The Wellbore Temperature and Pressure Behavior during the Flow Testing of Ultra-Deepwater Gas Wells

The transientflow testing of ultra-deepwater gas wells is greatly impacted by the low temperatures of seawater encountered over extended distances.This leads to a redistribution of temperature within the wellbore,which in turn influences theflow behavior.To accurately predict such a temperature distribution,in this study a comprehensive model of theflowing temperature and pressurefields is developed.This model is based on principles offluid mechanics,heat transfer,mass conservation,and energy conservation and relies on the Runge-Kutta method for accurate integration in time of the resulting equations.The analysis includes the examination of the influence of various factors,such as gasflow production rate,thermal diffusivity of the formation,and thermal diffusivity of seawater,on the temperature and pressure profiles of the wellbore.The keyfindings can be summarized as follows:1.Higher production rates during testing lead to increasedflowing temperatures and decreased pressures within the wellbore.However,in the presence of a seawater thermocline,a crossover inflowing temperature is observed.2.An increase in wellbore pressure is associated with larger pipe diameters.3.Greater thermal diffusivity of the formation results in more rapid heat transfer from the wellbore to the formation,which causes lowerflowing temperatures within the wellbore.4.In an isothermal layer,higher thermal diffusivity of seawater leads to increased wellboreflowing temperatures.Conversely,in thermocline and mixed layer segments,lower temperatures are noted.5.Production test data from a representative deep-water gas well in the South China Sea,used to calculate the bottom-seafloor-wellhead temperature and pressurefields across three operating modes,indicate that the average error in temperature prediction is 2.18%,while the average error in pressure prediction is 5.26%,thereby confirming the reliability of the theoretical model.

Fracture network types revealed by well test curves for shale reservoirs in the Sichuan Basin,China

Pressure buildup testing can be used to analyze fracture network characteristics and conduct quantitative interpretation of relevant parameters for shale gas wells,thus providing bases for assessing the well productivity and formulating proper development strategies.This study establishes a new well test interpretation model for fractured horizontal wells based on seepage mechanisms of shale reservoirs and proposes a method for identifying fracturing patterns based on the characteristic slopes of pressure buildup curves and curve combination patterns.The pressure buildup curve patterns are identified to represent three types of shale reservoirs in the Sichuan Basin,namely the moderately deep shale reservoirs with high pressure,deep shale reservoirs with ultra-high pressure,and moderately deep shale reservoirs with normal pressure.Based on this,the relationship between the typical pressure buildup curve patterns and the fracture network types are put forward.Fracturing effects of three types of shale gas reservoir are compared and analyzed.The results show that typical flow patterns of shale reservoirs include bilinear flow in primary and secondary fractures,linear flow in secondary fractures,bilinear flow in secondary fractures and matrix,and linear flow in matrix.The fracture network characteristics can be determined using the characteristic slopes of pressure buildup curves and curve combinations.The linear flow in early secondary fractures is increasingly distinct with an increase in primary fracture conductivity.Moreover,the bilinear flow in secondary fractures and matrix and the subsequent linear flow in the matrix occur as the propping and density of secondary fractures increase.The increase in the burial depth,in-situ stress,and stress difference corresponds to a decrease in the propping of primary fractures that expand along different directions in the shale gas wells in the Sichuan Basin.Four pressure buildup curve patterns exist in the Sichuan Basin and its periphery.The pattern of pressure buildup curves of shale reservoirs in the Yongchuan area can be described as 1/2/→1/4,indicating limited stimulated reservoir volume,poorly propped secondary fractures,and the forming of primary fractures that extend only to certain directions.The pressure buildup curves of shale reservoirs in the main block of the Fuling area show a pattern of 1/4/→1/2 or 1/2,indicating greater stimulated reservoir volume,well propped secondary fractures,and the forming of complex fracture networks.The pattern of pressure buildup curves of shale reservoirs in the Pingqiao area is 1/2/→1/4→/1/2,indicating a fracturing effect somewhere between that of the Fuling and Yongchuan areas.For reservoirs with normal pressure,it is difficult to determine fracture network characteristics from pressure buildup curves due to insufficient formation energy and limited liquid drainage.

