Rate transient analysis methods for water-producing gas wells in tight reservoirs with mobile water

Tight gas reservoirs with mobile water exhibit multi-phase flow and high stress sensitivity.Accurately analyzing the reservoir and well parameters using conventional single-phase rate transient analysis methods proves challenging.This study introduces novel rate transient analysis methods incorporating evaluation processes based on the conventional flowing material balance method and the Blasingame type-curve method to examine fractured gas wells producing water.By positing a gas-water two-phase equivalent homogenous phase that considers characteristics of mobile water,gas,and high stress sensitivity,the conventional single-phase rate transient analysis methods can be applied by integrating the phase's characteristics and defining the phase's normalized parameters and material balance pseudotime.The rate transient analysis methods based on the equivalent homogenous phase can be used to quantitatively assess the parameters of wells and gas reservoirs,such as original gas-in-place,fracture half-length,reservoir permeability,and well drainage radius.This facilitates the analysis of production dynamics of fractured wells and well-controlled areas,subsequently aiding in locating residual gas and guiding the configuration of well patterns.The specific evaluation processes are detailed.Additionally,a numerical simulation mechanism model was constructed to verify the reliability of the developed methods.The methods introduced have been successfully implemented in field water-producing gas wells within tight gas reservoirs containing mobile water.

Multistring analysis of wellhead movement and uncemented casing strength in offshore oil and gas wells

This paper presents a theoretical method and a finite element method to describe wellhead movement and uncemented casing strength in offshore oil and gas wells.Parameters considered in the theoretical method include operating load during drilling and completion and the temperature field,pressure field and the end effect of pressure during gas production.The finite element method for multistring analysis is developed to simulate random contact between casings.The relevant finite element analysis scheme is also presented according to the actual procedures of drilling,completion and gas production.Finally,field cases are presented and analyzed using the proposed methods.These are four offshore wells in the South China Sea.The calculated wellhead growths during gas production are compared with measured values.The results show that the wellhead subsides during drilling and completion and grows up during gas production.The theoretical and finite element solutions for wellhead growth are in good agreement with measured values and the deviations of calculation are within 10％.The maximum von Mises stress on the uncemented intermediate casing occurs during the running of the oil tube.The maximum von Mises stress on the uncemented production casing,calculated with the theoretical method occurs at removing the blow-out-preventer （BOP） while that calculated with the finite element method occurs at gas production.Finite element solutions for von Mises stress are recommended and the uncemented casings of four wells satisfy strength requirements.

Development Strategies for Achieving High Production with Fewer Wells in Conventional Offshore Heavy Oil Fields in Bohai Bay,China

Development strategy for heavy-oil reservoirs is one of the important research interests in China National Offshore Oil Corp. （CNOOC） that plans a highly effective development for heavy oil fields in multilayered fluvial reservoirs because of their significant influence on marine oil and even on China＇s petroleum production. The characteristics analysis of multilayered fluvial reservoirs in the heavy oil fields in Bohai Bay indicates that large amounts ofoil were trapped in the channel, point bar and channel bar sands. The reserves distribution of 8 oilfields illustrates that the reserves trapped in the main sands, which is 20%-40% of all of the sand bodies, account for 70%-90% of total reserves of the heavy oil fields. The cumulative production from high productivity wells （50% of the total wells） was 75%-90% of the production of the overall oilfield, while only 3%-10% of the total production was from the low productivity wells （30% of the total wells）. And the high productivity wells were drilled in the sands with high reserves abundance. Based on the above information the development strategy was proposed, which includes reserves production planning, selection of well configuration, productivity design, and development modification at different stages.

Study on a Gas Plunger Lift Model for Shale Gas Wells and Its Effective Application

The problem of efficient gas lift for gas well annulus packers that rely on their own energy plungers is considered.The complex related gas-liquid problem is addressed in the frame of model where the gas inflow dynamics and liquid inflow dynamics of the considered shale gas wells are weakly coupled.On this basis,and with the aiding support of indoor simulation experimental data,a new gas plunger lift design taking into account liquid leakage is obtained.Finally,a dedicated software relying on this approach is developed and used to verify the reliability of the model by means of field examples.

