In this paper, a general, hierarchical, structured and flexible drilling operation risk assessment system (DORA) is presented. The model, which is presented in this paper, is generated form the operator's point of view and it is applicable for different wells in a range form wild cat to re-entry types. In order to completely define the risk assessment system, its operation model is developed, the tools and methods for each phase are specified and the inputs and outputs are determined. The developed model has four main phases of beginning, preliminary risk analysis, secondary risk analysis and support. The inter-related position of these phases and their sub-phases with respect to the drilling operation steps, are also specified.
Oil and gas companies, every year spend billions of dollars for drilling the wells. Not this entire amount is spent correctly, indeed a notable amount-15 percent-is wasted . This fact shows that drilling operation risks play a significant role in its success or fail and drilling comprises a major part of production and exploration plans. As a rough estimate, at least 60 percent of the cots of exploring big reservoirs are related to drilling .
In recent decades, numerous plans are defined in exploration and production sectors in order to maintain and promote the position of Iran in oil markets. Development in Iranian oil fields is managed through client and operator companies which are subsets of National Iranian Oil Company. Given these facts, developing a comprehensive risk management system in drilling operation of oil and gas fields-regarding the special characteristics of the operation in Iran its organizational situations-is of a great importance. Therefore, this system is designed in order to tackle some of these problems and fulfill the need of the Iranian companies to this system for planning oil and gas wells drilling operation risk evaluation system.
The presented model is designed from the operator's point of view and therefore, situations, decision making limits, interference in executive affairs, types and levels of the supervisions and the benefits and losses to the operator are all considered. Of course, the general model, which is presented, can be implemented in client systems with some modifications.
In brief, the goal of designing oil and gas Drilling Operation Risk Assessment system (DORA) in this study, was to provide the needed informational base to take decisions about controlling the existing risks and therefore to drastically decrease the wasted time and money and direct financial losses to the system.
In this research, the common qualitative methods for management studies are generally, implemented as well as main data gathering and analysis strategies which are also based on this basis. The data are gathered through literature review, historical data analysis, questionnaire and observation. These data are summarized and analyzed in a comparative-inductive study , , , .
Assumptions and limitations play a significant role in any system determining the functional frameworks and outputs of the study and their field and method of application . Here some of the most important assumptions of the system are listed.
In this research, the real risks are studies; the risk which exit in the trilateral transaction of machine, human and earth. According to the guide of "Project Management Body of Knowledge", technical risks are studied from the subset of internal risks , , .
In each assessing team, the top range managers who are related to the operation under study are also included to have a better operational guaranty for following up the results of the studies .