Wellbore Casing Research Articles

Numerical simulation and parametric analysis for designing High Energy Gas Fracturing

This paper presents a new comprehensive approach to model High Energy Gas Fracturing (HEGF) process. This coupled model consists of 6 sub-quantitative modules, including (1) loading build-up due to propellant deflagration, (2) gas-liquid interface displacement caused by killing liquid column movement, (3) stress distribution around the casing wellbore and the perforation holes, (4) fluid penetration through the perforation holes, (5) rate dependent critical pressure of fracture initiation and (6) hydro-mechanical coupled fracture propagation. The solution to the coupled model is obtained combining the analytical method and finite difference method, which solves the mass conservation equation and energy conservation equation with the subsystem pressure and temperature as the main variables. Subsequently, The single pulse and the multi-pulse HEGF processes are simulated. The dynamic changes of the loading built-up of propellant deflagration, the movement of killing liquid column as well as the dynamic propagation of fracture are further studied. Meanwhile, in-depth analysis has been applied on the affect sensitivity of the five key parameters to the single pulse HEGF results as well as the mechanism of multi-pulse HEGF. The results indicate that the final lengths of fractures generated by single pulse HEGF can be extended with the increase of the perforation density, the diameter of perforation holes, the thickness of propellant column and the total propellant quality. However, the effect of the height of killing liquid column is insignificant. It also demonstrates that the multi-pulse HEGF could bring multiplier fractures length by concatenating series propellants with different burning rates. This coupled model could add new dimensions to the understanding of the coupled mechanism of single pulse and multi-pulse HEGF. In addition, the model could be applied as a parameters quantitative design tool to assist the field implementation of these technologies.

Метод расчета вертикальной нагрузки на крепь скважины при оттаивании вмещающих мерзлых пород

Метод расчета вертикальной нагрузки на крепь скважины при оттаивании вмещающих мерзлых пород

A novel mitigation on deepwater annular pressure buildup: Unidirectional control strategy

When completing deepwater wells, a significant portion of the completion fluid is often trapped in the casing annuli because of widespread use of multi-layer casing technology. When transferred into testing or production, the temperature field in the immediate vicinity of the wellbore is redistributed by any present thermally conductive fluids. Raising trapped completion fluid to a high temperature can trigger high thermal stress, and this stress has been proven to present a grave threat to the safety of deepwater wells. In this paper, a thermal conductivity model of fluid-filled annuli based on a typical well structure used in the South China Sea is established to determine the effect of different production parameters during the well production or testing process on pressure behavior. A numerical simulation of the effects of fluid trapped in the casing annuli on temperature distribution was conducted. Based on this simulation, a novel method for mitigating the pressure of the trapped fluid by a way of a unidirectional control strategy was studied, and a unidirectional pressure control casing nipple tool was developed. Laboratory simulations were then conducted using a prototype tool to determine the technical feasibility of the unidirectional control strategy. The change in trapped fluid pressure with time was obtained for different release pressures and tool valve orifice diameters, showing the effects of different valve orifice diameters and volumetric injection rates on the pressure release performance. Experimental results demonstrate that the pressure envelope decreases quadratically with the increase in the pressure grade, while the valve working duration decreases linearly with the increase in valve orifice diameter. The increase in the volumetric injection rate was found to have little effect on the cumulative volume displacement. The proposed unidirectional pressure control strategy for controlling the accumulation of pressure in the annuli of deepwater wellbore casings can effectively eliminate the fatal dangers presented by thermal stress. It can also reduce the risk of casing deformation due to thermal stress within trapped annuli and reduce occurrences of wellhead sealing damage.

Transient Flow Modelling of Start-up CO2 Injection into Highly-Depleted Oil/Gas Fields

Carbon Capture and Storage (CCS) represent a promising technology in mitigating global warming challenges. In this study, we developed a model for the numerical simulation of the highly transient phenomena taking place in a wellbore during start-up CO_{2} injection operations. The basic conservation equations are considered in the tubing. The wall friction factor and heat transfer coefficient between the fluid and the surrounding formation are also taken into account. The simulation results obtained show a significant drop in pressure and temperature at the wellhead during CO_{2} start-up injection. This is a serious safety concern and poses several risks, including hydrate and ice formation with interstitial water around the wellbore and thermal shocking of the wellbore casing steel and thus in response, ways of minimising its occurrence are recommended.

