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Bombay High (now Mumbai High) is an offshore oilfield located in the Arabian Sea, approximately 160km west of the Mumbai coast. Discovered in 1974, the field started production in 1976 and is operated by Oil and Natural Gas Corporation (ONGC).The oil field consists of two blocks named Mumbai High North (MHN) and Mumbai High South (MHS). The blocks were divided based on shale barrier assisting in independent exploitation of reserves at the north and south fields of Mumbai High.The field currently holds 1,659 million metric tonnes (MMt) and is producing approximately 12MMt a year.ONGC’s board granted approval for the second phase of MHN Redevelopment project in January 2009, followed by the third phase in June 2014.MHN phase three redevelopment is expected to be completed in 2018, while MHS phase three redevelopment is expected to be completed in 2019.#Discovery#Bombay High was discovered in February 1974 by the Russian and Indian team from seismic exploration vessel Academic Arkhangelsky while mapping the Gulf Cambay between 1964 and 1967.The discovery of Bombay High with subsequent other discoveries of oil and gas fields in western offshore changed the oil scenario of India.#Geology and oil reserves#Different oil and gas reservoirs namely, L-I; L-II; L-III; L-IV; L-V; basal clastics; and fractured basement from top to bottom, are present on the Mumbai High project. L-II and LIII are primarily the limestone oil reservoirs of Miocene age, further classified into several layers.Bombay High has approximately 1,659Mt of total reserves in place.#Field development#ONGC announced its plan for Mumbai High redevelopment in 2000. It planned to spend approximately Rs90bn in five years for redeveloping the field. The redevelopment plan has been divided into two phases. The first phase started in 2000 and was completed in December 2006.The phase one was expected to yield an additional crude oil production of 23.25MMt of crude oil and 6.10 billion cubic metres (bcm) of gas by 2030, from 73 new wells and ten side track wells drilled.The cumulative oil production from phase one redevelopment wells was 9.34MMt and cumulative gas production was 2.89bcm until March 2008.The field reached its peak production rate of 400,000 barrels of oil per day (bopd) in 1985 and continued at the same rate until 1989.Decline in oil and gas production led to the need for a redevelopment plan. The production declined gradually to reach 220,000bopd in 2001 and ten million metric standard cubic metres of gas per day (Mmscmd).ONGC invested approximately Rs80bn on phase one for enhancing the efficiency and controlling the decline in oil and gas production. Under phase one, 29% of the 1,659 million tons of total reserves were improved.#Mumbai High North phase two redevelopment details#Phase two redevelopment, announced in 2009, will result in an additional crude oil production of 17.354MMt and 2.987bcm of natural gas, totalling to 20.34MMt of oil equivalent by March 2030.The phase two of MHN redevelopment plan aimed to further enhance recovery rate from Mumbai High by focusing on drilling of 73 new wells and side tracking of 38 poor producers. The development of small reservoirs such as L-II and L-I was combined with major reservoir L-III to strengthen oil production and development programme.The MHN phase two was estimated to cost approximately Rs71.33bn.#Mumbai High North phase three redevelopment details#ONGC approved phase three redevelopment of MHN in June 2014. The phase three redevelopment is expected to add 6.997MMt of crude oil and 5.253bcm of gas by 2030.It will involve installation of five wellhead platforms, modifications at 13 platforms, one clamp-off facility for wells at an existing platform, and construction of associated pipelines. It will also involve drilling of 52 new wells and 24 sidetrack wells.The phase three redevelopment contract was also awarded to L&T in September 2014. The work is expected to be fully completed in May 2018, while part production has already begun partially. The phase three redevelopment is estimated to cost approximately Rs58.13bn ($955m).MHS phase three redevelopment is also in progress with an estimated investment of Rs60.69bn ($997m). It was started in 2014 and is expected to be fully completed by March 2019. SapuraKencana Petroleum subsidiary Kencana HL was awarded a $273m contract for the same in July 2015. It subcontracted OHCS India and Param Offshore Services for topside hook-up, modification and pre-commissioning of nine well heads and process platform.#Infrastructure#ONGC started construction of new process complex MHN near the old Bombay High North (BHN) platform during 2007. Due to a major fire in July 2005, the platform was completely destroyed, which affected oil production. Along the field’s redevelopment plan, the new MHN complex was also developed handling approximately 270,000 barrels of liquid, 6.9Mmcdm of compressed gas, and oil pumping capacity of 50,000 barrels a day.The MHN process complex consists of a process-cum-riser platform, a living quarter, a subsea-connected flare structure, subsea pipelines and adjoining topside modifications such as facilities for handling sour gas from B series marginal fields. The new MHN complex ensures optimised and safe operations at the field.L&T secured a $1.18bn contract from ONGC during August 2009. The contract included an order for MHN processing platform and living quarter projects, along with additional order for the supply of three process gas compression modules to be installed in MHN complex. The three compression modules constitute a total of 80,000t of structures. The scope of work included surveying, engineering, procurement, fabrication, installation and commissioning of the facilities by L&T. The contract work was to be completed within 33 months.The new MHN process platforms organise gas lift pipelines and oil exports lines of MHN field. The former BHN platform was replaced by new MHN process platform, and created additional facilities for gas processing from future platforms.To facilitate interconnectivity of the power generating system, an installation of high-voltage submarine composite electrical cable as grid interconnectivity project was initiated in 2007. The installation was completed in 2012.Laying submarine electrical cable to interconnect 26 well head platforms, electrical submersible pumps (ESP) 81 wells and associated surface facilitates were the components of grid interconnectivity. The ESP assists in oil production from high water cut (90-95%) wells of Mumbai High field.The board of company approved proposal for an investment of Rs39.9bn in the ‘C series’ development project in 2007. The investment would facilitate MHN to handle additional 3.0Mmscmd of gas from C series wells.#Pipelines#ONGC approved construction of seven pipelines with risers and associated top-side facilities in MHN in April 2007. These pipelines are vital for optimum utilisation from Mumbai High.#Production#Mumbai High reached its peak production level in 1998 with 20MMt a year. Along with its adjoining fields, it produced at the rate of 12.8Mmscmd of gas prior to the recent redevelopment projects.The production was approximately 265,000bopd with an average of 63% of water cut and an average production of 1,200 barrel of liquid a well during 2007.The cumulative production of crude oil including results of phase one development was 140.25MMt until January 2009.The field is exploited using the gas lifts method, a major artificial lift method used for oil production. Several gas compressors spread over the number of process complexes in the field to support the broad gas lift network.