Drilling horizontal wells at an average true vertical depth (TVDBRT) of 850-950m to exploit the high porosity and low permeability tight reservoir of Barmer Hill (BH 1 to BH12), in the Indian state of Rajasthan required overcoming many chal-lenges. These wells were drilled from both Aishwariya and Mangala fields. The highly layered BH reservoir is primarily composed of diatomite and porcellanite. Drilling ERD wells at such shallow depths and with land rigs that have limited capability (tubular and pump limitations) required detailed planning and flawless execution because of many inherent risks such as high torque and stand pipe pressures, poor hole cleaning, inadequate weight-on-bit transfer and stuck pipe events. Optimum trajectory in terms of good well placement, drillability and collision risk avoidance was a priority in planning these wells in a tight network of over 350 wells. An important concern was designing a Bottom Hole Assembly (BHA) to meet multiple requirements. It had to be planned to maximize achievable doglegs with Rotary Steerable System (RSS) to land the wells despite high uncertainty in reservoir depths.High drilling torque anticipated in 6″ hole and narrow operating window with re-spect to helical buckling were major concerns.WOB transfer while drilling ~1000 m horizontal section was critical. ECD had to be carefully managed by a combination of good hole cleaning and the use of smaller drill pipe in order not to exceed formation fracture gradient. Good drilling practices specific to ERD wells and meticulous engineering/planning led to successful drilling of these shallow TVD ERD wells.

This paper explains the successful execution of Expandable Liner Hanger and primary cementing job for ERD wells in Rajasthan block of North-West India. One of these wells has the longest horizontal 6in. hole section in the Indian Subcontinent. Zonal isolation is especially critical, as these wells are all candidates for multistage fracturing operations in the completion phase. The successful liner job in these wells face several challenges: placement of 4½ inch liner in 6 inch hole, hole conditioning, cement placement and ECD challenges due to low fracture gradient limit. An integrated Basis of Design was developed to mitigate the challenges. This includes The placement of liners with computer aided torque & drag analysis,Rotation of liner during hole conditioning & cementing at highest possible rpm within acceptable torque limits,Fine tune fluid properties with computer aided simulator to achieve sufficient cement coverage around the liner (displacement efficiency). The liner hanger system in this case study has an advanced running tool to facilitate the required rotating capability. The liner hanger also incorporates a contingency tertiary setting mechanism for liner expansion due to the challenging down hole condition. The expandable liner hanger is an integrated hanger packer system. Elastomeric elements are bonded on to the hanger body itself. As the hanger body is expanded, the elastomeric elements are compressed in the annular space, which provides primary annular isolation at liner top. This case study also examined the impact of liner rotation on displacement efficiency of the cement slurry with computer aided Finite Element Analysis. The results give engineers a better understanding of the relationship between rpm and displacement efficiency of the cement slurry. The technology and the practices established from this case study have become the standard operating procedures for liner cementing jobs in subsequent ERD wells.

Managed Pressure Drilling technology was deployed to drill Cairn India's first HTHP offshore well in Ravva offshore field of India. MPD feasibility study was carried out initially and this well proved as a candidate well for MPD in hole sections where narrow margin between pore pressure and fracture pressure exists. The use of MPD was further substantiated to mitigate non-productive time associated with wellbore problems like wellbore ballooning, kicks, loss circulation and stuck pipe which were encountered in offset wells. Therefore, a constant bottom hole pressure technique was chosen with mud weight closer to pore pressure & ECD profile being kept according to selected anchor point for each hole section. The fully automated MPD set-up comprising of a rotating head (with dual sealing function), MPD choke manifold and Coriolis flow meter (6” & 4”) guided by real time hydraulic modelling was used in the well. The mud program was designed close to pore pressure in conjunction with MPD, reduce ECD while drilling and maintaining rheology at high temperature. The deployment of MPD enabled to increase the section length of the 12.1/4” hole section (769 m), which proved to be a key step in in order to accomplish the well objectives in deeper sections. This paper by medium of actual case study talks about use of MPD technology, operational/ equipment problems faced and lessons learnt. This paper also highlights recommendations for use of MPD technology for similar wells.

