Test String Research Articles

Compressive load analysis of mechanical setting process of test string Packer in Ultra-high-pressure Gas Wells

ABSTRACT To address the packer setting problems under complex operating conditions in ultra-high pressure gas wells, a mechanical analysis model for the mechanical setting process of packer in ultra-high pressure gas wells is established. The model takes into account factors such as wellbore trajectory, bending moment, internal and external fluid pressure, and the coupled effect of axial load, frictional resistance and buckling. The established model can be used to calculate the axial force of tubing string in ultra-high pressure gas wells, and analyze the effects of the tubing string length below packer, line weight combination, friction coefficient and the released wellhead suspended load on the packer setting force. The case calculation and parameter sensitivity analysis indicate that the original design of a high-pressure gas well cannot meet the requirements of packer setting. The setting performance of the packer can be effectively improved by adjusting the released wellhead suspended load, optimizing the tubing string length below the packer, reducing the friction coefficient and optimizing the length configuration of tubing string with small diameter. An increase in wellhead release weight by 60 kN was accompanied by a corresponding increase in packer pressure of 12.48 kN. When the lower string length was extended by 600 m, the packer weight without suspension was reduced by 65.34 kN, whereas the packer weight with release was diminished by 21.69 kN. Furthermore, an augmentation in the friction coefficient by 0.15 resulted in a decrease in the pressure weight of the packer under release suspension by 55.79 kN. Additionally, a reduction in the small pipe diameter length by 1000 m caused an increase in the packer weight with a release load of 17.98 kN. The research content not only provides theoretical guidance for the long-term safety of test string in high-pressure gas wells, but also offers practical insights for the design and operation of packers.

Dynamic response of deepwater test string under fluctuations in axial force and internal pressure

In this study, a mechanical model suitable for deepwater test string was proposed. An analysis of the dynamic response of the test string under different frequencies, different water depths and different fluctuation amplitudes was carried out by using the finite element method based on the change in the internal pressure and axial force measured. The results of the analysis showed that the response parameters (maximum stress and maximum deformation) tended to be stable after one period of fluctuation in the axial force and half a period of fluctuation in the internal pressure, respectively. When a sine waveform fluctuation in the internal pressure and axial force occurred, the response parameters increased with an increase in the amplitude of the fluctuation and increased with an increase in the frequency of fluctuation, and the amplitude of variation decreased with an increase in the fluctuation period. Under fluctuation in the axial force, the response parameter decreased with an increase in the water depth. The response parameter decreased first and then increased with an increase in the water depth when the fluctuation in the internal pressure occurred with a sine waveform. The maximum deformation and stress of the test string always changed with a change in the load when the fluctuation in the internal pressure and axial force had a sine waveform, and the test string under a load with a sine waveform was prone to periodic fatigue failure. The relevant conclusions provide a basis for the analysis and prevention of fatigue failure in test strings.

Mechanical Analysis of a Multi-Test String in High-Temperature and High-Pressure Deep Wells

The mechanical behavior of the test string in deep wells is generally relatively complex as a result of the high temperature and high pressure, severe dogleg and buckling effects, which in some circumstances can even lead to string failure. Traditional computational methods for the analysis of these behaviors are often inaccurate. For this reason, here a more accurate mechanical model of the test string is introduced by considering variables such as temperature, pressure, wellbore trajectory, and buckling, as well as combining them with the deformation and string constraint conditions brought in by changes in temperature and pressure during the tripping, setting, and test operations. The model is validated by applying it to a specific high-pressure gas well (located in Northeast Sichuan).

