TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractRadioactive chemical logging sources have been used in the E&P industry for many years to help operators obtain valuable information about their reservoirs. Until recently, much of the information obtained using these sources could not be obtained with any other method. While the potential risks involved with the use of such sources have always been known, more awareness in the industry has led to increased efforts towards the reduction or even elimination of the use of chemical sources where possible.A new Logging-While-Drilling (LWD) tool has been developed, using innovative technology to provide a complete suite of formation evaluation measurements without having to use a chemical radioactive logging source. The use of a nonchemical radioactive source significantly reduces the environmental and operational risks normally involved with traditional LWD tools.The data delivered by this service include not only the traditional measurements such as gamma ray, resistivity, density, and neutron porosity, but also measurements not previously available in LWD such as formation capture cross section (sigma) and elemental analysis from neutron capture spectroscopy used to compute formation mineralogy. An entirely new LWD measurement has also been introduced with the tool, making it possible for the first time to determine formation density without the use of a chemical logging source.A case study is presented of a well situated in a field in southern Italy, inside an environmentally sensitive national park. Because of the location of the well, it has not been possible to use radioactive logging sources for formation evaluation. As a result, fully evaluating the reserves has been an ongoing challenge for the operator. In addition, because of the move towards high angle and horizontal wells, wireline

Radioactive chemical logging sources have been used in the E&P industry for many years to help operators obtain valuable information about their reservoirs. Until recently, much of the information obtained using these sources could not be obtained with any other method. While the potential risks involved with the use of such sources have always been known, more awareness in the industry has led to increased efforts towards the reduction or even elimination of the use of chemical sources where possible. A new Logging-While-Drilling (LWD) tool has been developed, using innovative technology to provide a complete suite of formation evaluation measurements without having to use a chemical radioactive logging source. The use of a non-chemical radioactive source significantly reduces the environmental and operational risks normally involved with traditional LWD tools. The data delivered by this service include not only the traditional measurements such as gamma ray, resistivity, density, and neutron porosity, but also measurements not previously available in LWD such as formation capture cross section (sigma) and elemental analysis from neutron capture spectroscopy used to compute formation mineralogy. An entirely new LWD measurement has also been introduced with the tool, making it possible for the first time to determine formation density without the use of a chemical logging source. A case study is presented of a well situated in a field in southern Italy, inside an environmentally sensitive national park. Because of the location of the well, it has not been possible to use radioactive logging sources for formation evaluation. As a result, fully evaluating the reserves has been an ongoing challenge for the operator. In addition, because of the move towards high angle and horizontal wells, wireline formation evaluation acquisition has been, at times, replaced by LWD. The new LWD tool allowed the operator to not only improve efficiency, but also brought with it the possibility of more completely evaluating the diagenetically complex tight carbonate reservoir through the use of the new measurements. The favourable environmental conditions (low temperature and low mud salinity) made it possible to obtain additional spectral data, which was used to correct the neutron porosity measurement for lithology effects, despite the presence of dolomite. The results of the formation evaluation studies are presented, together with an analysis of the impact on operational efficiency and environmental and operational safety as a result of not having to use a chemical logging source. Introduction and Geological Setting Understanding the porosity distribution and type within a reservoir is the first step in order to accurately quantify reserves and design proper field development scenarios. Porosity heterogeneities within complex carbonate sequences can cause the potential of a reservoir to be inaccurately evaluated when only conventional approaches, such as density, neutron and sonic logs, are used. Image logs and surface logging data have been recognized as being essential for correct petrophysical characterization of these reservoirs.

