GEO4270 EXERCISE 2 PROSPECT EVALUATION

Transcription

1 GEO4270 EXERCISE 2 PROSPECT EVALUATION

2 GEO4270 Integrated Basin Analysis and Prospect Evaluation 1. Integrated Seismic (reflection/refraction), Gravity and Magnetics and Basin Modelling Large Scale Structures of the Basin Deeper Parts of the Basin Tectonic Development of the Basin Maturation of Hydrocarbons 2. Prospect Evaluation 2

3 GEO4270 Prospect Evaluation Tampen Spur: Gullfaks; Snorre; Statfjord, Visund, Tordis Horda Platform: Troll, Oseberg Migration Mature HC 3

4 GEO4270 Prospect Evaluation Prospect, n. An examination or test of the mineral richness of a locality or of the material from which the ore, etc. is extracted OED, IV. 10. Mining b. Evaluation, The action of evaluating or determining the value of (a mathematical expression, a physical quantity, etc.), or of estimating the force of (e.g. probabilities, evidence) OED, 2. 4

5 GEO4270 Course Contents Introduction PETREL Introduction Course Exercise: Statfjord Field Data loading Interpretation Reservoir Modelling and Prospect Evaluation Report Follow up meetings Lecture on Geostatistical Reservoir Modeling 5

6 GEO4270 Prospect Evaluation Exercise Data Offshore Norway Northern North Sea What will we be using during the project: Seismic data 2D 3D Well data Formation Tops Geophysical well logs 6

7 WELL LOGGING / CORRELATION Resistivity Porosity SP GEO4250 Short summary

8 GEO4270 Well Logging / Correlation Formation Evaluation Formation evaluation, the process of using borehole measurements to evaluate the characteristics of subsurface formations. Helander, D.P., Fundamentals of Formation Evaluation 8

9 GEO4270 Well Logging / Correlation Formation Evaluation Objectives Identification of the reservoir (primary) Estimating hydrocarbons in place (primary) Reservoir properties Shape Thickness Porosity and permeability Lithology Well-to-well correlation Formation dip Surface seismic well tie A few more additional related to HC production 9

10 GEO4270 Well Logging /Correlation Hydrocarbons in Place N = initial oil in place (stb) 7758AhφS A = drainage area (acres) N = oi h = productive interval thickness (ft) B φ = effective porosity (fraction) G = oi 43,560Ah gi φ S oi S oi = initial oil saturation (fraction) B oi = initial oil formation volume factor (reservoir bbl/stb) G = initial gas in place (scf) B S gi = initial gas saturation (fraction) B gi = initial gas formation volume factor (ft 3 /scf) Oil formation volume factor: Oil and dissolved gas volume at reservoir conditions divided by oil volume at standard conditions. Gas formation volume factor: Gas volume at reservoir conditions divided by gas volume at standard conditions. 10

11 GEO4270 Well Logging / Correlation Hydrocarbon Reserves N N p = Oil Reserves (stb) φ φ e = effective porosity (fraction) = S har S o = Oil saturation (fraction) o h = productive interval thickness (ft) A = drainage area (acres) r = Recovery Factor p φ e 11

12 GEO4270 Well Logging / Correlation Important Parameters Saturation (S), n. [Formation Evaluation] The relative amount of water, oil and gas in the pores of a rock, usually as a percentage of volume. The pore space that does not contain formation water is assumed to contain hydrocarbons. Mathematically this can be expressed as: S hc = 1 S w Where S hc = hydrocarbon saturation S w = water saturation If S w is low, the formation is potentially productive 12

13 GEO4270 Well Logging / Correlation Important Parameters Porosity (φ), n. [Geology] The percentage of pore volume or void space, or that volume within rock that can contain fluids. Total Porosity (φ t ): The total pore volume per unit volume of rock Effective Porosity (φ e ): The interconnected pore volume or void space in a rock that contributes to fluid flow or permeability in a reservoir 13

14 GEO4270 Well Logging / Correlation Important Parameters Permeability (k), n. [Geology] The ability, or measurement of a rock's ability, to transmit fluids. Permeability is required to calculate the flow rate at which hydrocarbons can be produced, following Darcy law: u = k dp μ dx Permeability will not be addressed in the course 14

15 How can we measure these parameters?

16 GEO4270 Well Logging / Correlation Water Saturation Water saturation can be measured with the help of: Resistivity (R), n. [Formation Evaluation] The ability of a material to resist electrical conduction. It is the inverse of conductivity and is measured in ohmm. The resistivity is a property of the material, whereas the resistance also depends on the volume measured.!! Hydrocarbons are resistive while formation water is conductive!! 16

17 GEO4270 Well Logging / Correlation Water Saturation The Resistivity of a formation is dependent on: Presence of Formation water / Hydrocarbons Salinity of Formation water Temperature of Formation water Volume of water-saturated pore space Geometry of the pore space Morphology and species of clay minerals 17