Life-Cycle Bearing Capacity for Pre-Stressed T-beams Based on Full-Scale Destructive Test

To investigate the evolution of load-bearing characteristics of pre-stressed beams throughout their service life and to provide a basis for accurately assessing the actual working state of damaged pre-stressed concrete T-beams,destructive tests were conducted on full-scale pre-stressed concrete beams.Based on the measurement and ana-lysis of beam deflection,strain,and crack development under various loading levels during the research tests,combined with the verification coefficient indicators specified in the codes,the verification coefficients of bridges at different stages of damage can be examined.The results indicate that the T-beams experience complete,incom-plete linear,and non-linear stages during the destructive test process.In the complete linear elastic stage,both the deflection and bottom strain verification coefficients comply with the specifications,indicating a good structural load-bearing capacity no longer adheres to the code’s requirements.In the non-linear stage,both coefficients exhi-bit a sharp increase,resulting in a further decrease in the structure’s load-bearing capacity.According to the pro-visions of the current code,the beam can be in the incomplete linear stage when both values fall within the code’s specified range.The strain verification coefficient sourced from the compression zone at the bottom of theflange is not recommended for assessing the bridge’s load-bearing capacity.

A new tube chamber system for evaluation of anterior chamber pressure during phacoemulsification tested in porcine eyes

AIM:To measure the optimal anterior chamber pressure(ACP)for safe phacoemulsification using a new tube chamber system with internal pressure measurement function in the porcine eye.METHODS:The 20-gauge and 21-gauge straight tips with yellow and orange sleeves,respectively,were covered by a test chamber combined with a pressure sensor for measuring ACP.This was measured for 20s from 10s after starting aspiration in the linear mode using vacuum levels of 200 and 150 mm Hg with a 20-gauge tip,and 300 and 250 mm Hg with a 21-gauge tip.Using a porcine eye,a pressure sensor fixed with a 0.9 mm corneal incision measured ACP.For the posterior capsule contact assay,porcine eyes were treated as described above,and the ultrasonic needle tip was held at the height of the iris and aspirated for 30s in linear mode at a vacuum of 200 and 150 mm Hg for the 20-gauge tip,and 300 and 250 mm Hg for the 21-gauge tip.The bottle height at which the posterior capsule accidentally contacted the ultrasonic tip was recorded,and the estimated ACP was calculated.RESULTS:The internal pressure of the new tube chamber system and ACP from the porcine eye closely matched proportional changes at vacuum levels of 200 and 150 mm Hg with 20-gauge tips.Similarly,proportional changes at vacuum levels of 300 and 250 mm Hg with the 21-gauge tip were nearly equal.The bottle height at which the posterior capsule contacted with the tip and estimated ACP were 57.5±12.6 cm(20.2±7.9 mm Hg)at 200 mm Hg with a 20-gauge tip,35.0±10.0 cm(16.6±6.3 mm Hg)at 150 mm Hg with a 20-gauge tip,47.5±12.6 cm(18.7±8.7 mm Hg)at 300 mm Hg with a 21-gauge tip,and 32.5±5.0 cm(15.7±3.5 mm Hg)at 250 mm Hg with a 21-gauge tip.CONCLUSION:A comprehensive understanding of this chamber system’s characteristics and usage can resolve anterior chamber instability caused by changing preoperative settings on the phaco machine.

Large-scale shaking table test on unlined tunnel in fault zone under threedimensional earthquake

A fault is a geological structure characterized by significant displacement of rock masses along a fault plane within the Earth's crust.The Yunnan Tabaiyi Tunnel intersects multiple fault zones,making tunnel construction in fault-prone areas particularly vulnerable to the effects of fault activity due to the complexities of the surrounding geological environment.To investigate the dynamic response characteristics of tunnel structures under varying surrounding rock conditions,a three-dimensional large-scale shaking table physical model test was conducted.This study also aimed to explore the damage mechanisms associated with the Tabaiyi Tunnel under seismic loading.The results demonstrate that poor quality surrounding rock enhances the seismic response of the tunnel.This effect is primarily attributed to the distribution characteristics of acceleration,dynamic strain,and dynamic soil pressure.A comparison between unidirectional and multi-directional(including vertical)seismic motions reveals that vertical seismic motion has a more significant impact on specific tunnel locations.Specifically,the maximum tensile stress is observed at the arch shoulder,with values ranging from 60 to 100 k Pa.Moreover,NPR(Non-Prestressed Reinforced)anchor cables exhibit a substantial constant resistance effect under low-amplitude seismic waves.However,when the input earthquake amplitude reaches 0.8g,local sliding occurs at the arch shoulder region of the NPR anchor cable.These findings underscore the importance of focusing on seismic mitigation measures in fault zones and reinforcing critical areas,such as the arch shoulders,in practical engineering applications.