Selection of candidate wells for re-fracturing in tight gas sand reservoirs using fuzzy inference

An artificial-intelligence based decision-making protocol is developed for tight gas sands to identify re-fracturing wells and used in case studies. The methodology is based on fuzzy logic to deal with imprecision and subjectivity through mathematical representations of linguistic vagueness, and is a computing system based on the concepts of fuzzy set theory, fuzzy if-then rules, and fuzzy reasoning. Five indexes are used to characterize hydraulic fracture quality, reservoir characteristics, operational parameters, initial conditions, and production related to the selection of re-fracturing well, and each index includes 3 related parameters. The value of each index/parameter is grouped into three categories that are low, medium, and high. For each category, a trapezoidal membership function all related rules are defined. The related parameters of an index are input into the rule-based fuzzy-inference system to output value of the index. Another fuzzy-inference system is built with the reservoir index, operational index, initial condition index and production index as input parameters and re-fracturing potential index as output parameter to screen out re-fracturing wells. This approach was successfully validated using published data.

Effects of instantaneous shut-in of high production gas well on fluid flow in tubing

As the classical transient flow model cannot simulate the water hammer effect of gas well, a transient flow mathematical model of multiphase flow gas well is established based on the mechanism of water hammer effect and the theory of multiphase flow. With this model, the transient flow of gas well can be simulated by segmenting the curved part of tubing and calculating numerical solution with the method of characteristic curve. The results show that the higher the opening coefficient of the valve when closed, the larger the peak value of the wellhead pressure, the more gentle the pressure fluctuation, and the less obvious the pressure mutation area will be. On the premise of not exceeding the maximum shut-in pressure of the tubing, adopting large opening coefficient can reduce the impact of the pressure wave. The higher the cross-section liquid holdup, the greater the pressure wave speed, and the shorter the propagation period will be. The larger the liquid holdup, the larger the variation range of pressure, and the greater the pressure will be. In actual production, the production parameters can be adjusted to get the appropriate liquid holdup, control the magnitude and range of fluctuation pressure, and reduce the impact of water hammer effect. When the valve closing time increases, the maximum fluctuating pressure value of the wellhead decreases, the time of pressure peak delays, and the pressure mutation area gradually disappears. The shorter the valve closing time, the faster the pressure wave propagates. Case simulation proves that the transient flow model of gas well can optimize the reasonable valve opening coefficient and valve closing time, reduce the harm of water hammer impact on the wellhead device and tubing, and ensure the integrity of the wellbore.

Failure characteristics of surface vertical wells for relieved coal gas and their influencing factors in Huainan mining area

Based on data from through-hole and logging,we studied the failure characteristics of surface drainage wells for relieved coal gas in Huainan mining area and its influencing factors.The results show that the damaged positions of drainage wells are mainly located at the thick clay layer in the low alluvium and the lithological interface in the upper section of bedrock in west mining area.The failure depth of casing is 244-670 m and concentrates at about 270-460 m deep.These damaged positions are mainly located in the bending zone according to three zones of rock layers in the vertical section above the roof divided. Generally,the casing begins to deform or damage before the face line about 30-150 m.Special formation structure and rock mass properties are the direct causes of the casing failure,high mining height and fast advancing speed are fundamental reasons for rock mass damage.However,the borehole configuration and spacing to the casing failure are not very clear.

Progress and Development Direction of “Three-High” Oil and Gas Well Testing Technology

By reviewing the development of “three-high” oil and gas well testing technology of Sinopec in recent years, this paper systematically summarizes the application of “three-high” oil and gas well testing technology of Sinopec in engineering optimization design technology, and high temperature and high pressure testing technology, high pressure and high temperature transformation completion integration technology. Major progress has been made in seven aspects: plug removal and re-production technology of production wells in high acid gas fields;wellbore preparation technology of ultra-deep, high-pressure, and high-temperature oil and gas wells;surface metering technology;and supporting tool development technology. This paper comprehensively analyzes the challenges faced by the “three-high” oil and gas well production testing technology in four aspects: downhole tools, production testing technology, safe production testing, and the development of low-cost production test tools. Four development directions are put forward: 1) Improve ultra-deep oil and gas testing technology and strengthen integrated geological engineering research. 2) Deepen oil and gas well integrity evaluation technology to ensure the life cycle of oil and gas wells. 3) Carry out high-end, customized, and intelligent research on oil test tools to promote the low-cost and efficient development of ultra deep reservoirs. 4) Promote the fully automatic control of the surface metering process to realize the safe development of “three-high” reservoirs.

