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.

The 6"hole section in Raageshwari Field NW India (onshore) is typically between 600-800m long and highly challenging in terms of formation strength and abrasiveness. Lithology in the upper part is composed of sandstone, claystone and weathered basalt with unconfined compressive strength (UCS) between 3-5kpsi. The lower section contains basalt, felsic and sub-felsic igneous formations with UCS range of 15-30kpsi. Historically, a two bit strategy was employed. First, a PDC bit on a positive displacement motor (PDM) bottom hole assembly was used to drill the soft 6" section until ROP dropped to an unacceptable level. The BHA was then pulled and followed by a diamond impregnated bit on a turbine BHA to drill the very hard volcanics. Typical average on-bottom ROP for the entire section was 4.5m/hr and took approximately 170 hours to reach total depth (TD). To reduce costs, new technology was proposed to improve bit durability in the hard/abrasive volcanics and drill the entire 6" section in one run at a higher ROP. Recent bit and drilling data from offset wells was analyzed to assist in developing a new, cost effective PDC design to replace the expensive diamond-impregnated bits and drill the 6" hole section in one run. The study resulted in a new six-bladed PDC bit with 13mm cutters that incorporates superior cutter technology to improve durability and resist physical and thermal degradation. The design includes a row of backup cutters in the shoulder area to increase radial diamond volume for maximum durability. The new PDC bits have been run on a motor and rotary steerable bottom hole assemblies and drilled the 6" section on three consecutive wells in Raageshwari field totaling 2328meters with an average ROP of 10.7m/hr. This represents approx. 47% decrease in drilling time compared to that previously achieved by Impreg/TCI bit runs. Typically, the new bits are pulled in re-runable condition. This improved performance has saved the operator approximately six-days of rig time and approximately USD 480,000/well.

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.

During exploration activities in the Thar Desert of Rajasthan, India, Cairn India Ltd. discovered numerous oil fields in the Barmer Basin. The oil reservoirs are relatively shallow and benign in terms of pressure, temperature and corrosivity, but they posed significant flow assurance challenges due to relatively high crude viscosity, wax content and pour point. As a result, surface facilities are reliant on heat for flow assurance. Total reliability of power and fuel supply for the facilities was essential to ensure export product quality and for flow assurance for the waxy oil. The paper presents Cairn’s approach of utilizing state-of-the-art technology that integrates all relevant data scenarios for the drilling and production systems for this lean gas condensate reservoir. This development will provide the necessary power and heating fuel supply and the primary gas supply for the main oil processing terminals and for power generation stations along a 600km heated export pipeline.through the end-of-life for the major oilfields discovered in Western Rajasthan, India. Raageshwari Deep wells target tight, predominantly volcanic reservoirs with cost-effective monobore designs that include multiple fracture stimulations in various pay zones to maximize well productivity. The slimhole well design, dynamic completion design, and careful bit design and selection successfully enabled the drilling of these wells with 26% cost savings on the total budget for drilling ten wells ($ 2M per well). A program highlight was the drilling of volcanic tuff formations in a single run. The paper will describe detail aspects of monobore well planning and well design implementation including fracture stimulations. It will also demonstrate how this significantly improved the well delivery that contributed to effective development plans for these major oilfields.