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Can someone tell me what Shale Gas is ? Does it a gas trapped in Shale ? How Neutron, density and sonic, resistivity logs behave in shale gas zone. ??

High GR, should be above 100 API (400-5000)
Density: Low (< 2.58)
Neutron: High
Sonic: High transit time
Resistivity: Higher than in normal shales

to the first part of your question:
Shale gas is gas that has been generated in organic rich shales due to burial (high temperatures and pressures), and has not all been expelled out of the shale into more permeable rocks, such as reservoir sandstones or limestones. Such shales often give good gas shows on mud logs while drilling through them. In the past, when tested, they would give a short blow of gas because their permeability is very very low.
To be able to produce at economic rates, they need to be extensively fractured by high pressure fracking methods. However, once the gas in the artificial fractures has been depleted, the initial production declines rapidly, due to lack of permeability in the matrix.
There is an ongoing debate among geologists about whether the full life-cycle economics are profitable. Government regulators (e.g. SEC) are reviewing gas shale projects to find out if investors are being misled or not.
There´s a lot been written about gas shales. Let me know if you would like me to send you some references.

Shale gas refers to in situ hydrocarbon gas present in organic rich, fine grained, sedimentary rocks (shale and associated lithofacies) . Gas is generated and stored in situ in gas shales as both sorbed gas (on organic matter) and free gas (in fractures or pores). As
such, gas shales are self-sourced reservoirs. This is a class of continuous petroleum system in which shale that generated the gas also functions as low matrix permeability and low porosity reservoir rock. In terms of its chemical composition, shale gas is
typically a dry gas composed primarily of methane (at least 90 percent methane), but some formations do produce wet gas.