My base is several hundred blocks from original spawn and I have 2 sets of working portals but I wanted to link one to original spawn. So, I went back to original spawn and created a Nether portal but when the terrain loaded, I was stuck inside a solid wall of Nether rack. I was making the suffocating noise but my heart's were not going down at all. I broke a few blocks to free myself only to realize that I had no portal to return to the over world... I made sure to clear a large room to check for the portal but found nothing.