Shale high pressure isothermal adsorption curve and the production dynamic experiments of gas well

The high pressure static adsorption curves of shale samples from Silurian Changning-Weiyuan Longmaxi Formation were tested by using high pressure isothermal adsorption equipment.The physical modeling of depletion production was tested on single cores and multi-core series by using self-developed shale gas fluid-solid coupling experiment system.The adsorption and desorption laws were summarized and a high pressure isothermal adsorption model was established.The calculation formula of gas content was corrected,and the producing law of adsorption gas was determined.The study results show that the isothermal adsorption law of the shale reservoir under high pressure was different from the conventional low pressure.The high pressure isothermal adsorption curve had the maximum value in excess adsorption with pressure change,and the corresponding pressure was the critical desorption pressure.The high pressure isothermal curve can be used to evaluate the amount of adsorbed gas and the producing degree of adsorption gas.The high pressure isothermal adsorption model can fit and characterize the high pressure isothermal adsorption law of shale.The modified gas content calculation method can evaluate the gas content and the proportion of adsorbed gas more objectively,and is the theoretical basis of reserve assessment and production decline analysis.The producing degree of adsorption gas is closely related to the pressure,only when the reservoir pressure is lower than the critical desorption pressure,the adsorption gas can be produced effectively.In the process of gas well production,the pressure drop in the near-well area is large,the production of adsorption gas is high;away from the wellbore,the adsorption gas is low in production,or no production.

Improved Approaches Coupling the Method on Discharge Allocation and“High Kv in Wellblock”for Simulating Multiaquifer Wells

The mathematic models to simulate the multiaquifer well using the discharge allocation based on explicit transmissivity-weighted or the implicit transmissivity and the hydraulic gradient(TJ method),can not describe the actual well,especially with vertical flow along the wellbore.In order to improve the accuracy of the results,two improved approaches are established,by coupling the ideas of"High Kv in Wellblock"into the aforementioned methods on discharge allocation to consider the vertical flow

Flowback and early-time production modeling of unconventional gas wells using an improved semi-analytical method

Multiple fractured horizontal wells (MFHWs) currently are the only possible means of commercial production from the low and ultra-low permeability unconventional gas reservoirs. In early production time, flowback fluid, which constitutes of hydraulic water and gas flow within fractures, is collected and analyzed. Flowback analysis has been shown to be a useful tool to estimate key properties of the hydraulic fracture such as conductivity and pore volume. Until date, most tools of flowback analysis rely on empirical and approximate methods. This study presents an improved Green-function-based semi-analytical solution for performance analysis of horizontal gas wells during flowback and early production periods. The proposed solution is derived based on coupling the solutions of two domains: a rigorously derived Green’s function-based integral solution for single-phase gas flow in matrix, and a finite-difference, multiphase solution for gas–water two-phase flow in the fracture. The validity of proposed semi-analytical solution is verified by finely gridded numerical models built in a commercial simulator for a series of synthetic cases considering a variety of fluid and reservoir property combinations, as well as various different production constraints. Comparisons against available empirical and approximate methods are also provided for these cases.

Establishment of tensile failure induced sanding onset prediction model for cased-perforated gas wells

Sand production is a challenging issue in upstream oil and gas industry,causing operational and safety problems.Therefore,before drilling the wells,it is essential to predict and evaluate sanding onset of the wells.In this paper,new poroelastoplastic stress solutions around the perforation tunnel and tip based on the Mohr-Coulomb criterion are presented firstly.Based on the stress models,a tensile failure induced sanding onset prediction model for cased-perforated gas wells is derived.Then the analytical model is applied to field data to verify its applicability.The results from the perforation tip tensile failure induced sanding model are very close to field data.Therefore,this model is recommended for forecasting the critical conditions of sand production analysis.Such predictions are necessary for providing technical support for sand control decision-making and predicting the production condition at which sanding onset occurs.

