Barrier Failures Research Articles

Optimizing Well Integrity with Accurate Forecasting of Casing and Tubing Resistance Reduction Trends Through Innovative Numerical Modeling Techniques

Summary Well integrity is an essential aspect of well operations, and international standards are stringent on its application. Tubing and casing corrosion constitutes a major risk to well integrity and a challenge that must be analyzed preventively. Corrosion logs are programmed to verify the status of the barriers, but there is currently no methodology for planning future logs. In this paper, we propose a numerical modeling method to forecast tubular resistance reduction trends and estimate the barrier’s residual life. Corrosion logs are expensive and require the well to be shut in, which impacts the cost of the operation. Therefore, a numerical methodology for planning future logging is preferable to planning based on experience. Here we propose a methodology for predicting the point at which the downhole barriers will no longer satisfy the maximum allowable annular surface pressure (MAASP) criteria, using data from historical corrosion logs and a time-linear corrosion model. This innovative methodology recalculates MAASP for collapse and burst resistance of corroded pipes while considering well completion design and vertical depths resulting from the directional survey. The proposed methodology provides a comprehensive assessment of the corrosion progress, making it a more reliable tool for forecasting future corrosion trends. The methodology uses the last two corrosion logs for optimal prediction, but it also works when a single corrosion log is available. Numerical modeling is then used to calculate pipe resistance at each depth step of the LAS file, drawing a picture of the resistance vs. depth and time. The result of this new method is a chart that forecasts the progressive reduction of A-Annulus MAASP and the time at which it will cross the minimum criteria of the operator. Furthermore, the proposed methodology provides a probability window that takes into consideration the best- and worst-case scenarios. This is the first time that numerical modeling is used to recalculate MAASP and to forecast MAASP reduction trends in well barriers, based on corrosion/erosion measurements. The corrosion logging schedule can, hence, be programmed before MAASP reaches the operator’s limit, thus optimizing planning and costs for the operator. This, in turn, leads to a reduction in costs without affecting the overall operability and risking barrier failures.

Causes of Safety Barrier Failures at Oil and Gas Facilities in Nigeria: A Technical Approach

This study investigates the company-controlled causes of barrier failure in Niger Delta region of Nigeria. Also, it focuses on oil and gas facilities and their operations involving hydrocarbon handling. Safety Barriers in the oil and gas industry are crucial safety systems designed to prevent hazards and mitigate the consequences of incidents. These barriers, encompassing technical, operational, and organizational elements, play a significant role in handling hazardous substances and preventing their unintended release. Despite their importance, barrier failures have been identified as major causes of process safety incidents globally, including Niger Delta region of Nigeria. A cross-sectional research design, using a questionnaire to collect primary data from 132 personnel across 12 facilities, was employed. Statistical data analyses were carried out using XLSTAT Version 2016. Findings indicate that process upsets and technical/physical failures are significant risk influencing factors, while human and operational errors, though present, are less impactful. Key technical failures include degradation of valve sealing and flange gaskets, while process upsets often result from overpressure and malfunctioning transmitters. The study highlights the need for improved risk reduction strategies and periodic training to enhance safety practices in the Niger Delta's oil and gas industry. Recommendations include increasing technical components of risk strategies and ensuring regular maintenance and compliance with safety regulations; that is, proactive maintenance strategies to mitigate the identified risks.

Invasive fungal infections in liver diseases.

Patients with liver diseases, including decompensated cirrhosis, alcohol-associated hepatitis, and liver transplant recipients are at increased risk of acquiring invasive fungal infections (IFIs). These infections carry high morbidity and mortality. Multiple factors, including host immune dysfunction, barrier failures, malnutrition, and microbiome alterations, increase the risk of developing IFI. Candida remains the most common fungal pathogen causing IFI. However, other pathogens, including Aspergillus, Cryptococcus, Pneumocystis, and endemic mycoses, are being increasingly recognized. The diagnosis of IFIs can be ascertained by the direct observation or isolation of the pathogen (culture, histopathology, and cytopathology) or by detecting antigens, antibodies, or nucleic acid. Here, we provide an update on the epidemiology, pathogenesis, diagnosis, and management of IFI in patients with liver disease and liver transplantation.

