Dealing with mature offshore oilfield has complicated problems both surface and subsurface. In the reservoir condition high water cut wells make some bad impact in the production stages. Liquid handling facilities, tubing pipeline erosion, broken sand control, and high power consumption are several problem caused by high water cut wells. WW is an offshore oil field which has developed since 1990s with OOIP 758 MMBO. This reservoir was divided into several layer, 33 series is depleted reservoir with water injection since year 2000s (RF 23%) and 35 Series has strong water drive as its driving mechanism (RF 56%). Almost 85% of the oil wells is producing with water cut more than 97%. Increasing water cut or even watered out phenomenon was frequently happen during production stage, some of this problem was happen after well intervention such as after pump replacement. This paper will show the successful case of decreasing water cut significantly from WW D-29, WW H-12, II A-22. Laboratory test was firstly done to check the compatibility test of the rock with modified completion fluid. This chemical was mainly works as phase change water control and oil stabilize well for completion fluid. It was pumped simultaneously with regular completion fluid (filtered drill water and additives). Killing well was mandatory procedure when shut in wells will be repaired. GGR team supported by Production and Workover Team did integrated study to choose the chemical and well selection based on some criteria. WW D-29, WW H-12, and II A-22 are wells which have implemented modified completion fluid treatment. Those wells are produced from sandstone reservoir and drilled more than 10 years ago. During production period, water cut was significantly jumped due to several reason, such as pump replacement job, re-start up after the well trip off, etc. The result of the project were very excellent, WW D-29 (from 98% to 86%, gain +/− 180 bopd), WW H-12 (from 80% to 40%, gain +/− 250 bopd) and II A-22 (96% to 75%, gain +/− 130 bopd). These result give a lot of impact of increasing oil production in WW Field. This paper will elaborate how to solve the problem in offshore mature oil field special case for high water cut wells using modification of completion fluid treatment. We have succeeded increasing oil reserves.
Reservoir characterization in Windri field is complicated by complex lithology and difficulties in predicting changes in fluid distribution. 33-4 Sand body is interpreted as complex compartmentalized channel and part of water flood project associated with distributary channels, mouth bars and delta front shoals. Seismic amplitude mapping at the Base Upper Gita horizon reveals a system of meandering channels. In 2000 and 2004, 4D seismic data set was acquired and processed to take advantage of seismic AVO effects. The base line 1991 seismic data set was reprocessed in parallel. The primary reason for the monitor data set was to observe the reservoir pressure depletion state around a water-flooding project. Detection of 33-4 sandstone reservoir is feasible based on interpretation of AVO P, G, P*G, P(30°) attributes. Fluid replacement model created into three scenarios (oil, water, gas) to predict the hydrocarbon saturation. Integrated time lapse 4D seismic by using map differences in seismic response has been conducted for monitoring pressure decrease and subsequent water flooding sweep patterns. Windri area divided into 6 sweep patterns area to make improved connectivity analysis.AVO attributes using intercept (P), gradient (G), P*G, and P(30°) has been done to determine of 33-4 sand. Feasibility study on AVO analysis has been applied by using fluid replacement model on the well data. A more advanced interpretation of the expanded AVO analysis for 33-4 sand has been done by using simultaneous inversion and 4D time lapse seismic. Practically, this method is used to map differences in seismic response over time attributable to production related processes, especially amplitude response which directly interpreted as replacement of oil by dissolved gas, and also suggest re-pressurizing the reservoir. Reservoir characterization using 4D simultaneous inversion enhances interpretative resolution and reduces uncertainty sand and fluid prediction. Integrated analysis of time lapse 4D seismic has been well implemented for increasing infill and injector success ratio, as well as predominating pressure degradation in Windri field. This comprehensive study is essential for understanding of complex lithology, monitoring pressure decrease and subsequent water flooding sweep patterns in 33-4 sandstones reservoir. Knowing the concept of depositional setting, facies and reservoir behavior to be applied in the waterflood project is crucial to optimize the production.
Located offshore South East Sumatera Indonesia, C-SY field is a structural trap with 4-ways dip closure and multiple reservoir targets with excellent rock properties, considered a marginal field and currently idle for 8 years. Challenges faced in reactivating C-SY field are high investments compare to other well service proposal and have limited reserves. The objective of this paper is to revive idle marginal offshore brownfield C-SY by increasing value of reserves and economics value. In order to do so, all prospects within C-SY area need to be assesed, including exploration prospects with high geological chance factor. The evaluation process worked simultaneously by exploitation and exploration team. The exploitation team worked on re-estimate OOIP and reserves of existing reservoir by structural interpretation, reservoir characterization analysis using attributes, Decline Curve Analysis & Material Balance Analysis. While the exploration team worked on finding other reservoir prospects by doing prospect identification from 3D seismic analysis, structural play analysis, closure identification and migration pathway from kitchen to prospect area, calculate OOIP. Result from both teams were combined to estimate reservoir behavior and production forecast. The next step of evaluation was to create multiple cases of possibilities and calculate the economics to find the best and possible case with minimum calculated risk. Collaboration between Exploitation and Exploration has lifted the value of C-SY idle marginal brown field, new structure has been found with promising reserves and initial production. Initial production C-SY field after the collaboration is 1,200 BOPD from previously 150 BOPD, while remaining reserves increase 3 times higher up to block expiration contract in 2038. Developing marginal offshore mature asset is a risky business, especially considering high volatility in oil prices. Collaboration and technology are vital to escalate the economic value and achieve higher recovery factors. Application of the multidisciplinary methods was considered as an appropriate way to approach and manage a complex marginal mature field redevelopment.
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