Well Testing If the results are clear it may only be necessary to obtain a fluid sample by lowering a sampling device into the hole on wire line and recovering a fluid sample and bringing it to surface. These tools are variously known as RFT's, MDT's etc. If oil or gas is recovered by these samples this is very encouraging and may lead directly to production testing If the results of these wire line samples are ambiguous or if it is not considered appropriate to recover a fluid sample, a bigger and more definitive test may be made by lowering the drill pipe back into the hole and allowing any fluid to flow to surface. This test is known as a drill stem test (DST) and can give very definitive results if no mechanical problems are encountered. However, DST's are generally short in duration because of their cost and for safety reasons so they may not give a definitive result on the size of the reserves. Even if this step is positive, it will still not necessarily be clear if there is enough oil and gas to justify further development. Back f results from well testing are positive, the well will be completed and put on production test. In the case of oil, this would involve producing the well into temporary production facilities and selling the resulting production. For a gas well it may mean flaring the well, or if it is close to flow line, producing it for sale. The reason for production testing is to confirm the size of the reserves before a decision is made to spend further money on development or to enter into long term sales contracts. The cost of producing oil could and often is far more costly than the initial drilling. Offshore such production cost could well be in the 100s of millions before a drop of oil reaches the refinery. Just because a good flow rate is obtained in a DST does not necessarily mean that there will be sufficient reserves, however, production testing will normally be definitive. Summery An oil well will normally only be drilled once in it life time. This is carried out by the rig (Contractors) and their crews. Once finished the well is handed over to production. (Operators) and the rig move off the location. The time taken to drill a well or hole can very dependent on depth or any problems encountered. However not two hole will be the same. Similar yes, but never the same. Problems encountered vary, some have a simple solution and are common. Such a problem would be a well kicking. "an un invited formation fluid invading the well bore" Other problems although common may not have a simple solution,. Such as pipe getting stuck. It can be freed or it could cost the hole.  The drilling industry is an open book. Much of the problem solving come from experience. Many of the predetermine calculation offer a guide line to work from but can-not be held as hard and fast rules. It is in it's self a way of life,