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Compaction-induced casing damage, particularly adjacent to reservoir boundaries, has been observed in many fields. As part of mitigation planning for potential casing collapse due to reservoir compaction, expensive numerical models are often employed to quantitatively assess casing strain under simulated reservoir conditions. In order to simplify casing deformation analysis and reduce analysis time, the current study was initiated to quantify the effects of depletion magnitude, rock compressibility, borehole orientation, casing diameter-to-thickness ratio (D/t ratio) and grade on compaction-induced casing deformation using finite element modelling (FEM). The model results allowed an empirical equation to be derived to predict casing strain that is sufficiently accurate for engineering applications.
The objective of the study was achieved by building a series of 3D FEM models to systematically simulate the deformation of casings cemented perfectly within a horizontal reservoir that underwent up to 8.3% compaction due to depletion. To capture the pattern of casing strain variation adjacent to the reservoir boundaries, the simulations were run over a range of borehole deviations (0°, 22.5°, 50°,67.5° and 90°). For each borehole deviation, casing D/t ratios of 8.14, 19.17 and 32.67 and grades of 40 ksi, 90 ksi and 135 ksi were defined to evaluate their impact on casing strain variations.
The FEM models show that casing deformation adjacent to reservoir boundaries is accommodated by radial expansion and axial shortening in vertical wellbores, while the deformation is characterized by bending in deviated wellbores. The maximum strain adjacent to reservoir boundaries varies systematically, but nonlinearly with each variable evaluated. The maximum strain increases with reservoir compaction strain, i.e. increases with rock compressibility and depletion, but decreases with increasing hole deviation. Both casing D/t ratio and grade affect casing strain, but their effects are secondary. In general, the maximum strain is greater for casings with smaller D/t ratios and higher grades at any given borehole deviation and compaction strain. The variation of the maximum casing strain with compaction strain can be described by a power law. Both its constant and exponent are functions of borehole deviation, casing D/t ratio and grade.
Because of the complexity of borehole-reservoir geometry and casing plastic behavior, there is no analytical solution available to estimate compaction-induced casing strain adjacent to reservoir boundaries. Numerical models may be used to predict the casing strain, but the numerical analysis is time consuming and requires specialist knowledge. The equation proposed from this study is sufficiently accurate compared to numerical models in terms of casing strain prediction, but provides a much simpler and quicker analysis. In addition, the study provides insight on the variation of casing strain with the major controlling factors, leading to a more complete understanding of compaction-induced casing deformation.
A method and apparatus to test the annular seal of a casing string placed in a wellbore is presented. This method and apparatus, called the Annular Casing Seal Test (ACST), successfully measures the annular casing seal in the wellbore using a positive pressure test. Results presented document the experimental studies using prototypes under a variety of cemented casing conditions to determine the ability to detect effective and poorly cemented casing annular seals. When the interior of the tool is drilled out, an array of encapsulated bores is exposed, allowing pressure and flow communication between the interior and the annulus of the casing. Prototypes tested in experimental wellbores confirm the ability of the technology to detect casing annular conditions. A well-cemented casing annulus is easily detected, since the test pressure only encounters the annular cemented across the full circumference of casing. A poorly cemented annulus is similarly detected because pressure escapes the ports into the void in the cemented annulus. An important application of this method allows the annular seal at the surface casing shoe to be inexpensively and quickly tested, providing positive confirmation of the protection of the aquifer. This test is an improvement over the casing shoe test, which is in reality, a measure of formation strength and has demonstrated short comings in detecting poor cement jobs near the casing shoe in a variety of applications. This method is also an improvement over cement bond logs (CBLs), which are more expensive, time consuming, and do not provide a positive test of hydraulic isolation.
Dooply, Mohammed (Schlumberger) | Sianipar, Sakti (Schlumberger) | Rodriguez, Faiber (Schlumberger) | Poole, David (Chevron) | Fuenmayor, Cesar (Chevron) | Carrasquilla, Juan (Schlumberger) | Rosero, Ivan (Schlumberger)
Achieving successful cement placement in tieback casings and liners on deepwater wells is very critical. One of the design challenges is to displace compressible drilling fluid in the tight annulus within the mechanical limitations of downhole tubulars. Accounting for the compressible nature of drilling fluids with changing pressure and temperature, combined with fluid contamination level, will provide better understanding of cementing dynamic pressure during placement.
