Não!!.. São duas línguas diferentes!!.. muito parecidas mas não são compreensível entre elas... Uma pessoa que fala espanhol, sem estudar português, acho que pode entender so um 40% corretamente.! Porque tem muitos "Falsos Cognatos" (em português), e "Falsos Amigos" em espanhol, São palavras que podem ser iguais, mas tem significados totalmente diferentes! Esso acontece é porque são línguas que tem o mesmo origen, linguas "Ibero Romances" como Espanhol, português, que são originada do latim, como muitas mais.. ;)

I think that both languages are quite similar (unless more than spinach - English or Spanish - French). I have never studied Portuguese and when I have found some Portuguese people or there are some speech in Portuguese at TV I am able to understand the general context (maybe not all the word). Depending of the topic in can be easier or hardier to understand and require more willing by both sides but I think that it is one of the languages more similar to Spanish.

Spanish and Portuguese are very very similar languages, normally a spanish speaker that doesn't study portuguese, can understand the context, if the portuguese speaker speaks slowly.. probably a 50 or 60%.. In reading probably you can understand a 80% of the text. If you study portuguese after you have learnt spanish, it would be very easy for you, because most of the grammar is the same and words as well, maybe at the beginning you will have some troubles because the similarities, it would be easy to confuse spanish and portuguese. IF you want an Idea about similarities, here is an example: portuguese: eu vou comprar roupa muito bonita para a minha namorada, español: yo voy a comprar ropa muy bonita para mi enamorada.