Huizhou oil field, located offshore south China, has been in production for over 20 years. Most of the primary oil was produced from 1991 to 1996 by vertical wells and commingled production. Horizontal geometric drilling was first introduced in 1997. However, as the field became more mature, the rate of success could not be sustained, and a rapid production decline began in 2000. By 2006, the field average water cut reached 90%. A reservoir surveillance program was conducted to evaluate remaining reserves, delineate current oil water contacts, and update geologic and reservoir models. This work revealed that remaining reserves in the high-permeability reservoir accumulated in attic locations, while the reserves of low-permeability reservoirs remained unproduced despite years of commingled production with the high-permeability reservoirs. A new horizontal drilling program was initiated in 2007 to target the 3 m to 5 m thin attic oil column of high-permeability reservoirs overlying strong aquifers. The 1 m to 3 m thin and low-permeability interbedded shale reservoirs were also targeted. Because the reservoir targets are much thinner compared to original conditions, the standoff between lateral and oil water contact is very sensitive to well performance and reserve recovery. Precise landing and lateral placement of horizontal wells and the use of inflow control devices for completion, have become critical to the success of this campaign. The results have shown 39% higher production compared to the set targets, up to 15% improvement in reserves recovery, and 14% reduction in annual field production decline rate. Based on project results, best practices in finding and revitalizing remaining oil in mature fields and complex reservoirs were developed. Project success was also aided by applications of fit-for-purpose technologies, including advance multifunction formation evaluation and azimuthal logging-while-drilling, well placement, and inflow control devices, as an integrated solution.


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