Geomodels of interpreted seismic data and overlaying Geomodels of interpreted seismic data and overlaying attributes provide new ways to analyze structure.attributes provide new ways to analyze structure.

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

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

ATCATC

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

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

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: Pab SandstoneTime contour map: Pab Sandstone

Depth contour map: Pab SandstoneDepth contour map: Pab Sandstone

Time contour map: Chiltan LimestoneTime contour map: Chiltan Limestone

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

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

Well Log InterpretationWell Log Interpretation

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

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

Petro-PhysicsPetro-Physics

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

Pickett PlotPickett Plot

Conclusions:Conclusions: 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 strata exposing up till the Zindapir anticline, where Paleocene-createous strata is exposed on the surface.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. 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 throw of except at few places (e.g. in line 18, there is an about 100msec throw of fault ).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.

Since most of the faults terminates in the Eocene strata, therefore the Since most of the faults terminates in the Eocene strata, therefore the age of Eocene can be assigned to these faults.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 Dunghan & Chiltan formations, showing the time Isochors map between Dunghan & Chiltan formations, showing the time

thickness in the range of 600msec to 1300msec. Maximum variation is thickness in the range of 600msec to 1300msec. Maximum variation is on the southern side.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 in 3D visualization of the seismic and the other maps, provide the ease in the seismic data interpretation.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 corelatable Variation in the rock physical properties can directly be corelatable 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.

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 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.

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.

Density-Porosity cross plot shows linear trend of the data values Density-Porosity cross plot shows linear trend of the data values that lies in between the zone of Sandstone and Limestone.that lies in between the zone of Sandstone and 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, Most of the data points lies in the range of 10% to 20 % porosity, for the Impedance-Porosity cross plot.for 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.