Proactive Process Safety Management - Key to the Prevention of Incidents in Industry

Proactive process safety that works requires a thorough approach that takes into account every area of safety. It entails regular review and monitoring of safety performance in order to pinpoint problem areas and guarantee continued safety improvements. Failure to take proactive measures may result in catastrophic events, such as fires, explosions, or chemical discharges, which could have detrimental effects on nearby communities, the environment, and the workforce. Process effectiveness is continuously ensured through proactive safety, which involves processes, procedures, and people. The purpose of this study was to review proactive process safety management as the key to the prevention of catastrophic incidents in industry. The method adopted for this study was the use of selected process safety incidents to illustrate latent conditions and active failures using the Swiss cheese model and to identify the barrier failures that will lead to catastrophic incidents in industry. A large disaster caused by the effects of catastrophic discharges of hazardous, reactive, flammable, or explosive substances can be prevented to a great extent by implementing proactive systems to monitor process safety.

Characterization of the Internal Stress Evolution of an EB-PVD Thermal Barrier Coating during a Long-Term Thermal Cycling

Electron beam physical vapour deposition (EB-PVD) technology is a standard industrial method for the preparation of a thermal barrier coating (TBC) deposition on aeroengines. The internal stress of EB-PVD TBCs, including stress inside the top coating (TC) and thermal oxidation stress during long-term service is one of the key reasons for thermal barrier failures. However, research on the synergistic characterization of the internal stress of EB-PVD TBCs is still lacking. In this work, the stress inside the TC layer and the thermal oxidation stress of EB-PVD TBC during long-term thermal cycles were synergistically detected, combining Cr3+-PLPS and THz-TDS technologies. Based on a self-built THz-TDS system, stress-THz coefficients c1 and c2 of the EB-PVD TBC, which are the core parameters for stress characterization, were calibrated for the first time. According to experimental results, the evolution law of the internal stress of the TC layer was similar to that of the TGO stress, which were interrelated and influenced by each other. In addition, the internal stress of the TC layer was less than that of the TGO stress due to the columnar crystal microstructure of EB-PVD TBCs.

Machine-Learning Model Improves Gas Lift Performance and Well Integrity

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 205134, “Machine-Learning Application for Gas Lift Performance and Well Integrity,” by Mostafa Sa’eed Yakoot, SPE, Gulf of Suez Petroleum; Adel M.S. Ragab, SPE, Suez University; and Omar Mahmoud, SPE, Future University in Egypt. The paper has not been peer reviewed. _ The main objective of this work is to use machine-learning (ML) algorithms to develop a powerful model to predict well-integrity (WI) risk categories of gas-lifted wells. The model described in the complete paper can predict well-risk level and provide a unique method to convert associated failure risk of each element in the well envelope into tangible values. ML Model The model can be subdivided into four submodels as follows: - The predictive model, which predicts the risk status of wells and classifies their integrity level into five categories rather than three broad-range categories, as in qualitative risk classification. The five categories are -- Category 1, which is too risky -- Category 2, which is still too risky but less so than Category 1 -- Category 3, which is medium risk but can be elevated if additional barrier failures occur -- Category 4, which is low risk but features some impaired barriers -- Category 5, which is the lowest in risk - The failure model, which identifies whether the well is considered to be in failure mode. In addition, the model can identify wells that require prompt mitigation. - The suboptimal model, which identifies wells operating out of the integrity envelope. - The diagnosis model, which locates the root of cause of WI impairment and introduces an action plan. This classification was performed using ML algorithms such as logistic regression, decision trees, random forest, Gaussian, K-nearest neighbor, and support-vector machine classifiers.

