"sir, i just completed my I.sc and wants to apply for geology(hones). But my father wants me to opt for B.TECH but i am totally not interested in it.He is going with my opinion but one question is troubling him whether in the future there would be good job opportunities in geology.So suggest me a branch under geology which can help me in searching for good career.Branch whose demand would be there after 3 years sustainably.."
You are using a few terms I do not understand.
Waht is I.sc. and B.Tech.
With regard to geology career paths.
First, in most instances, you need a masters degree to get a "professional" position, rather than a technical or geotechnical position. A geotechnical position is one where you do field sampling, data collection, labratory processing, run labratory tests, and do data entry. You will not be doing much in the way of applying problem solving or interpretation of geological data. You will be a technician.
Now, most oil company jobs and environmetnal geologist jobs require a masters degree. You can be a geotech with a BS in geology.
I am not sure of the state of environmental consulting in India, I do know that there are a lot of problem areas, but I do not know how strict your environmetnal laws are requiring that cleanups or assessments be made to mitigate environmental problems.
I am sure that there will always be a demand for water, and you could always find a job on a water well drilling crew installing water wells or working for a small geological consulting firm doing geotechnical testing (soil and clay analysis for construction companies). A lot of these firms are called geotechnical engineering firms.
Anyway, it is probably up to you to do a little homework. Run a few searchs on line to determine what kind of open positions exist in your area of India for geologists. Look for BS geologist or geotechnician, or entry level geologist, mud logger, field sample collection, borehole logging, water well installation, waterwell drilling, water well installation...etc.
This might give you an idea of the kinds of jobs available. I am sure they will still be some available in 3 years. If you set your sights higher, there might be even more oil field exploration jobs open in 5 years if you work on your masters.