--> Test Data: @table1
declare @table1 table ([well_id] bigint)
insert into @table1
select 677 union all
select 23434 union all
select 12 union all
select 1234577 union all
select 12345 union all
select 1234521 union all
select 456
--> Test Data: @table
declare @table table ([a] varchar(100))
insert into @table
select 'policy_id=(×××××)+project_id=(×××××)+site_id=(×××××)+well_id=(12345)'

--Code
--select * from @table1
--select * from @table

declare @id varchar(100)
select @id=substring(a,charindex('well_id=(',a)+9,5) from @table
print 'well_id='+@id
select * from @table1 where [well_id] like '%'+@id+'%'
--Drop

--Result
/*
well_id=12345
well_id
--------------------
1234577
12345
1234521
*/