Cementing tight annulus normally requires managing high placement pressures within the tubulars mechanical limits. Field measurements from case studies in Gulf of Mexico, were analyzed comparing with simulated cementing dynamic pressure accounting for effect of synthetic based mud compressibility as it is displaced by viscous spacer and cement slurry. The rheology of contaminated mixture also provided an input for better interpretation of cementing surface pressure response. These analyses, including estimating hook load variations while cementing, allow selection of appropriate fluid placement rate without exceeding the mechanical limits while also achieving effective fluid displacement.
Comparison analysis of measured and simulated data shows that use of complete fluid rheology profile at various temperature and pressure provides a more accurate prediction of cementing dynamic pressure in tight annulus cementing with synthetic based mud. This approach also allows a better estimation of the minimum rate required for efficient mud displacement enabling an optimal design of the cement slurry thickening time, when coupled with a representative mud circulation schedule.
Precise annular clearance of tieback strings provides better understanding of fluid positions inside the tieback strings and annulus, which ensures achieving planned top of cement to mitigate annular pressure buildup. This is critical to protect the outer casing against any potential collapse loading in a blowout scenario in deepwater drilling environment.
Lost circulation while running casing, pre-cement job mud circulation, and cement placement can result in additional remediation, create challenges in achieving zonal isolation objectives, and potentially impact well integrity. Several mitigation methods are available to address lost circulation challenges. However, the focus of this article is on prevention.
Wellbore strengthening is utilized to strengthen low fracture gradient (FG) and permeable zones to a target maximum equivalent mud weight (EMW) value induced during tripping, circulating, or cementing. Engineered wellbore strengthening pills of specific particle concentration and size distribution are placed in the open hole and pressure is applied to the wellbore in a controlled fashion. As a result, a higher fracture gradient of the weak sands exposed in the entire interval is achieved, allowing permeable formations to withstand higher EMW during subsequent tripping, circulating, and cementing operations without inducing losses. This paper summarizes the field application of wellbore strengthening in deep-water Gulf of Mexico (GoM) to achieve zonal isolation. The design, execution, and post-well analysis of several wellbore strengthening applications in a variety of sands from shallow and soft overburden sands to deep producing reservoir sands with depletions greater than 4,000 psi, are discussed. A detailed case study for one of the wells is provided.
The track record of successful wellbore strengthening treatments performed demonstrates the potential for achieving adequate annular cement placement and zonal isolation in narrow pore pressure fracture gradient environments.
Doan, Angela (Baker Hughes, a GE Company) | Holley, Andrew (Baker Hughes, a GE Company) | Kellum, Matthew (Baker Hughes, a GE Company) | Dighe, Shailesh (Baker Hughes, a GE Company) | Arceneaux, Cory (Chevron Corporation) | Conrad, Ken (Chevron Corporation)
Extreme well conditions, especially higher temperatures, are becoming more commonplace. This in turn requires improvements to our wellbore fluids. This study focuses on the development of a new spacer system designed especially for those wells exhibiting extremely high temperatures.
A critical characteristic of this spacer is that the surface rheology must not be overly excessive as to maintain a pumpable fluid; however, the downhole rheology must not diminish due to thermal thinning or degradation of the gelling agent so the spacer remains stable. To ensure the spacer suitably meets these requirements, both ambient and elevated temperature rheologies are analyzed and reported. The stability of the spacer related to settling of solid particulates is examined by conducting dynamic settling tests at 300°F and above.
In this study, spacer compositions and densities were adjusted to examine effects on rheology and stability of the solids within the system at elevated temperatures. Results show that conventional spacer systems are not adequate at elevated temperatures especially above 300°F. The newly developed spacer system shows much improved results from dynamic settling tests even up to 400°F. Also, the surface rheology of the new spacer system is not significantly different from that of the conventional system.
The innovative spacer system within this paper was shown to add significant value to extreme cementing operations. In addition, by comparing the results between these two testing methods, the dynamic settling test should be considered as an alternate procedure for testing the stability of spacers under high temperature conditions.
Managers seek understanding of drilling performance, and visibility of how groups contribute to drilling results. The process described improves executive's understanding of drilling cost and performance. The principles are applicable to any drilling program (and even other, non-drilling operations), but are best suited to land drilling programs with many wells of common types.
In this method, a baseline budget is established for each type of well. As the program changes, a revised budget is created based on the wells actually drilled, plus those currently planned. The monthly revised budget measures performance against a consistent benchmark. The definition of well types, tracking of costs, adjusting for unusual situations, and calculations to apply the technique are discussed. The revised-budget process is used with traditional operational metrics to provide a complete spectrum of performance metrics for all levels of the organization.