The Enigma of Large-Scale Permeability of Gas Shale: Pre-Existing or Frac-Induced?

The existing commercial programs for simulation of hydraulic fracturing (aka fracking, or frac) of gas (or oil) shale predict parallel vertical cracks to spread in vertical parallel planes, with no lateral branching. These cracks emanate from the perforation clusters on the horizontal wellbore casing, typically spaced 10 m apart or more. For such a large spacing, the rate of gas production observed at the wellhead can be explained only upon making the hypothesis that the large-scale (or regional) permeability of shale is (even at 3 km depth) about 10,000 times higher than the gas permeability of shale measured in the lab on drilled (nondried) shale cores under confining pressures corresponding to shale at the depth of about 3 km. This hypothesis has recently been rendered doubtful by a new three-phase medium theory that takes into account the body forces due to pressure gradients of pore water diffusing into the pores. This theory predicts the fracking to produce a dense system of branched vertical hydraulic cracks with the spacing of about 0.1 m. This value matches the crack spacing deduced from the gas production rate at wellhead based on the actual lab-measured permeability. It is calculated that, to boost the permeability 10,000 times, the width of the pre-existing open (unfilled) natural cracks or joints (whose ages are distributed from one to several hundred million years) would have to be about 2.8 μm (not counting possible calcite deposits in the cracks). But this width is improbably high because, over the geologic time span, the shale must exhibit significant primary and secondary creep or flow. It is shown that the creep must close all the cracks tightly (except for residual openings of the order of 10 nm) even if the cracks are propped open by surface asperities. The inevitability of secondary creep (or steady-state flow) is explained theoretically by activation of new creep sites at stress concentrations caused by prior creep deformation. The time of transition from primary to secondary creep is taken equal to the Maxwell time estimate from geology. The overall conclusion is that the 10,000-fold increase of large-scale permeability is most likely not pre-existing but frac-induced. Although this conclusion will make little difference for long-term forecasts, it would make a major difference for the understanding and control of the frac process.

3D Geomechanical Modeling of Salt-Creep Behavior on Wellbore Casing for Presalt Reservoirs

Summary Exploration drilling is venturing into deeper regions of water. During the exploration of these deeper water depths, large hydrocarbon deposits have been found below salt formations. These reservoirs are called “presalts,” which are below the salt formations. Presalt reservoirs have been found in offshore Brazil, the Gulf of Mexico (GOM), West Africa, and the North Sea. Completions in salt formations can be difficult because of the creep behavior that the salt formations exhibit. Creep behavior results from the instability of the salt formation, which causes a slow flow and permanent deformations. Creep deformation occurs over time and begins once the salt formation has been penetrated. Completion of the wellbore does not stop formation creep. The constant creep of the salt formation causes excess stress on the wellbore casing, which may eventually cause the casing to collapse. In this study, a 3D geomechanical model is developed, by use of data such as wellbore pressure and temperature; formation stress and temperature; rock, cement, and casing properties, to predict the effects of salt-creep behavior on stress loading in the wellbore casing, which helps to assess the life expectancy of wells in presalt reservoirs. The simulation results of this model can provide quantitative results of casing stress and deformation as a function of time under various temperature, in-situ-stress, and operation conditions, which can be used as useful information for subsequent wellbore-casing design and wellbore-integrity analysis. In addition, possible methods that can mitigate the severity of salt mobility and reduce the risks of casing collapse are discussed.

