Thesis (M.Eng.)--Chulalongkorn University, 2013

Onshore petroleum reserves in Thailand have been developing since last three decades. Some production wells have been declined. Workover is part of well interventions, which are necessary to maintain production. However, the risk and uncertainty of the retrieving existing completion procedure, recovering technology and fishing planning create the complication of well workover operation, which directly affected its cost. To make the systematic decision concerning the uncertainty of the well workover cost evaluation, this study aims to present a decision model under risk using the probability approach from the operational historical data. In order to construct decision tree models using the spreadsheet from the case studies for onshore well workover operations, in Thailand. In addition, the outcomes of each decision alternatives and their probability assessments are also provided to evaluate the expected cost of the choices. The findings of the studies are provided the systematic decision approached from the lowest expected cost of workover.