GEO4250 Reservoir Geology

Transcription

1 GEO4250 eservoir Geology Basic Well Log Analysis Determination of Saturation

2 eminder N φ p e S hc har S S n 1 F S t hc n o t φ φ φ φ s den n e Δt Δt ρ ρ φ Δt Δt from log t log f matrix matrix ρ ρ matrix b f Density Porosity ( 1 V ) Effective Porosity sh matrix Sonic Porosity F 0 a φ m

3 eminder Determined from the Spontaneous Potential Determined φ t and φ e from porosity and gamma ray logs The only parameter e lack no is the true resistivity of the formation

4 esistivity The resistivity (specific resistance) of a substance is the resistance beteen opposite faces of a unit cube of that substance at a specific temperature Symbol, measured in Ω m (ohm m 2 /m) r A L With r resistance in ohms; A area in square meters; L length in meters esistivity is a basic measurement of a reservoir s fluid saturation and is a function of porosity, type of fluid, amount of fluid and type of rock Usually beteen 0.2 and 1000 ohm m

5 esistivity Dependent on: Presence of Formation ater / Hydrocarbons Salinity of Formation ater Temperature of Formation ater Volume of ater-saturated pore space Geometry of the pore space Morphology and species of clay minerals

6 Tools Conventional Electrical logs First developed before 1950 Normal devices Short Normal (SN) Long Normal (LN) Lateral devices Laterologs (LL, e.g. LL3, LL7, LL8, LLD, LLS, SFL) Induction logging First developed after 1950 Induction devices 6FF40 (combined tool: Induction, Normal and SP, 1960 s) DIL-LL8 (improved induction-normal combination) Induction SFL DIL-SFL Phasor Induction SFL Other abbreviations: ILD, ILM, ILS, D, M, S, T

7 Conventional Electrical Logging Normal Device Lateral Device Current of constant intensity beteen A and B esultant potential difference measured beteen M and N The larger the spacing, the deeper the measurement

8 Conventional Electrical Logging Normal and Lateral Curves Normal Device A: Beds more resistive than surrounding beds B: Beds less resistive than surrounding beds Lateral Device C: Beds more resistive than surrounding beds D: Beds less resistive than surrounding beds A B C D

9 Induction Logging D E C A B High frequency, alternating current of constant intensity is sent through a transmitter coil (A) The alternating magnetic field (B) created, induces currents in the formation surrounding the borehole (C) These currents flo in circular ground loops coaxial ith the transitter coil and create, is turn, a magnetic field (D) that induces a current in the receiver coil (E)

10 esistivity Logging Focusing Minimization of borehole and adjacent formation affects Focusing currents to control the path taken by the measure current

11 esistivity Logging Influence of ell bore variables and log correction esistivity measurements are influenced by: Borehole mud Adjacent beds Invaded zone eadings must be corrected, alays in the folloing ay: Borehole effect Adjacent bed effect Invasion correction

12 esistivity Logging Corrections - Borehole Effect

13 esistivity Logging Corrections - Adjacent Bed Effect

14 esistivity Logging Invasion Correction Tornado or Butterfly Chart

15 Laterolog vs Induction Both Bothhave unique characteristics that thatfavor their theiruse usein in specific, and and often different, situations and and application Induction Log Log ecommended in in holes holes drilled drilled ith ithmoderately conductive drilling drilling muds, muds, non-codunctive muds muds and and in in empty emptyor or air-drilled holes holes Most Most accurate in in lo- lo-to to mediumresistivity formations xo > xo t t Laterolog ecommended in in holes holes drilled drilled ith ithconductive muds muds (salt (salt muds) muds) Most Most accurate in in medium- to to highresistivity formations xo high- < xo t t

16 esistivity Scaling

17 Determination of Saturation m 0 a F φ n t F S t t 1 2,a m n t m n 1 S S a S φ φ φ

18 Determination of Saturation EXAMPLE 100% ater saturated formation S 1; t 0 0 vs φ is a straight line; φ t If S 1, but constant, all points also on a straight line From plotted points, assume some from 100% ater saturated rock line through f0, and through the most esterly plotted points Slope of this line defines the value of For φ10%, ohm m For compacted formations: F 1 / φ 2 So, in this case F 100 We also no that: 0 /F So, 6.5/ ohm m

19 Determination of Saturation Only possible for formations ith constant matrix and for constant Formation Water esistivities