Seismic data Interpretation On Dhodak field Pakistan

Geophysical Modeling of the part of Central Geophysical Modeling of the part of Central Indus Basin with the help of Seismic and Well Indus Basin with the help of Seismic and Well

datadata

By: Jamal AhmadBy: Jamal Ahmad(M.Phil Geophysics)(M.Phil Geophysics)

Supervisor: Dr. Shahid Nadeem QureshiSupervisor: Dr. Shahid Nadeem Qureshi

Department of Earth SciencesDepartment of Earth Sciences

QAU, IslamabadQAU, Islamabad

ObjectivesObjectives

To interpret surface structure on satellite image.To interpret surface structure on satellite image. Synthetic seismogram comparison using different Synthetic seismogram comparison using different

wavelets.wavelets. Picking horizons at different levels on seismic section, Picking horizons at different levels on seismic section,

using synthetic seismogram and well picks.using synthetic seismogram and well picks. Various 3D views of the interpretationVarious 3D views of the interpretation To interpret lithology using different well logsTo interpret lithology using different well logs To create cross plots using different well logsTo create cross plots using different well logs To analyze sand-shale for various zonesTo analyze sand-shale for various zones To estimate water saturation using Pickett-PlotTo estimate water saturation using Pickett-Plot AVO-AVA comparisonAVO-AVA comparison AVO-AVA SyntheticsAVO-AVA Synthetics

The Dhodak gas field is the Pakistan’s largest gas and The Dhodak gas field is the Pakistan’s largest gas and condensate producing field. The Dhodak field, with condensate producing field. The Dhodak field, with estimates 620Bcf of proven gas reserves and 30million estimates 620Bcf of proven gas reserves and 30million barrels of condensate, is located in the Central Indus barrels of condensate, is located in the Central Indus

basin approximately 15KM North of Safed koh Blockbasin approximately 15KM North of Safed koh Block. .

Introduction to Area

Location of study area on surface tectonic map of Location of study area on surface tectonic map of PakistanPakistan

Basemap of the data usedBasemap of the data used

Divisions of Central Indus Divisions of Central Indus

basin basin ((Raza et al, 1989Raza et al, 1989 ))

Cross Section

along the Central Indus basin

(Raza et al, 1989 )(Raza et al, 1989 )

General geology and stratigraphyGeneral geology and stratigraphy

Surface geological map Surface geological map

(Bakr & Jeckson, 1964 )(Bakr & Jeckson, 1964 )

Surface geological map

(sheikh et al, 1989)

Surface structure map and Surface structure map and satellite map satellite map (Kellogg, 1936)(Kellogg, 1936)

Stratigraphy of the areaStratigraphy of the area

Well Correlation along the Zindapir-Dhodak Well Correlation along the Zindapir-Dhodak anticlinesanticlines

Seismic data interpretationSeismic data interpretation

Ricker waveletRicker wavelet

Synthetic seismogram

created using Ricker wavelet

Klauder waveletKlauder wavelet

Synthetic seismogram

created using Klauder wavelet

Ormsby waveletOrmsby wavelet

Synthetic seismogram

created using Ormsby wavelet

Butterworth waveletButterworth wavelet

Synthetic seismogram

created using Butterworth

wavelet

Comparison of synthetics using all waveletsComparison of synthetics using all wavelets

Seismic sections used:Seismic sections used:

Interpreting well picks on seismic line 795-SK-06 Interpreting well picks on seismic line 795-SK-06 using synthetics of dhodak-01 and 03using synthetics of dhodak-01 and 03

Dunghan

Pab Sandstone

Mughalkot

Interpreting well picks on seismic line 795-SK-06Interpreting well picks on seismic line 795-SK-06

Interpreting well picks and lithological strip on Interpreting well picks and lithological strip on seismic line 795-SK-06 using Dhodak-03seismic line 795-SK-06 using Dhodak-03

Interpreting Well picks and lithological strip on Interpreting Well picks and lithological strip on seismic line 795-SK-06 using Dhodak-03 seismic line 795-SK-06 using Dhodak-03