Failure risk assessment of deepwater HTHP well completion test string based on uncertainty analysis

In deepwater HTHP well completion test, the stress of the test string changes violently under the influence of HTHP environment, which is easy to cause the string failure. To solve this problem, the test string is simplified as a thick-wall cylinder model with uniform loads under the influence of high temperature. Then, the failure risk assessment method of the string is established based on the generalized stress-strength interference theory, and the influence of gas production, bottom hole pressure and test fluid density on the failure risk of a case well are analyzed. The results show that the failure mode in this well is internal pressure resistance failure, and the risk positions are mainly concentrated near wellhead. Gas production increasing leads to the intensification of radial heat transfer, increases the annular pressure and reduce the pressure difference of the string, resulting in the reduction of failure risk. Increasing the bottom hole pressure will increase the positive pressure difference of string, which will increase its internal pressure resistance failure risk. The test fluid density has low impact on failure risk. This method can provide theoretical reference for ensuring the reliability of deepwater HTHP well completion test.

Application of combined test string of RD bypass pressure test valve and RD safety circulation valve

At present, in the test construction of high temperature, high pressure and high hydrogen sulfide wells, in order to simplify the pipe string structure and improve the process success rate, the combination of RD safety circulation valve and OMNI multiple circulation valve is often used to carry out the triple operation of perforation+acid fracturing+test, which can realize the operation of one opening and one closing. However, due to the complex structure, high failure rate and high construction cost of the OMNI multi-cycle valve, most operators are unwilling to use it, but without the pipe string of the OMNI multi-cycle valve, the slurry replacement operation cannot be completed. This paper introduces an RD bypass pressure test valve which can replace OMNI multi-cycle valve. It can not only realize the function of slurry replacement, but also increase the success rate of operation because of its simple structure, so it is more and more favored by users.

Confinement and Pseudoscalar Glueball Spectrum in the 2 + 1D QCD-Like Theory from the Non-Susy D2 Brane

We study two important properties of 2+1D QCD, namely confinement and Pseudoscalar glueball spectrum, using holographic approach. The confined state of the bounded quark-antiquark pair occurs in the self-coupling dominated nonperturbative regime, where the free gluons form the bound states, known as glueballs. The gauge theory corresponding to low energy decoupled geometry of isotropic non-supersymmetric D2 brane, which is again similar to the 2+1D YM theory, has been taken into account but in this case the coupling constant is found to vary with the energy scale. At BPS limit, this theory reduces to supersymmetric YM theory. We have considered NG action of a test string and calculate the potential of such confined state located on the boundary. The QCD flux tube tension for large quark-antiquark separation is observed to be a monotonically increasing function of running coupling. The mass spectrum of Pseudoscalar glueball is evaluated numerically from the fluctuations of the axion in the gravity theory using WKB approximation. This produces the mass to be related to the string tension and the levels of the first three energy states. The various results that we obtained quite match with those previously studied through the lattice approach.

Data-Driven Fault Detection Method for Electronic Boards in Intelligent Remote Dual-Valve System

Intelligent remote dual-valve (IRDV) tools are used to open and close two valves downhole in a well. One valve is aimed to control the flow from the formation being tested into the pipe string to the surface, which is known as the test valve. The other one is aimed to control the flow between the annulus and the ID of the test string and is called the circulating valve. Both valves are activated in the same manner using a power piston that responds to the pressure applied on its lower side (cylinder area) by the hydraulic actuator, which is forced up or down to operate the attached valve. The lower section of the tool is the actuator assembly, comprising a hydraulic section and an electronic section. The electronic section responds to annulus pressure commands and drives the hydraulic section to distribute hydraulic pressure to the valves. Such tools operate in extreme environment conditions, such as elevated temperature, shocks, vibrations, and pressures. Such conditions can lead to an increased degradation rate of different subsystems in these tools and failures. Consequently, operations may be compromised, as the tools may provide inaccurate information, deliverables maybe be delayed until the tool is repaired, or the whole operation maybe cancelled. This leads to nonproductive time and financial losses. To avoid such failures, field engineers are required to check the tool condition after each run by analyzing sensor signals recorded during tool operation and determine if the tool is ready for the next run or if it is faulty and should be sent to maintenance. A reliable analysis, however, is extremely difficult to perform due to the immense number of data channels generated at a record rate, which results in millions of data points from a single run. A manual analysis of this data is extremely time consuming in an environment that can be extremely time critical, and the complexity of the signals limits the effectiveness of manual analysis. An alternative approach is to identify critical subsystems in the tool and allow a domain expert to identify the channels that contain information about the tool condition and possible degradation of each subsystem. Statistical features are extracted from channels that indicate degradation of the system with time. Later, these features can be used to build machine learning models that estimate the tool condition from the recorded data. In this tool, an electronics subsystem was identified as the most critical component in the pareto chart, and thus it was decided to develop a fault detection algorithm to help the field users identify whether the electronics behaved as expected or not. In this work we present a data-driven fault detection method for electronic boards in an IRDV system. Data used to build this model consists of electronic sensor channels monitored over time. Characteristics and distribution of the data were analyzed through exploratory data analysis. The method is based on extracting relevant features from multiple channels. Classification prediction modeling is done on these features, and the features are used to a build support vector machine model that monitors and estimates the health status of the IRDV system after a particular job to learn patterns. The IRDV has two kinds of operating channels—slow channels and activation channels—with corresponding different components associated with them. Modeling is done on both these channels to provide a segregated classification. The model demonstrated excellent value for maintenance and field engineers, because in a few minutes, the physical condition of the IRDV electronics subsystem can be determined using run data. This work is part of a long-term project aiming to construct a digital fleet management system for downhole testing tools.

