Two-phase flow choke performance in high rate gas condensate wells

Document ID: 145576-MSAbstract Multiphase flow occurs in almost all producing oil and gas/condensate wells. Wellhead chokes are special equipment that widely used in the petroleum industry to control flow rate, to maintain well allowable, to protect surface equipments, to prevent water and gas coning and to provide the necessary backpressure to reservoir to avoid formation damage from excessive drawdown. Accurate modeling of choke performance and selection of optimum choke size is vitally important for a petroleum engineer in production from reservoirs due to high sensitivity of oil and gas production to choke size. Two main approaches have been proposed for prediction of multiphase flow through chokes can be classified as either analytical or empirical and majority of correlations were developed for critical flow conditions. Although most of the correlations available to petroleum engineers are for critical flow but in lots of high rate gas/condensate wells subcritical flow occurs in large choke sizes.There is no empirical correlation for wellhead choke performance under subcritical condition for high rate gas condensate wells, especially in large choke sizes. The first aim of this paper is to develop a new simple empirical Gilbert type correlation for high rate gas condensate wells under subcritical flow in large choke sizes (40/64 in. to 192/64 in.) using non-linear regression analysis based on 61 field data points of 15 wells from ten different fields. The second is to extend the work of Al-Attar for high rate gas condensate wells flowing through large choke size under subcritical flow conditions and check the applicability and advantages.Finally, statistical comparison between these two approaches is done with different error parameters.Hamid Reza Nasriani and Azim Kalantarias

Axi-symmetric two-phase suspension-colloidal flow in porous media during water injection

Injection of colloids and suspensions in natural reservoirs with particle capture results in well injectivity decline. However, some initial improvement in injectivity was observed during waterflooding of oilfields and explained by increasing mobility of two-phase fluid during the displacement of more viscous oil by water. We derive an analytical model for axi-symmetric two-phase flow with simultaneous deep bed filtration of injected particles, formation of external filter cake, and its stabilization due to particle dislodgement. The explicit formula for dimensionless pressure drawdown (impedance) yields the type curve for impedance history. It is shown that the initial injectivity increase, induced by varying two-phase mobility, adds three degrees of freedom to one-phase impedance growth model. This additional information is used for tuning the models with the Corey relative permeability and the pseudo-relative permeability under the viscous-dominant displacement. Treatment of the data from three synthetic cases results in good agreement with the initial data, validating the developed model adjustment method. Three field case data have been considered. Good agreement between the field and modeling data along with common values of the obtained constants validate the developed analytical model for injectivity decline during waterflooding and its adjustment method.Azim Kalantariasl, Abbas Zeinijahromi and Pavel Bedrikovetsk

Investigating the relative impact of key reservoir parameters on performance of coalbed methane reservoirs by an efficient statistical approach

The complex and unique production mechanism of CBM has been examined extensively; however, production from such reservoirs requires more investigation to be well-understood, predicted and enhanced. This study is aimed at probing the significance of some controlling parameters on CBM performance by a statistical approach. The relative impact of five CBM reservoir parameters (reservoir pressure, cleat permeability and porosity, Young's modulus and Langmuir pressure) on the performance of natural depletion as well as Enhanced Coalbed Methane (ECBM) were numerically investigated. Recovery factor (RF) for primary depletion and ECBM, original gas in place (OGIP) and CO₂ storage were the investigated responses. In order to conduct the research, a synthetic CBM reservoir model was constructed using a commercial reservoir simulator. Since the effects of reservoir parameters on CBM production are quite complicated, it was intended to explore the potential interaction effects between the parameters along with the relative impact of each parameter. Therefore, a professional statistical software, Design Expert, was selected to determine the parameters' effects. The results show that while recovery factor value in primary recovery has positive correlations with all of the five parameters, cleat permeability and Langmuir pressure play the most significant roles. For ECBM by CO₂ injection, cleat permeability has the most significant effect on recovery factor measure, followed by cleat porosity. The predicted model for ECBM recovery factor suggests that Young's modulus, opposite to the primary recovery condition, has an adverse relationship with RF and the cleat porosity-permeability interaction has a considerable negative effect on RF measure. The predicted coalbed methane OGIP model proposes that in comparison with pressure and Langmuir pressure, the relative impacts of the other three parameters are negligible. Furthermore, results reveal that CO₂ storage is positively affected by cleat porosity and permeability, and negatively affected by Young's modulus and Langmuir pressure.H. Akhondzadeh, A. Keshavarz, M. Sayyafzadeh, A. Kalantarias