Landslide model tests with a miniature 2D principal stress sensor

Understanding the stress distribution derived from monitoring the principal stress(PS)in slopes is of great importance.In this study,a miniature sensor for quantifying the two-dimensional(2D)PS in landslide model tests is proposed.The fundamental principle and design of the sensor are demonstrated.The sensor comprises three earth pressure gages and one gyroscope,with the utilization of three-dimensional(3D)printing technology.The difficulties of installation location during model preparation and sensor rotation during testing can be effectively overcome using this sensor.Two different arrangements of the sensors are tested in verification tests.Additionally,the application of the sensor in an excavated-induced slope model is tested.The results demonstrate that the sensor exhibits commendable performance and achieves a desirable level of accuracy,with a principal stress angle error of±5°in the verification tests.The stress transformation of the slope model,generated by excavation,is demonstrated in the application test by monitoring the two miniature principal stress(MPS)sensors.The sensor has a significant potential for measuring primary stress in landslide model tests and other geotechnical model experiments.

Model tests and numerical analysis of emergency treatment of cohesionless soil landslide with quick-setting polyurethane

Shotcrete is one of the common solutions for shallow sliding.It works by forming a protective layer with high strength and cementing the loose soil particles on the slope surface to prevent shallow sliding.However,the solidification time of conventional cement paste is long when shotcrete is used to treat cohesionless soil landslide.The idea of reinforcing slope with polyurethane solidified soil(i.e.,mixture of polyurethane and sand)was proposed.Model tests and finite element analysis were carried out to study the effectiveness of the proposed new method on the emergency treatment of cohesionless soil landslide.Surcharge loading on the crest of the slope was applied step by step until landslide was triggered so as to test and compare the stability and bearing capacity of slope models with different conditions.The simulated slope displacements were relatively close to the measured results,and the simulated slope deformation characteristics were in good agreement with the observed phenomena,which verifies the accuracy of the numerical method.Under the condition of surcharge loading on the crest of the slope,the unreinforced slope slid when the surcharge loading exceeded 30 k Pa,which presented a failure mode of local instability and collapse at the shallow layer of slope top.The reinforced slope remained stable even when the surcharge loading reached 48 k Pa.The displacement of the reinforced slope was reduced by more than 95%.Overall,this study verifies the effectiveness of polyurethane in the emergency treatment of cohesionless soil landslide and should have broad application prospects in the field of geological disasters concerning the safety of people's live.

基于WellTester的岩溶含水层水文地质参数估算

Well Tester是计算地热含水层水文地质参数的软件,该软件通过对水压力过程曲线进行拟合,进行参数计算。该软件界面友好、操作简单,且具有输出单井报告功能。文章对Well Tester软件各模块及各界进行简要介绍的基础上,以"北京岩溶水资源勘查评价工程"中新建岩溶水井为例,对各个操作步骤进行了介绍。通过对比分析Well Tester软件与经验法的结果,表明该软件可对岩溶裂隙含水层的水文地质参数进行计算,且该软件对成井质量评价有一定指导意义。目前该软件还未广泛应用于岩溶裂隙含水层,为获取较多的水文地质参数,笔者认为该软件在我国具有一定的推广价值。

Classification of carbonate gas condensate reservoirs using well test and production data analyses

Carbonate reservoir patterns play an important role in the production performance of oil and gas wells,and it is usually classified through static data analysis which cannot reflect the actual well performance.This paper takes the Tazhong No.1 gas field in the Tarim Basin,China as an example to investigate the classification of carbonate reservoirs.The classification method mainly combines well test analysis with production analysis—especially the Blasingame type curve method.Based on the characteristics of type curves for well test analysis and the Blasingame method,the relationship between the type curves and reservoir pattern was established.More than 20 wells were analyzed and the reservoirs were classified into 3 major patterns with 7 sub-classes.Furthermore,the classification results were validated by dynamic performance analysis of wells in the Tazhong No.1 gas field.On the basis of the classification results,well stimulation（i.e.water flooding in a single well） was carried out in three volatile-oil wells,and the oil recovery increased by up to 20%.

