Success towards waterflood optimization requires the accessibility of downhole contribution and injection, challenging on the conventional cased-hole multi-zone completion where contribution and injection are gathering through sliding sleeve. This paper will describe the success in defining flow profile behind tubing by utilizing Temperature and Spectral Noise Logging. With response in frequency and noise power when fluid flowing through completion accessories, perforation tunnels and porous media, fluid entry points for producer and water departure point can be located by noise logging. Additionally, conventional temperature logging can usually define degree of intake and outflow along with change in fluid phase as a result of change in temperature. In combination of these implications, downhole flow contribution and injection profile can certainly be determined even though fluid moving in and out through production tubing and casing. Regarding pilot field implemtation in Sirikit field, two multi-zone-completed candidates have been selected, operations were carried-out for producer and injector according to the programs individually designed including logging across perforation intervals and station stops for multi-rate flow, transient and shut-in periods. Longer well stabilization is necessary for injector. In addition to production/injection logging interpretation by incorporating pressure, temperature, density and spinner data, the temperature simulation model is generated to determine downhole flowing/injecting contribution with parameters acquired during logging, for example, pressure and temperature. The other reservoir and fluid properties, e.g. permeability, thickness, hydrocarbon saturation, skin, heat conductivity and capacity have been analog based on available data from neighboring areas. Therefore, the historical data on production and injection including nearby well performance may be crucial to define necessary input to the model. In association with the interpretation of noise logging which is utilized in locating contributing/injecting zones, the interpretation strongly relies on acquired temperature data and outputs of temperature simulation model to match with measured temperature profile. However, limitations have been documented when dealing with multi-phase flow, especially in low flow rate condition – considered 5 BPD as a threshold. Sensitivity run with associated paramenters in the interpretation can significantly reduce the number of uncertainties to match with measured temperature profile. Temperature and Spectral Noise Logging to provide input to temperature model can definitely help accessing downhole injection profile for the injector by taking benefit of one phase injecting and having contrast between injecting fluid and geothermal temperatures. This application can significantly improve the waterflood performance and optimization particularly in high vertical heterogeneous reservoirs – thief zones can be identified and shut-off consequently. However, defining downhole contribution for low-rate oil wells producing from multi-layered depleted reservoirs especially in undersaturated condition is still a challenge.
The Sirikit Field, a mature onshore field operated by PTTEP in northern Thailand, derives production from sandstone reservoirs. While production from many of the shallow pays have been well-developed and optimized, comparatively few of the deeper and tighter sands have been similarly produced. Various methodologies have been trialed to enhance production from these tight sands and an examination of results will be presented in the context of geology, engineering and economics. This field, like most in the world, was produced initially by primary recovery (natural flow and various artificial lift mechanisms). Later in the development phase, secondary recovery (waterflooding) was implemented in the Sirikit Main area with the aim of improving production from the shallower, higher permeability, reservoirs. The deeper, lower permeability, sands have not undergone secondary recovery. It is foreseen that the vast majority of STOIIP can be extracted from these tight sands and will ultimately be the future of Sirikit long term production. Several secondary recovery methods were evaluated. Waterflooding was ruled out as an option due to poor reservoir properties which were not favorable for flooding displacement as well as a high injection pressure requirement. The focus then became well stimulation as the main strategy to enhance production from these tight reservoirs. Initial well stimulation technology was the use of larger size perforation guns for the low porosity sands in order to improve reservoir penetration and overcome damage zones. Analysis after field trials showed that the deep penetration perforations had insignificant production improvement. Consequently, solid-propellant technology, which is capable of creating near wellbore fractures, was field trialed. Two types of solid-propellant were tested: "regressive" burning propellant and "progressive" burning propellant. The "regressive" burning propellant results were inconclusive; however, the "progressive" burning propellant results showed clear improvements in production. Moreover, in order to create deeper fractures, "hydraulic fracturing", which requires higher investment, was tested in parallel to the smaller scale investment perforation guns and solid-propellant; however, the results were no better than the "progressive" burning propellant. Consequently, the "progressive" burning propellant provided the positive results at the best economics. Different well stimulation technologies may be appropriate for varying geologic, engineering and economic conditions. For tight or damaged reservoirs, progressively burning propellant may prove to be the most efficient and cost effective technology for secondary recovery.
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