18 GEO4270 Well Logging / Correlation Water Saturation Relation between Water Saturation and Resistivity Archie s equation (Archie, G.E., 1942) FR w R S o w = = R R t t S w = Water saturation F = Formation Resistivity Factor (a/φ φ m ): Porosity (φ) Tortuosity factor (a) Cementation factor (m) R w = Resistivity of the formation water R t = Resistivity of a rock with HC, i.e. true resistivity R o = Resistivity of the 100% water- saturated rock 18

19 GEO4270 Well Logging / Correlation Porosity Direct measurements Conventional coring Sidewall coring Indirect Measurements Sonic Log Density Log Neutron Log 19

20 GEO4270 Well Logging / Correlation Porosity Sonic Log, n. [Geophysics] A type of acoustic log that displays traveltime of P-waves versus depth (recorded in interval transit time (Δt), μs/ft, which is the reciprocal of velocity). Sonic logs are typically recorded by pulling a tool on a wireline up the wellbore. The tool emits a sound wave that travels from the source to the formation and back to a receiver. Log symbol: DT 20

21 GEO4270 Well Logging / Correlation Porosity T Dependent on lithology and porosity Sonic porosity derived by: φ R 1 p p sonic Δ tl = Δt log f Δ t Δt matrix matrix 1 Cp φ sonic = sonic derived porosity Δt matrix = interval transit time of the matrix (table) Δt log = interval transit time of the formation Δt f = interval transit time of the fluid in the wellbore (fresh mud = 189; salt mud = 185) Cp = compaction factor = Δt R sh C with: Δt sh = interval transit time for adjacent shale C = a constant, normally

22 GEO4270 Well Logging / Correlation Porosity Density Log, n. [Formation Evaluation] A well log that records formation density. The logging tool consists of a gamma-ray source (e.g., Cs 137 ) and a detector shielded from the source so that it records backscattered gamma rays from the formation (Compton scattering). The backscattering depends on the electron density of the formation, which is roughly proportional to the bulk density. Log symbol: RHOB, DEN 22

23 GEO4270 Well Logging / Correlation Porosity Density Log 1. Identify evaporite minerals 2. Detect gas-bearing zones 3. Determine hydrocarbon density 4. Evaluate shaly sand reservoirs and complex lithologies 23

24 GEO4270 Well Logging / Correlation Porosity DRHO is a correction curve, if DRHO > 0.20 gm/cc the RHOB curve is invalid RHOB (formation bulk density) is a function of matrix density, porosity and density of the fluids in the pores, therefore: φ den = ρ matrix ρ b ρ ρ matrix f with: φ den = density derived porosity ρ matrix = matrix density (table) ρ b = formation bulk density ρ f = fluid density DRHO = 0.20 Log symbol: DPHI 24

25 GEO4270 Well Logging / Correlation Porosity Neutron Porosity, adj. [Formation Evaluation] Referring to a log of porosity based on the effect of the formation on fast neutrons emitted by a source. Hydrogen has by far the biggest effect in slowing down and capturing neutrons. Since hydrogen is found mainly in the pore fluids, the neutron porosity log responds principally to porosity. However, the matrix and the type of fluid also have an effect. Scaled in equivalent limestone porosity units, i.e. low NPHI values represent limestone Log symbol: NPHI, CN Hydrogen in pore water, hydrocarbons and shales NOT in quartz, feldspars and carbonates 25

26 GEO4270 Well Logging / Correlation Correlation Logs Gamma Ray Log A well log of the natural formation radioactivity level The log mainly reflects clay content because clay contains the radioactive isotopes of K, U and Th Often used in association with the SP-log 26

27 GEO4270 Well Logging / Correlation Correlation Logs Spontaneous Potential Log A record of Direct Current (DC) voltage (or Potential) that develops naturally (spontaneous) between a moveable electrode in the well and a fixed electrode located at the surface Used to Correlation Detect permeable beds Detect boundaries of permeable beds Determine formation-water resistivity (R w ) Determine the volume of shale in permeable beds Detection of hydrocarbons by the suppression of the SP curve Often used in association with the GR-log 27

28 SEISMIC INTERPRETATION Reservoir Identification Seismic Attributes GEO4240 Short summary

29 GEO4270 Seismic Interpretation Reservoir Identification Phase Polarity Amplitude Spatial Extent Frequency Velocity AVO Shear wave Seismic characteristics helping to identify HC 29

30 GEO4270 Seismic Interpretation Reservoir Identification Identify Phase and Polarity Minimum Phase RC+ Normal Polarity Zero Phase Reverse Polarity RC+ RC- RC- 30

31 GEO4270 Seismic Interpretation Reservoir Identification 31

32 GEO4270 Seismic Interpretation Seismic Attributes An attribute is a derivative of a basic seismic measurement All the horizon and formation attributes t available (see Fig. 8-1) are not independent of each other but simply different ways of presenting and studying a limited amount of basic information That basic information is time, amplitude, frequency and attenuation and these form the basis of our attribute classification Seismic attributes may be defined as all the information obtained from seismic data, either by direct measurements or by logical or experience based reasoning. (Taner, 1998) 32

