with t as (select 'A' well, date'2015-08-27' met_date, 100 amount from dual union  all
           select 'A' well, date'2015-08-28' met_date, 150 amount from dual union  all
           select 'A' well, date'2015-08-30' met_date, 200 amount from dual union  all
           select 'B' well, date'2015-08-27' met_date, 50 amount from dual union  all
           select 'B' well, date'2015-08-28' met_date, 80 amount from dual),
    d as (select date'2015-08-27'+level-1 dt
          from dual
          connect by level<=3
          )
select t.well
     , d.dt
     , t.amount
     , nvl(t.amount, lag(amount) over (partition by t.well
                                        order by d.dt)) amount
from d
left join t partition by (t.well)
on t.met_date = d.dt
order by 1, 2;