Dynamical characteristics analysis of a deepwater test string induced by high-pressure gas and its experimental verification

To explore the dynamical characteristics of the deepwater test string, a fluid–structure coupling vibration model of the deepwater test string was established, and the model was solved by using the method of characteristics. A similarity experiment of the deepwater test string was performed to verify the model. Combined with the related data of a well in the South China Sea, the dynamical characteristics of the test string were analyzed to obtain the vibration regulation of the test string. Results showed that the test string vibrated periodically when gas passed through it, and its lateral deformation in the seawater segment was evidently larger than that in the formation. The test string's largest deformation was in the middle of the seawater segment, and its deformation in the upper part of the formation segment was larger to the middle and lower parts. A large longitudinal amplitude occurred in the lower part of the formation segment. With the increasing of surface current velocity, the lateral and longitudinal displacements of the test string in seawater segment increased. The lateral and longitudinal displacements of the test string increased with gas production and decreased with test string's thickness. Besides, the interaction effect between the gas and the test string increased with the gas density increasing. These results are highly significant for reducing the vibration of the deepwater test string and protecting its safety.

Confinement and pseudoscalar glueball spectrum in the 2+1D QCD-like theory from the non-SUSY D2 brane

Here we study two important properties of $2+1$ dimensional QCD -- confinement and pseudoscalar glueball spectrum -- with holographic approach. We consider the low energy decoupled geometry of the isotropic non-susy D$2$ brane. We find the corresponding gauge theory is similar to the $2+1$-dim Yang-Mills theory with the running coupling $\lambda^2$. At the extremal limit (i.e. BPS limit), this gauge theory reduces to the super-YM theory. From the Nambu-Goto action of a test string, the potential of a \qq pair located on the boundary is calculated. At large \qq separation it gives the tension $\sigma$ of the QCD flux-tube. The parametric dependencies of $\sigma$ is shown pictorially. It is found that $\sigma$ is a monotonically increasing function of the effective coupling $\lambda^2$. In comparison, $\sqrt{\sigma}/g_\text{YM}^2N_c$ is found to match accurately with the previous results. In the next part, we consider fluctuation of the axion field in the aforementioned gravity background. From the linearized field equation of the fluctuation we calculate the mass spectrum of $0^{-+}$ numerically using the WKB approximation. The pseudoscalar mass is found to be related to the string tension approximately as $M_{0^{-+}}/\sqrt{\sigma}\approx 3(n+2)$ for first three energy states, $n=0,\,1,\,2$.

