Optimization of drilling acceptance criteria

The question “is a newly-drilled well good enough?” is addressed by considering the range of probable well results, the possible alternatives available, and their cost. Conceivable actions are to accept a well, to sidetrack it, or to dismiss the drilling rig and undertake a full well test. The distribution of productivity or injectivity within geothermal fields is generally lognormal. Given the distribution of productivity from field data, it is possible to determine expected results of drilling, and of well performance. Using a decision tree of possible actions (test/accept/sidetrack), drilling costs, and measurements of well injectivity, decision criteria to accept or redrill a well based on its predicted injectivity or productivity, are defined. Criteria are established for a decision immediately after well completion, or after a trial discharge (for a production well) or a period of stimulation (for an injection well).1,2