Basin architecture and petroleum systemof Krishna Godavari Basin, east coast of India S. K. GUPTA, Oil and Natural Gas Corporation, Dehradun, India K rishna Godavari Basin is a peri-cratonic passive margin basin on the east coast of India (Figure 1). The onland part consists of 28 000 km2 and is mostly alluvium covered. Krishna and Godavari are the two major river systems which drain the area and discharge in the Bay of Bengal. The offshore basinal area covers 24 000 km2 to the isobath of 200 m. However, the basin extends into deeper water and covers a much larger area. The basin’s characteristic feature is its enechelon horst and graben system which is filled with a thick pile of sediments of Permian-to-Recent age and emerging as one of India’s most promising petroliferous areas. Commercial accumulation of hydrocarbons occurs in sediments from the Permian to as young as the Pliocene. Krishna Godavari Basin is orthogonally juxtaposed to NW-SE trending Pranhita Godavari Gondwana graben in the north (Figure 2). The NE-SW basin margin is the most extensive fault trend over the area (Figure 3). It takes a bow-like swing and comes to the coast near Kakinada graben in the northeast and near Palar-Pennar graben in the southwest. The onland basinal area is characterized by en-echelon and arcuate horsts and grabens associated with major cross trends. In addition to the basin margin fault, three more regional faults developed further basinward: the onland Matsyapuri-Palakollu fault, a Miocene structure building fault in shallow water close to the coast, and a Pliocene structure building fault in deeper water. The arcuate horsts and the four regional arcuate faults are more or less parallel. Offshore, the sediments are mostly influenced by growthrelated tectonics. Stratigraphy. The sedimentary sequence of Krishna Godavari Basin ranges from Permian-to-Recent. The Precambrian metamorphic basement consists of gneisses, quartzites, charnokite, and khondalite. Subsurface knowledge is limited due to alluvium cover. However, isolated outcrops of Permian, Cretaceous, Paleocene, and Mio-Pliocene rocks are present near the basin edge. Figure 4 shows the geologic map of Krishna Godavari Basin and Figure 5 the generalized stratigraphy. Sedimentation in Gondwana Basin was initiated during the Early Permian over the crystalline basement and is known as Draksharama/Kommugudem Formation. Sediments of Triassic age are conspicuous by their absence. Golapalli sandstone of Early Cretaceous age lies unconformably over Mandapeta sandstone. The top of the Golapalli sandstone is a basinwide regional unconformity and is in turn covered by thick Late Cretaceous sediments and relatively thin Tertiary sediments. The areas of Gudivada graben and Krishna graben constitute the Jurassic rift basin. The Jurassic and Early Cretaceous sediments are the main fill for the Jurassic Basin. The overlying Tertiary and Recent sediments are relatively thin and generally undifferentiated. Bantumilli graben and Nizampatnam graben were created during the Cretaceous and therefore named the Cretaceous Basin. The Cretaceous sedimentation over the Gondwana, Jurassic, and Cretaceous basins began simultaneously during Aptian/Albian time. These sediments are called the Golapalli sandstone in Mandapeta graben and Bhimadolu graben, the Nandigama Formation in Bantumilli graben, and Gajulapadu shale/Kanukollu sandstone in 830 THE LEADING EDGE JULY 2006 Figure 1. Location of Krishna Godavari Basin. Figure 2. Tectonic map of Krishna Godavari Basin. Gudivada graben and Krishna graben. The overlying Raghavapuram shale and Tirupati sandstone of Late Cretaceous age, followed by the relatively thin Tertiary sediment, is widely distributed. Therefore it can be surmised that Krishna Godavari Basin was initially made up of Nandigama Formation (Aptian/Albian) is primarily marine shale with thin sandstone beds. Gajulapadu shale and overlying Kanukollu sandstone (Aptian/Albian) rest unconformably over the Bapatla sandstone in the Gudivada graben. The environment of deposition is fluvial-to-lagoonal. and they remained a unified basin until the Late Cretaceous. which