Remote Sensing and GIS Tool to Detect Hydrocarbon Prospect in Nagapattinam Sub Basin, India

The study area lies between North Latitudes 10°16′41″–10°59′14″ and East Longitudes 79°15′26″–79°51′56″ covering parts of Survey of India topo maps 58°N–5,6,7,9,10,11,13,14 and 15. Nagapattinam Sub-Basin covers Thiruvarur, Thanjavore, and Nagapattinam. The total study area occupies 5,249 sq km. The study area location map is shown in Fig. 1.

The rifting of Cauvery Basin was initiated during late Jurassic (Blanford 1865). The detailed tectonic map of the Cauvery basin is as shown in Fig. 2. However, the oldest sediments recorded in the subsurface by Oil and Natural Gas Corporation palynologists are Neocomian. The Neocomian sediments are devoid of microfauna and are dated with palynofossils. Therefore, it is evident that Cauvery Basin has not experienced marine transgression until Aptian. Granitic wash sediments derived from granitic provenance are rich in Biotite mica and Potash feldspar, and as a result, these sandstones with thin micaceous and carbonaceous shale intercalations exhibit a serrated high ‘γ’ in the ‘γ’ ray log. As these sands are tight, compacted, calcareous cemented with quartz overgrowth, chloritized mica occyping interstices form the Andimadam reservoirs that are of poor quality (Mani 1999).

The Cenomanian transgression has resulted in the deposition of finer clastics (Sathapadi Shale) followed by a fall in sea level producing in sandy sediments (Bhuvanagiri Formation) during Turonian, and the top of Turonian is an Unconformity.

Coniacian to Maastrichian is mostly finer clastics shaly with frequent input of sand (Nannilam reservoirs are sandwiched in shale. Again, the top of Maastritchian is an unconformity surface. Late Paleocene, Early Eocene period witnessed a major transgression in the Tri-junction area as witnessed by brown colored shales with abundant planktons such as globigerina and Orbulina (Rajagopalan 1965 Govindan and Chidambaram 2000. During Oligocene, shelf edge delta front sands were cyphoned into the slope, and ultimately, these high-density currents deposited their load and got frozen as sand pods one over the other at repeated intervals. Mio-Pliocene witnessed the development of the present delta with upland area occupied by laterite and lateritic soil. In the subsurface, Mio/Pliocene is dominated by deltaic sand, minor Kaolinitic clay, and lignite belt from Neyveli–Jayankondam–Mayavaram and end up at Mannargudi which is covered up by the Holocene Delta.

The lateritic uplands occur along the western margin of the basin and form the regional erosional plains. The Cauvery River, flowing through the uplands, has migrated anticlockwise from a pivotal point within the uplands, before occupying its present position, as evident from the positions of various paleochannels. The Cauvery delta lacks the protuberance which is regarded as one of the most essential elements of a delta. The recent long shore wave action has made a smooth and straight coastline fringed by beach ridges and swales. A few estuaries and lagoons have developed along the coast indicating submergence. (Mitra and Agarwal 1991) The detailed geomorphic map is shown in Fig. 3.

The surface lineaments are interpreted using the raw and digitally processed IRS LISS III and Landsat satellite data on 1:50,000 scale. These lineaments/faults are interpreted on the basis of tonal linearities, straightness of river course, soil tonal lineaments, vegetation alignment, etc. The flow chart methodology is shown in Fig. 4.

Lineament feature orientation is considered as one of the most important characteristics as far as petroliferous locales are concerned. In the present study, the lineaments, fractures, and their traces seen on the surface lineaments, gravity, magnetic linearities, and basement faults are analyzed for their orientations. Rose diagrams are one form of the most informative ways of representing orientation data. Rose diagrams for all the linear features acquired in the study area are shown in Fig. 6. They are generated based on their trends and frequency. However, one can see from these rose diagrams that the surface linear features in the study area have four preferred orientations: Northwest–Southeast, Northeast–Southwest, North–South, and East–West. Majority of the surface linear features in the area are oriented in two directions, i.e., one along Northwest–Southeast and the other along Northeast–Southwest. However, those surface linear features oriented in the North–South and/or East–West are less prevalent.

The rose diagram of the basement fault system in the area shows that they are preferably oriented in Northwest–Southeast direction. The gravity lineaments appear primarily in four sets: two major sets are oriented in Northeast–Southwest and East–West; and the other two minor sets are oriented in Northwest–Southeast and North–South. Fig. 7. Magnetic lineaments appear primarily in three sets: one major set oriented Northeast–Southwest, and two minor sets oriented in Northwest–Southeast and East–West, Fig. 8. A comparison of the surface and subsurface linear features indicates that the basement faults are very much congruent in orientation with the gravity, magnetic and surface lineaments in the region of study. The Precambrian basement fault system consists of a major set trending in the Northeast–Southwest direction, Fig. 9. These faults later were reactivated, and thus they acted as conduits for the upward propagation of hydrocarbon and were entrapped in the shallower/younger rocks, as reflected by the geophysical anomalies and the surface lineaments. During the process of reactivation and propagation, additional sets of faults and fractures were developed because of local structural and tectonic disturbances and their complications. The connectivity from the basement fault systems upward till the surface provides a mechanism for hydrocarbon migration and entrapment.

In GIS overlay analysis, satellite lineaments have been parallelism with subsurface magnetic linearities, gravity breaks, coincided with existing oil/gas fields. Based on the analysis, new prospective zones were identified and marked Fig. 10. Some of the locations of the oil fields are bounded by major surface linear features from both sides shaping the boundary of sub graben and sub basins in the area. Thus, the surface lineaments can be used as a guide to structural contouring, facies mapping, and delineation of areas of fracture-enhanced permeability. Also, their trends were used directly to conduct seismic programs and to select deeper exploration candidates in the area. Remote sensing and GIS can reduce the conventional method, be cost effective, and narrow down the study area while comparing with the geophysical method.