Volumetric Calculations

Transcription

1 olumetrc Calculatons I. Calculatng Ol n Place by the olumetrc Method Ol n place by the volumetrc method s gven by: (t) ( 1 - (t)) (p(t)) Bo(p(t)) w (1) Where: (t) ol n place at tme t, TB b 7758 A h bulk reservor volume, bbl 7758 bbl/acre-ft A area, acres h thckness, ft φ(p(t)) porosty at reservor pressure p, fracton w (t) water saturaton at tme t, fracton B o (p(t)) ol formaton volume factor at reservor pressure p, bbl/tb p(t) reservor pressure at tme t, psa II. Calculatng Gas n Place by the olumetrc Method Gas n place by the volumetrc method s gven by: G(t) ( 1 - (t)) (p(t)) Bg(p(t)) w () Where: G(t) gas n place at tme t, CF b 43,50 A h bulk reservor volume, ft 3 43,50 ft 3 /acre-ft A area, acres h thckness, ft φ(p(t)) porosty at reservor pressure p, fracton w (t) water saturaton at tme t, fracton B g (p(t)) gas formaton volume factor at reservor pressure p, ft 3 /CF p(t) reservor pressure at tme t, psa 1

2 EP-441: Petroleum Development Geology Calculatng Ol n Place by the olumetrc Method emester: Homework #: ame: #: The followng data are gven for the Hout Ol Feld: Area,700 acres et productve thckness 49 ft Porosty 8% Average w 45% Intal reservor pressure, p 980 psa Abandonment pressure, p a 300 psa B o at p 1.8 bbl/tb B o at p a 1.15 bbl/tb g at p a 34% or after water nvason 0% Calculate the followng: 1) Intal ol n place ) Ol n place after volumetrc depleton to abandonment pressure 3) Ol n place after water nvason at ntal pressure 4) Ol reserve by volumetrc depleton to abandonment pressure 5) Ol reserve by full water drve ) Dscuss your answers

3 oluton: b 7758 x A x h 7758 x,700 x MMM bbl 1) The ntal ol n place s gven by: B ( 1 - ) o w Whch yelds: (0.08) 1.8 ( ) ) MM TB ) Ol n place after volumetrc depleton to abandonment pressure s gven by: ( ) Bo w g Whch yelds: (0.08) 1.15 ( ) ) MM TB 3) Ol n place after water nvason at ntal reservor pressure s gven by: Whch yelds: Bo or (0.08) MM TB 4) Ol reserve by volumetrc depleton.e. RF 118/ 44% ( - ) ( - 148) 118 MM TB 1 3

4 5) Ol reserve by full water drve.e. RF 19/ 4% ( - ) ( - 97) 19 MM TB ) Dscusson of results: For ol reservors under volumetrc control;.e. no water nflux, the produced ol must be replaced by gas the saturaton of whch ncreases as ol saturaton decreases. If g s the gas saturaton and B o the ol formaton volume factor at abandonment pressure, then ol n place at abandonment pressure s gven by: ( ) B o w g On the other hand, for ol reservors under hydraulc control, where there s no apprecable declne n reservor pressure, water nflux s ether edge-water drve or bottom-water drve. In edge-water drve, water nflux s nward and parallel to beddng planes. In bottom-water drve, water nflux s upward where the producng ol zone s underlan by water. In ths case, the ol remanng at abandonment s gven by: Bo or 4

5 EP-441: Petroleum Development Geology Calculatng Gas n Place by the olumetrc Method emester: Homework #: ame: #: The followng data are gven for the Bell Gas Feld: Area 10 acres et productve thckness 40 ft Intal reservor pressure 350 psa Porosty % Connate water 3% Intal gas FF ft 3 /CF Gas FF at 500 psa ft 3 /CF Gas FF at 500 psa ft 3 /CF gr after water nvason 34% Fnd the followng: 1) Intal gas n place ) Gas n place after volumetrc depleton to 500 psa 3) Gas n place after volumetrc depleton to 500 psa 4) Gas n place after water nvason at 350 psa 5) Gas n place after water nvason at 500 psa ) Gas n place after water nvason at 500 psa 7) Gas reserve by volumetrc depleton to 500 psa 8) Gas reserve by full water drve;.e. at 350 psa 9) Gas reserve by partal water drve;.e. at 500 psa 10) Gas reserve by full water drve f there s one undp well 11) Dscuss your answers 5

6 oluton: b 43,50 x A x h 43,50 x MM ft 3 1) Intal gas n place s gven by: G B ( 1 - ) g w Whch yelds: (0.) G ( 1-0.3) ) 880 MM CF ) Gas n place after volumetrc depleton to 500 psa: (0.) G ( 1-0.3) ) 7080 MM CF 3) Gas n place after volumetrc depleton to 500 psa: (0.) G ( 1-0.3) ) 1303 MM CF 4) Gas n place after water nvason at 350 psa: (0.)(0.34) G3 391 MM CF ) Gas n place after water nvason at 500 psa: (0.)(0.34) G4 31 MM CF 0.007

7 ) Gas n place after water nvason at 500 psa: (0.)(0.34) G5 57 MM CF ) Gas reserve by volumetrc depleton to 500 psa: G - G.e. RF 7557/880 85% ( ) 7557 MM CF 8) Gas reserve by water drve at 350 psa (full water drve): G - G.e. RF 4948/880 5% 3 ( ) 4948 MM CF 9) Gas reserve by water drve at 500 psa (partal water drve): G - G.e. RF 5734/880 5% 4 ( ) 5734 MM CF 10) Gas reserve by water drve at 350 psa f there s one undp well:.e. RF 474/880 8% ( ) ( ) 474 MM CF G - G 7

8 1) Dscusson of results: The RF for volumetrc depleton to 500 psa (no water drve) s calculated to be 85%. On the other hand, the RF for partal water drve s 5%, and for the full water drve s 5%. Ths can be explaned as follows: As water nvades the reservor, reservor pressure s mantaned at a hgher level than f there were no water encroachment. Ths leads to hgher abandonment pressures for water-drve reservors. Recoveres, however, are lower because the man mechansm of producton n gas reservors s depleton or gas expanson. In water-drve gas reservors, t has been found that gas recoveres can be ncreased by: 1) Outrunnng technque: Whch s accomplshed by ncreasng gas producton rates. Ths technque has been attempted n Berwang Feld n West Germany where the feld producton rate has been ncreased from 50 to 75 MM CF/D, and they found that the ultmate recovery ncreased from 9 to 74%. ) Coproducton technque: Ths technque s defned as the smultaneous producton of gas and water, see Fg. 1. In ths process, as downdp wells begn to be watered out, they are converted to hgh-rate water producers, whle the updp wells are mantaned on gas producton. Ths technque enhances producton as follows: Frst: the hgh-rate downdp water producers act as a pressure snk for the water. Ths retards water nvason nto the gas zone, therefore prolongng ts productve lfe. econd: the hgh-rate water producton lowers the average reservor pressure, allowng for more gas expanson and therefore more gas producton. Thrd: when the average reservor pressure s lowered, the mmoble gas n the waterswept porton of the reservor could become moble and hence producble. It has been reported that ths technque has ncreased gas producton from % to 83% n Eugene Island Feld of Lousana. 8

9 Fg. 1: Cross secton of a water-drve gas reservor 9