This article by Hal Croasmun of ScreenwritingU gives insight into how to create drama in a scene that is primarily or even entirely composed of dialogue:
I’d like to take a look at how a talking heads scene might work by creating deeper meaning in the dialogue.
I’ll give you the punchline in advance. The key to your success when writing a talking heads scene is to deliver meaning, emotion, and entertainment — not exposition.
Keep reminding yourself that every scene in a script MUST entertain the audience in some way. So, if 95% of the scene consists of dialogue, that dialogue has to be entertaining, emotional, and deliver some powerful meaning.
To illustrate this, I’d like to use the famous “You had me at hello” scene from the movie JERRY MAGUIRE. In it, you’ll see that many different skills have been used to turn a talking heads scene into a total tear jerker.
To set this scene up…
We’re at the very end of the movie. Jerry has achieved his external goal of having his only client succeed. But there is an internal question about whether he can love anyone or not.