Krishna Godavari Basin: By: - Rishabh Tripathi
Krishna Godavari Basin: By: - Rishabh Tripathi
Krishna Godavari Basin: By: - Rishabh Tripathi
INTRODUCTION
GEOLOGY
GEOCHEMICAL PROSPECTING
SEISMIC
PETROLEUM SYSTEM
HYDROCARBON POTENTIAL
CHALLENGES
REFERENCES
INTRODUCTION
o The first gas discovery in the basin was in 1983, in Razole Well No 1 by ONGC
o The site is known for the D-6 block where Reliance Industries discovered the
biggest natural gas reserves in India in 2003
GEOLOGY
TECTONIC HISTORY
The basin came into existence following rifting along eastern continental margin of
Indian Craton in early Mesozoic.
The geological history comprises of following stages:
RIFT STAGE
DRIFT STAGE
o Krishna Graben
o Bapatla Horst
o West Godavari Sub basin
o Tanuku Horst
o East Godavari sub basin
DEPOSITIONAL ENVIRONMENT
Soil samples from oil and gas fields of Tatipaka and Pasarlapudi areas of the basin
show the presence of bacterial population for methane (3.46 105 cfu/g), ethane
(3.85 105 cfu/g) and propane (3.04 105 cfu/g) oxidizing bacteria in soil
samples.
The gas chromatographic analysis of 135 soil samples and the magnitude of each
of the organic constituents CH4, C2H6, C3H8 and n-C4H10 were measured and
expressed in ppb of the soil gas mixture. The concentrations of adsorbed soil gases
varied for methane (C1) from 1 to 115 ppb, for ethane (C2) from 1 to 99 ppb,
for propane (C3) from 1 to 34 ppb, for butane (nC4) from 1 to 9 ppb and for C2+
from 1 to 115 ppb
GEOCHMICAL EXPLORATION
The cross-plots between C1, C2, C3 and C2+ show good correlation and the data
gathered indicates that
(ii) hydrocarbons are not affected by secondary alteration during their migration
from subsurface to subsequent adsorption on to the surface soil
The interpretation followed the standard genetic diagram for correlating gas
wetness, i.e. C1/(C2 + C3) ratios with the 13C of methane to classify natural gas
types as biogenic or thermogenic. Molecular ratios of C1/(C2 + C3) less than
−50‰ are typical for thermogenic hydrocarbon gases with 13C1 values between –
25‰ and −50‰
GEOCHEMICAL PROSPECTING
The present study shows that microbial presence has a direct bearing with the
accumulation of hydrocarbons in sub-surface regions. The microbial prospecting and
adsorbed soil gas studies together indicate that hydrocarbon micro-seepage exists in
the area under review
SEISMIC COVERAGE
Conventional single fold surveys were initiated in 1965 and upto 1973 about 2,690
line km of data was acquired.
CDP surveys commenced in 1973 and so far about 34,642 Line Km. data with foldage
varying from 6 to 48 have been acquired.
More than 74,753 Line Km 2D and 26,508 Sq. Km. 3D seismic surveys have been
carried out
Additionally, during 1972-74, 2,028 km. Refraction data was acquired to study the
basement configuration and also shallow reflectors.
PETROLEUM SYSTEM
• Mandapeta Sandstone
Reservoir Rock
Several oil and gas fields are located both in on-land and offshore parts of the basin
Notable oil discoveries are Kaikalur, Vadali, Mori, Bantumilli, Lingala, Suryaraopeta,
Gopavaram, Kesanapalli, and Kesanapalli West.
About 71 discoveries have been made by Pvt./JV companies so far in NELP blocks
o Discoveries by RIL—31
o Discoveries by OIL—01
HYDROCARBON POTENTIAL
Total Oil and Gas Production from KG (On-land & Offshore) is 1.84 MMT
1507.38 MMSCM
0.33 MMT
CHALLENGES
GAS HYDRATE
Large quantities of gas hydrate were discovered while drilling in the Krishna
Godavari Basin in May-August 2006 with the research drillship JOIDES Resolution.
Much of the gas hydrate resource potential worldwide occurs filling the pore space of
sandstone reservoirs, and most of the research being done on the extraction of gas
from hydrates is focused on deposits concentrated in sands.
The reservoir rock with gas hydrate in the Krishna Godavari Basin is fractured shale.
CHALLENGES
Consequently, over the decades, even if much advancement has taken place in
seismic data processing to obtain accurate imaging of sub-surface structural details,
sub-basalt imaging in Krishna-Godavari basin has become a number one problem
embarked upon due to very poor signal to noise ratio as well as the presence of
multiples below trap.
The seismic data processing arena, presence of multiples, very poor signal to noise
ratio and impediments to velocity determination below trap causes serious distress to
image meticulously the Subsurface Intricacies In Krishna-Godavari basin.
REFERENCES
DGH website
http://dghindia.gov.in//assets/downloads/56cfd90962284Extensive_deltaic_plain.pdf