A New Correlation for Prediction of Critical Two-phase Flow through Wellhead Chokes

The first scope of this study is to develop a new accurate empirical Gilbert type critical flow correlation based on 361 actual production tests data from Middle Eastern oil fields by means of non-linear regression analysis. The second scope is to study the impact of temperature on Gilbert type critical flow correlation for these data sets. In order to modify the Gilbert type critical flow correlation for these data sets, correlations are tuned based on available field data points using nonlinear regression method. in this study, generalized reduced gradient (GRG) algorithm of iteration was used to find the correlation coefficients based on available field data and the convergence criteria is to minimize the value of the squared sum, SS, of the difference between the real data and the estimated one. Based on error analysis, for the oil fields, liquid flow rate prediction is improved when new approaches (including/excluding temperature) are used. It is also concluded that the accuracy of new approach to predict production rate is not expressively improved by including the temperature in choke performance correlation for this data set compared to the case without temperature

Nonuniform external filter cake in long injection wells

Buildup and stabilization of external filter cake is a well-known phenomenon in several environmental and industrial applications. Significant decline of the tangential rate along thick intervals in lengthy vertical wells yields a nonuniform external filter cake profile. We derive the mechanical equilibrium equations for the stabilized cake profile accounting for electrostatic particle−rock interaction, varying permeate factor, applying the torque balance to describe cake equilibrium, and calculating the lever arm ratio using Hertz’s theory for contact deformation of cake and particles. An implicit formula for the cake thickness along the well is derived. Two regimes of the stabilized cake buildup correspond to low rates, where the cake starts from the reservoir top, and for high rates, where the cake is formed in the lower well section only. The sensitivity analysis shows that the drag and permeate forces are the competitive factors affecting cake thickness under varying Young’s modulus, rate, and salinity. The main parameters defining external cake profile are injection rate, cake porosity, water salinity, and Young’s modulus.Azim Kalantariasl, Rouhi Farajzadeh, Zhenjiang You and Pavel Bedrikovetsk

An Experimental investigation of the effect of pressure gradient on gas-oil relative permeability in Iranian carbonate rocks

The authors examine the effect of pressure gradient on gas-oil relative permeability in horizontal and vertical immiscible displacement. The experiments are conducted on a core from lower Dalan formation in the South Pars oilfield of Iran, in constant pressure, unsteady-state condition, and different pressure gradients. The Toth method is used for calculating the relative permeability and plotting proper curves. Data analysis and the effect of pressure gradient on gas-oil relative permeability are investigated. Results show that relative permeability curves are affected by pressure gradient and this effect is much prominent at low pressures due to end-effect phenomena. The dependence of relative permeability curves on pressure gradient is correlated as a function of dimensionless capillary number. The accuracy of this correlation for relative permeability prediction is examined and a new method is introduced to minimize the end-effect phenomena on relative permeability curves.A. Keshavarz, H. Vatanparast, M. Zargar, A. Kalantari Asl and M. Haghigh

Produced water re-injection and disposal in low permeable reservoirs

Produced water re-injection (PWRI) is an important economic and environmental-friendly option to convert waste to value with waterflooding operations. However, it often causes rapid injectivity decline. In the present study, a coreflood test on a low permeable core sample is carried out to investigate the injectivity decline behavior. An analytical model for well impedance (normalized reciprocal of injectivity) growth, along with probabilistic histograms of injectivity damage parameters, is applied to well injectivity decline prediction during produced water disposal in a thick low permeable formation (Völkersen field). An impedance curve with an unusual convex form is observed in both coreflood test and well behavior modeling; the impedance growth rate is lower during external filter cake build-up if compared with the deep bed filtration stage. Low reservoir rock permeability and, consequently, high values of filtration and formation damage coefficients lead to fast impedance growth during deep bed filtration; while external filter cake formation results in relatively slow impedance growth. A risk analysis employing probabilistic histograms of injectivity damage parameters is used to well behavior prediction under high uncertainty conditions.Azim Kalantariasl, Kai Schulze, Jöerg Storz, Christian Burmester, Soeren Küenckeler, Zhenjiang You, Alexander Badalyan, Pavel Bedrikovetsk