rests unconformably over the Mandapeta sandstone as fill sediment. and shale section. Sedimentation took place under shallow marine conditions. is highly carbonaceous and rich in organic matter. Deposition took place in a marginal marine environment. clay. The depositional environment was shallow marine. overlain by sandstone. Lithostratigraphy. The basal part is coarser clastics with thin sandstone interbedded. The presence of relatively thick intervening shales suggests cyclic flood plain conditions. Tirupati sandstone (Early to Late Maastrichtian) unconformably overlies the Raghavapuram shale. It was deposited during the retreating Cretaceous sea and is predominantly sandstone with minor claystone. and Cretaceous Basin. Each kicked off a series of subsidiary growth faults which locally guided the sedimentation pattern. Kommugudem Formation is dominantly a shale sequence with interbedded coal and sand. Gondwana Basin. There are JULY 2006 THE LEADING EDGE 831 . Raghavapuram shale (Cenomanian to Early Maastrichtian) can be subdivided into lower and upper units. Razole Formation (Early Paleocene) consists of widespread volcanic flows over the Tirupati sandstone.Figure 3. The overlying Kanukollu sandstone is predominantly sandy and fairly consistent in distribution. It rests directly on the Archean basement. argillite (Draksharama Formation) is present underneath the Kommugudem. The high-resistivity lower unit is rich in organic matter. The basal section is claystone with thin sandstone layers interbedded. The overlying section is dominantly arenaceous with thin intercalations of shale and claystone. The coal beds are generally 1–6 m in thickness. Jurassic Basin. Kommugudem Formation (Early Permian is the oldest sediment deposited over the Archean basement although. deposited in a lacustrine environment. Bapatla sandstone (Late Jurassic) is a nonmarine sandstone. It is progressively shaly basinward and is called the Chintalapalli shale. The Gajulapadu shale. Golapalli sandstone (Aptian/Albian) is red claystone. A few interbedded sandstone layers are also present. The Godavari graben area to the south of the Eocene growth fault (Matsyapuri-Palakollu fault) is the main depocenter for Tertiary sediments. Mandapeta sandstone (Late Permian) is a thick nonmarine feldspathick and micaceous sandstone deposited in a fluvial environment. at places. Further basinward. The upper unit has thin interbedded layers of lenticular sand and shale. Tertiary sedimentation was successively influenced by the Miocene growth fault and the Pliocene growth fault. Time structure map on top of basement depicting tectonic elements of Krishna Godavari Basin. Antarctica. accumulated. Rift Stage I: Prior to drifting. Evolutionary history of Krishna Godavari Basin. Bhimanapalli limestone (Middle Eocene) is an algal dolostone with abundant dolomite crystal and red algal fragments. Pasarlapudi Formation (Early Eocene) overlies the Palakollu shale and consists of alternating sand and shale layers with some limestone. Interbedded sandstones within thick carbonates are common. The sands are separated by interbedded clay. Godavari Formation (Plio-Pleistocene) sediments are mainly clay with minor silt layers deposited south of the Miocene growth fault. Gondwanaland comprised the continents of Africa. This unit thickens basinward where it is called the Godavari clay. at least 2–3 submarine trap flows. The thickness of this lithounit increases basinward. The depositional environment was shallow inner-to-middle shelf.Figure 4. brought in by a deepwater river-fan system. The depositional environment was inner-to-middle shelf. It also represents the basinward clay facies of the Pasarlapudi Formation. between the Matsyapuri-Palakollu fault and the Miocene growth fault close to the coast. Palakollu shale (Middle to Late Paleocene) was deposited in an outer neretic to bathyal environment south of the Matsyapuri-Palakollu fault. Matsyapuri sandstone (Oligocene-Miocene) is a thick sandstone sequence with interbedded claystone. and Matsyapuri sandstone. and the top surface is altered and weathered into variegated clay. the Pasarlapudi