PGS-402 PROJECT ORIENTED DISSERTATIONBY

Rishabh ParmarMSc. Petroleum Geosciences

Sem – IVRoll No. 5

BHU

PROJECT ORIENTED DISSERTATIONON

The Petroleum System Of

Ahmedabad - Mehsana BlockBy

MR.RISHABH PARMARIn partial fulfillment for the award of degree

OfMASTER OF SCIENCE

InPetroleum GeosciencesDepartment Of Geology

Banaras Hindu UniversityVaranasi -221005

INTRODUCTION

REGIONAL TECTONIC FRAMEWORK

TECTONOSTRATIGRAPHY OF CAMBAY BASIN

LITHOSTRATIGRAPHY OF CAMBAY BASIN

PETROLEUM SYSTEM ELEMENTS

AHMEDABAD – MEHSANA PETROLEUM SYSTEM

Cambay basin covers an area of 56,000 sq.km between latitudes 210 and 250 N and longitudes 71030’ and 79039’ E.

Linear, sigmoidal basin trending NNW-SSE.

Bounded by Aravali – Delhi belt towards NE

SE Deccan traps , E is bounded by Champaner formation, W Saurashtra , S & SW Extends into Gulf of Cambay, N extends to Sanchor,Rajasthan.

LOCATION MAP OF CAMBAY BASIN

The extensional architecture of the Cambay Basin is defined by three major Pre-Cambrian trends :

NNW-SSE trend related to Dharwarian Orogeny

NE-SW trend related to Aravalli Orogeny.

ENE-WSW trend related to Satpura Orogeny.

Cambay is an Intracratonic graben bounded by marginal faults.

Six depressions separated by uplifts/faults.

The basin is divided into 5 tectonic blocks :

I. Narmada-Tapti Block

II. Jambusar-Broach Block

III. Tarapur-Cambay Block

IV. Mehsana-Ahmedabad Block

V. Sanchor- Patan Block.

Three distinct sedimentary sequences are identified during different tectonic stages:

Pre-rift late Cretaceous sediment

EarlyPaleocene sequence:unconformities;restricted to fault grabens only.

Eocene to Recent post rift succession

Source Rock

Reservoir rock

Cap Rock

Trap

Pressure , Temperature , Time

In the Northern part of the basin Cambay –Kadi/Kalol Petroleum System is the major patroleum system .Other speculative petroleum systems include Olpad – Kalol(?)

and Olpad Olpad (?)

In Mehsana-Ahmedabad block, the hydrocarbon accumulations are known from sands in Tarapur Formation, Kalol Formation, Kadi Formation and Cambay Shale.

OIL/GAS FIELDS OF AHMEDABAD- MEHSANA

Some of note worthy fields are Balol (gas in Tarapur Formation), Lanwa, Balol, Santhal, Bechraji (heavy oil in Kalol Formation), Sanand, Nawagam, Jhalora, Sobhasan, N.Kadi, Kalol (oil in Kalol Formation), Nawagam (Lr. Pay), Jotana (oil in Kadi Formation), South Kadi, Limbodra and Indrora (oil in Cambay Shale).

Source rocks >>

Several organic rich potential source rock sequences, which extend across the basin have been identified at:

- Base of the Kalol Formation and its equivalent (Middle Eocene)

-Cambay Shale Formation (Lower Eocene), and

- Top and base of Olpad Formation(Paleocene)

Source rock (SR) data reveal six laterally extensive potential sources (PS) with kerogen type II/III in the middle Eocene–lower Paleocene. The PSs are SR4 at the base of the Kalol Formation; SR5 and SR6 at the top and middle, respectively, of the Cambay Shale Formation; SR7 and SR8/9 at the top of the Olpad Formation; and SR11/12 at the base of the Olpad Formation. In the north, SR11/12, SR8/9, and SR7 attained peak oil generation (vitrinite reflectance [Ro] _0.75%) at 45, 5, and 1 Ma, respectively. The SR6 and SR5 attained generation threshold (0.5% Ro) recently.

In the north Cambay basin the maximum hydrocarbon generated (HCG) in Cambay shale is of the order of 4 million MT/Km. Kadi and Kalolformations represent the principle clastic reservoir facies in Mehsana block. The litho assemblage is characterized by sandstone — coal —carbonaceous shale suite deposited under paludal.

Oil – Source Correlation : carbon isotopic compositions of aromatics (-29.4 to -31.6) correlate well with Cambay shale (-26.1 to -29.8)

Reservoir rocks :. The reservoirs in different stratigraphic levels are :

Paleocene - Siltstones in Olpad Formation.

Lower Eocene - Lenticular sands in Cambay Shale, and sands and silts in Kadi clastic wedge in Mehsana block.

Middle Eocene -Siltstones and sandstones in Kalol Formation.

Upper Eocene - Oligocene - Lenticular sands in Tarapur Shales and sandstones .

The non-marine clastic wedge constituting Kadi Formation is present in Mehsana-Ahmedabad block and constitutes reservoirs in Sobhasan and a few other fields. The Kalol Formation is extensively present in north Cambay Basin in Ahmedabad-Mehsana and Tarapur-Cambay blocks, and is the main reservoir in Kalol, Sanand, Wavel, Nawagam, Ahmedabad, Bakrol, Dholka, North Kadi and Balol-Lanwa-Santhal fields.

The Tarapur Shales of Upper Eocene-Oligocene age are the principal cap rocks in northern Cambay basin

Structural Highs and fault closures & Stratigraphic traps (pinchouts / wedgeouts, lenticular sands, oolitic sands, weathered trap) in Paleocene to Miocene sequences have been proved as important plays of Cambay Basin.

Timing of migration & Trap formation: The peak of oil generation and migration is understood to have taken place during Early to Middle Miocene. The hydrocarbon migration occurred during early Miocene coinciding with the terminal phase of basin inversion. Most of the structures in northern Cambay basin are associated with basement controlled faults and are of early origin. These structures, thus, were formed earlier to the main phase of migration which took place sometimes during Miocene

In Ahmedabad Mehsana block the clasticreservoirs lie close to the source ,

These correlate well on the HCG HCE chart which show them close to highest hydrocarbon charge areas.

SR5/6 are still to achieve minimum 0.5% Vro

Critical moment occurred around Middle Miocene .

Neogene succession is still immature and provides the overburden for hydrocarbon expulsion.