 95°C.
da Silva, Ingrid Ezechiello (PETROBRAS) | Balthar, Vivian Karla Castelo Branco Louback Machado (COPPE/UFRJ) | Toledo Filho, Romildo Dias (COPPE/UFRJ) | de Sá Cavalcante, Gabriella de Medeiros (PETROBRAS) | dos Santos, Robert Lucian de Lima (PETROBRAS)
The plug and Abandonment (P&A) are the final stage of the life cycle of an oil well. This implies that the plugging material must withstand the chemicals, temperature and well pressure to ensure its long-term integrity. Portland cement is the most used material as a safety barrier in P&A operations. However, the extreme conditions of the well have challenged the mechanical properties of Portland Cement. In this context, the present work aims to identify the adequate systems as permanent plugging material and to characterize them with a qualification process based on international references and experimental validation.
Hence, four systems were tested for plug cementing operation with composition variations under pre-defined ageing conditions. Class G Portland cement slurry was used as reference to allow comparison of mechanical properties (compressive strength and tensile strength) between flexible cement paste, a system containing a mixture of Class G Portland Cement with epoxy resin and finally a system with epoxy resin only. Samples containing Class G Portland Cement were cured for 14 days under well bottom conditions (3000 psi and temperature of 174 degrees Fahrenheit) and cured for 14 days at well temperature (using a thermal bath). Samples containing resin were cured for 14 days under well bottom conditions (3000 psi and temperature of 150 degrees Fahrenheit) and cured for 14 days at well temperature (using a thermal bath).
Finally, the samples were aged for 60 days in a thermal bath at well temperature and exposed to the brine which is the completion fluid composition which will be above and below in contact with the well barrier in a P & A operation. The results of the compressive strength tests of the samples aged in brine showed tha in some systems tested the reduction of the modulus of elasticity occurred, however, it was also observed the increase of the modulus of elasticity in another system. The same was true of the results of tensile strength tests of aged samples, the increase of rupture loading in some systems and reduction in the other ones were observed.
The mechanical tests of the samples before and after ageing were performed to define the best system to be used in a well abandonment operation aiming for long-term integrity.
Since the 1970s, 12 deep vertical gas wells in the Thomasville area in Mississippi, USA have been producing high volumes of sour gas (3 to 21 MMcf/D per well). This production decreased to unsustainable levels, which required the field to be abandoned. Abandonment presented a rare combination of challenges including high temperature (>400°F), high sour gas and CO2 (more than 40% H2S and up to 9% CO2), depleted formation (0.1 psi/ft), scale buildup, unique well geometry, true vertical depth ranging from 20,300 ft to 23,600 ft, and nearby residential areas. A combination of special operating procedures, intelligent self-healing cementing slurries, and novel placement techniques enabled the wells to be successfully abandoned with layers of contingency to prevent a catastrophic environmental release.
The plug and abandon operations were divided into two phases. Phase 1 was rig-less operations to kill the well and isolate the formation by using an engineered ultralightweight 9.0-lbm/gal cement slurry that provides greater corrosion protection compared to a normal cement slurry. Novel placement techniques were used to place the engineered slurry across the production perforations and open hole to isolate both the tubulars and annuli. Advanced hydraulic simulations were run to model the complex placement. A traditional drilling rig was moved in for phase 2 of the operations. In phase 2, intelligent cement plugs, which included flexible and self-healing properties, were placed to add greater zonal isolation assurance accounting for unknown well conditions for the long-term abandonment of the well. Cement plugs were verified with robust negative and positive pressure tests.
It was determined that an ultralightweight slurry could be placed with a 0.1-psi/ft fracture gradient using nitrogen displacement, optimized slurry volume, and variable choke to regulate pressure on the backside to isolate the wellbore. Displacing with nitrogen proved to be challenging, and the many lessons learned will be documented in this paper. All 12 of the producing wells, along with 5 disposal wells in this field, were successfully killed and plugged. To date, none of the wells are showing pressure. This paper will review the challenges faced with designing a successful P&A program in this Thomasville area. Both phases of the final operations will be presented, and lessons learned along the way will be discussed.
These complex well conditions were overcome through sound designs in operational planning, cement slurry optimization, placement techniques, and isolation testing methods. The primary plug proved to be effective at being placed in a depleted environment and at ultrahigh temperatures while taking into account corrosion protection. The intelligent cement slurry offered long-term barrier assurance through both failure prevention and self-repair. The long-term solution outlined in this paper is key to preventing a catastrophic environmental release. The innovative placement techniques, contingencies taken, and lessons learned during the campaign will be useful to other technologists in other fields faced with similar conditions.
This paper discusses the effective application of a Combination Technologies and Processes that allowed successfull abandonment of wells with Sustained casing pressure (SCP), on the Karachaganak field. The planning and execution processes of SCP elimination are examined.
Previous experience in the abandonment of wells with SCP using existing procedures and methodologies for cement and bridge plug placement, on the Karachaganak field, has not always been successful. In some instances sustained casing pressure reappeared, resulting inadvertently in re-entry for intervention.
In 2015 several SCP wells were successfully abandoned using a combination of technologies. The processes will be described in detail in this paper, including:
Image log to enable selection of the interval for section milling Section milling - removal of a section of casing Under reaming to remove remaining cement sheath from the wall of the outer casing Inflatable Bridge Plug - mechanical barrier for placement in the opened window interval.
Image log to enable selection of the interval for section milling
Section milling - removal of a section of casing
Under reaming to remove remaining cement sheath from the wall of the outer casing
Inflatable Bridge Plug - mechanical barrier for placement in the opened window interval.
