Use of Perforation-Tunnel Permeability To Assess Cased Hole Gravelpack Performance
- R.C. Burton (Conoco Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 1999
- Document Type
- Journal Paper
- 235 - 239
- 1999. Society of Petroleum Engineers
- 3 Production and Well Operations, 2.4.3 Sand/Solids Control, 5.6.4 Drillstem/Well Testing, 2.4.5 Gravel pack design & evaluation, 2.2.2 Perforating, 2.4.6 Frac and Pack, 1.8 Formation Damage, 2 Well Completion, 5.3.2 Multiphase Flow, 1.14 Casing and Cementing, 1.6 Drilling Operations, 5.2.1 Phase Behavior and PVT Measurements
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This paper proposes a method for comparing the effectiveness of cased hole gravelpacks. The method employs effective perforation tunnel permeability as the primary indicator of gravelpack effectiveness.
Completion pressure losses in cased hole gravelpacked wells are subdivided into categories and systematically reviewed to show the relative importance of alternative design features. From this information, perforation tunnel permeability is shown to be the major determinant of completion skin and flow efficiency in cased hole gravelpacked wells. The technique is shown to be useful in both low velocity (darcy) and high velocity (non-darcy) flow regimes.
Field examples are used to show how this technique can be used to diagnose design flaws and improve well performance results. These examples show that effective perforation tunnel permeabilities in cased hole gravelpacked wells are significantly lower than surface measured gravel permeabilities. This has important implications for well design and remedial candidate selection.
It is difficult to quantitatively define the quality of a cased hole gravelpack. Studies have shown that traditional quality indicators such as the skin factor or well flow efficiency of a gravelpacked well cannot be adequately correlated from reservoir to reservoir and field to field.1,2 As a result some investigators have developed a range of ranking criteria or developed their own quality indices.2-4
This paper will discuss use of perforation tunnel permeability kpt as an indicator of cased hole gravelpack quality. It will be shown that low perforation tunnel permeabilities are the main determinant of cased hole gravelpack skin factors and completion pressure losses. For the purposes of this study the perforation tunnel is defined as the linear flow tunnel stretching from the well/formation interface radius rw to the internal casing radius rei This is shown in Fig. 1.
Flow to and through a Cased Hole Gravelpacked Well
Analysis of pressure losses in cased hole gravelpacked wells necessitates a brief review of the overall flow system. For this discussion the flow system will be subdivided into the following components:
Flow to the Well: Flow to a cased hole gravelpacked well is governed by a combination of reservoir and wellbore features. In a typical reservoir/well system, the fluid moves radially through the reservoir before the flow streamlines begin to be distorted by the specifics of the well's completion geometry. For single phase flow, the first deviation from reservoir flow occurs some distance away from the well as flow begins to converge from the reservoir's constant thickness, radial streamlines to the wellbore. Partial penetration, wellbore inclination, and/or combined partial penetration/inclination effects can make themselves felt considerable distances from the well.5-7 These effects are categorized as reservoir flow convergence effects. As the flow continues to approach the well, mud filtrate damage, perforation geometry and perforation damage effects begin to be felt.8-10 These effects are categorized as well entry effects. As the name implies, well entry effects conclude when the flow has crossed the wellbore/formation rw threshold and entered the well itself.
Flow through the Well: Once flow has crossed the well/formation interface radius rw corresponding to the end of reservoir rock, it enters the wellbore. For cased hole gravelpacked completions, flow will typically move from the exterior perforations into a confined perforation tunnel which penetrates impermeable casing and cement. This perforation tunnel may be filled with formation sand, gravel, completion debris, or some combination of the three. From the perforation tunnel, flow diverges into the relatively large flow area provided by the casing/screen annulus. The flow then converges to a wire-wrapped or prepacked screen, flows through the screen, and moves to the surface. Flow through the well is described by intrawell flow effects.2,11
The flow system described above is shown schematically in Fig. 1: cased hole gravelpack flow.
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