Assessment of Total Skin Factor in Perforated Wells
- Turhan Yildiz (Colorado School of Mines)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- February 2006
- Document Type
- Journal Paper
- 61 - 76
- 2006. Society of Petroleum Engineers
- 1.8 Formation Damage, 2.4.5 Gravel pack design & evaluation, 5.3.4 Integration of geomechanics in models, 1.6 Drilling Operations, 3.2.5 Produced Sand / Solids Management and Control, 1.11 Drilling Fluids and Materials, 2 Well Completion, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 4.1.5 Processing Equipment, 5.3.2 Multiphase Flow, 5.8.7 Carbonate Reservoir, 5.1 Reservoir Characterisation, 2.2.2 Perforating, 5.6.4 Drillstem/Well Testing, 3.2.4 Acidising, 3.2.8 Well Performance Modeling and Tubular Optimization, 2.4.3 Sand/Solids Control, 1.14 Casing and Cementing, 2.7.1 Completion Fluids, 4.3.4 Scale, 5.2.1 Phase Behavior and PVT Measurements
- 5 in the last 30 days
- 2,679 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 10.00|
|SPE Non-Member Price:||USD 30.00|
In this study, the available methods and software to predict the well productivity and total skin factor in fully perforated vertical wells have been reviewed. The methods have been compared against the experimental data obtained on an electrolytic apparatus, and their accuracy has been investigated. It has been observed that the 3D semianalytical model, SPAN 6.0 software, and the simple hybrid model described in this paper replicate the experimental results very well. On the other hand, the results estimated from the McLeod method and the Karakas-Tariq method substantially deviate from the experimental data; hence, these models/methods should be used with caution.
The literature hosts many equations to predict the total skin factor in partially perforated vertical wells. Some of the available models have been tested against the results from the 3D semianalytical model. It has been shown that total skin-factor equations based on the summation of individual components do not work.
The 3D semianalytical model has been modified to build an approximate model for fully and partially perforated inclined wells in isotropic formations. Additionally, a simple hybrid model to compute total skin factor in perforated inclined wells has been presented. The hybrid model for perforated inclined wells agrees well with the approximate 3D model. Some of the available models to calculate total skin factor in perforated inclined wells have been compared to the approximate 3D model, and their accuracy has been discussed.
Finally, a simple model to predict total skin factors in perforated horizontal wells has been developed. The application using the simple model has demonstrated that a combination of long wellbore length and perforations bypassing the damaged zone could overcome the destructive effect of severe formation damage around the wellbore.
The long-term productivity of oil and gas wells is influenced by many factors. Among these factors are petrophysical properties, fluid properties, degree of formation damage and/or stimulation, well geometry, well completions, number of fluid phases, and flow-velocity type. To isolate and identify the effect of any single parameter on the well performance, a sensitivity study on the parameter of interest is conducted, and the results are compared to a reference base case of an ideal vertical open hole. In the base case, the ideal vertical open hole produces single-phase fluid, the fluid flow obeys Darcy's law, and the formation is neither stimulated nor damaged. The influence of the individual parameters not considered in the base case is quantified in terms of skin factor.
Oil and gas wells may have permeability reduction around the wellbore caused by invasion by drilling mud, cement, solids, and completion fluids. This is generally referred to as formation damage. Formation damage around the wellbore causes additional pressure drop. On the other hand, stimulation operations such as acidizing may decrease the pressure drop in the near-wellbore region by improving the formation permeability around the wellbore. The impact of permeability impairment/improvement around the wellbore caused by drilling, production, and acidizing operations is quantified in terms of mechanical skin factor.
The fluid flow in the near-wellbore region is also influenced by well-completion type. Openhole completion yields a local flow pattern that is radial around the wellbore and normal to the well trajectory. However, in some cases, openhole completion may not be desirable. Different types of well completion may be needed to control/isolate fluid entry into the wellbore, to avoid gas/water coning, and to minimize sand production. Besides the openhole completion, wells may be partially or selectively completed with perforations, slotted liners, gravel packs, screens, and zonal-isolation devices. Also, wells with low productivity may need to be hydraulically fractured. In completed wells, the flow pattern around the wellbore is distorted. Completions result in additional fluid convergence and divergence in the near-wellbore region. For example, partial penetration creates a 2D flow field in the formation. On the other hand, a perforated well experiences 3D flow converging around perforation tunnels. Compared to an ideal open hole, the wells with completions are subject to additional pressure gain/loss in the near-wellbore region. The additional pressure change caused by well completion is quantified in terms of completion pseudoskin factor.