Time contour map: Dunghan LimestoneTime contour map: Dunghan Limestone

Depth contour map: Dunghan LimestoneDepth contour map: Dunghan Limestone

Time contour map: Pab SandstoneTime contour map: Pab Sandstone

Depth contour map: Pab SandstoneDepth contour map: Pab Sandstone

Time contour map: Mughalkot FormationTime contour map: Mughalkot Formation

Time contour map: Chiltan LimestoneTime contour map: Chiltan Limestone

Time contour map: AlozaiTime contour map: Alozai

Isochors map: Chiltan-alozaiIsochors map: Chiltan-alozai

Isochors map: Dunghan-ChiltanIsochors map: Dunghan-Chiltan

RMS Velocities along RMS Velocities along seismic seismic

line: 795-SK-04line: 795-SK-04

RMS Velocity Plot

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Time (msec)

RM

S V

eloc

ity (m

/sec

)

shot 145

shot 175

shot 190

shot 205

shot 220

shot 265

shot 295

shot 310

shot 325

shot 340

shot 355

shot 370

shot 385

shot 400

Average Velocities along seismic

line: 795-SK-04

Fault ModelFault Model

Time Surface grid at Dunghan level along with Time Surface grid at Dunghan level along with faults and well locationsfaults and well locations

Time Surface grid at Pab Sandstone level along Time Surface grid at Pab Sandstone level along with faults and well locationswith faults and well locations

Time Surface grid at Mughalkot level along with Time Surface grid at Mughalkot level along with faults and well locationsfaults and well locations

Time Surface grid at Chiltan level along with faults Time Surface grid at Chiltan level along with faults and well locationsand well locations

Time Surface grid at Alozai level along with faults Time Surface grid at Alozai level along with faults and well locationsand well locations

A-3D visualization with all interpreted Formations, A-3D visualization with all interpreted Formations, faults and well locationsfaults and well locations

B-3D visualization with all interpreted Formations, B-3D visualization with all interpreted Formations, faults and well locationsfaults and well locations

Dunghan surface with seismic line:795-SK-06Dunghan surface with seismic line:795-SK-06

Dunghan, Chiltan & Alozai Formation along the Dunghan, Chiltan & Alozai Formation along the seismic line: 805-SK-20seismic line: 805-SK-20

3D-Movie

Interpreted seismic line: 795-SK-04Interpreted seismic line: 795-SK-04

VaveVave VintVint VrmsVrms Bulk ModulusBulk Modulus Shear ModulusShear Modulus DensityDensity Poisson RatioPoisson Ratio VsVs VpVp

Interpreted seismic line: 805-SK-20Interpreted seismic line: 805-SK-20

Average Velocities along the seismic line: 795-SK-04Average Velocities along the seismic line: 795-SK-04Line:795-SK-04Line:795-SK-04

Interval Velocities along the seismic line: 795-SK-04Interval Velocities along the seismic line: 795-SK-04Line:795-SK-04Line:795-SK-04

RMS Velocities along the seismic line: 795-SK-04RMS Velocities along the seismic line: 795-SK-04Line:795-SK-04Line:795-SK-04

Rock Physical properties along the seismic Rock Physical properties along the seismic line 795-SK-04line 795-SK-04

General equations used:General equations used:

K= ρ * ((VK= ρ * ((VPP)) 2 2-(4/3)*(V-(4/3)*(Vss)) 2 2))

WhereWhere ρ = Densityρ = Density VVpp = Interval Velocity (km/sec) = Interval Velocity (km/sec)

VVss = Shear Velocity (km/sec) = Shear Velocity (km/sec)

KK = Bulk modulus = Bulk modulus

Shear Modulus= ρ * (VShear Modulus= ρ * (Vss)) 2 2

Where Where ρ = Densityρ = Density VVss = shear Velocity (km/sec) = shear Velocity (km/sec)

Density= 0.31 * (VDensity= 0.31 * (VPP)) 0.25 0.25

Where Where VVpp = Interval Velocity (m/sec) = Interval Velocity (m/sec)

• Poisson Ratio= (0.5* (Vpp2-2*Vss

2))/ (Vpp2-Vss

2)

Where

• Vpp = Interval Velocity (km/sec)

• Vss = Shear Velocity (km/sec)

• Shear Velocity= Vpp-1.36/1.16

Where

• Vpp = Interval Velocity (km/sec)

• Vpp has been calculated using acoustic log.