Safety barrier performance assessment by integrating computational fluid dynamics and evacuation modeling for toxic gas leakage scenarios

Toxic gas leakage represents a type of major process accident scenario threatening human life. Technical and non-technical safety barriers are employed to prevent toxic gas leakage accidents or mitigate the possible catastrophic consequences. Evacuation must be executed in severe toxic gas release scenarios. The performance assessment of technical safety barriers and evacuations in these accident scenarios, although very important, has never been investigated in previous studies. This paper proposes an approach integrating event tree analysis (ETA), computational fluid dynamics (CFD) simulation, and evacuation modeling (EM), for risk assessment of toxic gas leakage accidents in chemical plants. In the proposed approach, the spatiotemporal distribution of toxic gas is predicted by CFD simulations. A dynamic evacuation is determined by a cellular automaton (CA)-based model. Synergistic interventions resulting from technical safety barriers and evacuations are considered in the risk assessment. Considering safety barrier failures in the event tree analysis, individual fatality risks due to toxic gas leakage scenarios are calculated. For illustrative purposes, the proposed method is applied to a case of ammonia leakage. The results show that worse scenarios would be ignored without considering the failure probabilities of technical safety barriers, which can cause underestimated individual fatality risks. Timely gas detection & alarm has the potential to expedite the starting time of evacuations and thus may shorten the time that evacuees stay in the toxicity area to reduce individual fatality risks.

Considering aquatic connectivity trade-offs in Great Lakes barrier removal decisions

Globally, construction of dams has led to challenges for fishery managers and decision makers. Hundreds of thousands of dams, many of which no longer serve their intended purpose, are in need of repair. Resources to make those repairs are limited, and dam removal often seems like the most logical solution from an economic perspective. However, dams on the Laurentian Great Lakes tributaries often serve more than one purpose, with nearly 500 considered important to the continued success of controlling sea lamprey (Petromyzon marinus), blocking other invasive species, isolating native from non-native salmonids, stopping disease transfer, and holding back contaminated sediments. Removing dams can have unintended consequences at the local, regional, or basin-wide scale. Here, we explain the importance of considering potential fishery management trade-offs of barrier removals at those scales. We also suggest an organizational framework that, when supported by modeling, could improve communication and cooperation among partners, streamline the decision process, and provide a consensus-driven perspective about the highest priority projects to address. Consistent communication among and between management agencies, indigenous peoples, and local governments, along with an objective and proactive approach to barrier removal decisions could allow for greater success in habitat restoration and funding procurement while reducing the risk of barrier failures and the unintended spread of injurious invasive species, environmental contaminants, and fish disease.

Experimental study on the integrity of casing-cement sheath in shale gas wells under pressure and temperature cycle loading

During large-scale multistage hydraulic fracturing in shale-gas wells, the cement sheath loses its integrity easily because of repeated temperature and pressure variations in the wellbore. This is likely to form a potential leak path, subsequently leading to the loss of zonal isolation and sustained casing pressure. To prevent such barrier failures, it is crucial to investigate and understand the failure mechanism of cement sheath. In this study, an experimental apparatus and evaluation method of the sealing integrity and mechanical integrity for casing-cement sheath under temperatures and pressures cycle loading have been presented in this paper by which sixteen groups of full-scale integrity tests of general and high-strength cement sheath have been conducted under temperature ranging from 30 to 150 °C and pressure ranging from 0 to 70 MPa cycling loading. The anti-channeling/sealing performance and interface mechanical behavior of casing-cement sheath are measured and characterized respectively under different loading-unloading methods. The cycle numbers required for sealing integrity failure of cement sheath under different cyclic temperatures and pressures have been obtained. The interface mechanical properties (cementing force, friction force, shearing strength and lateral bonding strength) of cement sheath have been obtained, and effects of alternating temperatures and pressures on those mechanical properties and late integrity have been analyzed. Research results can provide a very important reference for the fracturing design of shale-gas wells.