A deep reinforcement learning(DRL)based approach for well-testing interpretation to evaluate reservoir parameters

Parameter inversions in oil/gas reservoirs based on well test interpretations are of great significance in oil/gas industry.Automatic well test interpretations based on artificial intelligence are the most promising to solve the problem of non-unique solution.In this work,a new deep reinforcement learning(DRL)based approach is proposed for automatic curve matching for well test interpretation,by using the double deep Q-network(DDQN).The DDQN algorithms are applied to train agents for automatic parameter tuning in three conventional well-testing models.In addition,to alleviate the dimensional disaster problem of parameter space,an asynchronous parameter adjustment strategy is used to train the agent.Finally,field applications are carried out by using the new DRL approaches.Results show that step number required for the DDQN to complete the curve matching is the least among,when comparing the naive deep Q-network(naive DQN)and deep Q-network(DQN).We also show that DDQN can improve the robustness of curve matching in comparison with supervised machine learning algorithms.Using DDQN algorithm to perform 100 curve matching tests on three traditional well test models,the results show that the mean relative error of the parameters is 7.58%for the homogeneous model,10.66%for the radial composite model,and 12.79%for the dual porosity model.In the actual field application,it is found that a good curve fitting can be obtained with only 30 steps of parameter adjustment.

Predictive value of hypo-osmotic swelling test to identifyviable non-motile sperm

Aim: To determine the predictive value of the hypo-osmotic swelling (HOS) test to identify viable, non-motile sperm. Methods: Semen samples from 20 men with severe asthenozoospermia underwent traditional seminal analysis, eosin-nigrosin (EN) staining and the HOS test. A further EN stain was then performed on a HOS pre-treated aliquot and a total of 2000 further sperm examined. Results: The median sperm density was 5.1 million/mL (IQR 4.3-13.1) and the median motility was 3.0 % (IQR 0-7). Seven samples showed complete asthenozoospermia. Initial EN staining showed 59 % viability (range 48-69) despite the poor standard parameters and 47 % (range 33-61) in the complete asthenozoospermia subgroup. The HOS test showed 49.9 % reacted overall (range 40-59) and 41.7 % (range 22-61) in the complete asthenozoospermia subgroup. The combined HOS/EN stain showed the positive predictive value of the HOS test to identify viable sperm was 84.2 % overall and 79.7 % in the complete asthenozoospermia subgroup. Conclusion: The HOS test can effectively predict sperm viability in patients with severe and complete asthenozoospermia.

Test of frequency characteristic for well and itsresponse to seismic waves

The permeation parameters have been calculated by forefathers on the basis of permeation theory by means of the Slug test (Yin, Zheng, 1992) and the restoration curves of well level. We are interested in oscillation of the well level when we make Slug test. Both the permeation parameters and frequency parameters, i.e., natural period and damping coefficients of well aquifer, have been calculated on the basis of vibration theory by means of the oscillation curves. Not only this has given a new method, but also the different response of well level to seismic waves has been explained by it in theory.

A well test model for stress-sensitive and heterogeneous reservoirs with non-uniform thicknesses

In view of the anisotropy,heterogeneity and stress-sensitive permeability in low permeability reservoirs,an analytical well test model was established by introducing the concept of permeability modulus.This model considered the permeability stress-sensitivity,wellbore storage effect,and the skin effect.The perturbation technique and Laplace transformation were used to solve the mathematical model analytically in Laplace space,and the bottom-hole pressure type curves were plotted and analyzed in real space by using the Stehfest numerical inversion.

Simulation of unconventional well tests with the finite volume method

The finite volume method has been successfully applied in several engineering fields and has shown outstanding performance in fluid dynamics simulation. In this paper, the general framework for the simulation ofnear-wellbore systems using the finite volume method is described. The mathematical model and the numerical model developed by the authors are presented and discussed. A radial geometry in the vertical plane was implemented so as to thoroughly describe near-wellbore phenomena. The model was then used to simulate injection tests in an oil reservoir through a horizontal well and proved very powerful to correctly reproduce the transient pressure behavior. The reason for this is the robustness of the method, which is independent of the gridding options because the discretization is performed in the physical space. The model is able to describe the phenomena taking place in the reservoir even in complex situations, i.e. in the presence of heterogeneities and permeability barriers, demonstrating the flexibility of the finite volume method when simulating non-conventional tests. The results are presented in comparison with those obtained with the finite difference numerical approach and with analytical methods, if possible.

