GMB 8 Geo Bawah Permukaan

1 Compiled by Sarju Winardi

PETROLEUM GEOLOGYDept. of Geological EngineeringGADJAH MADA UNIVERSITY

SUBSURFACE GEOLOGY

1. Stratigraphy Sequence2. Log Correlation3. Subsurface Section4. Subsurface Mapping5. Reserve Estimation



I. STRATIGRAPHIC SEQUENCES

1. ACCOMMODATION SPACE2. SEQUENCE BOUNDARY3. STACKING PATTERN4. SYSTEM TRACTS LOWSTAND TRANSGRESSIVE HIGSTAND



AccommodationSpace

ACCOMMODATION SPACE



SB-1



SB-2



STACKING PATTERN


PETROLEUM GEOLOGYDept. of Geological EngineeringGADJAH MADA UNIVERSITYWell-log Response of Parasequence Sets

( from Van Wagoner et al., 1992)



SYSTEM TRACTS



TYPE 1 SEQUENCE DEPOSITED ON A SHELF



TYPE 2 SEQUENCE



II. LOG CORRELATION

A. GUIDE LINES1. For initial quick look correlation, review major sandstone using GR & SP

2. For detailed Correlation, first correlate shale sections

3. Initially use the amplified short normal resistivity curve, with usually provide the most reliable shale correlation

4. Identify specific correlation point with certain color

5. Always begin correlation at the top of the log, not the middle

6. Do not force a correlation

7. In highly faulted areas, first correlate down the log and then correlate up the log

Tearpock and Bischke, 1991



B. TYPE LOG AND MARKER/DATUM

1. Type Loga. Exhibits complete stratigraphic section in a field

or regional area of study

b. Reflect the deepest and thickest stratigraphic section penetrated

c. Often composed of sections from several individual logs (composite type log)



Composite Stratigraphic Type Log

Tearpock and Biscke, 1991



2. Marker/Datum

Distinctive beds, certain character, laterally extensivea. Shale break (Flooding events)

b. Coals (Reflecting the regional nature of the cyclic deposition)

c. Shoreface sandstones (distinctive coarsening upward profile)

d. Paleosoils (stable surfaces during highstands events)

e. Thin limestones bed (observed in resistivity logs)

f. Benthonite in shale groups (resistiviy less than resistivity shale)



Marker beds

Stuart, 1995



C. VERTICAL WELL CORRELATION

1. Log Correlation Plana. Prepare a correlation type logb. Established to correlate by means of

closed loopsc. Correlate the most complete & thickest

stratigraphic sectiond. From down-structure position to up-

structure positione. Correlate nearest wellsf. Remember : rapid changes in stratigraphy

occur over short distance



2. Basic concepts in electrical log correlation





Vertical Correlation



D. DIRECTIONAL WELL CORRELATIONAL1. Log Correlation Plan

a. Construct a correlation type logb. Correlating deviated well after vertical well c. Organize the well according to their of

deviation d. Correlate the wells with the least amount of

deviation with respect to structural strikee. Continue correlating wells with incresed

deviation in the downdip directionf. Group to correlate are those wells deviated

along structural strikesg. Correlate the wells deviated updiph. Correlate wells located nearesti. Add other platform in the area



Directional Correlational




1. Structural identification (fault, fold, etc.)

2. Sand geometry guide line (lenses, wedge, sheet, etc.)

3. Depositional models-contour models (meandering, channel, etc)

E. THE FUNCTION OF SEISMIC DATA IN CORRELATION

CHRONOSTRATIGRAPHIC VS. LITHOSTRATIGRAPHIC CORRELATION



III. SUBSURFACE SECTIONPlanning a cross section* Determine the specific objective

StructuralStratigraphic

* Choose the orientation of the line of sectionDepend on type section (structural or stratigraphic)Type of geologic structureDepend on data which used (well log, structure map or surface data

