Rajasthan Basin

Basin Introduction :

Geographic Location of the basin
Rajasthan Basin forms the eastern flank of Indus geosyncline and comprises the sedimentary tract to the west and northwest of Aravallis upto Indo-Pakistan border. This pericratonic basin also forms a part of the great Thar Desert.

Category of the basin
The Rajasthan Basin comes under the Category – I basin (onland) with established commercial production.

Area of the Basin
Total Basinal area: 1,26,000 Sq. km (Onland)
Sub-basin wise distribution:
Barmer-sanchor: 11,000 sq. km
Bikaner-Nagaur : 70,000 sq. km
Jaisalmer : 45,000 sq. km

Age of the Basin
Age ranges from Cambrian To Recent
Barmer-sanchor: Tertiary basin
Bikaner-Nagaur : Paleozoic basin
Jaisalmer : Mesozoic & Cenozoic basin

Sedimentary thickness
Average thickness of sediments in Rajasthan basin is ~ 5000 m.

Tectonic History :

Type of Basin
Jaisalmer sub-basin – Pericratonic Basin
Bikaner- Nagaur & Barmer-sanchor – Intracratonic Basins

Tectonic Zones within the Basin
Rajasthan Basin has been divided into three Sub-basins separated from each other by basement ridges/faults. These Sub-basins are:
–Jaisalmer Sub-basin which is further divided into 3 depressions
~ Shahgarh Depression
~ Kishangarh Shelf
~ Miajlar Depression
–Bikaner- Nagaur Sub-basin
The major tectonic element in Bikaner- Nagaur Sub-basin is an almost east-west trending basement ridge, ‘the Bikampur Arch’.
–Barmer-sanchor Sub-basin
Prominent tectonic elements in this subbasin are : Devikot-Nachna Uplift with Fatehgarh Fault which marks the northern limit and an east-west trending Tharad Ridge marks the southern limit while separating it from Cambay Basin. Another cross trend along Sarnu Hill Fault divides Barmer-Sanchor Sub-basin into Barmer Depression in the north and Sanchor Depression in the south.

The Pokhran High separates the Bikaner-Nagaur Sub-basin from Jaisalmer Sub-basin. Devikot-Nachna uplift separates Jaisalmer Sub-basin from Barmer-Sanchor Sub-basin.

The tectonic evolution of Rajasthan Basin took place in four distinct phases corresponding to
– Precambrian – Triassic plate movement
– Breaking of Indian plate from southern continent during Jurassic
– Collision of Indian plate with the Asian plate from Eocene onwards
– Uplift of Sind-Baluchistan fold belt resulting in filling up of the Indus shelf

Major Lineaments

Three major trends along
~ NE-SW (Aravallis) direction
~ ENE-WSW or EW direction
~ NW-SE (Dharwarian) direction
The NE-SW trending lineament (Aravallis) being the oldest is offset by late sublatitudinal lineaments. Both NE-SW and ENE-WSW or E-W trends are affected by younger NW-SE Dharwarian lineament, which resulted in the formation of Barmer-Sanchor Sub-basin.

Stratigraphy :

Generalized & subsurface stratigraphy of Jaisalmer sub-basin

Generalized & subsurface stratigraphy of Bikaner – Nagaur sub-basin

Generalized & subsurface stratigraphy of Barmer – Sanchor sub-basin

Interbasinal Stratigraphic Relationship

Sedimentation History

The Western Rajasthan Shelf which forms an integral part of Indus Basin, originated during Pre-Cambrian period. The sediments range in age from Late Proterozoic to Recent with intermittent transgressions and regressions.

~ The first cycle of sedimentation corresponding to Proterozoic-Early Palaeozoic is designated as Birmania/Randha Formation representing deeper water sediments.

~ A prominent orogeny, probably resulting from the collision of older plates led to a major uplift and hiatus in this region. On the peneplained Birmania-Randha topography, the Karampur Formation of Permain age was deposited over the unconformable surface.

~ A major regression took place during the Triassic and Early Jurassic, which resulted in deposition of Shumarwali Formation and Lathi Formation The Jaisalmer sediments have been deposited in very shallow water depths. During this period the Bikaner-Nagaur Sub-basin became positive due to differential block movement.

~ During the Upper Jurassic, a narrow elongated Cambay rift graben was connected to Jaisalmer Sub-basin through Sanchor-Barmer Sub-basin. The resulting clastic sequence representing Baisakhi and Bedesir formations in Jaisalmer Basin continued to be deposited in an oscillating shallow marine environment whereas in Sanchor Depression conglomerates and pebbly sandstone facies was deposited under fluvial regime designated as Serau Formation.