sands grade into shale and are called the Vadaparru shale. Sediments were sub832 THE LEADING EDGE JULY 2006 jected to “push ups” and rotation because of the tectonics of the underlying Vadaparru shale. However. The basin appears to have gone through eight stages prior to assuming its present form. South America. Narsapur claystone (Pliocene) is a monotonous claystone section with a minor amount of intervening sand and silt. Aus- . Toward the south and east. Vadaparru shale (Miocene-Late Eocene) is a thick marine clay section deposited under outer shelf conditions. Geologic map of Krishna Godavari Basin. The depositional environment was outer neretic to bathyal. Sedimentation occurred in middle shelf conditions. Bhimanapalli limestone. Ravva Formation (Miocene) consists of thick and coarse clastics deposited south of the Miocene growth fault in an inner-to-middle shelf environment. The traps at times develop fractures. The depositional environment is outer neretic to bathyal. the depocenter is farther south of the Pliocene growth fault where thick coarser clastics. a major NE-SW Jurassic rift basin was created which accommodated thick Late Jurassic sediments. The Bhimadolu. The Figure 7. The Pranhita Godavari graben on the east coast of India belongs to such rifted troughs with possible rift continuity to eastern Antarctia. A series of concentric and parallel to subparallel weak planes also emerged. the uplifted mass of Triassic sediments over the emerging east coast of India were subjected to deep erosion in Gondwana graben. Conceptual model of Cretaceous deposition during Early Drift Stage I. During the fragmentation of India. Jurassic Basin deposited thick fluvial and lacustrine sediments (Bapatla sandstone) during the synrift stage. The Jurassic Basin is represented by Krishna graben and Gudivada graben. Tertiary depositional model showing influence of growth tectonics over the sedimentation during Late Drift Stage IV.Figure 5. Generalized stratigraphy. The absence of Triassic sediment is probably related to the breaking up and fragmentation of Gondwanaland during the Jurassic when the Permian and the Triassic sediments were subjected to thermal upwelling. and the Indian subcontinent. and Kakinada grabens form part of Gondwana Basin. tralia. Mandapeta. Figure 6. Kommugudem Formation (Early Permian) and the Mandapeta sandstone (Late Permian) were deposited. The main source of sediment was from JULY 2006 THE LEADING EDGE 833 . The newly emerged Jurassic rift basin cuts across the Krishna Godavari Gondwana graben orthogonally and is named the Trans Godavari graben. As a consequence. Conceptual model showing breakup of Trans Godavari horst and Trans Godavari graben into smaller en-echelon horst and graben systems during Early Drift Stage II. Figure 8. The Upper Carboniferous-to-Jurassic sediments deposited selectively in linear troughs traversing the unified continents. During this period. the Kanukollu sandstone (Aptian/Albian) was deposited under 834 THE LEADING EDGE JULY 2006 Figure 10. Prospect map of Krishna Godavari Basin.Figure 9. This fault ultimately transformed into a basin margin fault for the Krishna Godavari Basin. At a later stage because of rising sea level. the eastern margin of Trans Godavari graben was subjected to reactivation of the faults and emergence of a long and linear horst. . Rift Stage II: Intense tectonic activity took place at the end of the Jurassic. Early Drift Stage I: India and Antarctica started moving apart during the Neocomian. Geographic distribution of petroleum systems in Krishna Godavari Basin. Simultaneously. During this period. the Trans Godavari graben acquired half-graben configuration as a result of considerable accentuation of the fault on the graben’s western margin. At this time. This megahorst was due to basement uplift and collapse of the flanks. the surrounding granitic country rock. Bantumilli graben also emerged as an associated low southeast of the Trans Godavari Horst. named the Trans Godavari Horst. The period witnessed the initial deposition of shale (Gajulapadu shale) in lacustrine environment in the southern part of the