Al-Ajmi, Hadi (Kuwait Oil Company) | Al-Barazi, Nasser (Kuwait Oil Company) | Al-Rushoud, Abdul-Aziz (Kuwait Oil Company) | Trivedi, Ranjan (Kuwait Oil Company) | Maliekkal, Harish (Smith Bits, a Schlumberger Company) | Ghoneim, Osama (Smith Bits, a Schlumberger Company) | Saleh, Moustafa (Smith Bits, a Schlumberger Company) | Nair, Prakash (Smith Bits, a Schlumberger Company)
Kuwait Oil Company (KOC) is analyzing the feasibility of utilizing extended reach drilling to achieve a long lateral section to increase oil production in northern Kuwait. Several attempts were made to accomplish the objective with roller cone and PDC bits on various directional tools with limited success. The major problem was short bit life/cutting structure durability and steerability issues in the difficult Mauddud carbonate reservoir. A drilling optimization initiative would benefit the entire northern Arabian basin because Mauddud is an important oil reservoir with uniform thickness and extensive regional distribution.
Offset analysis showed three to four TCI bits were required to drill 3000 ft of lateral hole section. PDC bits display increased durability making up to 2500 ft of hole but were pulled for low ROP and unacceptable drilling inefficiency before reaching TD. A second PDC was required to finish the lateral and gain sufficient access to the reservoir. Before the optimization project, the longest single run with PDC was 2935 ft. The average footage drilled by roller cone TCI is approximately 1500 ft with average PDC footage around 2500 ft.
To improve PDC bit performance, a rock strength program was run to identify the unconfined compressive strength (UCS) of Mauddud for use in an FEA-based modeling system. The software pegged the formation's UCS range between 9-15 kpsi with peaks up to 24 kpsi. Analogous rock sample files were selected and laboratory tests were performed to duplicate fundamental shearing action under the appropriate confining pressures. The resulting data was entered into the modeling system and simulations were performed with a baseline PDC to identify how lithology influences the bit/BHA and to investigate was to mitigate destructive drillstring dynamics.
The engineering study produced a six-bladed PDC that drilled the longest lateral interval (5250 ft) in Kuwait through Mauddud. The bit displayed excellent steerability and completed the hole section without losing ROP. This resulted in 100% footage improvement against offset PDC runs and is more than 150% better than the best TCI performance. The completed well has provided a 200% increase in production capabilities making up to 4500 bbls/day.
The history of oil production in Kuwait dates back to the Burgan field discovery in 1938. In subsequent years, different reservoirs and fields were identified. After a nationwide seismic study was performed in the 1990's several new discoveries were identified, with the majority concentrated in the northern part of the country (Figure 1). The reservoirs identified for the large scale production plays were in Ratawi, Zubair, Burgan and Mauddud formations.1-5 This paper will describe the challenges associated with drilling through these carbonate reservoirs, which contain problematic thief zones, with the latest bit technologies enabling the operator to extend horizontal reach through the reservoir, increase wellbore quality and augment production capabilities.