Bulk Modulus along the seismic line: 795-SK-04Bulk Modulus along the seismic line: 795-SK-04Line:795-SK-04Line:795-SK-04

Shear Modulus along the seismic line: 795-SK-04Shear Modulus along the seismic line: 795-SK-04Line:795-SK-04Line:795-SK-04

Density along the seismic line: 795-SK-04Density along the seismic line: 795-SK-04Line:795-SK-04Line:795-SK-04

Poisson Ratio along the seismic line: 795-SK-04Poisson Ratio along the seismic line: 795-SK-04Line:795-SK-04Line:795-SK-04

Shear Velocity along the seismic line: 795-SK-04Shear Velocity along the seismic line: 795-SK-04Line:795-SK-04Line:795-SK-04

Primary Velocity along the seismic line: 795-SK-04Primary Velocity along the seismic line: 795-SK-04Line:795-SK-04Line:795-SK-04

Well Log InterpretationWell Log Interpretation

Well logs displayed for Dhodak-02Well logs displayed for Dhodak-02

Well logs displayed for Dhodak-01Well logs displayed for Dhodak-01

Well logs displayed for Dhodak-01Well logs displayed for Dhodak-01

Well Lathe on Dhodak-03 from 165 SP of the Well Lathe on Dhodak-03 from 165 SP of the seismic line: 795-SK-05Rseismic line: 795-SK-05R

Stratigraphic well correlation using four Dhodak Stratigraphic well correlation using four Dhodak wells:3-1-2-7 (S-N)wells:3-1-2-7 (S-N)

Sand-Shale analysis along the productive zone of Sand-Shale analysis along the productive zone of Dhodak-02Dhodak-02

Sand-Shale analysis along the Pab Sandstone zone Sand-Shale analysis along the Pab Sandstone zone of Dhodak-02of Dhodak-02

Lithological analysis along the Lower Ranikot zone Lithological analysis along the Lower Ranikot zone of Dhodak-02of Dhodak-02

Lithological analysis along the Pab Sandstone zone Lithological analysis along the Pab Sandstone zone of Dhodak-02of Dhodak-02

Lithological analysis along the Mughalkot zone of Lithological analysis along the Mughalkot zone of Dhodak-02Dhodak-02

Lithological analysis along the Parh Limestone zone Lithological analysis along the Parh Limestone zone of Dhodak-02of Dhodak-02

Petro-PhysicsPetro-Physics

Sonic-Density cross plot for Dhodak-01 with overlay Sonic-Density cross plot for Dhodak-01 with overlay on the generalized Sonic-Density lithological plot.on the generalized Sonic-Density lithological plot.

Sonic-Density cross plot for Dhodak-01 with overlay Sonic-Density cross plot for Dhodak-01 with overlay on the generalized three minerals crossplot.on the generalized three minerals crossplot.

Sonic-Neutron Porosity cross plot overlaid on the Sonic-Neutron Porosity cross plot overlaid on the generalized cross plot for lithological interpretationgeneralized cross plot for lithological interpretation

Sonic-Porosity cross plot overlaid on the generalized Sonic-Porosity cross plot overlaid on the generalized cross plot for lithological interpretationcross plot for lithological interpretation

Density-Porosity cross plot overlaid on the Density-Porosity cross plot overlaid on the generalized cross plot for lithological interpretationgeneralized cross plot for lithological interpretation

