NOISE REMOVAL

Desired seismic signals from the reservoir interfaces or interfaces of our interest cannot be recorded without noise. So, understanding of noise generators as well as characteristics of receivers are vital for effective removal of the noise, both in land and marine surveys.

Common noise issues can be categorized as Coherent and Random. The Coherent noise category (Other than Multiples) includes :
Onland: Noise due to Road movement, electric signal noise, ground roll, air blast, guided waves
Marine: Noise generated by nearby vessels, vessel itself, side scatters

Random noise category includes :
Onland: Wind noise, Culture noise
Marine: tides, swells, tow noise Our tools to attenuate above noises include

• F-X Deconvolution
• Tau-p Deconvolution
• F-K filter
• Radon filter
• Despike
• Surface wave Noise Attenuation (SWNA)based on low frequency array formation

MULTIPLE REMOVAL

Addressing the issue of multiples (Free surface, Peg-leg, Interbed etc) through proper attenuation approach is key to retain only signal in the final processed seismic data.

For this purpose, our approach include techniques based on – Deconvolution, Velocity analysis and Modelling Whereas, the key in Deconvolution based technique is selection of appropriate operator that corresponds to the two way travel time of the multiple, Velocity driven approaches depend upon the ability to differentiate the multiple from the primary, based on differences in their move out velocities.

At times, these two approaches work well, yet success of these being largely data dependent, requires processors to look for model based multiple removal techniques.

At Samit, we combine these approaches judiciously with an objective to get a multiple free processed output.

STATIC CORRECTIONS

Time shifts caused by undulating topography and near-surface velocity anomalies can distort the geometry of reflecting horizons, reducing the signal to noise and making interpretation difficult.

SAMIT provides statics solutions for all relevant types of static shifts, including a bulk shift for datum corrections to bring source and receiver to a common datum and solutions for source/receiver refraction statics, which are necessary in data processing. 3D viewing facility of source and receiver elevations ensures to take care of even astray points of elevation variation.

Elevation Statics: Elevation statics involve the computation and removal of the effect of different source and receiver elevations. This involves bringing the source and receiver to common datum, usually below the elevation of the lowest source or receiver. For this we need replace a replacement velocity for the material between the datum and the source or receiver. The replacement velocity is either assumed from prior knowledge of the area or can be estimated from up hole times or direct arrivals.

Refraction Statics: Refraction statics provides for first break pick editing on linearly moved out shot records, layer selection and editing, refractors velocity analysis and editing, refractor delay time computation and editing, quality control displays of various solutions, depth model display and editing, shot and receiver static display, and database output. Static solution methods for Refraction statics include-

Diminishing residual matrices (DRM)

Generalized reciprocal method (GRM)

RESIDUAL STATICS

Traces in a CMP gather are cross correlated with pilot trace to compute residual static shifts. This is effective in data of poor signal to noise ratio.