Well Performance Model

Abstract

Summary This paper describes the development and application of a comprehensive wellperformance model. The model contains six distinct sections: simulation design, tubing and/or casing flow, reservoir and near-wellbore calculations, productionforecasting, wellbore heat production forecasting, wellbore heat transmission, and economics. These calculations may be performed separately or in anintegrated fashion with data and results shared among the different sections. The model analysis allows evaluation of all aspects of well completion design, including the effects on future production and overall well economics.production and overall well economics. Introduction The well performance model can evaluate completion design alternatives andpredict well performance. The model consists of six distinct parts: hydraulicfracture modeling, well completion evaluation, gas backpressure analysis, production forecasting, wellbore heat transmission, and economic evaluation. These separate functions have been integrated into a single package thatprovides sharing of data and results. The provides sharing of data and results. The model features interactive input with on-line help, data checking, and unitconversion. This work describes the engineering calculations used in the modeland illustrates the results that can be obtained In the following sections thesix major parts of the well performance model are parts of the well performancemodel are developed. Hydraulic modeling is discussed with a 2D fracturegeometry model. The model can predict the behavior for either proppant or acidfracturing. Well completion evaluation is performed by plotting both reservoirinflow and tubing flow plotting both reservoir inflow and tubing flow curves ona single plot. Equations are developed to account for the wide variety oftubing, near-wellbore, and reservoir effects that can be modeled. Theconstruction of wellhead, bottomhole, and transient backpressure plots formonitoring well performance or predicting deliverability is performance orpredicting deliverability is described. These plots can be constructed frommultipoint field test data, well-test-derived skin, or full specification ofthe well completion design. Production forecasting is performed by combiningtransient and pseudo-steady-state analytical solutions with pseudo-steady-stateanalytical solutions with a single-cell material balance. Single-phase gas andoil or two-phase gas/oil production can be predicted. The effects of waterinflux on the production forecast is developed. Also, a simple multicell coningproblem is constructed to illustrate the workstation's ability to submitcomputer intensive jobs to a supercomputer interactively. The program also canrun domestic or international economics. The calculation of wellboretemperature profiles and the prediction of hydrate f are described. Examplesillustrate the model. Stimulation A 2D hydraulic fracture model, which can predict both propped and acidfracturing is predict both propped and acid fracturing is incorportated in thewell performance model. The model uses a modified Geertsma and deKlerkformulation to describe the behavior of the linear, 2D fracture. Thisformulation predicts width and length assuming a rectilinear propagation of thefracture from a line source. The model is based on the program developed by Rybicki et al. For the program developed by Rybicki et al. For the U.S. DOE. Rybiciki et al. extended the original work of Geertsma and deKlerk to includenon-Newtonian fluids, fluid leakoff, mill proppant transport. The total fluidleakoff is cal internally or may be entered directly. Fracture height is set bythe user and normally is greater than the pay height. The proppant transportmodel allows different proppants to be used in different stages. Thepredictions of this model are highly dependent on the proppant settlingcalculations used. The model of Acharya is used exclusively in the wellperformance model. Thirty-eight proppants are supported by the program. Theprogram has been modified to estimate dimensionless fracture conductivity assuggested by Economides and Nolte. The suspended (slurry) and settled (bed)concentrations of proppant contained in the pay zone are obtained first. Thecell concentration (in pounds proppant per gallon is combined with the fracturewidth modeled for that cell to obtain the propped concentration (in pounds persquare foot). The dimensionless fracture conductivity then is obtained on acell-by-cell basis. These cell conductivities are averaged to obtain thefracture conductivity. Tables of proppant data are used to provide therelationship between concentration of proppant, closure stress, and thefracture conductivity. The closure stress is taken to be constant along thefracture and is calculated as the difference between the bottomhole treatingpressure (BHTP) and the bottomhole flowing pressure (BHTP) and the bottomholeflowing pressure (BHFP) when the well is put on pressure (BHFP) when the wellis put on production.

Assessment of Total Skin Factor in Perforated Wells

“…The results from these nomographs may be digitized, tabulated, and integrated into well-performance models. Thomas et al (1992) used a table lookup procedure to incorporate the results from Locke's nomograph into their well-performance software.…”

“…25 agree very well. The models proposed by Vrbik (1991), Bell et al (1995), Thomas et al (1992), Penmatcha et al (1995), Golan and Whitson (1991), Samaniego-V. and Cinco Ley (1996), Economides and Boney (2000), and Elshahawi and Gad (2001) predict substantially different results. The total skin equations for the different methods are listed in Table 1.…”

“…A great number of experimental, numerical, empirical, and semianalytical models have been constructed to predict the perforation pseudoskin and perforation total skin (Jones and Slusser 1974;Harris 1966;Klotz et al 1974;Hong 1975;Locke 1981;Tariq 1987;McLeod 1983;Karakas 1991;Bell et al 1995;SPAN 1999;SPAN 2002;Thomas et al 1992;Yildiz 2002;Pan and Tang 1989). Some of these models will be described briefly below.…”

“…Many previous studies (Vrbik 1991;Thomas et al 1992;Penmatcha et al 1995;Golan and Whitson 1991;Samaniego-V. and Cinco Ley 1996;Economides and Boney 2000;Elshahawi and Gad 2001;Beggs 1984Beggs , 1991 have focused on quantifying total skin factor in partially perforated vertical wells. In some publications (Beggs 1984(Beggs , 1991, the pseudoskin due to partial completion and the pseudoskin due to perforations are completely mixed up.…”

Optimization of Well Production System by NODAL Analysis Technique

“…Flow from a vertically fractured well can be calculated with the radial flow equation and the appropriate shape factor, C A , which is a function of fracture half length and reservoir half length, x f =x e (Thomas et al, 1992). The equation for infinite conductivity (uniform flux) is CA D 1:04728 0:020904.x f =x e / 0:23864.x f =x e / 2 :…”