Randomly distributed interfacial arc cracks within the inclusion-inhomogeneity-matrix system

The theory of eigenstrains is employed to solve the problem of n partial annular cracks along the cemented interface of a pipe or more specifically are oil wellbore casing. This approach provides the possibility to study the interacting effect of two or more arc cracks with different lengths and angles. Partial annular cracks around the casing-cement and/or cement-formation interfaces are considered to experience leaking fluid pressure p, and the matrix is considered to be under the applied stresses $$\sigma_{ij}^{0} , i,j = 1, 2$$ at infinity. Although problems dealing with partial arc cracks are limited to bi-materials (a circular inclusion embedded in a matrix) in the presence of one or two symmetric partial cracks, this work provides an analytical solution for the hollow cylindrical casing-cement sheath-formation rock system with randomly distributed partial annular cracks scattered within the above-mentioned interfaces. The proposed solution can be utilized in different engineering problems like fiber corrosion related problems.

Elucidating hydraulic fracturing impacts on groundwater quality using a regional geospatial statistical modeling approach

Hydraulic fracturing operations have been viewed as the cause of certain environmental issues including groundwater contamination. The potential for hydraulic fracturing to induce contaminant pathways in groundwater is not well understood since gas wells are completed while isolating the water table and the gas-bearing reservoirs lay thousands of feet below the water table. Recent studies have attributed ground water contamination to poor well construction and leaks in the wellbore annulus due to ruptured wellbore casings. In this paper, a geospatial model of the Barnett Shale region was created using ArcGIS. The model was used for spatial analysis of groundwater quality data in order to determine if regional variations in groundwater quality, as indicated by various groundwater constituent concentrations, may be associated with the presence of hydraulically fractured gas wells in the region. The Barnett Shale reservoir pressure, completions data, and fracture treatment data were evaluated as predictors of groundwater quality change. Results indicated that elevated concentrations of certain groundwater constituents are likely related to natural gas production in the study area and that beryllium, in this formation, could be used as an indicator variable for evaluating fracturing impacts on regional groundwater quality. Results also indicated that gas well density and formation pressures correlate to change in regional water quality whereas proximity to gas wells, by itself, does not. The results also provided indirect evidence supporting the possibility that micro annular fissures serve as a pathway transporting fluids and chemicals from the fractured wellbore to the overlying groundwater aquifers.

Embodied Energy and GHG Emissions from Material Use in Conventional and Unconventional Oil and Gas Operations.

Environmental impacts embodied in oilfield capital equipment have not been thoroughly studied. In this paper, we present the first open-source model which computes the embodied energy and greenhouse gas (GHG) emissions associated with materials consumed in constructing oil and gas wells and associated infrastructure. The model includes well casing, wellbore cement, drilling mud, processing equipment, gas compression, and transport infrastructure. Default case results show that consumption of materials in constructing oilfield equipment consumes ∼0.014 MJ of primary energy per MJ of oil produced, and results in ∼1.3 gCO2-eq GHG emissions per MJ (lower heating value) of crude oil produced, an increase of 15% relative to upstream emissions assessed in earlier OPGEE model versions, and an increase of 1-1.5% of full life cycle emissions. A case study of a hydraulically fractured well in the Bakken formation of North Dakota suggests lower energy intensity (0.011 MJ/MJ) and emissions intensity (1.03 gCO2-eq/MJ) due to the high productivity of hydraulically fractured wells. Results are sensitive to per-well productivity, the complexity of wellbore casing design, and the energy and emissions intensity per kg of material consumed.

A cement interface enhancer and its action mechanism

A cement interface enhancer (CIE) to improve the well cementing quality for fresh water-based drilling fluid was prepared and its action mechanism was studied. The composition and the proper dosage of CIE were studied with mud cake strength test and steel plate immersion test. CIE contained inorganic mineral fibers such as calcium silicate, silica nanoparticles, and low polarity polymers; the proper proportion was about 1.8:1.2:1. The cementing strength simulation experiments showed that the cementing strengths of the interfaces between the cement and the wellbore casing (the first interface), and the cement and the borehole wall (the second interface) were increased by three and four times, respectively, when 0.8 % (weight) of CIE was added into the drilling fluid. This was due to the support effect, inductive effect, and electrostatic repulsion of CIE, and the bonding of cement with mud cake was improved. The application of CIE in Daqing Oilfield showed that the cementing perfection rate could be increased by 30 % that indicated CIE could improve the well cementing quality effectively.

