Effects of Formation Damage and High- Velocity Flow on the Productivity of Perforated Horizontal Wells
- Yula Tang (Scandpower Petroleum Technology) | Turhan Yildiz (Colorado School of Mines) | Erdal Ozkan (Colorado School of Mines) | Mohan G. Kelkar (U. of Tulsa)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- August 2005
- Document Type
- Journal Paper
- 315 - 324
- 2005. Society of Petroleum Engineers
- 4.3 Flow Assurance, 5.6.4 Drillstem/Well Testing, 3.3.6 Integrated Modeling, 1.8 Formation Damage, 2.2.2 Perforating, 5.1.5 Geologic Modeling, 5.1 Reservoir Characterisation, 2.4.3 Sand/Solids Control, 5.3.2 Multiphase Flow, 1.6 Drilling Operations, 5.3.1 Flow in Porous Media
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A comprehensive semianalytical model has been built to investigate theeffects of drilling and perforating damage and high-velocity flow on theperformance of perforated horizontal wells. The model incorporates theadditional pressure drop caused by formation damage and high-velocity flow intoa semianalytical coupled wellbore/reservoir model. The reservoir modelconsiders the details of flow in the vicinity of the wellbore, including 3Dconvergent flow into individual perforations, flow through the damaged zonearound the wellbore and the crushed zone around the perforation tunnels, andnon-Darcy flow in the near-wellbore region. The wellbore flow model includesthe effect of frictional pressure drop. Both oil and gas wells areconsidered.
The expressions provided in this paper for additional pressure losses causedby perforating damage, drilling damage, and high-velocity flow can be used tooptimize perforating parameters and decompose the total skin into itscomponents (perforation pseudoskin, damage skin, and non-Darcy skin).
The performance of oil and gas wells may be influenced by the simultaneouseffect of mechanical skin, high-velocity (non-Darcy) skin, and completionpseudoskin factors. The skin factors caused by formation damage and perforatingdamage constitute the mechanical-skin factor. The extra pressure drop caused byhigh-velocity flow is known as the rate-dependent or non-Darcy flow factor.Compared to an ideal open hole, the wells with completions and other geometriessuch as perforations, slotted liner, or partial penetration may experienceadditional pressure loss or gain. The additional pressure change caused by wellcompletion and geometry is quantified in terms of pseudoskin factor. Thecombined effects of all the skin factors lead to a total skin factor that maybe estimated from pressure-transient data. The total skin factor, however, isnot simply the sum of the individual skin components, and the computation ofthe individual skin components is not straightforward (the interaction betweenthe individual components of total skin is nonlinear).
Many studies have concentrated on the effects of formation damage andhigh-velocity (non-Darcy) flow on well performance. For perforated verticalwells, McLeod's analytical model has been a widely accepted approximation toaccount for the additional pressure drop caused by formation damage andhigh-velocity flow. Karakas and Tariq presented a semianalytical model topredict the pseudoskin and productivity of perforated vertical wells withformation damage. The models suggested by McLeod and Tariq, however, may notwork for selectively completed wells in which the flux distribution may benonuniform. An example of this case is selectively perforated horizontalwells.
Tang et al. presented models for horizontal wells completed with slottedliners or perforations. The additional pressure drop in the vicinity of thewellbore because of formation damage, perforating, flow convergence, andhigh-velocity flow was included in their models in the form of a total-skinterm. The existing horizontal-well models are not capable of explicitlyrelating the skin factor to the physical parameters controlling the additionalpressure drop around the wellbore. In addition, the interplay between the skinand flux distribution and its impact on the productivity of perforatedhorizontal wells have not been discussed, especially for selectively perforatedhorizontal wells. Non-Darcy flow effect in perforated horizontal wells isanother topic that has not been addressed adequately in the literature.
In this study, we present a semianalytical model to predict the productivityof perforated horizontal wells under the influence of formation damage,perforating damage, and high-velocity flow. The nonlinear interaction betweenthe individual skin components is accurately represented in the model. Themodel is applicable to both single-phase oil and gas wells (the pseudopressureconcept is used to extend the oil-flow model to the gas wells). Using themodel, the combined effects of formation damage, the crushed zone around theperforation tunnels, and the high-velocity flow on the horizontal-wellperformance have been investigated in detail. The completion and damageparameters controlling the well productivity were identified throughsensitivity studies.
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