Water and Gas Control Jobs in Indian Offshore Field (Bombay High) - Trends and Case Studies.

摘要

Bombay high, an offshore oil field was discovered in the yearrn1974 and was put on production in May1976. Water injectionrnin this field was started in 1984. The main pay zone L-III is ofrnmiocene age. L-III is a multilayered, anisotropic limestonernreservoir with a gas cap and partial water drive. L-III reservoirrnof this has 13 different sub layers, which are separated byrnshale streaks.rnWater Shut off jobs: Bombay high wells startedrnproducing water since 1984-85. Preferential depletion of highrnpermeability layers in a set of high and low permeabilityrnlayers perforated together and subsequent preferential floodingrnof these layers has led to an early break through of water asrnwell as water loading of wells. This has also led to the leavingrnoil un-drained in less permeable layers. Earlier attempts tornshut off water with conventional squeeze jobs met with a littlernsuccess. However candidate selection with proper diagnosticsrnand mechanical isolation of the squeezed layer has resulted inrnremarkable success. But this could not address to the middlernwater producing zones. In order to overcome the limitations ofrnconventional cement squeeze jobs and in search of betterrnsuccess ratio on sustained basis and with the advent of variousrngel–chemicals, a number of gels of reputed companies werernused during 1993-97 for water shut off jobs. However thernresults were not encouraging either. Recently during 1999-rn2000, extensive lab studies were done on cores simulated atrnreservoir conditions and the compatible gels were used. Threernwater shut off jobs have been done using these gels.rnGas shut off jobs: Success ratio remained low withrnthe cement squeeze in between the oil producing and gasrnbearing layers. This increased remarkably with improvedrndiagnosis by multidisciplinary team, use of clean work overrnfluid and mechanical isolation of the squeeze point withrnpacker. Recently during 1999-2000, various gels were testedrnfor compatibility with reservoir rock and fluid andrnaccordingly the compatible gels were used in combinationrnwith cement cap for Gas shutoff jobs in 6 wells. Test resultsrnof 4 wells have shown that two of the four wells have beenrnsuccessful. With improved placement technique the jobs arernexpected to be more successful.