ON DATA:
For DESIGN of facilities one needs STREAMDAY CAPACITIES and for ECONOMICS one needs YEARLY AVERAGES over the life of the project. The differences are caused by the client (load factor) or by the producer (varying production, decreasing production in time and/or plant shut downs).
ON ACCURACY:
Always be aware of the accuracy of your cost- and production estimates.
A "back of the envelope" cost estimate provided within a day can have an accuracy of minus 50% / plus 100% even for an experienced engineer. A two month "scouting study" may improve this to - 40% / + 40%, but getting a higher accuracy takes man-months of effort and needs the input from cost experts!! Tell the economist what you think the accuracy is. He then will be able to do the proper sensitivity runs and know that the earning power he calculated is not 18.3% but is between 16 and 20%.
In a later stage of a project when one compares costs of two or more similar schemes (thus making the same errors in the total cost estimate but achieving a better feel for the difference) the accuracy of the difference will be better, but still one should not give figures with more than two significant numbers (see also the wisecrack on numbers). The same is true for the liquid or gas production numbers you give the economist. There are many reasons why in the end the actual will be more than 10% different from the calculated numbers. An estimated production of 8345 m3 per day is a ridiculous number; say 8300 or better 8000. By the time the detailed design is done we will know whether the number is closer to 7000 , 8000 or 9000 m3.
ON CHANGING NUMBERS:
For the reasons mentioned above, do not make the economist mad by supplying often new numbers which are slightly different every time. Only significant changes count. "Significant" varies by project but is certainly more than 10%. The same of course is true for the petroleum engineer supplying the engineer with basic data.
ON SCOPE OF WORK:
WE OFTEN THINK THAT WE HAVE TO- OR ARE BEING ASKED TO GIVE FAR MORE DETAIL THAN REQUIRED TO DO SCREENING ECONOMICS.
In 9 out of 10 cases it can be said instantly that a project is FEASIBLE or not.
The only important matter left then is to estimate the production quantities and the cost.
The exact process required is of later concern!!
In 9 out of 10 cases the PRODUCTION VOLUMES can be determined within a + or - 20% accuracy in a very short time.
In 9 out of 10 cases the COST ESTIMATE can be given with sufficient accuracy to do screening economics, in a short time.
It is the unnecessary detail, the additional case dreamt up by the non-engineer, the red
herring brought up by a government or other partner that causes scouting studies to go
out of hand in time and money.
DO NOT WASTE TIME BY GOING INTO TOO MUCH DETAIL