Well performance is naturally influenced by the geometry of the well itself. Based on their geometrical shape, wells may be classified as vertical, inclined, horizontal, undulating, and multibranched. In the literature, the reference well geometry has been that of a fully penetrating vertical open hole. Historically, the differences in the productivity of vertical openhole and other well geometries have also been formulated in terms of pseudoskin factor. However, when it comes to the assessment of completion effects on well productivity, rather than comparing the given completed nonvertical well to an ideal vertical open hole, it may be more appropriate to work with the considered well geometry only and compare the completed and openhole cases of the same well geometry. For this reason, the term geometrical pseudoskin factor is proposed to quantify the differences between the productivities of vertical wells and other well geometries.
Multiphase flow in the formation may evolve because of gas/water coning around the wellbore, gas evaporation from the liquid-hydrocarbon phase, and liquid dropout from gas condensate. Compared to single-phase fluid flow, multiphase flow in the formation creates an additional pressure drop because of the relative permeability effect. If multiphase flow is intensified in the near-wellbore region, only then may the impact of multiphase flow be formulated in terms of multiphase pseudoskin factor.
|File Size||2 MB||Number of Pages||15|
Beggs, H.D.: Gas Production Operations, OGCI Publications, Tulsa(1984) 85.
Beggs, H.D.: Production Optimization, OGCI Publications, Tulsa (1991)51.
Bell, W.T., Sukup, R.A., and Tariq, S.M.: Perforating, MonographSeries, SPE, Richardson, Texas (1995) 16.
Besson, J.: "Performance ofSlanted and Horizontal Wells on an Anisotropic Medium," paper SPE 20965presented at the 1990 SPE European Petroleum Conference, The Hague, 22-24October.
Carnegie, A.: "Application ofComputer Models To Optimise Perforating Efficiency," paper SPE 38042presented at the 1997 SPE Asia Pacific Oil and Gas Conference, Kuala Lumpur,14-16 April.
Cinco-Ley, H., Miller, F.G., and Ramey, H.J.: "Unsteady-State Pressure DistributionCreated by a Well With an Inclined Fracture," JPT (November 1975a)27, No. 11, 1392; Trans., AIME, 259.
Cinco-Ley, H., Ramey, H.J. Jr., and Miller, F.G.:"Pseudoskin Factors forPartially-Penetrating Directionally-Drilled Wells," paper SPE 5589presented at the 1975 SPE Annual Technical Conference and Exhibition, Dallas,28 September-1 October (1975b).
Daltaban, T.S. and Wall, C.G.: Fundamental and Applied PressureAnalysis, Imperial College Press, London (1998) 514.
Earlougher, R.C.: Advances in Well Test Analysis, Monograph Series,SPE, Richardson, Texas (1977) 5.
Economides, M.J. and Boney, C.: "Reservoir Stimulation in PetroleumProduction," Reservoir Stimulation, M.J. Economides and K.G. Nolte(eds.), John Wiley & Sons, New York City (2000) 1-12.
Elshahawi, H.M. and Gad, K.H.: "Estimation of Skin for HighDeliverability Gas Well Tests," paper SPE 68144 presented at the 2001 SPEMiddle East Oil Show, Bahrain, 17-20 March.
Golan, M. and Whitson, C.: Well Performance, Prentice-Hall Inc.,Englewood Cliffs, New Jersey (1991) 331-336.
Gringarten, A.C. and Ramey, H.J. Jr.: "An Approximate Infinite ConductivitySolution for a Partially Penetrating Line-Source Well," SPEJ (April1975) 15, No. 2, 140; Trans., AIME, 259.
Harris, M.H.: "The Effect ofPerforating on Oil Well Productivity," JPT (April 1966) 18,No. 4, 518; Trans., AIME, 237.
Hawkins, M.F.: "A Note on the Skin Effect," Trans., AIME (1956)207, 356.
Hong, K.C.: "Productivity ofPerforated Completions in Formations With or Without Damage ," JPT(August 1975) 27, No. 8, 1027; Trans., AIME, 259.
Jones, L.G. and Slusser, M.L.: "The Estimation of Productivity LossCaused by Perforations—Including Partial Completion and Formation Damage,"paper SPE 4798 presented at the 1974 SPE Midwest Oil and Gas Symposium,Indianapolis, Indiana, 28-29 March.
Jones, L.G. and Watts, J.W.: "Estimating Skin Effect in a PartiallyCompleted Damaged Well," JPT (February 1971) 23, No. 2, 249;Trans., AIME, 251.
Joshi, S.D.: Horizontal Well Technology, PennWell Publishing Co.,Tulsa (1991) 75.
Karakas, M. and Tariq, S.M.: "Semianalytical Productivity Modelsfor Perforated Completions," SPEPE (February 1991) 6, No. 1,73; Trans., AIME, 291.