In a technically challenging & high cost environment such as HTHP wells, careful selection and adoption of advanced technologies for the successful completion of the well is paramount. As per the original well design of the subject well, it was planned to drill with a bit & under reamer which was actuated by a ball drop mechanism. This led to the restriction of placing the under reamer close to the bit as MWD/LWD had limited pass through & hence the under reamer had to be run above the tools leaving approximately 25-30 m of rat hole un-opened along with inability to retrieve radioactive source in an event the BHA was lost in hole. This required two separate BHA runs to open the rat hole in order to place the casing shoe as deep as possible. The additional hole opening trip would have resulted in extra time and hence additional cost, moreover it was prudent in HTHP well to place the casing shoe exactly at right depth to achieve well objectives. Hence, use of Bi-center bit to simultaneously drill & under ream without any pass through restriction was evaluated. Several critical issues, related to application and BHA design, were faced by the Well Engineering team. Reaming while Drilling (RWD) with bi-center bits has always been challenging in terms of vibration-related inefficiencies. Due to the asymmetrical geometry of the bit, imbalances in force and mass have been responsible for the vibration related problems. Secondly, due to the minimum pass through requirements, these assemblies are virtually always run with under-gauged stabilizers as it allows a certain degree of lateral movement within the constraints of the enlarged hole. All of these issues could have caused the pilot-bit drilling an over-gauged hole along its axis which results in the bit drilling off center giving an overall under-gauged hole as the pilot of the bit is not centralizing the reamer. A unique eccentric vibration dampening tool (ideally located in the string) was used to mitigate the drillstring vibration & bit whirl. This paper describes the well specific BHA design & placement of the vibration dampening tool used to improve hole opening performance. A total of 4 bi-center bit runs over three hole sections & different sizes i.e.12.¼″× 14.¾″, 10.3/8″ × 12.¼″ & 5.7/8″ × 6.¾″ are also discussed in the paper. Unusual problems were encountered while drilling shoe track & landing collar for liners in 10.3/8″ × 12.¼″ and 5.7/8″ × 6.¾″ hole section. Lessons learnt, recommendations & contingencies to be planned for successful application of bi-center bit are discussed.

In Cairn India’s first ultra HPHT well RX-11, the biggest challenge was the narrow margin between pore and fracture pressures in the deeper HPHT sections of the well. In HPHT wells, high annular frictional losses while pumping causes increase in ECD, thus inducing lost circulation because of narrow pressure margins and, in very severe cases it can even lead to well control events. Such problems were experienced extensively in offset wells and therefore to reduce the annular frictional losses, the use of micronized particle drilling fluid was thought of & introduced in Cairn for RX-11. Extensive research went into the application aspect of Micronized particle drilling fluid as various simulations & lab tests were done at the time of contract award. HSE risks owing to the suspension tendency of micronized barite in air were identified & mitigated. One big challenge lay in the mixing of mud at rig site as large volumes were required for drilling (due to hole size) and accordingly mud mixing plan was formulated to ensure uninterrupted supply at rig site. Post all the planning, the micronized particle drilling fluid was used to drill the last three HPHT sections of the well and it proved highly successful in reducing the ECDs as well as providing good hole cleaning (at low flow rates) with minimal maintenance, which enabled drilling to continue through the narrow pressure margin sections of the well. In high temperature conditions, the drilling fluid was found to be stable & undegraded even after 10 days of static condition with no change in hole condition upon re-entry. In addition, caliper log recorded a ‘gun barrel’ 12.1/4″ hole drilled using the same drilling fluid and further it contributed in a near perfect 9.7/8″ casing cementation recorded by CBL-VDL log. This paper via a case study showcases the concept, project planning & successful implementation of Micronized particle drilling fluid in RX-11 well & makes recommendations for its use in similar projects.