It is an acceptable Chinese name. As you can see from the examples below there are people in China who carry such name. Go by​ this name =) Zhai Xiaochuan (Chinese: 翟晓川); born March 24, 1993) is a Chinese professional basketball player. He currently plays for the Beijing Ducks of the Chinese Zhou Xiaochuan (Chinese: 周小川; pinyin: Zhōu Xiǎochuān) (born January 29, 1948) is a Chinese economist, banker, reformist and bureaucrat. Wang Xiaochuan (Chinese: 王小川; pinyin: Wáng Xiǎochuān; born October 3, 1978) is a Chinese computer programmer and Internet entrepreneur. He is the founder...

I t is a decent last name, but I recommend you think up your first name too.

you don't have to 'make up' a family name unless you have just choose what you like. it only matters if the name has weird meaning in it. but yours has not.

小川 does not sound like a Chinese surname. If you want one with the similar meaning to the Portuguese, maybe 江 is pretty fine. Otherwise, you can choose one that has the similar sound to Ri(beiro), let's say, 李 or 雷 may be good choices. So you'll be called 江/雷/李 迪亚/迪奥..... :)