Surveillance in deep water wells is cost prohibitive. There is a need for significant hydrocarbon production or water shutoff incentive to justify the intervention in such wells. The wells straddle multiple stacks of soft sediment reservoirs, being completed with open hole gravel pack. While laterally extensive barriers between various sands units might help the water shutoff / containment, the gravel pack annulus still provides a conduit for water to move upwards and jeopardize the shutoff success. In this campaign a meltable alloy was deployed to plug the flow in both annulus and screens. In deep water subsea wells, water conformance control is often attempted blindly without flow diagnostic surveillance or production logs as a minimum. This can impact the production due to plugging substantial hydrocarbon production or inadequate flow from the remaining zones. Candidate wells or techniques for shut-off require robust diagnostics to improve the success rate and limit loss of oil or gas production. In a recent well work campaign production logs were acquired to optimize the water shut-off. Well access is challenged by limited rigup height (short lubricator) and well deviation. The well trajectory impacts the phase presence, mixing and recirculation. It requires a short array of sensors conveyed on tractor. Logging while tractoring capabilities in surface readout mode is required to minimize the rig time, improve depth control and perform real time data quality assurance. The multiple mini-spinners, electrical and optical probes are all positioned to the well's vertical axis to capture all local changes in the flow regimes. Sensor arrangement is sufficiently compact in this tool to minimize flow disturbance by tool occupancy and movement along the well. Real-time profiling of the complex flow regimes during the acquisition provided better log control and understanding of the downhole phase dynamics. Changing the mindset about subsea deep-water reservoir surveillance paid dividends in water shutoff operations, both for immediate decision make and for longer term well and reservoir performance management. There was a net benefit by deploying a compact axial array production logging string that allowed accurate rate and phase allocation and further identification of zones to be isolated using an innovative plug-back method that significantly reduced the water production.
A key factor in managing mature fields is to establish adequate surveillance in each phase of their life. The complexity increases when the field is developed with horizontal wells. Differences in data quality and resolution should be taken into consideration when planning such surveillance. Current uncertainties in Harding field relate to unreliable well conformance data using conventional production logs (PL) and assumptions in the reservoir description, which are subseismic resolution. We describe the learning from a horizontal well in Harding, where appropriate surveillance enhanced reservoir understanding and quality of decision making.Based on the initial understanding from the reservoir model, an insert string well work option was proposed to reduce water cut. Historically in this field, conventional PLs provided unreliable well conformance data in horizontal multiphase flow. To improve the characterization at the well scale, an array PL was deployed for the first time on this field.The flowing results revealed that the insert string solution was inappropriate and would result in lost oil production. The shut-in data identified crossflow between two zones separated by a shale section. In the initial model, this shale was mapped only at local level. Post surveillance, it was remapped on seismic as an extensive baffle having an impact on an area with more mobile oil to recover. There is a potential upside with a new infill target being identified toward the toe of this well.Most of the initial decisions about the insert string were based on seismic and modeling work. The new array PL data brought additional information into the model, increasing confidence in the results. Data resolution at the well level matters and this highlights the need to take more PL measurements to calibrate the seismic response and improve the reservoir model.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe keys to proactive production and reservoir management are production logs that profile fluid entries and diagnose problems in producing wells. Designing optimal production strategies and remedial operations requires highconfidence diagnosis. Production logging in high angle and horizontal wells producing mixtures of various phases is challenging because of complex flow regimes.In this paper we present a field example that uses a new compact, integrated production-logging tool that incorporates the latest technological advances and best practices to address complex production-logging requirements. We are able to demonstrate the added value in terms of comprehensive flow diagnosis.A production logging operation using the new tool, which specializes in horizontal and deviated well logging, was planned to obtain key inputs for the reservoir model and investigate reasons for low well productivity. Production logs from the new tool resulted in accurate flow diagnosis and led to better understanding of complex flow mechanisms across the horizontal section. These enhanced measurements were integrated with borehole imaging information leading to a better understanding of flow contribution from the matrix and fractures. The tool provides a recording of holdup and velocity profiles along the vertical diameter of the borehole cross-section. Three sensor arrays, consisting of six optical probes, six electrical probes, and five spinners, are spread across the wellbore on retractable arms that can be opened and closed with a hydraulic sub to better locate holdup interfaces. The optical probes use the fluid's reflectance to derive the gas holdup, and the electrical probes measure the fluid's impedance to derive the water holdup. The spatial location of the different sensors is accurately known through the use of an integrated relative bearing sensor and a caliper measurement. The direct measurement of the velocity and fluid holdup enhances the capability of the analyst to determine an accurate downhole flow profile.
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