Logs and Correlations

PAB2084

3

Techniques

Course PAB2084 outcome:

Describe the properties of rocks and fluids that produce characteristic log signals.

Analyze and interpret the log to determine porosity, fluid saturation, lithology and hydrocarbon types.

Calculate Rock and Net Hydrocarbon VolumeWell logs application/uses..

Well Log CorrelationsFacies & Stratigraphic Correlations; 3D @

Fence Diagram; Log Facies Analysis

Subsurface Map & Volumetric CalculationSubsurface data; Contours ; isopach &

isochore ; faulted block ; unconformity layer ; folding block; volumetric calculation

Objectives/learning outcomes:

Explain the use of well logs for correlationPerform correlation across wells with the

right tool & method/technique

Correlation: Why??

To develop depositional model of the reservoir sands and bounding shales in order to understand the facies distribution within the reservoir interval

To understand the lateral continuity and variation of the reservoir sands in the field so that the field can be developed optimally

*seismic well logs cores*more data more evidence more confidence and

interpretation may change accordingly..

Well logs for correlation

Electric Logs : GR (Gamma Ray) Resistivity Log (ILD or MSFL) SP (Spontaneous Potential) Sonic Density Log Neutron Porosity + etcs.

Others-annotate/tie Microfossils data Core description data Seismic picks (Converted from TWT to Depths)

Data preparation:

Select curves to useSplice logsAnnotate ie formation tops, markers,

casing.. Display at comparable scale, 1:500, 1: 1000Same depth reference

Log splicing:

DFE

tvssahbdf

TDTD

ahbdf

sea levelsea level

DEPTH REFERENCES, UNITS, MEASUREMENTS

ss = subseabdf = below derric floortv = true verticalah = along holeTD = total depthDFE = derric floor elevationft/m, kb, rt, mudline

tvss

Correlation: Steps/method

Identify a common surface/markers to be used as datum (i.e coal)

Positions and 'hangs' all wells on this surface according to its sequence from the map

Identify 'sand unit' and try to correlate them laterally

Correlate 'minor' events to complete the correlation for detail facies interpretation

Correlation: Tips

Faults?If correlation is 'lost' or similar event do not

exist between wells - A break in the sedimentary layers

Missing layer - Normal faultCreated duplicate layer - Reverse fault

SIMPLE LOG CORRELATION EXERCISE:

set 3(ARBITARY SCALE)

set 4(ARBITARY SCALE)

GR GR GR GR

GR GR GR GR

LOG CORRELATION SAMPLE ANSWER

set 4(ARBITARY SCALE)

GR GR GR GR

set 3(ARBITARY SCALE)

GR GR GR GR

LOG CORRELATION EXERCISE

set 5(ARBITARY SCALE)

set 6(ARBITARY SCALE)

GR GR GR GR

GR GR GR GR

LOG CORRELATION SAMPLE ANSWER

set 5(ARBITARY SCALE)

set 6(ARBITARY SCALE)

GR GR GR GR

GR GR GR GR

Cleaning-up trend (funnel shape): a gradual upward decrease in gamma response. In shallow marine settings, this trend reflects a change from shale-rich into sand-rich lithology and upward increase in depositional energy with shallowing-upward and coarsening. In deep marine settings, this trend reflects an increase in the sand contents of turbidite bodies. This trend also may indicate gradual change from clastic to carbonate deposition.Dirtying-up trend (bell shape): a gradual upward increase in gamma response: This trend may reflect upward fining (eg: a lithology change from sand to shale) or upward fining of sand beds in a thinly interbedded sand-shale unit. This trend usually implies a decrease in depositional energy. In a non-marine setting, fining upward is predominant within meandering or tidal channel deposits with an upward decrease in fluid velocity within a channel (coarser sediments at base of channel). In a shallow-marine setting, this trend usually reflects an upward deepening and a decrease in depositional energy (shoreline retreat). In deep-marine settings, this trend reflects waning of submarine fans (reducing of sand contents).Boxcar trend (cylindrical or block shape): with low gamma and sharp boundaries and no internal change: this trend is predominant in fluvial channel sands, turbidites (typically with greater range of thickness), and aeolian sands. Evaporites also can have a cylindrical gamma trend.Additionally two in-between trends can be recognized:Bow trend (symmetrical or barrel): with gradual decrease then gradual increase in gamma response: this is usually the result of progradation and retrogration of clastic sediments.Irregular trend (lack of character): this trend represents aggradation of shales or silts and can occur in other settings.

Correlation:

Stratigraphic litho, chrono/sequence strat...

Structural

STRUCTURAL CORRELATION

Datum : on the same depths (usually TVD) for all wellsTo represent the GOC/GWC or OWC contacts on its true

structural position

For field development, the correlation is to display other applicable well information that needs true structural positions

2500

2600

2500

2600

2500

2600

STRUCTURAL CORRELATION

Fault

Well 1 Well 2 Well 3

Datum on same TVDSS

Like flattened

2500

2600

2500

2600

C-Marker

D Sand

E Sand

2500

2600

STRUCTURAL CORRELATION

Fault

Well 1 Well 2 Well 3

Base sand

Fence diagram (fr SLB)

A graphical display of three-dimensional data and interpretations in two-dimensional perspective view. Geologic cross sections can be displayed in a network to form a fence diagram. Stratigraphic changes can be displayed clearly in fence diagrams

CORRELATION IN PETREL?

NO. 3 NO. 27 NO. 15 NO. 10 NO. 2SP Amplified

Short Normal

E1 MARKER = DATUM

CORRELATION EXERCISE in class

CORRELATION EXERCISE in class

GR GR GR GR GR

Structures

RIP-UP CLASTS, PEBBLESWAVE RIPPLEHUMMOCKY X-BEDS

CURRENT RIPPLEPLANAR BEDS

THROUGH X-BEDS

0 140 0 140 0 140 0 140 0 140

NO. 3 NO. 27 NO. 15 NO. 10 NO. 2SP Amplified

Short Normal

CORRELATION EXCERCISE = SOLUTION

E1 MARKER = DATUM

CORRELATION EXCERCISE = SOLUTION

FS/SB

SB

C1

C2

C3

C4

C5

Truncated stacked sands

GR GR GR GR GR

Fluvial Channel

Shoreface

Tidal Delta

Shelf Mudstone(Marine)

Swamp Mudstone-TerrestrialFS

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