The revised-budget method provides a clear perspective of performance, more insightful than standard "actual vs budget" comparisons. Additionally, deviations from benchmarks are quantified by performance, pricing, and scope changes. These categories correspond to organization groups that contribute to performance. The use of the revised-budget technique focuses discussion on the correct issues (performance, pricing, and scope) for each group. Historically, discussion of cost deviations often bogged in debate over which group was responsible. With this system, the contribution of each group to results is identified.
The revised-budget technique does not replace, but enhances traditional drilling metrics such as cost-per-foot, feet-per-day, flat time, non-productive time, and others. Traditional analysis methods are of most value to drilling groups in seeking specific actions to improve.
The system is the result of 10 years of evolution of measures to manage drilling more than 16,000 wells globally. The system has delivered best-in-class performance.
The novel aspect is that it is a complete system encompassing a workable benchmark, it adapts to the constant changes in the drilling program, it identifies how groups contribute to results, and it connects to traditional drilling metrics. The revised-budget technique using granular benchmarks is applicable to many types of operations and solves a chronic budget review problem.
The Barlow equation for tubular internal yield pressure is widely used in American Petroleum Institute (API) and International Organisation for Standardisation (ISO) standards, but its provenance and accuracy have never been established: indeed, until very recently, the original reference had been lost to the industry. This has led to doubt and confusion about its use. This paper presents the work done by ISO TC67 SC5 workgroup 2 to remedy this, and explains the background and technical basis for the upcoming revisions to ISO TR 10400.
It is shown that Barlow's 1836 derivation violates the 3D constitutive law, and the result is therefore incorrect as originally purposed (a thick wall hoop stress). Moreover, hoop stress is a uniaxial (1D) check: the modern approach is 2D or 3D checking, based on a material failure condition such as the Von Mises yield criterion.
However, the result also happens to represent the thin wall approximation to the VME failure pressure for plane stress (i.e., zero axial load), which gives an accurate measure of the yield pressure. Remarkably, this does not seem to have been recognised in previous work. The derivation is given, and the assumptions and limitations explained.
Present design practice is over-conservative for thick wall pipe, and potentially unconservative for thin wall. This is not the fault of the Barlow equation
The industry should therefore consider revising OCTG burst ratings and accompanying design practice to achieve a more uniform safety level over the full D/t range of casing and tubing.
Tonner, David (Diversified Well Logging) | Swanson, Aaron (Diversified Well Logging) | Hollingshead, Ron (Diversified Well Logging) | Hughes, Simon (Diversified Well Logging) | Seacrest, Stephen (PetroLegacy Energy) | McDaniel, Bret (PetroLegacy Energy) | Leeper, Jay (Solid Automation)
From the very early days of oil and gas exploration, appraisal and development drilling, samples have been collected at the rig by mud logging personnel to conduct a preliminary geological analysis of the rock being drilled. This collection typically involves a sample collection recipient, board or bucket to collect a sample of rock over the desired interval. The sample is then sieved and cleaned in the appropriate way depending on the type of drilling fluid being used. As penetration rates have increased in some instances to more than 400 ft. / hr. the sample resolution has deteriorated exponentially. From an ergonomics perspective, the highest frequency to which a person onsite can collect a sample is once every 20 minutes. At 300 ft. / hr. this translates to 100 ft. of drilled rock. A new device has been developed and deployed which automates this manual process and thus ensures faster and more accurate collection of geological samples of the drilled rock interval. Sample resolutions of 5ft rock intervals have been attained at 400 ft./ hr. This technology has provided an important technological breakthrough and enables reduction of personnel at the rig site with a subsequent reduction in cost and HSE risk, particularly in areas of H2S. It further has provided for the potential integration with Measurement while drilling personnel. For both conventional and unconventional play development, this has provided oil and gas operators with an important and cost and risk reducing modus operandi compared to conventional drilling and evaluation techniques. The tool was deployed for an operator in West Texas where both manually collected traditional mudlog samples and automatically collected samples were taken. The samples were analyzed and compared for rock content. In addition, comparisons were made between point sampling with the automated system versus samples collected over a defined interval manually. Results of these comparisons will be presented.
A new method of automated drill cuttings sample collection has been successfully deployed. The new method provides a step change improvement in accuracy and resolution for sampling the rock record during drilling.
Additional data of the rock record provides potential insights to optimize wellbore placement and provide increased geo-mechanical data to optimize completions.
