Designing a new well always brings the need to estimate how long drilling and completion will last in order to evaluate expensive costs like offshore rig rental. A new software, named E&P-Risk, based upon the Monte-Carlo statistical method, has been developed for helping the well designer estimating drilling and completion duration as well as rig rental costs. Up to 200 operations can be added, each of them with its typical fitting function, which can be chosen from the program default or specified by the user, based upon previous field data. The number of replications for combining each operation in the Monte Carlo simulation can be set to more than 2000, aiming at higher accuracy or smaller numbers for faster computation of the total time. The software can easily recalculate the total duration, for last minute project changes, by simply combining the fitting functions of the new operations and the remaining ones, through the editing capabilities. The program output presents a time histogram and a final report with the average expected time and cost, associated to the event probability (P10, P50, P90.). The minimum, average and maximum duration assumed for each operation, as well as the percentage in which they affected the total duration is also available in the final report. One application for a Brazilian offshore well is shown as an example of the method utility.
Estimating how long will take and how much will cost for drilling and completing a well includes several uncertainties, which can only be analyzed by considering the field history and a risk analysis methodology.
While the probability theory is frequently associated with geological and reservoir estimations, the same cannot be said regarding well constructions, even though the process can represent up to 50% of the total field development cost.
For many years Petrobras as well as other companies have based their technical-economical feasibility studies upon deterministic values only, not considering the risk associated with the decision-making process (1,2,3). It is now a question of instead telling the manager how long one expects to drill and complete a well, but what are the calculated probabilities for each duration or cost estimative.
There are several commercial statistical tools available in the market, but very few are ready-to-use in the drilling/completion area for the petroleum industry.
A new software for analyzing well drilling and completion performance based upon the Monte Carlo method and a reliable database is presented in this paper. The final goal is to define a range with the probability of success associated to time and cost predictions, for managerial decision. An initial application of the Monte Carlo method is shown for a case study from Petrobras (offshore Brazil), where the duration of the drilling operations was evaluated by statistically analyzing the company database. The maximum, minimum and most likely duration of each operation, as well as the best fitting function, were calculated allowing the duration of the whole drilling project to be estimated for economical evaluation purposes.