33 GEO4270 Seismic Interpretation Seismic Attributes Time-derived attributes provide structural information Amplitude-derived derived attributes provide stratigraphic and reservoir information Frequency-derived attributes are not yet well understood but there is wide-spread optimism that they will provide additional useful stratigraphic and reservoir information Attenuation is not used today, but there is a possibility that in the future it will yield information on permeability Most attributes are derived from the normal stacked and migrated data volume but variations of basic measurements as a function of angle of incidence (and hence source to receiver offset) provides a further source of information. The principal examples of these pre-stack attributes is AVO 33

34 GEO4270 Seismic Interpretation Seismic Attributes 34

35 GEO4270 Seismic Interpretation Seismic Attributes 35

36 GEO4270 Seismic Interpretation Seismic Attributes Time Slice! 36

37 Property Modeling (or Reservoir Modeling) It is better to have a model of uncertainty than an illusion i of reality Andre Journel

38 GEO4270 Property Modeling Introduction Goal of Property modeling: Capture geology and build realistic property models Goal of Reservoir modeling: Predicting rock properties at unsampled locations and forecasting the future flow behaviour of complex geological and engineering systems (Deutsch, 12002) by use of Geostatistics ti ti 38

39 GEO4270 Property Modeling Why create a realistic reservoir property model? We are making big decisions based on limited data Maximize the usage of all information optimise production Correct upscaling of logs and a proper facies interpretation is important Reservoir properties are critical factors affecting production 39

40 GEO4270 Property Modeling Geostatistics Geostatistics is a branch of applied statistics that places emphasis on: The geological context of the data The spatial relationship between the data Data measured with different volumetric support and precision Business Need: make the best possible decision i in the face of uncertainty. Uncertainty exists because of our incomplete knowledge of a dataset (always incomplete data). One of the biggest uncertainties is the numerical description of the subsurface 40

41 GEO4270 Property Modeling Examples of Geostatistics Analysis of variables in space Samples located close to each other are probably more similar than samples located far from each other The spatial coordinates of the observed samples are built into the statistic formulas Examples: Gold content in ore (ppm) Reservoir sandstone porosity (%) Reservoir sandstone bed thickness (meter/feet) 41

42 GEO4270 Property Modeling Incorporate the Maximum Amount of Data Well data Seismic data Production Outcrops Other geological studies Integrated study Deterministic information Structure (horizon, fault) Stratigraphic correlation Facies images Framework Sedimentological model Facies description Connectivity Conceptual information Statistical information Histogram Variogram Correlation Trend Variation 42

43 GEO4270 Property Modeling Sequential Approach to Property Modeling 1. Defining the geometry and stratigraphic layering of the reservoir interval to be modeled Involves the development of a conceptual model for the major architecture and continuity of facies, porosity and permeability witihin each layer 2. The facies rock types are modeled by either (1) cell-based or (2) object-based techniques within each stratigraphic layer 3. The porosity is modeled on a by-facies basis before permeability because there are more reliable porosity data available 4. The 3-D models of permeability are constrained to the porosity, facies and layering previously established 5. Multiple equally likely realizations are created by repeating the entire process Each realization is equally likely to be drawn ; however, some realizations are more similar to others, hence their class has higher probability 6. These models are input to a simulator or visualized and used to aid in decision making 43

44 Tampen Spur Introduction

45 Tampen Spur Location F B H 45 10/14/2008 GEO Michel Heeremans

46 Statfjord Field Facts Discovery well: 33/12-1 Discovery Year: 1974 Gullfaks producing since Total production of saleable products : mill. Sm 3 o.e. Recoverable reserves: Oil: mill Sm 3 Statfjord Production Gas: bill Sm 3 NGL: mill tonne Total number of wells: Sm3 NGL: Natural Gas Liquids, incl. propane, butane, pentane, hexane and heptane, but not methane and ethane 1 tonne NGL: 1.9 Sm 3 o.e Year 1994 Oil [mill Sm3] Gas [bill Sm3] Sm3o.e. [mill] Water [mill Sm3]

47 Tampen Spur Stratigraphy 47 From: Evans et al, 2003, Millenium Atlas

48 Tampen Spur Cross Section 48

49 GEO4270 Prospect Evaluation IMPORTANT! PETREL is just a tool which helps you with your interpretation and modeling This exercise e is meant for leaning reservoir identification, reservoir evaluation and reservoir modeling The results depend completely on your own interpretation and the accuracy of the available data 49

50 Important links +statistikk/fakta-start.htm (Norway Wells) (UK Wells) 50

51 Rf References Asquith, G. and Krygowski, D. (2004). Basic Well Log Analysis Brown, A. (2004). Interpretation of Three-Dimensional Seismic Data Deutsch, C. (2002). Geostatistical Reservoir Modeling Evans, D. et al. (2003). Millenium Atlas Schlumberger (2006). Petrel Seismic to Simulation Software Property Modeling Course, v