OCIEnvCreate failed to create environment handle after installing oracle_fdw
You have to set the environment variables LD_LIBRARY_PATH and ORACLE_HOME for the user postgresql. Then you have to set the service to conncet in the file tnsname.ora, the you have to create a foreign server with dbserver=Service (you should have defined the Service in the file `tnsname.ora

I send you my files configurations in Debian:

I added to /etc/profile (apply for all system user) but you can use .bashrc or another for only one user.

Oracle

ORACLE_HOME=/usr/lib/oracle/xe/app/oracle/product/10.2.0/client
export ORACLE_HOME
LD_LIBRARY_PATH=$ORACLE_HOME/lib:$ORACLE_HOME:$LD_LIBRARY_PATH
export LD_LIBRARY_PATH
PATH=$PATH:$ORACLE_HOME/bin
export TNS_ADMIN=$ORACLE_HOME/network/admin


Postgresql Path

PATH=$PATH:/usr/local/pgsql/bin
export PATH
MANPATH=$MANPATH:/usr/local/pgsql/man
export MANPATH


The variable TNS_ADMIN will be a directory where you install a tnsnames.ora

tnsnames.ora:

ORA11 =
 (DESCRIPTION = 
   (ADDRESS_LIST =
     (ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))
   )
 (CONNECT_DATA =
   (SERVICE_NAME = ORA11)
 )
)


Then create a foreign server for oracle_fdw with option dbserver=ORA11