Application of Multiphysics Coupling FEM on Open Wellbore Shrinkage and Casing Remaining Strength in an Incomplete Borehole in Deep Salt Formation

Drilling and completing wells in deep salt stratum are technically challenging and costing, as when serving in an incomplete borehole in deep salt formation, well casing runs a high risk of collapse. To quantitatively calculate casing remaining strength under this harsh condition, a three-dimensional mechanical model is developed; then a computational model coupled with interbed salt rock-defective cement-casing and HPHT (high pressure and high temperature) is established and analyzed using multiphysics coupling FEM (finite element method); furthermore, open wellbore shrinkage and casing remaining strength under varying differential conditions in deep salt formation are discussed. The result demonstrates that the most serious shrinkage occurs at the middle of salt rock, and the combination action of salt rock creep, cement defect, and HPHT substantially lessens casing remaining strength; meanwhile, cement defect level should be taken into consideration when designing casing strength in deep salt formation, and apart from the consideration of temperature on casing the effect of temperature on cement properties also cannot be ignored. This study not only provides a theoretical basis for revealing the failure mechanism of well casing in deep complicated salt formation, but also acts as a new perspective of novel engineering applications of the multiphysics coupling FEM.

Quantifying drag on wellbore casings in moving salt sheets

Quantifying drag on wellbore casings in moving salt sheets

Effect of Dynamic Loading on Wellbore Leakage for the Wabamun Area CO2-Sequestration Project

Summary The most viable options for permanent removal of carbon dioxide (CO2) from the atmosphere include large-scale injection of CO2 from stationary sources, such as coal-fired power plants and heavy-oil production, into brine-filled formations. One of the main risks identified with storing CO2 in the subsurface is the potential for leakage through existing wells penetrating the caprock. The wellbore system has several components that can fail and create leakage pathways, including type and placement of wellbore casing and cements, completion method, abandonment, and wellbore expansion or contraction by changes in temperature and pressure. Of the 1,000 wells in the study area near Wabamun Lake, Alberta, 95 wells penetrated the immediate caprock above the proposed Nisku injection formation and were identified as potential leakage pathways. The leakage risk of these wells was evaluated on the basis of knowledge of the well design, current well status, and historical regulations in the area. Only four wells, for the subset of 27 wells studied, were identified as requiring workover, which was less of a problem than anticipated. To evaluate the risk of creating leakage pathways by thermal and pressure changes caused by CO2 injection, a 3D finite-element model was built by use of poroelastoplastic material models for cement and formation. Multistage simulations for casing/cement and cement/ formation interactions with temperature-enabled elements were conducted. A parametric study of cement properties was conducted to investigate cement design and its mechanical properties for injection wells. The simulation results indicated that thermal cooling might reduce near-wellbore stresses, which would increase the risk of integrity loss in casing/cement and cement/formation. The parametric study revealed that the risk of debonding and tensile failure would increase with increasing Young’s modulus and Poisson’s ratio of the cement under dynamic-loading conditions. In addition, low mechanical cement strength would increase the risk of shear failure in the cement.

Numerical Analysis of Fluid Flow Properties in a Partially Perforated Horizontal Wellbore

The pressure drops in horizontal wellbores, acceleration, wall friction, perforation roughness, and fluid mixing are analyzed in a partially perforated wellbore. It was demonstrated that the perforation inflow actually reduced the total pressure drop. The pressure drop due to perforation roughness was eliminated by the perforation inflow when the ratio of radial perforation flow to axial pipe flow rate reached a certain limit. Three dimensional numerical simulations on a partially perforated pipe with 150 perforations, geometrically similar with wellbore casing (12 SPF, and 60 phasing) were presented and analyzed. Numerical simulations by commercial code CFX were also conducted with Reynolds numbers ranging from 28,773 to 90,153 and influx flow rate ranging from 0 to 899 lit/hr to observe the flow through perforated pipe, measure pressure drops, friction factors and pressure loss coefficients. The acceleration pressure drop might be important compared with the frictional pressure drop. The numerically calculated results using k-ε model were compared with the experimental results. The numerical solutions agreed well with the experimental data.

