Need help in digging a borewell in an existing well

Hello,

We have a well of 20 feet depth and 2ft 9inches dia in the north east point of our plot. During summer there is no water in the well. We wish to drill a borewell with the help of small bore drillers for a depth of 100-150 feet.

Please suggest appropriate method of drilling in a narrow well like this which is surrounded by three walls. 

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