The Study of Tubing Vibration Mechanism in High Pressure Gas Well

Deep gas wells and gas fields have the characteristics of high pressure. The vibration of the tubing string during the production of gas wells causes the string to be subjected to severe stress and even dynamic fatigue failure. Therefore, this article is based on the dynamic finite element theory, aiming at the characteristics of large-size tubing strings in deep gas wells. The finite element mechanics model and mathematical model of the tubing string vibration of the packer of high-pressure gas wells were established, and the ANSYS software was re-developed. The finite element analysis program for the vibration dynamics of the unbuckled and buckled strings of gas wells was compiled with APDL, and the displacement of the longitudinal vibration of the tubing string of high-pressure gas wells was studied. According to different sizes of tubing strings currently used in deep gas wells and gas fields, simulation calculations are carried out, and the axial impact load and buckling damage laws of the tubing strings of the entire well section under different production rates are obtained. It provides a theoretical basis for the prediction of tubing string vibration law and measures to prevent tubing string vibration.

Wellbore Stability Problems in Deepwater Gas Wells

The analysis of wellbore stability in deepwater gas wells is vital for effective drilling operations, especially in deepwater remote areas and for modern drilling technologies. Wellbore stability problems usually occur when drilling through hydrocarbon formations such as shale, unconsolidated sandstone, fractured carbonate formations and HPHT formations with narrow safety mud window. These problems can significantly affect drilling time, costs and the whole drilling operations. In deepwater gas wells, there is also the possible of gas hydrate problems because of the low temperature and high pressure conditions of the environment as well as the coexistence of gas and water inside the wellbore. These hydrates can block the mud line, surface choke line and even the BOP stack if no hydrate preventive measures are considered. In addition, the dissociation of these hydrates in the wellbore may gasify the drilling fluid and reduce drilling mud density, hydrostatic pressure, change mud rheology and cause wellbore instabilities. Traditional wellbore stability analysis considered the formation to be isotropic and assumed that the rock mechanical properties are independent of in-situ stress direction. This assumption is invalid for formations with layers or natural fractures because the presence of these geological features will influence rock anisotropic properties, wellbore stress concentration and failure behavior. This is a complicated phenomenon because the stress distribution around a wellbore is affected by factors such as rock properties, far-field principal stresses, wellbore trajectory, formation pore pressure, reservoir and drilling fluids properties and time. This research work reviews the major causes of wellbore stability problems in deepwater gas wells and outlines different preventive measures for effective drilling operation, because real-time monitoring of drilling process can provide necessary information for solving any wellbore stability problems in a short time.

Experimental Study on the Attenuation Law of Vibration Wave Propagation in Natural Gas Wells in Coal-Gas Cross-Mining Area

Aiming at the safety distance between coal mining working face and natural gas wells in the cross-mining area of multiple mineral resources, the cross- mining area of gas and coal resources in the Ordos Basin is taken as the engineering background. An anti-collision early warning technology method based on vibration wave propagation attenuation monitoring is proposed to prevent collision accidents between road headers and natural gas wells. Through the steel pipe and steel pipe concrete knocking vibration test and underground digging vibration test, the research results show that: The exponential decay coefficients of the vibration wave in steel pipe, steel pipe concrete and coal rock respectively are 0.1, 0.1140 and 0.03, which are all in accordance with the exponential decay law, and the vibration wave firstly decays sharply and then decays slowly;the formula for the distance from the road header to the natural gas well was derived based on the vibration attenuation formula, to provide a new method for realizing the problem of precise and coordinated extraction by surface monitoring of the distance from down hole road headers to gas wells, collision prevention prediction and warning and prevention of collision of extraction equipment with gas wells.

APPLICATION OF HIGH-RESOLUTION MAGNETIC METHOD AND GRADIENT METHOD TO LOCATE ABANDONED BRINE-WELLS IN HUTCHINSON, KANSAS, U.S.A.