Digital Cement Integrity: A Methodology for 3D Visualization of Cracks and Microannuli in Well Cement

Leakages of greenhouse gases, such as methane and carbon dioxide from wells, may have considerable environmental consequences. Although much emphasis is currently put on understanding well barrier failures, and thus, preventing well leakages, especially for an important barrier material as cement, there are still several knowledge gaps and unknowns. However, a step-change in well integrity understanding may be obtained by applying advanced characterization techniques and scientific approaches to studying well barrier materials and their failure mechanisms. This paper describes the development of an experimental methodology that uses X-ray computed tomography to obtain 3D visualizations of cracks and microannuli in annular cement sheaths. Several results are included that demonstrate the value of using such digital methods to study well cement, and it is shown that such experimental studies provide an improved understanding of cement sheath integrity. For example, it is seen that radial cracks do not form in symmetrical patterns and that microannuli do not have uniform geometries. Such experimental findings can potentially be used as benchmark to validate and improve cement integrity simulation tools.

Opportunities to enhance barrier management through incident analysis

Many high hazard industries use bowties to analyze and assess risks. In the bowtie risk analysis model, barriers are identified which aim to prevent, control or mitigate unwanted scenarios.However, despite best effort risks assessments, incidents and near misses may still occur. When they do, organizations typically conduct investigations to come up with recommendations to avoid similar situations in the future. Unfortunately, in many cases these investigation reports end up as a collection of largely unstructured documents. They are often treated as single events, making it difficult to clearly identify trends over multiple events.Scenario-based Incident Registration (SIR) aims to provide a more structured process. A user selects a specific scenario from a set of bowties and assesses the effectiveness of the barriers identified on the original bowtie. Specific questions are asked per barrier about the reasons of the failure. These findings are stored on a barrier level. If this process is repeated, the bowtie will accumulate barrier failure data of multiple incidents in a single diagram. This information helps the organization to identify the strength of their barriers, which in turn facilitates risk-based decision-making.Some incidents require in-depth investigations and a registration only is not enough. However, this registration can be used as a starting point for the incident analysis. Doing barrier-based incident analysis allows you to learn from barrier failures and improve their performances in order to prevent similar incidents from happening. This incident data together with the SIR data can be linked back to the bowtie diagram in order to spot the strengths and weaknesses of your visual risk assessment.SIR is a continuous process which is more than a reporting system. The reporter does not require knowledge about the bowtie methodology, while incident managers receive valuable insight to their pro-active risk assessment.

UAE Case Study Highlights Challenges of a Mature Gas-Condensate Field

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 188422, “Well-Integrity Management: Challenges in Extending Life of a Mature Gas-Condensate Field—A Case Study,” by S. Jain, M.A. Al Hamadi, H. Saradva, SPE, and J. Asarpota, Sharjah National Oil Company, and S.J. Sparke, SPE, M. Volkov, and H. Abu Rahmoun, TGT Oilfield Services, prepared for the 2017 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 13–16 November. The paper has not been peer reviewed. Three onshore fields in the Emirate of Sharjah, United Arab Emirates, have more than 30 years of production history from more than 50 gas-condensate wells. While existing resources could be recovered by drilling additional wells, the most economical solution would be to confirm that existing well stock has sufficient well integrity to allow the continued use of these wells safely. Introduction The Sajaa asset consists of three retrograde condensate onshore fields. All wells are naturally flowing, with support from wellhead compression to reduce the effect of liquid loading on these mature gas producers. The reservoir was blown down to produce gas associated with rich condensate, water, and liquefied petroleum gas. With the reservoir’s long production history, its pressure has been greatly reduced. Through use of a highly simplified upstream production technique, the wells continue to produce condensate-rich gas with the low-pressure regime. But, because of the reservoir-pressure decline, the production rate remains reduced. Therefore, surface gas compression is required to reduce backpressure and pump the gas to a nearby production facility for separation and, ultimately, custody transfer and sale. Mature Well Status The asset wells were completed with 5-in. tubing along with a nominal 7-, 9-, and 13-in. completion scheme. For production-optimization purposes, 10% of the wells produce directly up the production casing, while all the wells are completed packerless. The main purpose of the open annulus completion was to avoid the extensive problems and costs encountered previously with packer completions in the hostile environment and allow for chemical corrosion inhibition along the conduit of the A annulus (Fig. 1). The cement behind the casing is generally accepted as accomplishing vertical isolation, though not radial isolation, with the natural pore pressure being applied laterally through the cement as a worst case. Collapse is considered to be more critical as a parameter than burst during production, even more so in mature reservoirs with cemented barriers that support against burst conditions. Actual well-integrity failures in a well stock do not always imply a situation in which uncontrolled flow of fluids reaches the surface. Individual barrier failures in a specific well group depend on a variety of factors, such as geographical area, operator, drilling era, well type, and maintenance quality. Gas is expected to be the primary fluid lost when a multibarrier failure occurs. The Sajaa asset features comprehensive active and passive barrier systems. Cemented-to-surface annuli and heavy-duty wellheads account for the passive barriers; continuous remote monitoring of the annuli and weekly visits to the well location are effective active barriers.

