Reservoir sections in MRC (Maximum Reservoir Contact) & ERD (Extended Reach Drilling) wells are mainly designed to drill 8 ½" hole, because of drilling limitations with smaller hole size. However, slim hole sizes offer opportunities to revitalize existing wells using re-entry drilling techniques in association with MRC and ERD designs. This paper discusses the best practices to be implemented in order to mitigate risk, reduce complexity and ensure improved drilling performance. Re-Entry wells in the field have a risk of well integrity issues such as corroded 9 5/8" casing. In order to mitigate this risk, the corroded 9 5/8" casing should be covered by 7" liner & tied-back to surface before drilling reservoir section. In this situation up to 18,000 ft of 4" DP is used in the wells to drill 6" hole and run 4 ½" lower completion. Offset well analysis, whip stock selection criteria, BHA design, drilling fluid selection, drilling and tripping practices based on torque & drag and hydraulics calculations are most important to achieve the well objective. The Slim hole MRC well was completed without any issues and achieved good drilling performance. It was observed that the actual drilling parameters such as torque, drag and stand pipe pressure were less than simulated parameters. NAF was selected in the section to reduce the friction factor, while motorized RSS and a reamer stabilizer were used in the BHA to reduce torque, drag and ensure a smooth well profile. A back reaming practice was implemented in hole section to reduce dog leg severity and the open hole was eventually displaced to viscosified brine to minimize the friction factor for running the 4 ½' lower completion. 8500 ft of 6" hole section was drilled and TD was reached at +/- 19,000ft within 50 days including recovering the existing completion, drilling 8 ½" & 6" hole and running completion. This paper aims to contribute to the oilfield industry by sharing the successfully implemented engineering design and operation execution methodology to overcome the complexities present in Re Entry Wells MRC/ERD wells required to be drilled with slim hole conditions under an optimal cost, time effectiveness and low risk.

Drilling & Completing of the wells faster, safer and at lower costs has always been the primary target for the operating companies worldwide. While it has been achieved by several means through Technology, Innovation, Operational Optimization, Cost Reduction Techniques, Application of Best Practices etc; the operating company still has to deal with multiple contractors, vendors, suppliers and service providers, with each of them having different drivers for success that may or may not align with the primary goal. The concept of Integrated Operations / Services brings in this required polarization of drivers for success to deliver the projects under budgeted AFE & planned times. In one of such Integrated Drilling Operations Campaign, at an Artificial Island located in Offshore United Arab Emirates, with single focal point for various drilling well services, the learning curve of the project has been very steep with numerous optimization measures taken at the early phase of the project under the continuous improvement process to enhance the drilling efficiency in order to speed up the well delivery. The step change achieved in the drilling efficiency for delivering the 16″ section will be detailed in this paper. The same concept has been applied in other sections with similar success. The drilling optimization has never been so thorough and need of the hour with the current prolonged challenging market conditions. This paper revisits the drilling optimization by integrating all the associated well drilling services to improve and pursue higher drilling efficiencies. It details in steps, starting with identifying the opportunities of improvement, how the traditional methods & practices were challenged and the revised practices were adopted in design & operational execution to better the performance and deliver the section faster consistently with every well. The drilling performance of this section after integrated drilling optimization currently holds several records (best footage/day, best footage/24 hours, best onbottom ROP, best average ROP including connections, best connection times, days/1000 ft, faster casing running speeds) in the subject field and also stands out when compared to the other nearby offshore fields in the country. These drilling performance records are combined with good hole quality which have contributed to delivering the fastest 16″ section when one includes casing running and other flat time activities. With the planned changes alongside the detailed engineering planning & constantly monitored execution, the section has been delivered well after well with improved times. Overall, the drilling phase of this section has been delivered 3 days earlier than the offset wells and contributing to potential savings of up to 18 million USD to the project drilling campaign cost.

In 2020, A Major Offshore Operating Company in UAE faced a high differential pressure stuck event. This took place, during the execution of formation evaluation with a conveyed pipe sampling BHA. It is well known that after a differentially stuck pipe event happens, the success ratio will be time dependent (i.e. the less time a pipe remains stuck, the more chances there will be for it to become released) and the chances of releasing the BHA are always limited to the logging tools tensile limitations. One of the most common and successful methods to release differentially stuck BHA's specifically in limestone formations is by pumping and soaking acid pills. However, under such a high differential pressure environment, the use of acid may induce losses in the so called "thief zones", causing worse problems. The standard release procedure started by working the string within the tensile limits, followed by pumping acid pills (using the available volume mobilized before spudding each drilling section). During the first acid pills pumped to attempt to release the stuck pipe, loss volume pump rates, acid pill position(s) and coverage in the annulus was assessed and evaluated. Based on the results it was observed that the thief zone was in direct contact with the Pipe Conveyed circulation port, at the latching assembly. This then created a situation whereby, the acid pills were lost immediately after the acid came into contact with the formation. Utilizing low acid concentration pills also had the same effect. The solution was to pump an Obturating pill made-up of a weighting agent as a spacer behind the high volume, low concentration acid pill with crosslinking divergent chemicals, pumped at a high flow rate. This solution reduced the acid losses across the thief zone and once the Obturating pill came into contact with the loss zone, it facilitated the seal and cured the losses, by allowing the acid to move up the annulus until it reached the differentially stuck point and soaked across the problematic area. Once the acid pill was successfully placed at the required location using this method, the string was worked and successfully released. This combination of low concentration acid along with crosslinking divergent chemicals coupled with the Obturating pill behind the acid helped a major offshore operating company to pump the acid pill under partial losses only, to regain full circulation after only 10 bbl. of Obturating pill had entered inside the annulus. It allowed the acid pill to react across the stuck point, while keeping the string under low torque and compression. The operator was able to release the sampling BHA and bring it back to surface avoiding a lost in hole cost of around 4 MM$. The Obturating pill combined with low concentration CDC acid pill is proven to be a successful method in drilling operations when trying to release differentially stuck BHA's within a wellbore.