Reaction and transport in wellbore interfaces under CO2 storage conditions: Experiments simulating debonded cement–casing interfaces

Debonding-defects at the interfaces between wellbore casing and cement are widely recognized as providing potential pathways for CO2 escape from geological storage systems. This study addresses how chemical reaction between CO2, cement and steel may affect the transport properties of such defects under near-static conditions, representative for early stages in leakage pathway development, prior to formation of a fully connected defect network. Debonded cement–steel interfaces were simulated by constructing composite samples, containing a spacer-imposed gap. These were subjected to batch reaction with CO2 and a variety of aqueous solutions, in multiple consecutive runs (6×5 days plus 1×42 days). The experiments were conducted at 80°C and 14MPa applied CO2-pressure. Permeability was measured after each run. Two ranges in gap-width were investigated, namely 50–120μm (SA-samples) and 270–350μm (LA-samples). Reaction-induced permeability changes were less than 1 order in all samples, and occurred in the early stage of testing. SEM study showed Fe-carbonate scale films developed on both cement and steel. Calcium carbonates precipitated on the cement beneath the gap-spacers, where corrosion scale did not form. We infer that corrosion scale formation on the cement wall inhibited both CaCO3 precipitation and healing effects previously observed in fractured cement.

Numerical Simulation on Open Wellbore Shrinkage and Casing Equivalent Stress in Bedded Salt Rock Stratum

Most salt rock has interbed of mudstone in China. Owing to the enormous difference of mechanical properties between the mudstone interbed and salt rock, the stress-strain and creep behaviors of salt rock are significantly influenced by neighboring mudstone interbed. In order to identify the rules of wellbore shrinkage and casings equivalent stress in bedded salt rock stratum, three-dimensional finite difference models were established. The effects of thickness and elasticity modulus of mudstone interbed on the open wellbore shrinkage and equivalent stress of casing after cementing operation were studied, respectively. The results indicate that the shrinkage of open wellbore and equivalent stress of casings decreases with the increase of mudstone interbed thickness. The increasing of elasticity modulus will reduce the shrinkage of open wellbore and casing equivalent stress. Research results can provide the scientific basis for the design of mud density and casing strength.

Potential for environmental impact due to acid gas leakage from wellbores at EOR injection sites near Zama Lake, Alberta

AbstractThe potential for environmental impact from future leakage of toxic hydrogen sulfide (H2S) at an enhanced oil recovery (EOR) and acid gas sequestration site near Zama Lake, Alberta, is examined. Over 800 pinnacle reefs are potentially suitable for EOR by injection of acid gas. Leakage rate as a function of time through a reference wellbore is determined for various scenarios including leakage through the annulus of the wellbore and leakage through the central plug seal of the wellbore with an intact and failed wellbore casing. Potential plumes of H2S in the air and in shallow aquifers emanating from a single reference wellbore and from 350 wellbores are modeled. Leakage rates from the 350 wellbores are calculated from randomly sampled wellbore seal failure times, reservoir permeability, and initial amounts of acid gas, and from reference values of other reservoir parameters. Results indicate that for hundreds of years after injection, the entire Zama Lake area of 12 000 km2 could have lethal concentrations of H2S over each of the leaking wellbores. The shallow aquifers over the entire Zama area and over 30 kilometres in the direction of aquifer flow could be undesirably tainted with dissolved H2S. The entire Zama Lake area and hundreds of kilometres beyond could become uninhabitable for more than 1000 years after injection due to toxic plumes of H2S in the air and in shallow aquifers. This analysis has implications for the potential use of acid gas for EOR and for subsurface sequestration in general in areas with large numbers of abandoned wells. © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd

Finite element analysis on Casing Failure Based on ADINA

Casing dislocation is one of the most serious forms for casing damage in petroleum engineering, especially casing failure in oil field will cause the great economic losses. Aimed at wellbore casing in oil field, dislocation mechanism and fracture theory of casing are introduced. Rupture model and Fracture model for casing failure crossing fault are established by ADINA. According to numerical results, the effects of various factors on casing failure are analyzed, such as the damage level of casing under different casing thickness and the fault angle. Crack propagation of broken casing has been investigated. It can provide theoretical basis for safety production and protection of oil field.