Density-Poisson Ratio Density-Poisson Ratio cross plotcross plot

Density-Shear sonic cross plot

Sonic-density cross plotSonic-density cross plot

Porosity-Shear Sonic cross plot

Porosity-Density cross Porosity-Density cross plotplot

Porosity-Poisson Ratio cross plot

Sonic-porosity cross plotSonic-porosity cross plot

Poisson Ratio-Shear Sonic cross plot

Poisson Ratio-Vs cross Poisson Ratio-Vs cross plotplot

Density-Vp cross plot

Vp-Poisson Ration cross Vp-Poisson Ration cross plotplot

Vp-Shear Sonic cross plot

Vp-Vs cross plotVp-Vs cross plot

Vs-Poisson Ratio cross plot

Sonic-Density Cross plotSonic-Density Cross plot

Plots for Dhodak-02 wellPlots for Dhodak-02 well

Vp-Vp/Vs cross plotVp-Vp/Vs cross plot

Vp-Vp/Vs cross plot overlay

SP – Volume of Shale SP – Volume of Shale cross plotcross plot

GR-Volume of Shale cross plot

Pickett PlotPickett Plot

AVO/AVA SyntheticsAVO/AVA Synthetics

AVO Synthetics:AVO Synthetics: AVO Synthetic displays are used to study of the effects of trace offset on reflection AVO Synthetic displays are used to study of the effects of trace offset on reflection

amplitude. The AVO (amplitude variation with offset) Synthetics simulates the effects amplitude. The AVO (amplitude variation with offset) Synthetics simulates the effects that offset distance has on trace amplitude. The AVO traces displayed are equivalent that offset distance has on trace amplitude. The AVO traces displayed are equivalent to a CMP (common midpoint) gather that is used to observe these amplitude to a CMP (common midpoint) gather that is used to observe these amplitude variations. variations.

Trace gathers can also be displayed with NMO (normal moveout) effects applied and Trace gathers can also be displayed with NMO (normal moveout) effects applied and offset limited stacks can be generated from the CMP gathers.offset limited stacks can be generated from the CMP gathers.

AVA Synthetics:AVA Synthetics: AVA Synthetic displays are used to study of the effects of reflection angle on trace AVA Synthetic displays are used to study of the effects of reflection angle on trace

amplitude. The AVA (amplitude variation with angle) synthetics program simulates the amplitude. The AVA (amplitude variation with angle) synthetics program simulates the effects that changing reflection angle (with offset distance) has on trace amplitude.effects that changing reflection angle (with offset distance) has on trace amplitude.

The result is an angle sorted gather used to observe these amplitude variations. All The result is an angle sorted gather used to observe these amplitude variations. All gathers are corrected for NMO (normal moveout). gathers are corrected for NMO (normal moveout).

AVA Synthetics are primarily used as an analytical tool to compare the effects of AVA Synthetics are primarily used as an analytical tool to compare the effects of geology on trace amplitude that are independent of trace offset. In other words, an geology on trace amplitude that are independent of trace offset. In other words, an amplitude effect such as a phase reversal, caused by the same geological conditions amplitude effect such as a phase reversal, caused by the same geological conditions of density, velocity and Poisson’s ratio contrast, will generate the same anomaly at of density, velocity and Poisson’s ratio contrast, will generate the same anomaly at the same incidence angle regardless of the depth of the anomaly. the same incidence angle regardless of the depth of the anomaly.

On an AVA display, the general trace character (variation in amplitude with time) will On an AVA display, the general trace character (variation in amplitude with time) will appear approximately the same as an AVO display, but anomalies (on an AVO appear approximately the same as an AVO display, but anomalies (on an AVO display) similar to the one described above will appear at different offsets, rather than display) similar to the one described above will appear at different offsets, rather than at the same angle. This makes the AVA display useful for identifying anomalies that at the same angle. This makes the AVA display useful for identifying anomalies that are expected to occur at specific reflection angles. are expected to occur at specific reflection angles.