Application of wellhead suction anchor technology in the second production test of natural gas hydrates in the South China Sea

Traditional suction anchor technology is mainly used in the fields of subsea structure bearing foundations,single-point mooring systems and offshore wind power.It is characterized by providing sufficient lateral and vertical bearing capacities and lateral bending moment.The anchor structure of a traditional suction anchor structure is improved with wellhead suction anchor technology,where a central pipe is added as a channel for drilling and completion operations.To solve the technical problems of a low wellhead bearing capacity,shallow built-up depth,and limited application of conductor jetting in the second production test of natural gas hydrates(NGHs)in the South China Sea(SCS),the China Geological Survey(CGS)took the lead in independently designing and manufacturing a wellhead suction anchor,which fulfilled the requirements of the production test.This novel anchor was successfully implemented in the second production test for the first time,providing a stable wellhead foundation for the success of the second production test of NGHs in the SCS.

Automatic well test interpretation based on convolutional neural network for a radial composite reservoir

An automatic well test interpretation method for radial composite reservoirs based on convolutional neural network(CNN) is proposed, and its effectiveness and accuracy are verified by actual field data. In this paper, based on the data transformed by logarithm function and the loss function of mean square error(MSE), the optimal CNN is obtained by reducing the loss function to optimize the network with "dropout" method to avoid over fitting. The trained optimal network can be directly used to interpret the buildup or drawdown pressure data of the well in the radial composite reservoir, that is, the log-log plot of the given measured pressure variation and its derivative data are input into the network, the outputs are corresponding reservoir parameters(mobility ratio, storativity ratio, dimensionless composite radius, and dimensionless group characterizing well storage and skin effects), which realizes the automatic initial fitting of well test interpretation parameters. The method is verified with field measured data of Daqing Oilfield. The research shows that the method has high interpretation accuracy, and it is superior to the analytical method and the least square method.

New Regularization Algorithms for Solving the Deconvolution Problem in Well Test Data Interpretation

Two new regularization algorithms for solving the first-kind Volterra integral equation, which describes the pressure-rate deconvolution problem in well test data interpretation, are developed in this paper. The main features of the problem are the strong nonuniform scale of the solution and large errors (up to 15%) in the input data. In both algorithms, the solution is represented as decomposition on special basic functions, which satisfy given a priori information on solution, and this idea allow us significantly to improve the quality of approximate solution and simplify solving the minimization problem. The theoretical details of the algorithms, as well as the results of numerical experiments for proving robustness of the algorithms, are presented.

A method for preventing hydrates from blocking flow during deep-water gas well testing

Based on the research of the formation mechanism and evolution rule of hydrate flow obstacle during deep-water gas well testing,a new method for the prevention of hydrate flow obstacle based on safety testing window is proposed by changing the previous idea of"preventing formation"to the idea of"allowing formation,preventing plugging".The results show that the effective inner diameter of the testing tubing and the wellhead pressure decrease gradually with the formation and precipitation of hydrates during deep-water gas well testing,and it presents three typical processes of slow,fast and sudden changes.There is a safety testing window during deep-water gas well testing.The safety testing window of deep-water gas well testing decreases first and then increases with the increase of gas production rate,and increases with the increase of hydrate inhibitor concentrations.In the case with different testing production rates,a reasonable testing order with alternate low and high gas production rates has been proposed to further reduce the dosage of hydrate inhibitor and even avoid the use of hydrate inhibitors considering the decomposition and fall-off of hydrates.Compared with the traditional methods,the new method based on safety testing window can reduce the dosage of hydrate inhibitor by more than 50%.

Safety Control Technology of Deepwater Perforated Gas Well Testing

Due to the high difficulties, high investment, and high risks in deepwater oil and gas well testing, major safety problems can occur easily. A key to prevent accidents is to conduct safety assessment and control on deepwater testing and to improve the testing technology. The deepwater of the South China Sea has some special environmental features: long distance from offshore, frequent typhoons in summer and constant monsoons in winter, and the presence of sandy slopes, sandy ridges and internal waves, coupled with the complex properties of oil and gas reserves which bring more challenges to deepwater well testing. In combination with deepwater well testing practice in the South China Sea, this paper analyzes the main potential risks in deepwater well testing and concludes that there are risks of failures of testing string, tools, and ground processes. Other risks are gas hydrate blockage, reservoir stratum sanding, and typhoon impacts. Specific precautions are also proposed in response to these risks in the paper.

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

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.