Kiran, Raj (School of Petroleum and Geological Engineering, University of Oklahoma) | Salehi, Saeed (School of Petroleum and Geological Engineering, University of Oklahoma) | Jeon, Jiwon (Department of Industrial & System Engineering, University of Oklahoma) | Kang, Ziho (Department of Industrial & System Engineering, University of Oklahoma)
Lack of situational awareness in drilling operations has become an important factor in causing safety accidents or cause of non-productive time. Process safety is another critical aspect for such high risk operations and cannot be ignored. A review of testimony from offshore rigs worker suggests long working shifts and fatigue as one of the crucial issues impacting performance.
The study here presents results from experiments conducted in a Virtual Reality Drilling Simulator (VRDS) equipped with eye tracking technology. The eye tracking technology can be used to distinguish between less and more aware/alert participants which is most of the times related to fatigue or onsite distraction. The ocular activity can be used to obtain visual cues that can quantify the state of drilling operator while operating. These cues can help in generating some warning alarms to alert the driller. Therefore, the system can reduce not only accidents but can also save a tremendous amount of non-productive time by improving their efficiency. Since human eyes express the most direct reaction during less alert or distracted mental state, ocular activity data has been used as the basis for quantification of situation awareness by researchers. In recent years, eye tracking system has been developed in the form of static and dynamic devices. The camera installed in these devices capture different characteristics of the participants' ocular movement in real-time. These oculomotor data such as eye fixation count and duration and pupil size, has been implemented in several industries such as aviation and medical to assess the performance of participants in recent years.
In this paper, we use eye tracking techniques for investigation of alertness and awareness of participants while conducting different drilling operations on the simulator. Results obtained from this study indicate that the system can detect the distraction and alertness exhibited by humans. The results show the very promising application of this technology on the drilling rigs. The novelty in this work is the development of framework for implementation of real-time eye tracking technology in various drilling operations such as drilling rigs and Real Time Operation Centers (RTOCs).
Dupal, K. (Shell International Exploration and Production Inc.) | Curtiss, J. P. (Shell International Exploration and Production Inc.) | van Noort, R. H. (Shell International Exploration and Production Inc.) | Mack, C. (Shell International Exploration and Production Inc.) | Greer, S. (Stena Drilling)
Operations were being conducted with a drill ship in deepwater, harsh environment conditions offshore Nova Scotia. After securing the well, the rig disconnected the Lower Marine Riser Package (LMRP) from the lower Blow Out Preventer (BOP). After disconnecting, dynamic loads caused an uplift of the marine riser, ultimately resulting in a failure of the tensioner ring support and loss of the riser/LMRP to the seabed. No personnel were injured in this incident and no spilling of synthetic base mud to the environment occurred. This paper provides a summary of the root causes and contributing factors for the incident.
The Tripod beta method was used to conduct the review of the incident. The scope of the review included the following:
Measured data (rig heave, tensioner stroke, tensioner pressures)
Moonpool video camera recording of riser and tensioners during and after disconnect
Analytical models for vessel & marine riser dynamics, including the riser tensioner anti-recoil system
Rig/moonpool geometry, riser tensioner ring design, and space-out
Based on initial findings, further studies and analyses were conducted to better understand the dynamic behavior during the transition phase from initial disconnect to the hang-off position.
Forecasted Metocean conditions from a late winter storm indicated the potential to exceed the threshold for rig heave, with the marine riser connected to the well.
In preparation for disconnecting the LMRP, the well was secured with two barriers, a storm packer and closed blind shear rams. Once the rig heave limit was reached, the LMRP was disconnected from the lower BOP stack. Seven minutes after unlatching the LMRP, the riser tensioner profile on the slip joint outer barrel lifted off the riser tensioner ring and landed back onto the tensioner ring off-center. This uneven loading caused the tensioner ring halves to separate, dropping the LMRP and riser to the sea floor.
Analysis showed that one of the most critical phases of disconnecting the LMRP from the BOP occurs immediately after disconnecting and prior to moving the rig a safe distance from well center. The investigation indicated that the root causes of the event included human factors, such as adding additional air to tensioner system and re-setting of the Riser Anti Recoil System (RARS) prior to final hang-off condition. Contributing factors included the dynamic behavior of the riser and a lack of specific procedures for addressing the dynamic system conditions during the critical transition phase.
The paper provides additional information for riser/tensioner configuration and riser dynamics analyses during harsh environment conditions. In particular, additional analyses are presented for the transition phase from disconnect to hang-off position. Initial data is provided for further development of a smart disconnect algorithm, based on machine learning techniques of hind cast data.