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Published byAmanda Lehtilä Modified over 6 years ago
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PERMEABILITY CORRELATIONS FOR CARBONATE & OTHER ROCKS
Paper # GSA Meeting 2003 Seattle Wa. Presentation rev. 2 Otis P. Armstrong, PE
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The form: k (md) =101.5(1/Sw-c - 1)1.9
(if k calc exceeds 200, use 1, not 10) It is presented to improve description of potentially productive zones of carbonates. Equations that do not use the form: (1/Sw-c - 1) cannot accurately describe k at both low & high Swc, ie at Swc=1, k must equal zero. Following Graphs present comparisons:
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MOBILE HC VALUE Provided, a min k can be established, mobile HC factor is simply a mapping of the Bulk Volume Water Term, BVW. More correct K forms, with (1/Swc - 1)^n are just more complex. Below is a simple derivation: Sw-c =BVW/ in Timor’s equation gives: Kmin ={92.6()2.2/(Sw-c)}2 => min ={√Kmin *BVW/92.6}0.313 and using these terms in the movable HC formula: (Swc0.2 – Swc)7760 = 7760{(BVW/)0.2 – BVW}= BBL/AcFt = 7760{0.8(BVW)0.2 – BVW} = BBL/AcFt = 7760[{√Kmin /92.6}1.113(BVW)1.31 – BVW]
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At each BVW, a zero permeability BBL/AcFt is defined
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For opa & Schl.’97 Eqns this zero point = 28ln(BVW) +220
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Minimum BBL/AcFt from Mobility Ratio & BVW Range
A similar result is arrived at using the Ratio Method: In logging terms: movable HC is: BBL/AcFt = 7760[a]*[(Rmf/Rxo) - (Rw/Rt) ] Where a is term to make F = (a/2) , typically a=1 in carb. Sections If porosity log unavailable this may be the only evaluation method
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Still not convinced? Then try this: (BBl/AcFt)mo =7760[(Sxo) -(So)]
= 7760(So)[ (1/So)(So) ], by using (Sxo)= (So)0.2 with (So) = (BVW), then (BBL/AcFt)mo =7760(BVW)[(So) ] By ratio method Sw max = 0.64 in SS & 0.53 Carbs, & the min mobility ratio is 3330BVW in SS & 5136BVW in Carbs. Using typical lithology BVW values shows: In ideal conditions, Mobile HC values may exceed 1250bbl/ac-ft. In summary, Mobile HC expressed as BBL/Acft is a handy way to express various min/max rules, provided deposit lithology is understood. The closer values are to litho-minimums, the less the chances of economic HC extraction. Low mobility values also indicate low permeability.
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Summary Rocks with <160 bbl/AcFt = cap rocks unless Vug or coarse ss porosity types. Higher values indicate higher porosity. Watch for chalk & silt porosity types as they have higher min’s.
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Upper Ordovician Zone, Clean Carbonate, Western Latvia
Indication in 36 wells: this zone is a Cap Rock, typically <140 & does not contribute to oil flow, remove this zone in Htests.
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Indications are: oil flow is from thin lower sucrosic LS/Dolo
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‘otis-a@sbcglobal.net’
Thanks for hearing my considerations. A more detailed Discussion is available by request.
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