Nesting error in Excel macro - Changes to If

I'm currently trying to record a macro for my excel spreadsheet, but keep recieving the message "The specified formula cannot be entered because it uses more levels of nesting than are allowed in the current file format can anyone help me out in fixing the formula to make it smaller?

=IF(ISNUMBER(SEARCH("Conductor + Surface",B3)),"Conductor + Surface",IF(OR(ISNUMBER(SEARCH("17 
1/2",B3)),ISNUMBER(SEARCH("Drilling",B3)),ISNUMBER(SEARCH("12 1/4",B3)),ISNUMBER(SEARCH("8 
1/2",B3)),ISNUMBER(SEARCH("Run Screens",B3)),ISNUMBER(SEARCH("Temporay",B3)),ISNUMBER(SEARCH("BOP 
Hop",B3)),(ISNUMBER(SEARCH("Data Acquisition",B3)))),"Inter, Res, Lower Comp., & 
TP&A",IF(ISNUMBER(SEARCH("Maintenance",B3)),"BOP Maintenance",IF(OR(ISNUMBER(SEARCH("Re- 
entry",B3)),ISNUMBER(SEARCH("Wellbore Prep",B3)),ISNUMBER(SEARCH("Run 
Completion",B3)),ISNUMBER(SEARCH("Install TH",B3)),ISNUMBER(SEARCH("BOP 
Pull",B3)),ISNUMBER(SEARCH("Subsea Move Off",B3)),ISNUMBER(SEARCH("BOP Run - 
Completion",B3))),"Upper Comp & TH",IF(ISNUMBER(SEARCH("Rig Move - N and C",B3)),"Rig Move - N and 
C",IF(ISNUMBER(SEARCH("Install XMT",B3)),"Install XMT w/ Rig",IF(ISNUMBER(SEARCH("Open 
Plugs",B3)),"Open Plugs",IF(ISNUMBER(SEARCH("Rig Move - S and B",B3)),"Rig Move - S and 
B",IF(ISNUMBER(SEARCH("Install VXT",B3)),"Install VXT","ERROR IN EXCEL FORMULA")))))))))