Sound Barriers Management in Process Safety: Bow-tie Approach According to the First Official AIChE - CCPS Guidelines

Safety barrier-based management systems are widely adopted because of the advantages coming from the barrier approach. Different methods are available to implement it and the Bow-tie is one of the most recognized methodology. The Bow-tie method allows the risk analyst to have, in a single shot, the complex picture about the relations linking threats, preventive barriers, top events, mitigative barriers, consequences, and escalation factors. From this perspective, without a proper reference, there are significant possibilities to misuse the method and create confusion about the right role of each component of a Bow-tie diagram. This work intends to support the approach of the guidelines developed by the Center for Chemical Process Safety (CCPS) of the American Institute of Chemical Engineers (AIChE), to drive the analyst in the proper usage of the method, avoiding to misinterpret key elements like the human errors or the barrier failures, and helping in a congruent definition of the elements, thus resulting in a high-quality risk analysis and in a sound barriers management.

Accident types and barrier failures in the construction industry

The paper identifies frequent accident types in the construction industry, characterises the accident sequence, and identifies barrier failures for the most frequent accident types. 176 accidents in the Norwegian construction industry investigated by the Norwegian Labour Inspection Authority in 2015 are analysed. The most frequent accident types include: fall from roof, floor or platform; contact with falling objects; fall from scaffold; and contact with moving parts of a machine. A comparison of the study sample to other injury samples, showed that the distribution of accident types varied regarding severity and different construction types. This can be explained by differences in work type, hazard, and energy type and energy amount. An analysis of barrier failures showed that many accidents are explained by the lack of physical barrier elements. The results indicate that there is significant potential for accident prevention in the construction industry by systematic barrier management.

Probabilistic analysis of risk and mitigation of deepwater well blowouts and oil spills

The development of robust risk assessment procedures for offshore oil and gas operations is a major element for the assessment of the potential feedback between planned activities and the environment. We illustrate a methodological and computational framework conducive to (1) a quantitative risk analysis of deepwater well barrier failures and subsequent hydrocarbon release to the environment and (2) the analysis of the value of the deployment of conventional and/or innovative mitigation measures. Our methodological framework is grounded on historical records and combines the use of Dynamic Event Trees and Decision Trees from which we estimate probability of occurrence and impact of post-blowout events. Each sequence of response actions, which are undertaken immediately after the event or in the subsequent days, is considered within the context of appropriately structured event paths. This approach is conducive to an estimate of the expected value of key decisions and underlying technologies, with an emphasis on their potential to reduce the oil spill volume, which can critically impact the environment. Our study yields an original comparative analysis of diverse intervention strategies, and forms a basis to guiding future efforts towards the development and deployment of technologies and operating procedures yielding maximum benefit in terms of safety of operations and environmental protection.

