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Innovative Completion Technique for Perforation, Single Trip Placement of the Completion String, and Effective Frac-Packing Long Intervals: Case Study from Natuna Sea, Indonesia
This paper provides an overview of the decision process to select completion hardware, the method for fluid loss control, the placement technique used to mitigate premature screenouts, and discuss the results, observations, and challenges from the completion operation in Conoco's Tembang subsea field in the Natuna Sea.
Six design challenges were confronted in order to determine the optimum completion method for the Tembang Zone 4 high permeability, highly laminated sandstone interval to be completed from a semisubmersible rig.
1. Need for high inflow area and effective gravelpacking to insure high deliverability in this highly laminated, loosely consolidated sand/shale sequence
2. A frac-pack design was opted for to optimize connectivity between the multiple sand layers within the overall reservoir and minimize shale exposure
3. A one-trip system was desired to allow perforating, screen placement, and gravelpacking to be conducted in one trip, thereby minimizing fluid loss and formation damage during completion operations
4. After underbalanced perforating, an injectivity and fall-off test was required for analysis of pregravelpack well and reservoir performance
5. The completion consisted of five perforated intervals comprising 88% of the 322' MD gross interval. Based on log derived permeability, the perforation intervals ranged from 20 md to multi-Darcy, complicating the risk of prematurely screening-out in the most permeable zone and then forming a bridge which would prevent effective packing of the remainder of the interval.
6. Use of flapper valve to control post-gravelpack losses
The Single Trip Perforating and Packing system was elected as the most effective completion method to minimize gas migration and fluid loss. To satisfy the requirement for the ability to perform an injectivity test, recent advents in the development of the servicetool equipment provided a methodology to perform a simple drill stem test treatment. A frac-pack sand control technique in conjunction with Alternate Path Technology (APT) screens provided the best option for formation gravel placement, as well as, complete annular coverage across the screens (Jones et al., 1991). This was critical to job success since the long, high angle (322' MD at 50 degree inclination) perforated interval would be prone to premature screen out using conventional technology.
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