Prospects of Casing While Drilling and the Factors to be Considered During Drilling Operations in Arabian Region

Abstract

Abstract Casing While Drilling technology is one of the greatest developments in drilling operations. The Casing While Drilling involved drilling and casing a well simultaneously and hence, overall cost of drilling may be reduced significantly by lessening drilling time and drillstring problems encountered during conventional drilling process. This technology is highly applicable in depleted reservoir as an alternative to the underbalanced drilling, which requires special equipment. This paper presents the applicability of the concept of Casing While Drilling in context of the Arabian (Middle East) drilling operations. Attempts are made in order to overcome some unscheduled hole problems, such as lost circulation, differential sticking and casing stuck due to tight hole during running casing after drillstring pulled out. This paper also presents simplified method that has been developed to predict the torsional and drag forces subjected to the casing string. Method of evaluating fatigue life of casing string has also been developed using simplified analytical techniques based on prevailing drilling conditions in Arabian fields. Both the static and dynamic cyclic loads as encountered in vertical and deviated wells are considered for the evaluation of fatigue life of casing string used for Casing While Drilling. Valuable guidelines are provided based on field representative case studies in order to minimize the various problems of conventional drilling operation through using the Casing While Drilling approach for Arabian field condition. Introduction Casing While Drilling has been employed in many countries to improve drilling performance. This technology was applied successfully to drill through depleted reservoir due to wellbore instability and to minimize mud losses into the depleted zones1,2,3. Casing drilling is an alternative option to conventional drilling and will use standard oilfield casing instead of drillstring4. Moreover, Casing While Drilling approach may be better suitable to drill soft formations, which are encountered at the top sections associated with different hole problems. In many fields in Arabian Gulf countries, the surface and intermediate hole sections showed often unscheduled events when drilled conventionally, mainly due to borehole instability and lost circulation. In many situations, wellbore instability contributed to apply timely backreaming when tripping out the drillstring and some times the drillstring could not be pulled out resulted in sidetracking the well. Applying Casing While Drilling in such hole sections will replace the drillstring and reduce the operation time spent due to hole problems and for tripping. At the same time, the casing is run to the bottom. However, prior to apply Casing While Drilling in any particular well, the hole conditions, such as unscheduled events and lithological characteristics of the formations have to be examined in order to evaluate the design criteria of the casing and to improve drilling performance. One of the main objectives of this paper is to evaluate the prospect of Casing While Drilling system for improving drilling performance in Arabian Gulf region. For this purpose, different data have been collected and analyzed for different hole sections drilled conventionally. Based on these analyses, Casing While Drilling approach has been found as best alternative to overcome various hole problems. In addition, successful application of Casing While Drilling approach requires accurate prediction of different loads, such as torque, drag and fatigue. Simplified methods of predicating both static and fatigue loads on Casing While Drilling are developed and presented systematically.