Improving safety of DP operations: learning from accidents and incidents during offshore loading operations

The risk caused by DP vessels in offshore marine operations is not negligible, due to wide applications of DP vessels in complex marine operations, and the sharp increase of DP vessel population. The DP accidents/incidents on the Norwegian Continental Shelf (NCS) that have occurred after 2000 indicate a need for improving safety of DP operations, which calls for new risk reduction measures. The focus of this paper is particularly on the offshore loading operations with DP shuttle tanker in offloading from floating production storage and offloading (FPSO) vessels on the NCS, but the results may be relevant also for other types of DP vessels in offshore oil and gas operations. In the paper, Man, Technology and Organization (MTO) analysis is applied to investigate the cause and barrier failures of nine reported accidents/incidents occurring over a 16-year period (2000–2015). MTO is based on three methods, including structured analysis by use of an event- and cause-diagram, change analysis by describing how events have deviated from earlier events or common practice, and barrier analysis by identifying technological and administrative barriers which have failed or are missing. The results are categorized into technical failures, human failures, organizational failures, as well as a combination of failures. The main finding is that the majority of the accidents are caused by the combination of technical, human and organizational failures. Critical root causes, results of change analysis and barrier analysis, and combination of failures are focused in the discussion. Recommendations of potential safety improvements are made on the aspects of the assessment of the actual system function, barrier management for marine systems, risk information to support different decision-makings, and the development of an on-line risk monitoring and decision supporting system.

Risk Assessment of Fluid Migration Into Freshwater Aquifers in Colorado Basins

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 181680, “A Continued Assessment of the Risk of Migration of Hydrocarbons or Fracturing Fluids Into Freshwater Aquifers in the Piceance, Raton, and San Juan Basins of Colorado,” by C.H. Stone, SPE, A.W. Eustes, SPE, and W.W. Fleckenstein, SPE, Colorado School of Mines, prepared for the 2016 SPE Annual Technical Conference and Exhibition, Dubai, 26–28 September. The paper has not been peer reviewed. Wellbore-construction methods, especially casing-and-cementing practices for the protection of freshwater aquifers, have been reviewed in the Piceance, Raton, and San Juan Basins in Colorado. The assessment confirms that natural-gas migration occurs infrequently but can happen from poorly constructed wellbores. Analysis confirmed no occurrence of hydraulic-fracturing-fluid contamination. The significance of these results is to help quantify the risks associated with natural-gas development as related to the contamination of surface aquifers. Introduction The prevention of contamination of freshwater aquifers has been a prime concern in drilling operations since the inception of drilling. Surface casing has long been the primary barrier to prevent contamination of freshwater aquifers through wellbores. The probability of leakage into aquifers from wellbores during shale development has a wide range of estimates, complicated by the presence of hydrocarbons at shallow depths in many parts of the world. An earlier paper reviewed the process and outcomes of a study for the Wattenberg Field in the Denver-Julesberg Basin. This study continues the examination of the contamination of aquifers in the subsurface during the completion and the production phases of the well and quantifies the risk of contamination of aquifers through failure of the wellbore for three other major basins in Colorado, the Piceance, Raton, and San Juan Basins. This synopsis focuses on the assessment of the Piceance Basin. Barrier Definition. Common vertical, deviated, and horizontal subsurface wellbore-barrier designs were grouped and ranked on the basis of the risk of multiple barrier failures (Fig. 1). For the sake of clarity, pressure monitoring of the casing annulus [surface annulus pressure (SAP)] was not assumed to be an additional barrier during the production phase even though it is frequent and often required by state regulations. Well-barrier designs can vary from field to field depending on geology, trajectory, depths, anticipated pressures, expected hydraulic-treatment rates, and estimated production rates. Whether a well is horizontal, vertical, or deviated has no significance with respect to the ultimate protection of freshwater aquifers because the wells are designed to protect the shallow vertical section of each oil and gas well. Multiple barriers must be in place near the depth of the freshwater aquifer to prevent breaching of a single barrier potentially leading to contamination.