AVA-AVO comparisonAVA-AVO comparison

Tpsv = Tpp ((1 + Vp / Vs) / 2)

Where:Tpsv is the P-SV travel time.  Tpp is the P-P travel time. Vp/Vs is the ratio of P and S average velocities to the reflector

Zoeppritz Equation: Shuey 2-term and 3-term equations:

AVO model for Dhodak-02AVO model for Dhodak-02

AVA model for Dhodak-02AVA model for Dhodak-02

AVA model for Dhodak-01 using Zoeppritz equationAVA model for Dhodak-01 using Zoeppritz equation

AVA model for Dhodak-01 using Shuey02 equationAVA model for Dhodak-01 using Shuey02 equation

AVA model for Dhodak-01 using Shuey03 equationAVA model for Dhodak-01 using Shuey03 equation

AVO model for Dhodak-01 using Zoeppritz equationsAVO model for Dhodak-01 using Zoeppritz equations

AVO model for Dhodak-01 using Shuey2 equationAVO model for Dhodak-01 using Shuey2 equation

AVO model for Dhodak-01 using Shuey 03AVO model for Dhodak-01 using Shuey 03

Conclusions:Conclusions:

From surface Geology of the areaFrom surface Geology of the area:: Eocene strata is exposed at the surface of study area.Eocene strata is exposed at the surface of study area. On moving towards the south of the study area, older strata go on On moving towards the south of the study area, older strata go on

exposing up till the Zindapir anticline, where Paleocene-createous exposing up till the Zindapir anticline, where Paleocene-createous strata is exposed on the surface.strata is exposed on the surface.

Pop-up structure prevails the whole area.Pop-up structure prevails the whole area. Extension of the structure is North-South.Extension of the structure is North-South.

From seismic interpretationFrom seismic interpretation:: There is very small variation in the synthetics, created using various There is very small variation in the synthetics, created using various

wavelets.wavelets. Normally the throw of these faults is very low (25msec to 80msec), Normally the throw of these faults is very low (25msec to 80msec),

except at few places (e.g. in line 18, there is an about 100msec except at few places (e.g. in line 18, there is an about 100msec throw of fault ).throw of fault ).

Velocity of these formations is very high, ranging from 4000m/sec to Velocity of these formations is very high, ranging from 4000m/sec to 7000m/sec.7000m/sec.

Depth converted maps have been prepared using SRD rather than Depth converted maps have been prepared using SRD rather than depth from KB.depth from KB.

Since most of the faults terminates in the Eocene strata, therefore Since most of the faults terminates in the Eocene strata, therefore the age of Eocene can be assigned to these faults.the age of Eocene can be assigned to these faults.

Chiltan formation is highly fractured and distorted.Chiltan formation is highly fractured and distorted. Isochors map between Chiltan and Alozai formations, showing the Isochors map between Chiltan and Alozai formations, showing the

time thickness in the range of 700msec to 1300msec. Maximum time thickness in the range of 700msec to 1300msec. Maximum variation is on the southern side. variation is on the southern side.

Isochors map between Dunghan & Chiltan formations, showing the Isochors map between Dunghan & Chiltan formations, showing the time thickness in the range of 600msec to 1300msec. Maximum time thickness in the range of 600msec to 1300msec. Maximum variation is on the southern side.variation is on the southern side.

RMS and average velocity graphs showing continuously increasing RMS and average velocity graphs showing continuously increasing trend of velocities.trend of velocities.

3D visualization of the seismic and the other maps, provide the ease 3D visualization of the seismic and the other maps, provide the ease in the seismic data interpretation.in the seismic data interpretation.

Variation in the velocity lines along the seismic line give hint of the Variation in the velocity lines along the seismic line give hint of the presence of faults. presence of faults.

Variation in the rock physical properties can directly be co relatable Variation in the rock physical properties can directly be co relatable with the structure, interpreted.with the structure, interpreted.

In order to get production from Chiltan Limestone, Dhodak-09 well In order to get production from Chiltan Limestone, Dhodak-09 well would have to be deepen for a few meters more.would have to be deepen for a few meters more.

For well Log Interpretation:For well Log Interpretation:

Some of the well logs have been estimated using the general curve Some of the well logs have been estimated using the general curve estimation relations.estimation relations.

