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.
Asri basin has been on producing since July 1989, currently there are 9 fields has been developed with strong water drive reservoir driving mechanism characteristic. Peak production was 196,000 bopd, presently producing 34,000 bopd with water cut of 99 %. Challenge faced in the studies had to deal with mature reservoir, declining production, depleted reservoir pressure, unrealistic recovery factor and the need to enhance asset value. Beyond that complexity, commercial challenge in rejuvenating the field becoming more critical due to falling oil prices. This paper present how integrated evaluation of mature offshore oil field performance and investigated various scenarios could add more value to the asset. Water flood, water shut off, and single field revitalization project has been implemented and it shows satisfaction result in reducing and maintaining production decline rate even increasing oil production volume. Recommendations also made to sustain and gain oil production by implementing successful projects to other field and also trying to implement Polymer Injection pilot project in Indonesia. The important thing in revitalizing a mature field is to define a customized asset evaluation approach to managed large amounts of data and identify the most important mechanisms in creating value-added solutions, while minimizing costs. The team captured this through innovative systems planning and operation, displacing the traditional lab-to-field R&D search in that multiple options were generated from within functional technology contributions. As expected, the results of full project implementation are satisfying. Depleted reservoir problem in major field producer has been solved by water flood project, the pilot project has been conduct in 1999 and shows great result in increasing oil production rate, within 2 years the oil production rate increase from 2,000 bopd to 12,000 bopd. Another project has been implemented in this major field is facies re-analysis, from this analysis new map are created, therefore new point of view can be extracted to support more comprehensive analysis, and the new analysis are very useful to gain oil production. Marginal field also part of the revitalization program in Asri Basin, in 2012 rejuvenation project has been conducted, and the result shows 4 times oil rate incremental, from 264 bopd to 908 bopd. One of other successful project is water shutoff, 2 wells are implemented for this project, and it can reduce water cut up to 17%, from 99% to 82% water cut. Those successful projects will be implemented for other field in Asri basin North Business Unit Area to Sustain and Gain Oil Production Rate.
The main challenge in offshore Southeast Sumatra, as one of Indonesia's mature fields, is to increase production in existing assets. The approach taken by the operator is through side-track drilling from historical wells, planned as a series of infill development wells, whilst evaluating new potential plays. This case study examines the logging-while-drilling (LWD) data acquisition in the Krisna-XX well in the Krisna field, which was designed to drain the remaining reserves from the Lower Baturaja limestone formation in the Sunda basin and maximize undrained area oil potential. Based on simulation analysis, the estimated reserves in the Lower Baturaja were 581 MBO with an initial rate of 426 BOPD. Additionally, the completion strategy required a rat hole to be drilled into the basement, which elsewhere in the basin can be hydrocarbon bearing. The first two wells drilled in the Krisna Field experienced severe mud losses while drilling, which had caused significant invisible non-productive time (NPT). The losses were associated with potential natural fracture swarms in the limestones and basement formations, but the fracture apertures were below the resolution of the LWD density image tool used in those wells. Hence, to refine evaluation of the fractures, an azimuthally focused resistivity tool was utilized in the third well (Krisna-XX), providing omni-directional laterolog resistivity and high-resolution resistivity images. The high-resolution resistivity tool was run in combination with quad-combo LWD tools to drill and log the high-angle (>70° inclination) 8.5-in. reservoir section. While drilling both the reservoir and basement intervals, this well also experienced high dynamic loss rates of water-based drilling fluids, which were treated with a lost circulation material, minimizing impact on the reservoir productivity. The well was drilled to total depth (TD) without incident. The aim was to utilize borehole imaging memory data acquired from this section as a benchmark for examining the current state of the Sunda Basin's formation. Post-run analysis of the memory image data yielded excellent quality high-definition images over the interval of the carbonate reservoir, coal, claystone, and basement sequences, improving knowledge of the Sunda Basin's detailed geological structure. This result helped the operator to understand the reservoir facies characterization of the Lower Baturaja formation, while overcoming potential fluid-loss conditions of up to 250-300 bbl/hr. The images clearly showed sedimentary structures, natural fracture networks, drilling induced fractures and vugs. Subsequently, by comparing against actual production (which has reached up to 1,842 BOPD), analysis of weak zones will improve reservoir insight to be incorporated into future subsurface models. In addition, high-resolution images combined with pressure-while-drilling data complements drilling operations analysis. Correlation to the intervals of fluid loss has allowed the operator to improve time and cost efficiency of the drilling operation and forthcoming planning.
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