Analysis of in-situ wellbore integrity data for existing wells with long-term exposure to CO2

Abstract An important aspect of the risk associated with geological carbon dioxide sequestration is the integrity of existing wellbores that penetrate geological layers targeted for CO 2 injection. CO 2 leakage may occur through multiple pathways along a wellbore within the “disturbed zone” surrounding the well casing. The disturbed zone is defined as the annular region along the exterior of the steel wellbore casing that includes the Portland cement sheath, the damage zone of the host rock and the casing-cement-rock interfaces. The effective permeability of this zone is a key parameter of wellbore integrity required for validation of numerical models. Effective permeability may depend on a number of complex factors, including long-term attack by aggressive fluids, poor well completion or actions related to production of fluids through the wellbore. Field tests are essential to understanding the in situ leakage properties of the millions of wells that exist in mature sedimentary basins in North America. We present results from recent field studies of different CO 2 producing wells from both natural CO 2 reservoirs and enhanced oil recovery (EOR) operations. These surveys have included a particular downhole pressure test, the vertical interference test (VIT), designed to determine the extent of hydraulic communication along the exterior of the well casing. The VIT test involves perforating the well casing in two separate intervals, both of which are located within the shale caprock and bracket a zone of cement identified to have a lower quality bond. Once the intervals are isolated with an inflatable packer, the system is pressurized from surface and held at a constant pressure, while simultaneously, the transient pressure response is measured in the lower isolated interval. The pressure transient data is an indicator of the extent of hydraulic communication and is the focus of subsequent analysis. The effective wellbore permeability can be determined through numerical analysis of the VIT data. Our objective is to identify to most effective method of analysis for estimating wellbore permeability. We evaluate two different automated parameter estimation methods, nonlinear regression and shuffled complex evolution metropolis methods. Within this study, we also estimate parameters such as permeability and compressibility of the low permeability shale zone to determine their effect on the resulting estimate of wellbore permeability. The results of this work demonstrate that parameter estimation can be effective at identifying the key parameters associated with wellbore integrity from VIT field tests, and ultimately reducing the uncertainty regarding the integrity of existing wellbores.

A feasibility study of borehole radar as a permanent downhole sensor

Permanent downhole sensors provide the eyes and ears to the reservoir and enable monitoring the reservoir conditions on a real-time basis. In particular, the use of sensors and remotely controlled valves in wells and on the surface, in combination with reservoir flow models provide enormous benefits to reservoir management and oil production. We suggest borehole radar measurements as a promising technique capable to monitor the arrival of undesired fluids in the proximity of production wells. We use 1D modelling to investigate the expected signal magnitude and depth of investigation of a borehole radar sensor operating in an oilfield environment. We restrict the radar applicability to environments where the radar investigation depth can fit the reservoir size necessary to be monitored. Potential applications are steam chamber monitoring in steam assisted gravity drainage processes and water front monitoring in thin oil rim environments. A more sophisticated analysis of the limits of a radar system is carried out through 2D finite-difference time-domain simulations. The metal components of the wellbore casing can cause destructive interference with the emitted signal. A high dielectricmedium surrounding the production well increases the amplitude of the signal and so the radar performance. Other reservoir constraints are given by the complexity of the reservoir and the dynamic of the fluids. Time-lapse changes in the heterogeneity of the background formation strongly affect the retrieval of the target reflections and gradual fluid saturation changes reduce the amplitudes of the reflections.