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Wellbore fluid flow profiles in both producers and injectors tend to change over time due to preferential depletion, formation damage, cross-flow, channelling or tubing or casing leaks. These changes can result in excess water production through channelling, coning, non-uniform water breakthrough (fingering) or out-of-zone injection – all leading to uneven flow, pressure and sweep profiles. Ignoring these complications can result in missing key points on reservoir behaviour, selecting wrong units for a 3D full-field flow model or misleading redevelopment planning. Therefore, it would be logical to check for changes in flow geometry before embarking on costly workovers, recompletion or infill drilling programs. This paper compares and integrates the results of conventional Production Logging Tool (PLT) surveys that use spinners and multiphase sensors with those acquired by reservoir-oriented production logging surveys employing a combination of Spectral Noise Logging (SNL) [1,2] and High Precision Temperature (HPT) Logging [3–5]. PLT and HPT-SNL produce similar results when wellbore and completion conditions are good but they may differ dramatically in cases of non-uniform formation damage, channelling behind pipe or plugging of perforations by scale. Generally, HPT-SNL would assess the flow geometry and invaded zones of the reservoir while PLT would point out where fluid enters or leaves the wellbore or tubing. The paper provides case studies from a mature offshore waterflooded field producing a mix of oil, gas, formation water and injection seawater, which complicates the identification of flow geometry and invasion zones and represents a challenge for reservoir engineers in developing proper drilling or workover programmes to target residual reserves [6, 7]. The HPT-SNL-PNL surveys and further studies described here led to successful workovers and drilling. The redevelopment results can be easily assessed by decline curve analysis. Introduction Since 2007, Dubai Petroleum Establishment (DPE) has performed more than 150 integrated PLT-HPT-SNL surveys to monitor vertical wellbore injection and production profiles that resulted in valuable and often surprising findings including unexpected water breakthrough intervals, bypassed oil zones and layers and water channelling behind casing in producers and injectors. These findings, in turn, led to a better understanding of how water propagated through reservoir from injectors to producers and were used to calibrate a 3D full-field flow model and identify optimum infill drilling locations for the redevelopment of the highly fractured crestal area of the field.

TX 75083-3836, U.S.A., fax +1-972-952-9435. AbstractThe candidate selection criteria, job design, and improved implementation techniques are important parameters for success in remedial acidization jobs in mature fields.Effective acid diversion across heterogeneous carbonate reservoirs has always been challenging and is even more difficult when stimulating high-water-cut wells. For these types of wells, it is crucial to stimulate the oil-saturated layers rather than the watered-out layers. Bullheading conventional stimulation treatments tend to result in the aqueous-based stimulation fluid being injected into the high-water-saturated zones and away from the high-oil-saturated zones. This often results in a dramatic increase in water productivity and a minimal gain in incremental oil.Recently, several of Dubai Petroleum's offshore oil wells have been treated using 15% hydrochloric acid (HCl) and a viscoelastic-surfactant (VES)-based diverter, resulting in a significant uplift in oil production and a decrease in water cut. The VES diverter permits the oil-saturated zones to be stimulated while minimizing the stimulation impact of the water zones, despite large permeability contrasts. This VES fluid is able to maintain its viscosity when in contact with water and it breaks when in contact with oil. The increase in production with decreasing water cut showed the success of this stimulation diversion technique.This paper describes the candidate selection criteria, design, and implementation of successful carbonate matrix stimulation for high-water-cut wells in mature, water-flooded offshore fields.

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