landlocked Trans Godavari graben (represented today by Krishna and Gudivada graben). creating the ocean floor for the emerging Bay of Bengal. The sediment supply was mostly from the newly emerged horst and the exposed areas north of the basin margin (Figure 6). the subduction Trans Godavari graben is represented at present by the of the Indian Plate below the Tibet Plate intensified. deposited marine shale (Nandigama Formation). reservoirs. This Bhimadolu. a strong southeasterly basinal tilt occurred with the basin margin fault Figure 12. As a conseFigure 13.Godavari rivers. acting as the hinge. Paleozoic trends oriented NW-SE. During the regional transgression. Now. Seismogeologic section of Gudivada Graben showing source. During the period. and structure. marginal marine environment. almost the entire area underwent deposition as a single basinal unit. sandstone) were deposited in the northern part of the basin. The continued tilting caused a fresh supJULY 2006 THE LEADING EDGE 835 . and traps in the Palakollu-Pasarlapudi system. The northeastern part of the Late Drift Stage II: During the Paleocene. Late Cretaceous marine sediments (Raghavapuram shale) were deposited over the Early Cretaceous sediment fill with a well marked regional unconformity (Raghavapuram regional unconformity). Five such cross trends are identified over the basin. coarser clastics (Tirupati and reservoirs. These triggered volcanic eruptions (Razole Formation) over most grabens were deposited as thick coarser clastics (Golapalli of Krishna Godavari Basin. the Trans Godavari graben filled up and achieved peniplaination. During the same period. the Bantumilli graben. nessed regression/emergence of the Krishna and the Sedimentation took place under a marginal marine environ. Subsequent to the sediment fill a critical tolerance level was exceeded (Early Eocene). for the first time. Late Drift Stage I: The top of the Early Cretaceous sediment was subjected to wide erosion and peneplanation when most horsts ceased to be a positive area. Geologic section depicting source. Mandapeta. The postvolcanic period witsandstone) due to its proximity to the basin margin.ment. although time equivalent (Aptian/Albian). and Kakinada grabens. reservoirs. All these lithounits. Seismogeologic section of Bhimadolu graben showing rotated fault blocks with source quence. During the period. exposed on the south to the open sea. and the stress was released through the breaking up of the Trans Godavari horst and graben at different places and then dislocating them in the direction of older Figure 11. This was followed by Cretaceous sea transgression. This geologic phenomenon therefore resulted in the formation of series of smaller en-echelon horst and graben systems from the single megahorst and graben (Figure 7). As a result. Early Drift Stage II: The Trans Godavari horst and graben system emerged transverse to the NW-SE Paleozoic Gondwana trends. The basinal tilt toward the southeast increased considerably during the Maastrichtian. the newly emerged megahorst and graben were under great stress. and flooding of the entire basinal areas. It is at this stage that the present form of Krishna Godavari Basin took shape. had different depositional settings. This success has continued.carbon accumulation. and unconformity-related trapping conperiod.important producer in Krishna Godavari Basin. accompanied by rapid loading. includes a large offshore area and a narrow coastal strip of Godavari graben.to medium-grained. 2000). and is called the Matsyapuri-Palakollu fault. and Mori and Gudivada graben. Mahadevapatnam. ditions are common. and started prograding basinward and built the Miocene delta. The importuated due to basin tilt. During the period. Seismogeologic section of Mandapeta graben depicting structural entrapment of gas. subangular-to-subrounded. In addition. The reservoir shows updip wedgings 836 THE LEADING EDGE JULY 2006 . The Miocene and Pliocene growth faults also marked the birth of Godavari graben. Endamuru. migration. Widespread Rapid loading of sediments resulted in a well developed Palakollu shales are the main source rock and the