Klotz, J.A., Krueger, R.F., and Pye, D.S.: "Effect of Perforation Damage on WellProductivity," JPT (November 1974) 26, No. 11, 1303;Trans., AIME, 257.
Kuchuk, F.J. and Kirwan, P.A: "New Skin and Wellbore Storage TypeCurves for Partially Penetrating Wells ," SPEFE (December 1987)2, No. 4, 546.
Locke, S.: "An Advanced Methodfor Predicting the Productivity Ratio of a Perforated Well ," JPT(December 1981) 33, No. 12, 2481.
McLeod, H.O. Jr.: "The Effectof Perforating Conditions on Well Performance," JPT (January 1983)35, No. 1, 31.
Nisle, R.G.: "Effect of Partial Penetration on Pressure Build-Up in OilWells," Trans., AIME (1958) 213, 85.
Odeh, A.S.: "Steady-State FlowCapacity of Wells With Limited Entry to Flow," SPEJ (March 1968)8, No. 1, 43; Trans., AIME, 243.
Odeh, A.S.: "Pseudosteady-StateFlow Capacity of Oil Wells With Limited Entry and an Altered Zone Around theWellbore," SPEJ (August 1977) 17, No. 4, 271; Trans.,AIME, 263.
Petrol, J.: "An Equation forCalculating Skin Factor Due to Restricted Entry," JPT (June 1980)964.
Ozkan, E. and Raghavan, R.: "AComputationally Efficient, Transient-Pressure Solution for Inclined Wells," SPEREE (October 2000) 3, No. 5, 414.
Pan, Y. and Tang, Y.: "Study on Underbalanced and Deep PenetratingPerforating Technology," Technical Report, Southwestern Petroleum Inst.,Nanchong, Sichuan, China (1989).
Papatzacos, P.: "ApproximatePartial-Penetration Pseudoskin for Infinite-Conductivity Wells ,"SPERE (May 1987) 2, No. 2, 227; Trans., AIME,283.
Penmatcha, R., Fayers, J., and Aziz, K.: "Skin Factor Calculations forVertical, Deviated, and Horizontal Wells (Task 2)," Productivity andInjectivity of Horizontal Wells, Annual Project Report, DOE/BC/14862-10,Stanford U., Palo Alto, California (July 1995).
Pucknell, J.K. and Clifford, P.J.: "Calculation of Total SkinFactors," paper SPE 23100 presented at the 1991 SPE Offshore EuropeConference, Aberdeen, 3-6 September.
Rogers, E.J. and Economides, M.J.: "The Skin Due to Slant of DeviatedWells in Permeability-Anisotropic Reservoirs ," paper SPE 37068 presentedat the 1996 SPE International Conference on Horizontal Well Technology,Calgary, 18-20 November.
Saidikowski, R.M.: "NumericalSimulations of the Combined Effects of Wellbore Damage and PartialPenetration," paper SPE 8204 presented at the 1979 SPE Annual TechnicalConference and Exhibition, Las Vegas, Nevada, 23-26 September.
Samaniego-V., F. and Cinco-Ley, H.: "Well Test Analysis in CarbonateReservoirs," Carbonate Reservoir Characterization: A Geologic-EngineeringAnalysis, Part II, G.V. Chilingarian, S.J. Mazzullo, and H.H. Rieke (eds.),Elsevier Science B.V., Amsterdam (1996) 589.
SPAN user guide, Version 6.0, Schlumberger Perforating and Testing, SugarLand, Texas (June 1999).
SPAN user guide, Version 6.11, Schlumberger Perforating and Testing, SugarLand, Texas (August 2002).
Streltsova-Adams, T.D.: "Pressure Drawdown in a Well WithLimited Flow Entry," JPT (November 1979) 31, No. 11,1469.
Tariq, S.M.: "Evaluation ofFlow Characteristics of Perforations Including Nonlinear Effects With theFinite-Element Method," SPEPE (May 1987) 2, No. 2, 104;Trans., AIME, 283.
Thomas, L.K., Evans, C.E., Pierson, R.G., and Scott, S.L.: "Well Performance Model,"JPT (February 1992) 44, No. 2, 220; Trans., AIME,293.
Vrbik, J.: "A SimpleApproximation to the Pseudoskin Factor Resulting From Restricted Entry ,"SPEFE (December 1991) 6, No. 4, 444.
Yildiz, T.: "Productivity ofSelectively Perforated Vertical Wells," SPEJ (June 2002) 7,No. 2, 158.
Yildiz, T. and Cinar, Y.: "Inflow Performance and TransientPressure Behavior of Selectively Completed Vertical Wells," SPEREE(October 1998) 1, No. 5, 467.