~ The Lower Cretaceous (Neocomian) Pariwar Formation represents further regression with shallow marine and brackish condition towards the lower part and complete regression with setting in of continental conditions towards the top.

~ The next phase of sedimentation started with the deposition of shallow marine Habur Formation in Jaisalmer Sub-basin which continued during Turonian and ended in Coniacian times with the development of predominantly marine marls and carbonates with clastic interbeds.

~ A major uplift of the axial belt gave rise to a prominent hiatus ranging in age from Maestrichitian to Danian and brought an end to this marine cycle. During this interval there was a major volcanic eruption in Sanchor Depression, which obliterated the pre-existing topography. The volcanic activity was more intense south of Sanchor.

~ The next cycle of sedimentation began with the deposition of clastic sequence of Sanu/Akli/Balutri Formation representing brackish to shallow marine environment probably during early Paleocene and Early Eocene.

~ The Khuiala and Bandah formations of Jaisalmer Sub-basin, and Mandai and Kapurdi formations of Barmer Depression indicate a somewhat stable condition during Lower Eocene. However, Sanchor Depression witnessed a minor pulse of regression, resulting in deposition of Lower Tharad Formation.

~ In the central part of Indus Basin, clastic deposition continued under slightly oscillating shallow marine condition represented by Mari and Gaj formations of Oligocene and Lower Miocene. The eastern flank of the Indus Shelf including, Bikaner-Nagaur, Jaisalmer and Barmer-Sanchor remained uplifted from Middle Eocene to Pliocene and supplied clastics to the fluvial Basin to the west and southwest. However, during Quaternary a thin veneer of fluvial sediments covered Middle Eocene sediments.

~ The Sanchor Depression had a continuous sedimentation from Early Miocene to Recent, deposited under minor pulses of transgressions and regressions.

Depositional Environment

Jaisalmer Sub basin :

Bikaner-Nagaur sub-basin :

Petroleum System :

Source

Reservoir

Trap

Petrolrum Plays :

Jaisalmer sub-basin
~ Paleocene extensional fault blocks with Cretaceous age reservoirs
~ Early Tertiary stratigraphic subcrop closure of Sanu clastics beneath the shales of the lower Khuiala Formation
~ Mesozoic subcrop of either Cretaceous age sediments below Base Tertiary or early-mid Jurassic Lathi Formation beneath Jaisalmer Limestone.
~ Lowstand Fan mounds at the base-of-slope (intra Baisakhi Formation)
~ Relative sea-level fall, forced regression sands at shelf break.

– Mesozoic plays
Mesozoic sediments are expected to hold good prospects on Jaisalmer – Mari platform. The rising flank of Jaisalmer Sub-basin is the target for subtle traps. Lunar and Daw are considered to be good prospects for Mesozoics. Bhuana structure has a potential of estimated 2BCM of gas. The Mukleri structure is expected to host about 1 MMt of oil. In Lunar area eight drape structure have been identified which are most favourable targets for hydrocarbon entrapment.

– Cretaceous plays
Probability of striking oil in Kharotar – Sadewala area in Cretaceous sediments appear to be high.

Bikaner-Nagaur subbasin
~ Early Cambrian Transpressional fault-blocks.
~ Early Cambrian Transpressional reactivation combined with salt swells.
~ Sands developed at the toe-set end of ‘clinoform sequence’.
~ Sands developing structure within prograding clinoform.
~ Tertiary reactivated fault-blocks, extensional movement along existing faults.
~ Late Tertiary transpression of pre-existing faults.

– Cambrain plays
Available evidence indicates that the Cambrian sediments have gererated both oil and gas. Oil is discovered in Cambrain dolomites in the well Karampur-1. Heavy oil is present in multiple zones within Cambrian sediments (Bilara Limestone and Jodhpur Sandstone) in Baghewala, Tavriwali and Kalrewara structures. Presence of light oil has been reported in an exploratory well drilled in an exploration block RJ-ON-90/5.

Barmer-Sanchor Sub-basin

– Mesozoic plays
Updip migration from Cambay basin northwards is considered to have sourced the hydrocarbons encountered in Barmer-Sanchor sub-basin. However latest data suggests that thick sediments of tharad formation having good source rock characteristics constitute a significant source sequence within kitchen areas of Barmer-Sanchor basin itself. Hydrocarbon entrapment is established in structural as well as strati-structural traps with possibility in updip pinchout prospect towards the basin margin. Potential oil and gas bearing reservoirs range from the upper Cretaceous volcanic basalts to the Eocene – Oligocene arenaceous units. Mesozoic sediments are also possible reservoirs in the northern part of Barmer- Sanchor basin.