overlygrowth fault. period and deposition of sediments near the coastal areas. Ravva. G-1-12. Wedge-outs onshore. formed as The underlying Vadaparru shale was subjected to wide shale a result of bulging of the underlying shales. Bhimanapalli Matsyapuri-Palakollu fault. The sustained exploration effort in Krishna sandstone reservoir. Vadaparru acted as the main source rock. GS-23. the youngest Tertiary petroleum system in Krishna Godavari Basin. and Pasarlapudi Formation were deposited during this geomorphic highs. large anticlinal structures and for the hydrocarbons. The sands are fine. sequently discovered oil and gas fields are (onshore) The Gajulapadu-Kanukollu system is restricted to Mandapeta. are the best traps tectonism. numerous fault closures formed. Tirupati sandstone commercial discovery was made in 1980 by offshore prospect reservoirs are capped by the overlying Razole Formation. many small gas fields were discovered Traps are mainly over the flanks of the horst. the Pliocene over Gudivada graben and Bantumilli graben confirmed oil. thrust. and Dhirubhai Gajulapadu shale is the source for the overlying Kanukollu (Figure 9). poorly Godavari Basin has generated a rich knowledge base with fissile. The sands within the oil in the offshore Ravva Field and Eocene gas onshore in mounded geobodies are also favorable locales for hydroPasarlapudi Field. The (offshore) GS-29. the numerous channel and Late Drift Stage III: Sea level lowered during the Oligocene fan geobodies generated stratigraphic or stratistructural traps. which formed caused large anticlinal structures by triggering shale tectonthe depocenter for Tertiary sediments. The Raghavapuram shale is the main source rock. Rangapuram. and Dhirubhai are structural and stratistructural traps of Pliocene clastic reservoirs. Exploratory drilling Jurassic basin margin fault. limit is marked by the pronounced Pliocene/Pleistocene toe gas. The presence of hydrocarbons in reservoir. and entrap. Bantumilli. At times intervening shales under the growth fault regime and were influenced by shale also act as local seals for the reservoirs. Alternating sand and silt within Raghavapuram shale forms the Petroleum systems. These faults provide an excellent updip clastic input triggered formation of the Pliocene growth fault. The Miocene reservoirs of Ravva Formation are fine. was minor. Miocene sediments were deposited effective regional cap (Figure 11). G-1. The Palakollu shale ics in the underlying Vadaparru shale. over the area caused a series of parallel-to-subparallel NELate Drift Stage IV: During the Pliocene. Lingala. It is interesting that all three Raghavapuram-Tirupati is the dominant system in the major growth faults described above are parallel to the Late west of the Krishna Godavari Basin.. The initial by overlying and underlying shales.are fine. For both Miocene and Pliocene reservoirs. In 1981–86. The Formation of Late Paleocene-to-Early Eocene age. The sands within Raghavapuram shales are sealed Krishna Godavari Basin was established in 1979. Miocene and fault closures are also common. As a result. by the Bengal fan system (Figure 8). Figure 10 efficient cap to the underlying Kanukollu sandstone resershows their geographical distribution. G-4. the Godavari River tant finds are Pasarlapudi. more or less parallel to the ing Pasarlapudi sandstone forms the reservoir. The shales are moderately hard. Further basinward. and called the Miocene growth limestone overlying the Pasarlapudi reservoirs provides an fault. The consistently distributed Kanukollu respect to hydrocarbon generation.The Vadaparru-Ravva/Godavari clay system.to medium-grained and at times extensive ply of clastics. Gokarnapuram prospects.sandstone is dominantly sandstone with minor shales. voirs (Figure 12). and condensate from the Kaikalur. Tatipaka. G-4. and compact. complex. The subthrust and the area beyond it are dominated Nandigama. The Raghavapuram shale provides an in Krishna Godavari Basin (Gupta et al. Two major discoveries occurred in 1987. The anticlinal structures. mation established the presence of five petroleum systems and fairly sorted. Discovered