Karachaganak is a giant gas-oil condensate field with presence of H2S and CO2. Due to that, during well abandonment SCP issue must be eliminated to comply with Republic of Kazakhstan regulation and oil industry standards. SCP, regardless of its value can pose hazards not only to the environment but also be a source of formation of man-made deposits. To ensure industrial safety, environmental expediency and to meet regulatory requirements, the wells with SCP require regular monitoring.
The above mentioned technologies and processes were successfully implemented in wells abandonment and elimination of SCP on wells in the Karachaganak field. All wells were monitored throughout the year, considering the huge variance in the severe ambient weather conditions throughout, and it was proved that no issues with SCP have reoccurred so far.
This paper provides well construction and integrity teams’ information on a solution that could be used in many other wells around the world. The benefits achieved by the Kazakhstan operator open up opportunities to solve SCP problems and prevent future intervention.
Plug and Abandonment, P&A, operation is inevitable for each and every well. Most oil and gas wells are plugged at lowest cost possible complying with requirements set by regulatory agencies. Geopolymers can be used as an alternative material for P&A operations. Unlike many other alternatives such as resin, they are cost efficient and easy to pump down the wellbore. They can be mixed easily onsite and activated by addition of an alkali activator. The research presented in this paper shows they can have a good pumpability, low shrinkage, and high compressive and shear bond strength.
The Geopolymer mixtures in this work were composed of Class F Fly Ash rich in Silicate and Aluminum, with elements of Potassium, Calcium, Iron, Sodium, and Titanium. A mixture of Sodium Hydroxide and Sodium Silicate was used to activate the Fly Ash mixtures. Geopolymer mixture designs tested in this work showed high compressive strength, low shrinkage, and suitable thickening time for applications in well abandonment. In addition, these alternative P&A materials can be produced cheaper with less environmental impact, which is a proper fit in the applications oil and gas well cementing.
In deepwater Gulf of Mexico, cement placement through coiled tubing (CT) has been proven over several decades to be a valuable, versatile, and cost-effective tool for the through-tubing plug and abandonment of depleted oil and gas producers. In this paper, several present-day recommendations and best practices in relation to CT cementing for well abandonment are described.
CT cementing is typically used for well abandonment when leaving part of the production tubing in place is deemed beneficial from an economic or operational risk standpoint. As demand for the reliable placement of permanent cement barriers during well abandonment continues to grow, the importance of optimal design methodology, laboratory practices, and placement techniques associated with CT cementing has also increased. For instance, one of the most important aspects is to design a thin yet stable cement slurry. In addition, thickening time tests must account for the time a slurry is in the CT reel at surface before travelling downhole. Fluid placement techniques should account for the use of any downhole tools and be adjusted accordingly.
In recent well abandonments, a high success rate in the placement of cement plugs through CT has been observed. The main contributor to this success is the consistent manner in which the best practices described in this paper were followed. These methodologies also include some that have slowly evolved over time. For example, during well abandonment, one procedure that appears to be gaining popularity in some situations is the running of inflatable cement retainers with the ball on seat. In regards to CT cementing, this has often resulted in modified strategies, with fluid placement techniques counteracting the inability to pump any fluids through the CT prior to setting the retainer.
This paper is based on several recent abandonment campaigns using an intervention vessel in the Gulf of Mexico in 2016. Throughout the course of these particular campaigns, a total of 32 cement plugs were placed through CT, all of which were successfully verified, thus avoiding costly remedial placement. Although different conditions and well-specific challenges can slightly alter the approach taken, there are several steadfast techniques that appear to be effective in the consistent delivery of desired results.
Extensive set of experimental setups have been designed and build to evaluate the sealing performance of systems for zonal isolation and well abandonment. The fully automated test procedure enables the comparison of systems under identical conditions (P, T). Additionally a novel setup has been built to concurrently measure the internal and external volumetric change during the hydration reaction of cement systems at well conditions.
This paper describes the workflow, concepts, and techniques that operators should consider during abandonment planning to help ensure effective isolation for fields in which thermal recovery is executed.
In the Chichimene field of the Llanos basin of Colombia, several wells were drilled that now require permanent abandonment. However, previous abandonment projects performed in other fields were challenging because several interventions were required to ensure isolation, which increased operational expenses. Additionally, the operator implemented new techniques to improve oil recovery in the Chichimene field, which presents additional challenges for isolating intervals of abandoned wells because of thermal cycles with high temperatures that can exceed 500°F. Sour gasses are also encountered in this field.
These challenges require nontraditional techniques for successful isolation of the intervals as well as an enhanced methodology for decision making, such as an assessment of the current downhole conditions using ultrasonic logs to evaluate casing corrosion and cement sheath integrity. This allows evaluation of the well before and after abandonment and includes measurement of the sour and explosive gases at surface to validate the barrier, design of fit-for-purpose cement slurries to withstand downhole conditions, and use of displacement fluids to help minimize casing damage. This holistic cost-effective abandonment method has been performed in seven wells in the area with excellent results, indicating that the approach can be a beneficial option for other fields with similar conditions and requirements. Additionally, oil and gas operators can use this methodology as an alternative to help improve results for well abandonment. Zero nonproductive time (NPT) or health, safety, and environmental (HSE) incidents were recorded during these projects.
This paper also discusses the importance of safety and environmental risks associated with abandoning an asset, which can be mitigated through engineering for optimal zonal isolation in unconventional fields.