"Abstract: The seismic interpretation is an art of assuming the real geology at particular depth from theprocessed seismic record. Nowadays, the modern multichannel data have increased both the quantityand quality of interpretable data by experts for best possible and correlated interpretation. But still itrequires the interpreter’s geological understanding to select the best possible interpretation from themany possible interpretations for the given data. The seismic signal contains two fundamental elements which helps the interpreter to study thesection. First, the time of arrival of any reflection from a geological surface as the actual depth from anyinterface is a function of the thickness and velocity of overlying rock layers. Second is the shape of thereflection that includes the signal with its intrinsic frequencies and the behaviour of frequenciesdistribution with each impulse. The interpretation process can be classified into three interrelated categories: 1. Structural, 2. Stratigraphic, and 3. Lithological.Structural seismic interpretation is directed toward the creation of structural maps of the subsurfacefrom the observed three-dimensional configuration of arrival times. Seismic sequence stratigraphicinterpretation relates the pattern of reflections observed to a model of cyclic episodes of deposition. Theaim is to develop a chronostratigraphic framework of cyclic, genetically related strata. Lithologicinterpretation is aimed at determining changes in pore fluid, porosity, fracture intensity, lithology, and soon from seismic data. Direct hydrocarbon indicators (DHI, HCIs, bright spots, or dim-outs) are elementsemployed in this lithologic interpretation process.Seismic Interpretation After processing of seismic reflection data with computers it passes through another phase of seismicprospecting which is called as Interpretation. It is also known as a relationship between reflectinginterface and the record surface. The primary objective of interpretation is to map the geologic horizonsthus the geologic structure. There are four main stages of interpretation:• Structural interpretation• Stratigraphical interpretation• Lithological prediction• Fluid detection or Rock PhysicsStructural analysis involves study of reflector geometry on the basis of reflection events. Stratigraphicanalysis involves the analysis of reflection sequences as the seismic expression of lithologically distinctdepositional sequences. In lithological interpretation we use a model to interpret data. Both structural and stratigraphic analysis are assisted by seismic modelling, in which syntheticseismograms are constructed for layered models to derive the physical significance of reflection eventscontained in the seismic sections. Reflection signatures with terminations:1. Lapout: lateral termination of a reflector at its depositional limit.2. Truncation: reflector cut by any geological feature.3. Baselap: lapout of reflections against any underlying seismic surface.4. Downlap: when underlying surface dip is less than overlying strata.5. Onlap: when underlying surface dip is greater than overlying strata.6. Toplap: termination of inclined reflectors against an overlying lower angle surface.Figure 1: A typical cartoon is shows different Stratigraphical depositionpatterns. Erosional truncationTermination of strata against an overlying erosional surface suddenly than toplap implies thedevelopment of erosional relief or an angular unconformity. Exploration geophysics is involves, finding a number of parameters that describe the types andstates of rocks in a particular region. Many tools and techniques are generally used in this search, amongthose being the sonic log and vertical seismic profile (VSP). One of the chief purposes of these in-situsurveys is to find a rock velocity or travel time as a function of depth; this velocity is then used in thelithological demarcation and mapping process. The surveys can also help in understanding wavepropagation in an complex medium. Usually, the travel time outcomes of the two surveys show some discord. Because, for example,as the VSP or a check-shot survey is normally used to calibrate the sonic log that is used to generatereflection synthetic seismograms.Stratigraphical InterpretationSeismic stratigraphy is a method for interpreting stratigraphic features from seismic data. In thestratigraphic interpretation is to estimate the vertical and horizontal scale of the section. It is a geologicapproach to the stratigraphic interpretation of seismic data. Hence, Seismic reflections allow the directapplication of geologic concepts based on physical stratigraphy. Primary seismic reflections are generatedby physical surface consisting mainly of strata and unconformities with acoustic impedance contrastcontrasts. A seismic section is a record of chronostratigraphic (time-stratigraphic) depositional andstructural patterns and not a record of the time-transgressive lithostratigraphy . Its objective is to define the inherited reflection events by the surfaces that enclosed with seismicsequences and systems tracts. These discontinuities are recognized on the basis of reflection signatures.Boundaries are demarcated on a seismic line by identifying the closure of seismic reflectors at thediscontinuity interfaces.Generally, below a discontinuity and the delineation of the upper sequence boundary. For example,Toplap (i.e. termination of strata against an overlying surface of non-deposition) and Onlap (i.e. base inwhich initially horizontal strata progressively terminate against an initially inclined surface. Practical work:The utmost and very initial work is to pick the water bottom horizon since it gives a very clear and brightreflectivity in seismic section. After picking the WB horizon one must move to another 2D line and so on.After cross checking of the mis-tie in horizon picking, a grid map is generated in TWT. As velocity of watercolumn is always 1500m/s thus, this map can convert in depth. Ultimately, the map gives informationabout the depth of the sea bed along with the shelf edge.Secondly, it is recommended that one should pick basement horizon because below basementseismic gives chaotic characteristics and the interface/boundary of basement again gives bright amplitudein seismic reflectivity. But due to rifting processes, basement generally has a lot of fractures and faults. Ifany well information is available within a zone then one can have more control on picking a right horizon.Results and conclusions:The seismic line OS90A-05 is located in Otway basin with an orientation of NNW- SSE. As the Otway basinalso has an orientation in NW-SE striking with divergent (Passive margin) margin. It is well known basinhaving formations of Late Jurassic to Cenozoic period. Seismic reflections from a high impedance contrast interface can be easily identified in seismic section ofthe line. It firmly depicts that these are major stratigraphical boundaries with possible unconformities orlithological variation within the formations.Starting from the identification of interface of basement rock (which is always assumed as predepositional stratigraphical environment) and overlained sedimentary strata, it has been identified thatthe seismic section is more chaotic and structure less.(As shown in below figure)Basement is consisted of numerous complex faults with lows and highs. Syn-rift with downlapstratigraphical feature has been observed with the alternative lows. Also, the highs have been consideredwith consecutive normal faults. The thickest formation has been interpreted as Top Otway group which is underlained by thebasement boundary. A hydrocarbon play can be found along the flanks of highs. Structurally, any closureof shale or any impermeable strata truncated with faults can help in increasing hydrocarbonprospectively. The thinnest formation of the seismic section is found to be Top EV formation overlained by TopBoonah formation. Information from the well log data of Wild Dog 1 has already confirmed about a very less prospectivelyof HC upto 1200m of depth. "