pools are few and small. The shale tectonics tectonics. G1. A systematic study that integrated the available infor. Some sub. Sands ment. Ellamanchilli gas fields and Mori oil field. a most area of sediment source in the north was continuously accen.to medium-grained sands with interbedded clay. arcuate in shape. more or less parallel to the basin clay). The PlioPleistocene reservoirs were deposited under a deepwater channel and fan Figure 14. seal for the reservoirs. another spurt of SW arcuate faults. The regional cap to the Miocene reseruation of this process produced a major Eocene growth fault voirs is the widespread Pliocene clay sequence (Godavari which is arcuate in nature.and substantially thick. The contin. and the cap for the Pliocene reservoirs is the overlying margin. As a consequence. Palakollu-Pasarlapudi system includes the Pasarlapudi which were at places subjected to erosion. GS-23. GS-15. Kesanapalli west. Rotated fault blocks. and GS29 are Miocene clastic reservoirs. This Pleistocene clay. GS-15. rifted graben and horst system was created during the Jurassic and named the Trans Godavari graben and Trans Godavari horst. widespread and thick. India. “Genesis of petroleum systems in Krishna Godavari Basin” by Gupta et al. (AAPG 2000 International Conference). The evolution of Krishna Godavari Basin began during the Permian when the linear-trending (NE-SW) Gondwana graben was formed. and Endamuru. Krishna Godavari Basin Stratigraphy. the limit of Tertiary deposition is marked by a PlioPleistocene toe thrust. The end of the Early Cretaceous was marked by dislocation of this horst and graben along five major cross trends. and Plio-Pleistocene. The Mandapeta sandstone is overlain by thick red claystone belonging to the lower part of the Golapalli sandstone. long and linear (NE-SW). Known hydrocarbon areas are classified into five petroleum systems. and Eocene. “Pre rift. Petroleum Geochemistry and Petroleum Geology by Robertson Research Group (ONGC report. Both structural and stratigraphic traps are common in these systems. Suggested reading. Cretaceous. The basement faults cut across the reservoir section to create fault closures. 1983). the entire basinal area was under deposition. The Raghavapuram shale overlying the Golapalli sandstone reservoir.against the rising flanks of the Kaza and Kaikalur horsts. The major source rocks are Early Permian. Corresponding author: drgupta333@yahoo. syn rift sedimentation and hydrocarbon potentials of Krishna Godavari Basin” by Gupta et al. provides a good cap to the reservoir (Figure 13). The thick and widespread Kommugudem coal/shale sequence is a proven source. ONGC. The Paleocene was charac- terized by subaquous lava flow.com JULY 2006 THE LEADING EDGE 837 . Conclusion. A major. and Pliocene regional growth faults were formed with a corresponding depocenter. TLE Acknowledgment: The author is thankful to Oil and Natural Gas Corporation. Kommugudem-Mandapeta/Golapalli is the oldest petroleum system of Krishna Godavari Basin. Eocene. A series of smaller en-echelon horst and graben systems were formed from the existing single megasystem. “Geology and hydrocarbon prospects of Krishna Godavari and Cauvery Basin” by Kumar (in Petroliferous Basins of India. Further basinward. The important gas fields are Mandapeta. Lithostratigraphy of Indian Petroleum Basin Document VIII. Miocene. Mandapeta West. Cretaceous. Krishna Godavari Basin (ONGC Publication. Paleocene. during this period. The postvolcanic period witnessed active Tertiary sedimentation and. creating a stratistructural trap. Entrapment is due to fault closures and anticlinal structures (Figure 14). 1987). Eocene. The sandstones are feldspathic and micaceous with thin intercalations of shale and claystone. 1993). for the first time. Miocene. The overlying Golapalli and Mandapeta sandstones are the main reservoir sequences. Favorably placed clastic reservoirs are from Late Permian. (AAPG 1997 International Conference). The Late Cretaceous witnessed widespread marine transgression when.
Report "Basin Architecture and Petroleum System of Krishna Godavari Basin, East Coast of India"