The huge number of horizontal wells drilled in complex reservoirs and the development of more accurate logging while drilling (LWD) technologies offer to the oil&gas companies the opportunity to reduce operational risks and save time and costs, by replacing wireline acquisition with LWD tools. This paper describe a new acquisition strategy based on advanced LWD tools recently made available also in 6" hole size. Thanks to this technology it was possible to provide a reliable reservoir characterization and to identify the best fluid path in horizontal infilling wells drilled into tight and fractured carbonatic reservoir. Economic and HSE aspects have been strongly considered in the illustrated strategy. The integrated analysis of advanced sonic and resistive image while drilling logs provided the essential information to quantify the matrix and the secondary fractured porosity as well as the "mixed" porosity, and, in addition, fundamental data to clarify the reservoir quality where Tough Logging Conditions (TLC) cannot be through. The acoustic compressional arrivals contribute to porosity evaluation while the Stoneley waves interpretation allowed the detection of "open" natural fractures. In addition, recognized "open" fractures have been matched with mud losses events, Gas While Drilling and temperature profile. The producible intervals identified by the illustrated methodology agree with the response of the main production results. The approach has been validated by means of an accurate comparison between wireline and while drilling logs response, both available along an interval of a reference well section. The LWD technology has shown its capability to capture the different scale of phenomena occurring into fractured reservoirs. Thanks to the combination of technology, knowledge and people, well data acquisition can be conducted safely and with significant saving in term of operating time reduction. The additional information about fluid path detection can improve the efficiency of the well completion. INTRODUCTION AND SCOPE OF WORK The strong and continuous need to drill and produce high deviated or horizontal wells in the oil business was a heavy impulse to change vision on tool conveyance method moving from Wire Line (WL) to Logging While Drilling (LWD) acquisitions. The service companies in the last years spent a lot of effort in the LWD tool development and now days the quality and the completeness of the last generation LWD is comparable with the wire line technology in most case, and more useful in others. The operators choose the logging data acquisition strategy, while drilling or after drilling, based on project requirements. The LWD tool application not only can provide good performance but can also be an important opportunity to increase efficiency and safety. Few technologies have had a larger impact on these results than Logging While Drilling (LWD).

A "creative" approach to reservoir characterization is not always the best choice while integration should be the appropriate methodology, if properly planned and developed. This paper describes the integrated sedimentology-petrophysics-geomechanics methodology used to characterize the reservoir and cap-rock that will be interested by gas storage activity at overpressure conditions. The determined data are then used in the modelling phase aiming at evaluating the safe injection/storage maximum operating pressure.The analyzed sequence is located in Central Italy and is represented by sand-shale intervals. The available data are: conventional and high last technology logs, mini-frac tests, laboratory core analysis, sedimentological and fracture description on cores.The advantage of the approach relies in the use, during the different project tasks, of each provisional result to drive the work group for finding the solution which better honours the response of different disciplines, looking therefore for an 'integration on the job'.The two shales, bounding the reservoir, had similar geomechanical properties but different petrophysical ones (different sedimentological process). The overburden ("cap-rock") is mostly massive with maximum horizontal stress direction 155 N while acoustic logs showed also anisotropy surfaces. The underburden shales ("argille basali") show different sedimentological features and diffuse slumping surfaces. The stress direction is similar for both shales, therefore an unique stress profile was needed throughout the layers and the mini-frac/stress tests were used to constraint the minimum horizontal stress. The geomechanical data allowed to derive reliable mechanical and failure parameters. The sand reservoir shows laminations with few fractures. From a geomechanical standpoint, these results allowed a statistical analysis of the main parameters, for the use in the subsequent modelling activities.An earlier integration approach was the key for the quality of a reservoir/sealing sequence characterization for the appropriate and safe storage operation. Scope of workThe option of delta-pressuring, exceeding the discovery pressure in a depleted gas storage field, is one of the most costeffective ways used by Stogit to increase working gas capacity and deliverability. The feasibility study of the "P>Pi Projects" needs to collect new and detailed information about geological and structural features of the field (Bruno et al., 1998).A geognostic well was recently drilled by Stogit in a gas storage field located in Central Italy, expressly targeted to acquire geological information, both in the reservoir and in the cap-rock units. The well will be besides equipped with downhole permanent microseismic and geodetic monitoring network, aimed to check the cap-rock strain and integrity, in order to minimize the risk of gas leakage through the weakest parts of the cap-rock.An integrated petrophysical and geomechanical study has been finally achieved, which contributed, together with the new interpretation ...