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.

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.

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.

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.

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.

MATHEMATICAL AND COMPUTER SIMULATION TECHNOLOGY OF CONDENSATE OIL AND GAS WELLS STIMULATED BY ELECTROMAGNETIC HEATING

In this article, the recent research achievements on the theory and technology of condensate oil and gas wells stimulated by electromagnetic induction heating during middle or late exploitation period were introduced for the first time at home and abroad. A new kind of electromagnetic wave induction heating equipment XAEMH-1 was developed. Taking near wellbore zone temperature field as the main research object, which is the key factor for the condensation and retrograde vaporization during electromagnetic heating, the mathematical simulation model for a condensate oil and gas well stimulated by electromagnetic heating to eliminate blockage near wellbore region was established. A corresponding computer system was developed to dynamically predict and evaluate the efficiency of this electromagnetic heating process. Through this computer system, the near wellbore region distributions of several important factors such as temperature, pressure, condensate oil saturation and relative permeability can be described quantitatively. A condensate gas well in a late exploitation period reservoir here in China was chosen as a practical example to test the effectiveness of this new technology and some satisfactory results were obtained. These results proved that it is feasible to eliminate the near wellbore region blockage by electromagnetic heating. A new prospective stimulation method was given for the condensate oil and gas reservoirs during middle or late exploitation period.

A new method of deliverability prediction by steady point in gas wells

Calculating the absolute open flow potential timely and investigating production capacity so as to adjust working system of production wells is one of main means to effectively recovery gas reservoirs during intermediate and late development stage.In order to obtain the open flow potential of gas wells accurately,a new method which utilized a single steady point was proposed in this research,which was based on deliverability formula of a gas well in pseudo-steady state flow with pseudo-pressure form.The influence on factor B in binomial productivity equation caused by the changed permeability was taken into consideration.According to the stable production data,reservoir permeability K can be determined by iterative method firstly,and the coefficient A,B in binomial productivity equation can be calculated with the open flow potential subsequently.It illustrated clearly by a practical example that the new method was suitable for gas wells especially when the producing pressure drop is large.Additionally,the error between the open flow potential value and interpretation result from the multi-point test was small,which proved it to be more simple,economic and effective than the common one.

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.

A proposed NMR solution for multi-phase flow fluid detection

In the petroleum industry,detection of multi-phase fluid flow is very important in both surface and down-hole measurements.Accurate measurement of high rate of water or gas multi-phase flow has always been an academic and industrial focus.NMR is an efficient and accurate technique for the detection of fluids;it is widely used in the determination of fluid compositions and properties.This paper is aimed to quantitatively detect multi-phase flow in oil and gas wells and pipelines and to propose an innovative method for online nuclear magnetic resonance(NMR)detection.The online NMR data acquisition,processing and interpretation methods are proposed to fill the blank of traditional methods.A full-bore straight tube design without pressure drop,a Halbach magnet structure design with zero magnetic leakage outside the probe,a separate antenna structure design without flowing effects on NMR measurement and automatic control technology will achieve unattended operation.Through the innovation of this work,the application of NMR for the real-time and quantitative detection of multi-phase flow in oil and gas wells and pipelines can be implemented.

Assessing the effect of well completion types on productivity in a class 1G gas hydrate reservoir under pseudo steady state

This work focuses on the assessment of the effect of well completion types on gas productivity in subsea gas hydrate reservoirs of class 1G type where the gas hydrates have decomposed into gas and water.Three types of vertical well completions are considered:frac-packed well with vertical hydraulic fracture;frac-packed well with horizontal hydraulic fracture,and a cased-hole gravel-packed well.Sensitivity analysis was conducted with analytical well inflow models to determine factors that affect the gas well productivity.The results of the analyses indicated that proppant mass pumped during fracture treatment slightly improves well productivity for frac-packed natural gas hydrate wells.Well productivity increases nonlinearly with fracture productivity up to a threshold value of 50,000 md for fracpacked well with horizontal fracture,above which further increase in fracture conductivity would create no benefit.With a proppant mass of 50,000 Ibm and a corresponding proppant volume of 504 ft3,commercial gas production rates of 14.9 MMscf/d,5.621 MMscf/d,and 11.35 MMscf/d are possible for frac-packed well with vertical fracture,frac-packed well with horizontal fracture,and cased-hole gravelpacked well,respectively.Because hydraulic fracture orientation depends on the in-situ formation stress,whether a well should be hydraulic-fractured or not depends on in-situ formation stress.

Artificial intelligence method for predicting the maximum stress of an off-center casing under non-uniform ground stress with support vector machine

The situation of an off-center casing under non-uniform ground stress can occur in the process of drilling a salt-gypsum formation,and the related casing stress calculation has not yet been solved analytically. In addition,the experimental equipment in many cases cannot meet the actual conditions and the experimental cost is very high. These comprehensive factors cause the existing casing design to not meet the actual conditions and cause casing deformation,affecting the drilling operation in Tarim oil field. The finite element method is the only effective method to solve this problem at present,but the re-modelling process is time-consuming because of the changes in the parameters,such as the cement properties,casing centrality,and the casing size. In this article,an artificial intelligence method based on support vector machine(SVM) to predict the maximum stress of an offcenter casing under non-uniform ground stress has been proposed. After a program based on a radial basis function(RBF)-support vector regression(SVR)(ε-SVR) model was established and validated,we constructed a data sample with a capacity of 120 by using the finite element method,which could meet the demand of the nine-factor ε-SVR model to predict the maximum stress of the casing. The results showed that the artificial intelligence prediction method proposed in this manuscript had satisfactory prediction accuracy and could be effectively used to predict the maximum stress of an off-center casing under complex downhole conditions.