A prevention and control method for natural gas hydrate in pipe strings during deepwater gas well production tests

The prevention and control of natural gas hydrate (hereinafter, “hydrate” for short) blockage during deepwater gas well production tests is very important in ensuring the test safety. In this paper, the distribution of wellbore temperature and pressure field under different test conditions was analyzed, and the changes of hydrate deposition and blockage degree in the pipe string in the whole process of test under different test systems were evaluated using the hydrate generation–deposition–decomposition calculation method. On this basis, a deepwater gas well production test method based on hydrate prevention and control was proposed. And the following research results were obtained. First, in the process of deepwater gas well tests, the vapor–liquid phase of annular-mist flow pattern with the greatest risk of hydrate blockage is often formed in the wellbore. Therefore, it is more reasonable to take measures to prevent hydrate blockage in the process of tests than to prevent the formation of hydrate. Second, when the conventional four-point test method is used, it is required to set low gas production measurement points with lower flowing temperature. In the wellbore with high temperature and low temperature, however, hydrate tends to form and deposit easily, and a long period of test will increase the risk of test string blockage. Third, the mixed-sequence test system suitable for deepwater gas well tests can change wellbore temperature by adjusting the sequence of measuring points without changing the production rate and duration, so as to decompose hydrate sediment layers and reduce the maximum blockage degree of test string in the process of tests. Fourth, a three-point or two-point test method is recommended for deepwater gas wells without sand production, stress sensitivity, retrograde condensation and water production. Superior to the conventional four-point test method, three-point and two-point test methods can effectively reduce the risk of hydrate deposition and blockage in the test string, and it can shorten the testing time and reduce the test cost on the premise of ensuring the accuracy of the productivity equation. In conclusion, the research results are of help to the field test construction of deepwater gas wells.

Prediction of wax precipitation region in wellbore during deep water oil well testing

Abstract During deep water oil well testing, the low temperature environment is easy to cause wax precipitation, which affects the normal operation of the test and increases operating costs and risks. Therefore, a numerical method for predicting the wax precipitation region in oil strings was proposed based on the temperature and pressure fields of deep water test string and the wax precipitation calculation model. And the factors affecting the wax precipitation region were analyzed. The results show that: the wax precipitation region decreases with the increase of production rate, and increases with the decrease of geothermal gradient, increase of water depth and drop of water-cut of produced fluid, and increases slightly with the increase of formation pressure. Due to the effect of temperature and pressure fields, wax precipitation region is large in test strings at the beginning of well production. Wax precipitation region gradually increases with the increase of shut-in time. These conclusions can guide wax prevention during the testing of deep water oil well, to ensure the success of the test.

THE METHOD OF GEOMETRIC CALIBRATION OF OPTOELECTRONIC SYSTEMS BASED ON ELECTRONIC TEST OBJECT

Designing remote sensing of the Earth devices is requires a lot of attention to evaluation lens distortion level and providing the required accuracy values of geometric calibration of optoelectronic systems at all. Test- objects known as most common tools for optical systems geometric calibration. The purpose of the research was creating an automatically method of distortion correction coefficients calculating with a 3 μm precision in the measurement process. The method of geometric calibration of the internal orientation elements of the optical system based on the electronic test object is proposed. The calculation of the test string brightness image from its multispectral image and filtered signal extrema position determination are presented. Ratio of magnitude of the distortion and interval center is given. Three variants of electronic test-objects with different step and element size are considered. Оptimal size of calibration element was defined as 3×3 pixels due to shape of the subpixels with the aspect ratio of the radiating areas about 1 : 3. It is advisable to use IPS as an electronic test object template. An experimental test and measurement stand functional diagram based on the collimator and optical bench «OSK-2CL» is showed. It was determined that test objects with a grid spacing of 4 and 8 pixels can’t provide tolerable image because of non-collimated emission of active sites and scattering on optical surfaces – the shape of the elements is substantially disrupted. Test-object with a 12 pixels grid spacing was used to distortion level analyzing as most suitable.Ratio of coordinate increment and element number graphs for two photographic lenses (Canon EF-S 17-85 f/4-5.6 IS USM and EF-S 18-55 f/3.5-5.6 IS II) are presented. A calculation of the distortion values in edge zones was held, which were respectively 43 μm and 51.6 μm. The technique and algorithm of software implementation is described. Possible directions of the method development are mentioned.