After successfully locating one abandoned brine well by an electromagnetic method during testing in 2001 and five abandoned brine wells by a high resolution magnetic method during 2002, a high resolution magnetic method was again proposed to search for wells in 2003 when a second sensor was employed to acquire data for calculating the pseudo vertical gradient of magnetic fields. Total area surveyed in 2003 was 1,024,000 ft 2, which was divided into grids with an average size of 10,000 ft 2 and distributed across eight different sites. Magnetic anomalies and their vertical gradients from known brine wells were first recorded as signatures to identify anomalies caused by possible buried brine wells. Of fifty one verified anomalies, thirty one anomalies were due to wells buried at depths from 0 to 8.5 ft: twenty one 6 to 9 inch abandoned brine wells, seven 1.5 to 3 inch probable water wells, one 16 inch dewatering well for a construction site at a depth of 3 ft, and two 4 inch wells on the ground surface. Approximate monopole shaped anomalies were observed from all these wells after data corrections. However, the range of amplitudes of magnetic anomalies from 7,000 to 28,000 nT from these abandoned brine wells was measured. This range of anomalies is mainly due to the thickness and depth of buried wells. Anomaly amplitudes from 1.5 to 3 inch wells are 4,000 to 8,000 nT and linearly correlate with the buried depth. One 3 inch well that caused an anomaly of 13,000 nT could be the inner pipe of a brine well. Gradient anomalies are roughly in a range of 100 to 200 nT/inch for 1.5 to 3 inch wells and 200 to 300 nT/inch for brine wells.As indicated by the potential field theory, gradient data possess higher horizontal resolution than the magnetic field itself. Gradient data provide valuable assistance in determining horizontal locations of anomaly sources for excavation. In practice, however, improvement in the horizontal resolution is limited by survey line spacing. If only one sensor is used in a survey, there is rapid decrease in the horizontal resolution when sensor height increases from 14 to 44 inches. This indicates that it is critical to keep the sensor as close to the ground as possible when hunting buried wells that are close to each other. It also suggests that the downward continuation is useful to increase the horizontal resolution in well hunting.

Classification of Chinese Traditional Drug-"Beimu" (Bulbus Fritillariae) by Pyrolysis High Resolution Gas Chromatography-Pattern Recognition

The combination of pyrolysis high resolution gas chromatography and pat- tern recognition techniques is a powerful tool for the classification of traditional Chinese drug.A study has been completed on 55 Beimu samples of five different geographic origins: Eastern China.Central China.South-western China,North-western China and North-eastern China.Principal component analysis and SIMCA are applied to effectively classifying the samples according to the origin of the plants.The chemical information contained in the high resolution gas chromatographic data is sufficient to characterize the geographic origin of sam- pies.

D-二聚体、超敏C反应蛋白联合Wells评分对早期静脉血栓栓塞症的诊断价值

目的D-二聚体、超敏C反应蛋白(hs-CRP)联合Wells评分对早期静脉血栓栓塞症(VTE)的诊断价值。方法选取2014年4月至2020年4月常州市第七人民医院收治的80例VTE患者作为观察组和80例非VTE患者作为对照组,比较两组患者的D-二聚体、hs-CRP水平和Wells评分,以及其与VTE发病的相关性。以受试者工作特征(ROC)曲线和曲线下面积(AUC)评估D-二聚体、hs-CRP、Wells评分单独及联合检测对早期VTE的诊断效能。结果观察组患者D-二聚体、hs-CRP水平和Wells评分均明显高于对照组,差异均有统计学意义(P<0.01)。观察组患者栓塞性疾病的可能性高于对照组,差异有统计学意义(P<0.05)。Spearman相关分析结果显示,D-二聚体、hs-CRP水平、Wells评分与VTE发生均呈正相关(r=0.422、0.502、0.392,P<0.05)。D-二聚体、hs-CRP、Wells评分联合诊断VTE的AUC为0.830(95%CI:0.766~0.894),灵敏度、特异度分别为75.00%、85.00%。结论D-二聚体、hs-CRP、Wells评分联合检测对早期VTE的诊断价值较高。

Applications of high-gravity technologies in gas purifications: A review

The traditional gas purification techniques such as wet gas desulfurization, with their advantages of large-scale implementation and maturity, have still been widely used. However, the main drawback of these techniques is the low transfer efficiency, which normally needs towers as tall as tens of meters to remove the pollutants. Therefore, new technologies which could enhance the mass transfer efficiency and are less energy-intensive are highly desirable. As a process intensification technology, high-gravity technology, which is carried out in a rotating packed bed(RPB), has recently demonstrated great potential for industrial applications due to its high mass transfer efficiency, energy-saving, and smaller volume. This consequently provides higher efficiency in toxic gas removal, and can significantly reduce the investment and operation costs. In this review, the mechanism,characteristics, recent developments, and the industry applications of high-gravity technologies in gas purifications, such as hydrogen sulfide, nitrogen oxide, carbon dioxide, sulfur dioxide, volatile organic compounds and nanoparticle removal are discussed, most of the demonstration projects and practical application examples in gas purification come from China. The perspective and prospective of this technology in gas purification and other fields are also briefly discussed.