This verse does not say,
The Lord went his way when Abraham had finished speaking to Him. It says,
When He had finished speaking to Abraham. In other words, Abraham did not quit here, God did. The verse suggests that God initiated this whole conversation with Abraham and led him along all through it, and when he had responded in fullness as God desired, God terminated the dialogue and went His way. So Abraham was not asking God to do something for him; it was God who prayed in Abraham and set the limits of the conversation.
This agrees fully with what we read in the New Testament about prayer. In Romans Paul says,
We do not know what we ought to pray for (Romans 8:26b). Do you know what to pray for about yourself or anyone else? No, you do not.
But, he says,
the Spirit himself intercedes for us with groans that words cannot express. And he who searches our hearts knows the mind of the Spirit (Romans 8:26c-27).