Concepts for dynamic barrier management

Safety barrier management is an important activity to maintain or reduce process safety risk of an operating facility. Barriers can be hardware, human or organizational, or some combination of these. Barriers are normally fully functional after installation or commissioning when all equipment has been tested and all staff trained, and the facility risk will be at or better than target level, as the design risk assessment this will have assumed some barrier failure probability. However, barriers degrade at different rates, and these degradations start to increase facility risk. Some barrier failures can increase risk dramatically, especially where barrier dependencies exists. Conventional barrier management applies fixed inspection and maintenance intervals to these with the intent to return these to full functionality and the risk to target, but take no account of dependencies.Dynamic barrier management uses the full suite of information available, including direct and indirect indicators of barrier performance to infer barrier status in near real-time. This can be through a smart combination of inspection, preventive maintenance, audit, sensors, process control, and near-miss or incident records, and big data concepts. Barrier maintenance can then be planned optimally based on quantitative barrier importance to risk control, in a manner similar to risk based inspection (RBI). Higher Importance barriers (i.e. risk affecting) would be assigned higher priority than other barriers. This can achieve better safety at lower cost than current barrier management processes.This paper presents the concepts for dynamic barrier management. All the details have been developed and this completes the design phase activity. A practical application will be next to prove these ideas.

Completion difficulties of HTHP and high-flowrate sour gas wells in the Longwangmiao Fm gas reservoir, Sichuan Basin, and corresponding countermeasures

For safe and efficient development of the sour gas reservoirs of the Cambrian Longwangmiao Fm in the Anyue Gas Field, the Sichuan Basin, and reduction of safety barrier failures and annulus abnormal pressure which are caused by erosion, corrosion, thread leakage and improper well completion operations, a series of studies and field tests were mainly carried out, including optimization of well completion modes, experimental evaluation and optimization of string materials, sealing performance evaluation of string threads, structural optimization design of downhole pipe strings and erosion resistance evaluation of pipe strings, after the technical difficulties related with the well completion in this reservoir were analyzed. And consequently, a set of complete well completion technologies suitable for HTHP (high temperature and high pressure) and high-flowrate gas wells with acidic media was developed as follows. First, optimize well completion modes, pipe string materials and thread types. Second, prepare optimized string structures for different production allocation conditions. And third, formulate well completion process and quality control measures for vertical and inclined wells. Field application results show that the erosion of high-flowrate production on pipe strings and downhole tools and the effect of perforation on the sealing performance of production packers were reduced effectively, well completion quality was improved, and annulus abnormal pressure during the late production was reduced. This research provides a reference for the development of similar gasfields.

Environmental Risk Arising From Well-Construction Failure—Differences Between Barrier and Well Failure, and Estimates of Failure Frequency Across Common Well Types, Locations, and Well Age

Summary Do oil and gas wells leak to the environment? This paper will show the great majority of wells do not pollute. The purpose of this paper is to explain basic concepts of well construction and illustrate differences between single-barrier failure in multiple-barrier well design and outright well-integrity failure that could lead to pollution by use of published investigations and reviews from data sets of more than 600,000 wells worldwide. For US wells, while individual-barrier failures (containment maintained and no pollution indicated) in a specific well group may range from very low to several percent (depending on geographical area, operator, era, well type, and maintenance quality), actual well-integrity failures are very rare. Well-integrity failure occurs when all barriers fail and a leak is possible. True well-integrity-failure rates are two to three orders of magnitude lower than single-barrier-failure rates. When one of these rare total-well-integrity failures occurs, gas is the most common fluid lost. Common final-barrier leak points are failed gaskets or valves at the surface and are easily and quickly repaired. If the failure is in the subsurface, an outward leak is uncommon because of a lower pressure gradient in the well than in outside formations. Subsurface leaks in oil and gas wells are rare, and routinely comprise exterior-formation salt water leaking into the well toward the lower pressure in the well. Failure frequencies are estimated for wells in several specific sets of environmental conditions (i.e., location, geologic strata, produced-fluid composition, and soils). Estimate accuracy depends on a sufficient database of wells with documented failures, divided into (1) barrier failures in a multiple-barrier system that did not create pollution, and (2) well-integrity failures that created a leak path, whether or not pollution was created. Estimated failure-frequency comparisons are valid only for a specific set of wells operating under the same conditions with similar design and construction quality. Well age and construction era are important variables. There is absolutely no universal definition for well-failure frequency.