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Research Papers: Petroleum Engineering

Determination and Implication of Ultimate Water Cut in Well-Spacing Design for Developed Reservoirs With Water Coning

[+] Author and Article Information
Samir Prasun

Department of Petroleum Engineering,
Louisiana State University,
Apartment 1252, 275 West Roosevelt Street,
Baton Rouge, LA 70802
e-mail: Prasoonsamir@gmail.com

A. K. Wojtanowicz

Professor
Department of Petroleum Engineering,
Louisiana State University,
3212A, PFT Hall,
Baton Rouge, LA 70803
e-mail: awojtan@lsu.edu

Manuscript received November 8, 2017; final manuscript received March 13, 2018; published online April 9, 2018. Assoc. Editor: Arash Dahi Taleghani.

J. Energy Resour. Technol 140(8), 082902 (Apr 09, 2018) (12 pages) Paper No: JERT-17-1629; doi: 10.1115/1.4039743 History: Received November 08, 2017; Revised March 13, 2018

Theoretically, ultimate water-cut (WCult) defines stabilized well's oil and water production rates for uncontained oil pay underlain with water. However, in a real multiwell reservoir, the well's drainage area is contained by a no-flow boundary (NFB) that would control water coning, so the WCult concept should be qualified and related to the well-spacing size. Also, the presently used WCult formula derives from several simplifying assumptions, so its validity needs to be verified. The study shows that in multiwell bottom-water reservoirs, the production water-cut would never stabilize (after initial rapid increase) but would continue increasing at slow rate dependent on the production rate and well-spacing size. At each production rate, there is a minimum well-spacing size above which water-cut becomes practically constant at the value defined here as pseudoWCult. A new formula—developed in this study—correlates the minimum well-spacing with reservoir properties. Further, formula for pseudoWCult is derived by considering radial flow distortion effects in the oil and water zones. It is found that for well-spacing larger than the minimum well-spacing, the two effects-when combined-do not change the water-cut value. Thus, in practical applications, for sufficiently large well-spacing, the pseudoWCult values can be computed from the presently used WCult formula. The pseudoWCult concept has potential practical use in well-spacing design for ultimate recovery determined by the water cut economic limit, WCec. When the water-cut economic margin (WCec–WCult) is large, well-spacing has little effect on the ultimate recovery, so large well-spacing could be designed. However, when the water-cut economic margin is small, reservoir development decision should consider increase of final recovery by reducing well-spacing below the minimum well-spacing.

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Topics: Reservoirs , Water
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References

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Figures

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Fig. 1

Oil and water horizontal flow in their respective zones

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Fig. 2

Typical patterns of water cut showing partial or no stabilization—after (Kuo and Desbrisay 1983)

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Fig. 3

Radial model of oil with constant pressure bottom water

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Fig. 4

Water cut pattern (reservoir # 7) for different size of well-spacing (Q = 2000 bbl/day) depicting pseudo-stabilization at well-spacing greater than threshold spacing

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Fig. 5

Oil and water inflow schematics representing the flow distortion due to partially penetrating oil-zone and the semispherical flow due to water-sink

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Fig. 6

Comparison of ultimate water-cut using presently used formula, Eq. (2) and new formula, Eq. (9)

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Fig. 7

Ultimate recovery versus well-spacing (reservoir # 7; minimum (threshold) well-spacing = 4400 ft, pseudoWCult = 0.9): recovery becomes independent of well-spacing at (WCec-pseudoWCult) ≫ 0

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Fig. 8

Higher recovery for smaller well-spacing at (WCec-pseudoWCult)≅0—reservoir#12 (pseudoWCult = 91%)

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Fig. 9

Recovery factor versus water-cut (reservoir # 12, pseudoWCult = 0.91): ultimate recovery increases with reduced well-spacing when WCec <= pseudoWCult, whereas it converges when (WCec-pseudoWCult) ≫ 0

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