Risk Planning and Mitigation in Oil Well Fields: Preventing Disasters

Introduction

Drilling of oil, gas or geothermal well is technically demanding process that often accompanied by a variety of unexpected problems which result in additional cost and time. One of them is certainly lost circulation. Lost circulation or lost returns can be simple defined as the uncontrolled flow of mud into a thief zone. Although this problem as well as his cause is well known for many years, there isn´t unique technical solution. Based on recent data the petroleum industry spends millions of dollars a year (e.g. expenses associated with rig, drilling fluid costs and equipment delays) to prevent and cure lost circulation problems. The new challenges in drilling such as drilling high temperature and high pressure well, drilling through complex lithology, drilling through unconventional shale, and drilling extended rich drilling wells (ERD) require finding the new solutions for already known problems.

There are several potential problems associated with lost circulation during drilling. They include: loss of mud, lost time, poor cement job, reduced safety, stuck pipe, additional casing string, failure to reach target depth, blowout and kill operations, downhole blowouts, environmental incident, and the abandonment of expensive wells. Moreover, lost circulation has even been blamed for minimized production because the losses have resulted in failure to secure production tests and samples, while the plugging of production zones have led to decreased productivity.

The complete prevention of lost circulation is impossible because some formations, such as inherently fractured, vugular, cavernous, unconsolidated (high-permeability zones) or depleted low-pressure formations (usually sands), are not avoidable if we want to reach the target zone (Al Ubaidan et al., 2000; Algu et al., 2007; Bell et al. 1987; Davidson et al., 2000; Ferras et al., 2002). The problem of lost circulation was considerably magnified when operators began drilling deeper and/or depleted formations (Sanders et al., 2003; Suyan et al., 2009). The petroleum industry has invested a significant effort into understanding the mechanisms behind lost circulation, developing new tools to help locate the thief zone, and implementing new steps to minimize or eliminate this problem because prevention is more effective than remediation (Whitfill et al., 2007).

Literature Review

In past decades, scientific (researches) from different companies tried to find a new innovative solution for lost circulation problem that occurs in increasingly demanding subsurface conditions as the result of drilling technology development.