Temperature Transients Affect Reservoir–Pressure Estimation During Well Tests: Case Study and Model

Summary This paper discusses how the pressure measured by the downhole gauges during a drillstem test (DST) is affected not only by hydrostatic, friction, or kinetic-energy pressure losses, but also by changes in temperature. In oil wells, the bottomhole temperature is decreasing when the pressure is building up after a flow period. The change in temperature is inducing a change in the wellbore-fluid density, itself affecting the bottomhole pressure. Most numerical-simulators modeling flow in pipes do not take into account this effect, because it is not significant for low- to moderate-productivity wells. In high-productivity wells, however, the temperature change can affect dramatically the bottomhole pressure measured above the reservoir, and the pressure can even decrease at the end of a static period. A mathematical model is presented to compute the pressure drop caused by the nonisothermal effects, and it can be used to correct the measurements. Field examples are discussed to illustrate this effect, and recommendations are made on how new technology can improve pressure measurements during well tests. To measure the effects on the pressure measurements caused by the position of the gauges in the DST string, two gauge carriers were run in some well tests in deepwater wells offshore Brazil, one at the level of the tester valve and one below the packer, as deep as possible in the test string. The gauges could transmit data with a wireless telemetry system that allowed the operator to monitor in real time the pressure changes and the difference between the two sets of gauges. In high-permeability wells, using the uncorrected pressure measured with a gauge 50 to 100 m above the reservoir, as is typically the case, can result in a wrong productivity index (PI) and, at times, in uninterpretable results. Locating pressure gauges as close to the reservoir as possible is crucial in high-permeability reservoirs, to minimize the measurement errors, but also to avoid misinterpretations when an obstruction forms below the tester valve. With the new wireless telemetry systems, it is possible to monitor in real time gauges mounted below the packer, much closer to the perforations than the standard gauges placed at the level of the tester valve, thus avoiding making wrong decisions during the test. A long pressure-transient test could be uninterpretable because the gauges are at the wrong depth. Ideally, the pressure gauges should be placed in front of the perforations, but it is not always possible. Therefore, nonisothermal effects on pressure measurements during a well test need to be clearly understood and taken into account when designing and interpreting well tests, particularly in high-productivity reservoirs.

Dissociating Medial Temporal and Striatal Memory Systems With a Same/Different Matching Task: Evidence for Two Neural Systems in Human Recognition

ABSTRACTThe medial temporal lobe and striatum have both been implicated as brain substrates of memory and learning. Here, we show dissociation between these two memory systems using a same/different matching task, in which subjects judged whether four-letter strings were the same or different. Different RT was determined by the left-to-right location of the first letter different between the study and test string, consistent with a left-to-right comparison of the study and test strings, terminating when a difference was found. This comparison process results in same responses being slower than different responses. Nevertheless, same responses were faster than different responses. Same responses were associated with hippocampus activation. Different responses were associated with both caudate and hippocampus activation. These findings are consistent with the dual-system hypothesis of mammalian memory and extend the model to human visual recognition.

Chaos in Lifshitz spacetimes

We investigate the chaotic behavior of a circular test string in the Lifshitz spacetimes by considering the critical exponent z as an external control parameter. We demonstrate that two primary tools to observe chaos in this system are the Poincaré section and the Lyapunov exponent. Finally, the numerical result shows that if z = 1, the string dynamics is regular while in a case slightly larger than z = 1, the dynamics can be irregular and chaotic, which implies that the space time anisotropy, which breaks Lorentz symmetry, may cause the system to be chaotic.