* Selection the scaleSame horizontal and vertical scalesVertical exaggeration



A. STRUCTURAL SECTION

1. Illustrate structural features such as dips, faults, and folds

2. Prepared to study structural problems related to subsurface formations , fault geometry and general correlation

3. Drawn the same horizontal with vertical scales

4. Use Relative Sea Level (RSL) as the datum



Structural Section

Tearpock & Bischke, 1991



B. Stratigraphic Section

Reksalegora, 2001



Stratigraphic Section

Zainal, 2000



C. SECTION DESIGN1. Extensional Structure




2. Salt Dome Structure




3. Compressional Structure




3. Wrench Fault Structure




D. EXAGGERATIONS


IV. SUBSURFACE MAPPINGA. PHILOSOPHY

1. Understanding of the basic principal of structural geology, petroleum geology, stratigraphy etc.

2. Techniques and methods correct3. Accurate (well log and seismic)4. Fault and structure map integration5. Balanced cross section6. Multiple horizon mapping7. Interpretative contouring8. Use all subsurface data9. Documentation10. Sufficient time

B. CONTOURING TECHNIQUES

1. Contourable Data

DATA

ElevationThickness of sedimentsPercentage of sandFeet of payPressureTemperatureLithology

TYPE OF MAP

Structure, Fault, SaltInterval Isopach (Isochore)Percent sandNet Pay IsopachIsobarIsothermIsolith

2. 3-D Perspective


3. Rules of contouring

1. A contour line cannot cross itself or any other contour except under special circumstances

2. A contour line cannot merge with contours of the same value or different values

3. A contour line must pass berween points whose values are lower and higher than its own value

4. A contour line of a given value is repeated to indicate reversal of slope direction

5. A contour line on a continuous surface must close within the mapped area or end at the edge of the map

4. Methods of Contouring

a. Mechanical b. Parallel


Methods of Contouring

c. Equal spaced d. Interpretative


C. KIND OF SUBSURFACE MAP

1. Structure Contour Map

Show subsurface structural element (faults, anticline, syncline)

Show the depth (subsea depth) of subsurface geological features

Show oil and gas accumulation limits

Reksalegora, 2001

Reksalegora, 2001

2. Isopach Map

Interval Isopach Mapshow the thickness of bed (stratigraphic thickness) isopach : use TST, isochore : use TVT if dip < 10o, isochore map = isopach map

Net Sand Isopach mapshow total thickness of sand layer (reservoir)

Net Pay Isopach Mapshow vertical thickness of hidrocarbon in reservoir

Net Sand Isopach map Net Pay Isopach Map

Reksalegora, 2001

A. HORISONTAL SLICE METHOD

1. Pyramidal Equation, (A1/A0) < 1/2

V. RESERVE ESTIMATION

2. Trapezoid Equation, (A1/A0) > 1/2

PETA KONTUR STRUKTUR KEDALAMAN TOP REEF X

1050 m

1060 m

1070 m

1080 m

Top REEF X

1050 m

1060 m

1080 m

1070 m

1050 m

1060 m

1080 m

1070 m

A0

A1

A2

A3

Vo

V1

V2

V3


1050 m

1060 m

1070 m

1080 m

Top REEF X

OWC

1050 m

1060 m

1080 m

1070 m

OWC

1050 m

1060 m

1080 m

1070 m

OWC

A1A2

A0

A3

VoV1

V2 V3

B. VERTICAL SLICE METHOD


1050 m

1060 m

1080 m

1070 m

1050 m

1060 m

1070 m

1080 m

Top REEF X

PETA KETEBALAN SAND X

100 15 20 102025

1050 m

1060 m

1070 m

1080 m

Top REEF X

025 155 5

010

15

25

205

1050 m

1060 m

1080 m

1070 m0

10

15

25

205


1050 m

1060 m

1080 m

1070 m

OWC

1050 m

1060 m

1070 m

1080 m

Top REEF X

OWC

PETA KETEBALAN SAND X

100 15 20 102025

1050 m

1060 m

1070 m

1080 m

Top REEF X

025 155 5

010

15

25

205

OWC

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GMB 8 Geo Bawah Permukaan