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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

Logging-while-drilling (LWD) services are today often provided by several separate tools that, when used in combination, result in some measurements being made far from the bit. Time to make up and break out LWD tools, memory dumping, as well as multiple tool reliability issues can significantly add to the well construction costs. An innovative new LWD tool has been developed to simultaneously provide drilling-related measurements and an industry standard suite of formation evaluation measurements, equivalent to the classic "triple-combo" service, but co-located and closer to the bit, using only a single short collar. This means that less rathole is needed for logging, and fewer collar connections have to be made, resulting in a more efficient drilling operation. In addition, the co-location of the sensors reduces uncertainties in the interpretation of measurements that rely on multiple sensors. A key focus during the development of the tool has been improvement in service delivery. This has been achieved through increased operational efficiency, higher rate of penetration (ROP) capability, significantly improved reliability throughout the system, and greater ease of maintenance. The use of a pulsed neutron source instead of a chemical source also dramatically reduces the environmental and operational risks normally encountered with the use of traditional LWD tools. Pulsed neutron measurements delivered by this service include formation capture cross section (sigma) and elemental analysis from neutron capture spectroscopy. These new measurements are used to compute mineralogy while drilling. Azimuthal measurements are also available, allowing the formation and borehole to be imaged using a variety of properties. The result is a robust and complete interpretation with significantly reduced uncertainty, as well as a large choice of steering methods for effective well placement. In this paper we describe the development of this new LWD service and show field-test examples of improved formation evaluation, increased drilling efficiency, and more effective well placement that the tool has provided. Tool Overview The new tool is a multifunction LWD tool that combines both drilling and formation evaluation measurements in a single collar (Fig. 1). These measurements include APWD* Annular Pressure While Drilling, calipers, gamma ray, resistivity, density, and porosity. At the heart of the new LWD tool is a pulsed neutron generator (PNG) that allows neutrons to be generated only when the tool is powered, eliminating the need for an americium beryllium (AmBe) chemical neutron source. The PNG provides several new measurements to LWD, such as Best-Phi* porosity, a hydrogen index equivalent, elemental capture spectroscopy providing detailed lithology, formation capture cross section (sigma) providing an alternative to resistivity for fluid saturation calculations, and NGD* Neutron Gamma Density, which is a density measurement obtained from the gamma rays generated from neutron interactions with the formation.1 Therefore, the use of a PNG in the new LWD tool gives the option of obtaining nuclear logs without the use of a chemical logging source.

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.