Why IPv6 has been invented? do you see that IPv6 will replace IPv4 in near future?

IPv6 was invented because IPv4 is getting out of ip addresses . It's been introduced to replace IPv4.  yeah .. as the internet usage is increasing rapidly IPv4 will be replaced in future.

IPv6 is required because of the fast deplection of IPv4 addresses. IPv6 will enhance security of the TCP/IP stack, but most importantly increase the number of IP addresses availabe to use. This will essentially remove the need for NAT.