The frontier exploration drilling campaign in the Kingdom of Saudi Arabia for LUKOIL Saudi Arabia Energy Ltd started in January 2006. LUKSAR, a joint venture between Lukoil & Saudi Aramco, took pragmatic approach to project management. A careful analysis of campaign challenges with proper planning to meet the drilling campaign targets. One major challenge was to stick to well program to ensure well targets are met and exploration objectives achieved. The reduction of wellbore diameter due to hole problems during well construction has always posed a great challenge to well completion. Having said that, there are few technologies at present that provide the capability to execute well intervention/work-over in slim hole wells and where there are available, they usually cost a fortune. The restriction created in reduced hole sizes typically results in a complicated drill stem testing program (DST), formation fracture pressure limitation, decrease in production rate due to restriction in tubing selection and high intervention cost. On Luksar Expl well #4, the above mention challenge was a reality. While drilling, encountered severe loss circulation in Shu'aiba carbonate formation compounded with sloughing shale problems in the shallower Wasia formation. As a result, it became difficult to drill further and set planned casing at bottom. Utilizing expandable tubular across loss circulation zone enabled Luksar to restore the original well casing design. Introduction Losses of whole mud to subsurface formations is called lost circulation or lost returns. Historically it is one of the primary contributors to high mud cost. Other hole problems such as wellbore instability, stuck pipe and even blowouts have been the result of lost circulation. Besides the obvious benefits of maintaining circulation, preventing or curing mud losses is important to other drilling objectives such as obtaining good quality formation evaluation and achieving an effective cement bond on casing. The Shu'aiba Formation consists mainly of different types of carbonates (limestone and dolomite) depending on the well location. The vast extent of Shu'aiba is porous with fast ROP. Shu'aiaba is an oil and gas reservoir in some of the off-shore wells. In 90% of areas it is a loss of circulation zone like in all Gulf States and especially in the Kingdom of Saudi Arabia. Estimated pore pressure range 8.4–8.5 lbm/gal with recommended mud weight 8.7–9.9 lbm/gal. The majority of non-productive times associated with drilling through this reservoir include:Lost CirculationUnexpected high-pressure areasHole integrity and wellbore stabilityFormation to formation cross flow Drilling through such formations provides many opportunities to experience one or more of these risks either while RIH, drilling or POOH. These risks potential means that at least one additional string may be needed to isolate the troublesome zone and to drill ahead to the planned casing point.
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