Well lathe shows the sharp variation of amplitudes in the lower part.Well lathe shows the sharp variation of amplitudes in the lower part. Well correlation shows the pinching out in the Eocene strata but Well correlation shows the pinching out in the Eocene strata but

linear trend of strata, below it.linear trend of strata, below it. Unit-2 of the Lower Ranikot showing the higher value of porosity Unit-2 of the Lower Ranikot showing the higher value of porosity

and lower values of water saturation. This gives hint of the presence and lower values of water saturation. This gives hint of the presence of some hydrocarbon accumulation (Well-01). Similar is the situation of some hydrocarbon accumulation (Well-01). Similar is the situation with Pab Sandstone.with Pab Sandstone.

For Petrophysical interpretation:For Petrophysical interpretation:

Sonic-Density cross plot showing the increasing trend and the data Sonic-Density cross plot showing the increasing trend and the data values fall in the range on the sandstone and lime stone zone.values fall in the range on the sandstone and lime stone zone.

The same plot has also been overlaid on the three minerals plot, The same plot has also been overlaid on the three minerals plot, which showing the data values to be residing in the calcite zone and which showing the data values to be residing in the calcite zone and trending towards sandstone.trending towards sandstone.

Density-Porosity cross plot shows linear trend of the data values Density-Porosity cross plot shows linear trend of the data values that totally resides in between the zone of Sandstone and that totally resides in between the zone of Sandstone and Limestone.Limestone.

various other cross plots showing the linear trend, in increasing various other cross plots showing the linear trend, in increasing order.order.

If a curve estimated from the other curve and plotted against its If a curve estimated from the other curve and plotted against its native curve, the output trend of the data point is linear line.native curve, the output trend of the data point is linear line.

Most of the data points lies in the range of 10% to 20 % porosity, for Most of the data points lies in the range of 10% to 20 % porosity, for the Impedance-Porosity cross plot.the Impedance-Porosity cross plot.

There is a linear trend of volume of shale both against SP and GR.There is a linear trend of volume of shale both against SP and GR. Pickett plot showing the water saturation lines, with decreasing Pickett plot showing the water saturation lines, with decreasing

order, for the Dhodak-02 well, cropped for the reservoir zone. order, for the Dhodak-02 well, cropped for the reservoir zone.

For AVO/AVA modeling:For AVO/AVA modeling:

Phase reversal in AVA/AVO gives hint of the presence of some Phase reversal in AVA/AVO gives hint of the presence of some hydrocarbon accumulation.hydrocarbon accumulation.

The output of the AVO may vary from AVA, for the complex areas, The output of the AVO may vary from AVA, for the complex areas, with sharp dipping of horizons and presence of faults.with sharp dipping of horizons and presence of faults.

Very distortions can be seen in the AVA models as compared to the Very distortions can be seen in the AVA models as compared to the AVO models.AVO models.

Clear phase reversal can be seen for both AVA and AVO models, Clear phase reversal can be seen for both AVA and AVO models, using the data of Dhodak-01 well.using the data of Dhodak-01 well.

There is a very small difference between the output AVO/AVA There is a very small difference between the output AVO/AVA models, created using Zoeppritz, Shuey2 and Shuey3 equations.models, created using Zoeppritz, Shuey2 and Shuey3 equations.

Shuey3 and Shuey2 equations gives smooth trend for the output Shuey3 and Shuey2 equations gives smooth trend for the output AVA model as compared to the AVA model, created using Zoeppritz AVA model as compared to the AVA model, created using Zoeppritz equation.equation.

Zoeppritz equation give sharp edges at the reflections of the output Zoeppritz equation give sharp edges at the reflections of the output AVO model as compared to the AVO models, created using either AVO model as compared to the AVO models, created using either Shuey2 or Shuey3 equations.Shuey2 or Shuey3 equations.

The results of AVA, created using Shuey2 equation gives more The results of AVA, created using Shuey2 equation gives more accurate results.accurate results.