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An Integrated Downhole Logging Suite Including Spectral Noise Logging to Improve Reservoir Characterization


 The location of producing intervals in multi-layer reservoirs and the determination of current formation pressures in these intervals are critical aspects of reservoir management. The identified not-producing layers in multi-layer wells can be activated to start contributing to the field production. Another challenge that grows over the time during the development of a mature multi-layer reservoir is excessive water production that can be caused either due to water breakthrough over some target layers (the edge water or water from nearby injectors) or can come along the channels in cement from a water-bearing reservoir, located above or below the target reservoir. This effect impacts the vertical sweep efficiency in the field and leads to early abandonment of the wells. The common solution to avoid it is to find the source of water and perform water shut-offs based on the pre-monitoring results.
 A specific technology has been worked out to detect fluid flows that happen both in well and reservoir. It is based on the analysis of data acquired by broadband high-definition spectral acoustic logging tool. The acoustic signal component produced by fluid flow through the rock matrix can be distinguished from other acoustic signals caused, for example, by wellbore or channel flows by its frequency features. The layer formation pressure was determined by numeric simulation using an empirical correlation between the reservoir fluid flow velocity, pressure gradient and the reservoir-related component of acoustic power. The interpretation results were used also to track, distinguish, and quantify flows behind pipe both in reservoir and through channels in cement. Multiphase sensors were used to determine phase composition inside the wellbore. This helped to identify the source of water in well production.
 Three tasks mentioned above - (1) location of producing layers, (2) determination of layer formation pressure, and (3) identification of water source in the well production - described in the paper was part of the field-monitoring programme carried out to optimize well production such as gas and water shutoffs, recompletion, switching from natural to artificial lift production, and others. The target is a sandstone oil reservoir consisting of many layers with variation of reservoir rock types, permeabilities, thicknesses and formation pressures in Cheleken Block, Turkmenistan.
 This paper presents survey results from a number of production wells being a part of 20-well logging campaign. Producing layers were identified in surveyed wells, with some of them equipped with sand screens, which made it difficult to identify producing intervals using conventional production logging tools. These results have been correlated with permeability model. The acquired spectral acoustic data showed that not all layers of the target multi-layer reservoir were producing. Additionally, the calculated layer formation pressure values were analysed and it was discovered that in the two wells producing from the same layers the top layer had a higher formation pressure than the others. The layer formation pressure values calculated using numeric simulations proved to be in a good agreement with the formation pressure measurement data, acquired in nearby infill wells.
 Regarding the water source, a case with successful remeadial job have been described. This paper demonstrates how the integrated logging suite complemented by acoustic and temperature logging tools can prove effective in identifying a water source in the complicated cases such as dual-completion wells producing from a multi-layer reservoir. The acquired information was used to increase the chances for successful remedial operations. Workovers performed based on survey results allowed eliminating water production in both wells.
 The evaluation methodology is cost effective because it does not require wells to be shut in and it can be applied riglessly. The acquired data and integrated evaluation logs can help the reservoir development team to optimize well performance and improve reservoir management in the field.