Nonlinear dynamic analysis and fatigue damage assessment for a deepwater test string subjected to random loads

The deepwater test string is an important but vulnerable component in offshore petroleum exploration, and its durability significantly affects the success of deepwater test operations. Considering the influence of random waves and the interaction between the test string and the riser, a time-domain nonlinear dynamic model of a deepwater test string is developed. The stress-time history of the test string is obtained to study vibration mechanisms and fatigue development in the test string. Several recommendations for reducing damage are proposed. The results indicate that the amplitude of dynamic response when the string is subjected to random loads gradually decreases along the test string, and that the von Mises stress is higher in the string sections near the top of the test string and the flex joints. In addition, the fatigue damage fluctuates with the water depth, and the maximum damage occurs in string sections adjacent to the lower flex joint and in the splash zone. Several measures are proposed to improve the operational safety of deepwater test strings: applying greater top tension, operating in a favorable marine environment, managing the order of the test string joints, and performing nondestructive testing of components at vulnerable positions.

Acoustic Wireless Telemetry Reduces Uncertainty in Deepwater Drillstem Tests

Technology Update The drillstem test (DST) is one of the oldest methods used to test a formation’s capability to produce hydrocarbons. An early patent filed on drillstem testing in 1926 describes it as a method for “testing the productivity of formations encountered in drilling oil and other deep wells.” While frontiers such as deepwater drilling were far in the future, the industry was already seeking methods and equipment that were more efficient and economical than those in use then. Technology has continued to advance from mechanical openhole testing to modern annulus pressure controlled cased hole drillstem testing. An impressive array of annulus pressure-operated downhole test tools is available and provides operators with versatility and flexibility in drillstem testing. Downhole tool technology has advanced to extreme limits, with tools capable of handling bottomhole conditions of 35,000 psi and 500°F. Meanwhile, drilling technology has also progressed, with wells drilled to greater depths and in deeper water. Operating conditions pose new challenges to cost efficiency and annular pressure limitations. The inherent complexity of deepwater DST operations implies that a significant number of downhole test tools require some form of annular pressure manipulation. Tubing string tester valves, primary and backup circulating valves, bottomhole sampler triggers, and primary and backup firing heads for tubing-conveyed perforating are some examples. In deep water, the maximum allowable casing pressure has become the limiting factor in an increasing number of instances, and this reduces flexibility in designing the downhole test string. Advances in acoustic wireless telemetry have led to a novel and reliable alternative approach to operating downhole test tools in drillstem testing and providing real-time feedback of tool status, bottomhole pressure and temperature, and bottomhole fluid sample conditions. Wireless Telemetry Although wireless telemetry for downhole applications in the oil industry has been used since the 1940s, it did not gain much traction until the 1990s. Different wireless technologies have been studied and tested. Mud pulse telemetry found little use in drillstem testing because of low bandwidth and operational limitations. Electromagnetic telemetry saw some early use but also had limited data transmission capabilities, and the method does not work in subsurface salt layers.

String Test Preparation for the Superconducting SIS100 Accelerator of FAIR

GSI plans to build a test string in the Series Test Facility (STF) for SIS100 at GSI. The SIS100 cryomagnetic modules and local cryocomponents will be assembled and intensively tested. The purpose of the string test is to confirm technical systems of cryogenic, vacuum, interlock and quench protection, and powering under normal and extreme conditions. Acquirement of knowledge through experiences in test string construction, commissioning, and testing is crucial for the SIS100 construction and operation. We present the planning and preparation status of the string test.

Generalized states in SFT

The search for analytic solutions in open string fields theory à la Witten often meets with singular expressions, which need an adequate mathematical formalism to be interpreted. In this paper we discuss this problem and propose a way to resolve the related ambiguities. Our claim is that a correct interpretation requires a formalism similar to distribution theory in functional analysis. To this end we concretely construct a locally convex space of test string states together with the dual space of functionals. We show that the above suspicious expressions can be identified with well defined elements of the dual.

Artificial Neural Network based String Matching Algorithms for Species Classification A Preliminary Study and Experimental Results

e preliminary research in the area of applications of neural networks and pattern matching algorithms in species classification is presented. Artificial neural networks for classification and different pattern matching algorithms for matching the given DNA patterns or strings with the existing DNA sequences available in the databases are specifically studied. A set of local searching algorithms were experimented for different test string lengths and their time complexity is tabulated. Conclusions and future directions are also presented. KeywordsANN, DNA sequencing, Species classification, String matching