What to do after completing my B.Tech in Petrochemical/petroleum engineering?

By going through the question what I feel is you should concentrate on your GATE score. GATE score is very important not only for a seat in M. Tech but also for a job in government organisation or institute. Your M.Tech may not help much for a job except for teaching job. As you are not interested in teaching concentrate on getting a good job. GAIL, HPCL,BPCL and other oil companies offer good posts. There are good chances for you in Gulf countries and other oil producing countries. So work hard for GATE score and once you have good score with you there are many chances to you to get a good job.

Based on the several queries which you have raised, this is what you can do:
1. Give GATE exam. GATE score is required for a good PSU job. Your degree is in a niche field, and there are a variety of job options here. GATE preparation is tedious and a serious concern. Prepare well for GATE but using standard GATE Exam book: GATE 2019 is already available in the market.
2. Give GATE or some colleges admit directly for MTech after their entrance exam and interview. You will be spending two years in MTech. also check the college since they arrange for Placements. MTech colleges in yuor stream will be few. MTech will lead to a job in the Petroleum sector and there is not need to take up any teaching position since it does not interest you . Study for GATE if you have a technical bent of mind.
3. In case you have an inclination for a managerial position, have administrative, managerial and leadership aptitude then you can opt for MBA. This requires GMAT or University wise an entrance exam followed by a 2 year curriculum.
Decide carefully, based on where you want to ten years from now.

The best alternative for you is to go abroad, and do a post graduate course in what is now called Renewable energy.

Please do note, with a huge amount of negative publicity, and the actual truth about pollution created by petroleum based products, the entire world is trying to switch to alternate fuels. Am told in the USA, the biggest change is happening in terms of electric cars.

We will soon have solar powered cars and this will simply mean that petroleum engineering will not be a favorite subject of study in the years to come.

However, wind energy, solar energy, and even bio gas energy will assume center stage in the years to come. There are a huge number of advanced courses and, in the USA and elsewhere, there is a multi-billion dollar industry, already engaged in doing cutting edge research, into alternate fuels, and alternate sources of energy. In India, the R&D investment is pathetic. Even if you try to make a mark, one hundred old guys will simply pull you down.

However, in the USA or elsewhere, once you do a good course, people will simply engage you in research. You will do well to do a good course abroad in the field of electric cars and also the alternate sources of energy. All private transportation, in the near future, will not be driven by petroleum products. The next ten years are going to be crucial.

Also, follow your M.Tech or MS with a good doctorate in the aforesaid areas. Am sure that will stand you in good stead.

After doing Petroleum engineering there are various options available for career. The most prominent is to apply for executive posts in oil and gas industry by applying against the advertisement released time to time by organisations like IOC, HPCL, ONGC, Oil India, GAIL, BPCL, GSPC etc. Some of these organisations are recently merged with each other and that aspect also to be considered while applying. These organisations conduct written exam and then call the meritorious candidates for interview. This is one of the good options for making a career in petroleum industry.

Apart from this there are options in teaching line like lecturership in engineering or science colleges for which you have to go for M Tech followed by the NET test which if you can qualify will enable you to apply for coveted posts of lecturer.

Another option is to go for exams for various Govt posts in administrative machinery. For this, one has to prepare for IAS or state level public service commission. There is a lot of rush and competition for these prestigious positions and one has to work hard and focus for it.

You can also try to get a job in private sector where opportunities exist in refineries, private oil and gas companies etc. If you get a job like that it makes sense to join it and then fulfil your academic goals through correspondence or evening classes. This I am insisting because the job condition in our country is deteriorating day by day and one has to readily accept a job if he is getting one today.

You can also register in sites and job portals like naukri.com and apply against the posts advertised in your core area.