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One of today challenges to increase reserves and gas production in Argentina is to develop low permeability reservoirs, with particular characteristics regarding reservoirs considered as conventional. Therefore assessment and characterization of tight gas reservoirs should be conducted differently from conventional reservoirs, adapting data acquisition, processing and interpretation to these low permeability reservoirs. In a tight gas field operated by Petrobras in the Neuquen basin, an adapted methodology is implemented for analysis and integration of data in order to identify the best areas of the reservoir, called "sweet spots", to assess their potential and optimize completion programs. The field has 7 wells with data acquired from the 70's to recent days. Petrophysical analyses on rock samples are scarce and unrepresentative related to the total sand thickness of Punta Rosada Formation, and were conducted with an inappropriate methodology for this type of reservoir. The set of logs shows strong variation both in used technology and in the acquisition. Thus in new wells it has been decided to acquire new logs and rock samples in order to characterize these tight gas reservoirs with an adapted methodology allowing the identification of the "sweet spots". This paper shows the results obtained with this methodology that uses information from petrophysical laboratory analysis and well-logs (including conventional logs, image logs and NMR). This "tight gas" methodology is based on the integration among capillaries pressures with NMR logs and interpreted data from conventional logs. Finally, to validate this petrophysical characterization, the rock types obtained with the new methodology are compared with the results of production tests and PLT logs.

Unconventional shales reservoirs are complex in terms of composition, variable scales of analysis (from centimeter to nanometer) and petrophysical properties. To characterize these reservoirs, detailed analyses are required, including studies of rock samples in a wide range of scales. Extracted from a shale gas well (El Mangrullo Field, southwest of Neuquén Basin), the studied core involves a 123 m thick section within the lower enriched section (informally subdivided into Cocina, Parrilla, Orgánico Inferior y Orgánico Superior intervals) of Vaca Muerta Formation. This study consists in processing, interpreting, and integrating all the information from routine petrophysical laboratory studies (Tight Rock Analysis - TRA), well logs and high-resolution rock analysis (Digital Rock Analysis - DRA) using a customized and tailored workflow that provides quantitative and qualitative results. Permeability, total and effective porosity, organic porosity, and their distribution and another petrophysical properties (like pore size distribution, etc.) are characterized. The integration of the laboratory and DRA results allows the elaboration of a permoporous properties model. This model allowed us to integrate petrophysical model with the production of horizontal wells drilled in different sections of Vaca Muerta Formation.

Atlas b) Stratigraphic, such as paleo-currents, reservoir geometries, widths and sedimentary paleoenviroments. TX 75083-3836, U.S.A., fax 01-972-952-9435.The identification of high-water-saturation zones in a reservoir is an important task but it has proven to be very difficult if it is based only on logging interpretations. The intention of this study is to include the response from electrical images for the identification of high-water-saturation zones which may produce high volumes of water or only water.Some special responses from borehole electrical images were observed in some wells of Borde Montuoso and Puesto Hernández fields in the Neuquén basin. The integration of openhole logs data, core studies and production information proved to be a useful complementary tool for the accurate identification of high-water-saturation zones and oil-water contacts. AbstractTraditionally, wellbore images logs have been used to perform structural and stratigraphic analyses. This study presents an approach of the resistivity image oriented to the identification of aquifers, further enlarging the application scope of this tool. From the analysis of borehole resistivity image logs, special image characteristics were observed, which were not related to their traditional application. Consequently, an analysis was carried out integrating well logs and interpreted core data for two different areas and formations located in Argentina in the Neuquén Basin: once at Lower Troncoso Member of the Huitrin Fm (Aptian), and the other at the Sierras Blancas Fm (Kimeridigian). This particular response from resistivity images was calibrated to reservoir zones with high water saturation, corresponding to aquifers.Hence, the objective of this work is to provide information about the use of a tool with high vertical resolution and accurate readings and which under certain conditions can be used for the identification of high-water-saturation zones.

Traditionally, wellbore images logs have been used to perform structural and stratigraphic analyses. This study presents an approach of the resistivity image oriented to the identification of aquifers, further enlarging the application scope of this tool. From the analysis of borehole resistivity image logs, special image characteristics were observed, which were not related to their traditional application. Consequently, an analysis was carried out integrating well logs and interpreted core data for two different areas and formations located in Argentina in the Neuquén Basin: once at Lower Troncoso Member of the Huitrin Fm (Aptian), and the other at the Sierras Blancas Fm (Kimeridigian). This particular response from resistivity images was calibrated to reservoir zones with high water saturation, corresponding to aquifers. Certain features were observed in the studied cases which constitute a condition for positively identifying aquifers by means of borehole electrical images. These are as follows:Clastic reservoirs (sand/clay).Reservoirs with good petrophysical conditions.Drilling mud salinity values similar to formation water salinity values. The high resolution rendered by this image logging tool makes it possible to identify high-water-saturation zones and accurately locate oil-water contacts. No special processing is required, and decisions can be made based on the direct observation of the recorded image. Introduction Traditionally, wellbore images logs have been used to perform two kinds of interpretations:Structural, such as the determination of paleo-stress fields, faults and fractured reservoirs analysis.Stratigraphic, such as paleo-currents, reservoir geometries, widths and sedimentary paleo-enviroments. The identification of high-water-saturation zones in a reservoir is an important task but it has proven to be very difficult if it is based only on logging interpretations. The intention of this study is to include the response from electrical images for the identification of high-water-saturation zoneswhich may produce high volumes of wateror only water. Some special responses from borehole electrical images were observed in some wells of Borde Montuoso and Puesto Hernández fields in the Neuquén basin. The integration of openhole logs data, core studies and production information proved to be a useful complementary tool for the accurate identification of high-water-saturation zones and oil-water contacts. Hence, the objective of this work is to provide information about the use of a tool with high vertical resolution and accurate readings and which under certain conditions can be used for the identification of high-water-saturation zones. STAR Imager[SM]: Measurement Principles. The STAR Imagen[SM] provides high-resolution resistivity formation images in conductive mud systems. Six pads with 24-sensors are mounted on articulated arms, resulting in a total of 144 micro-resistivity measurements, with a vertical and azimuthal resolution of 0.2" (~5 mm). Fig. 1. A known constant voltage difference between the return electrode and pads is used to create a current flow through the formation. The pads and the current electrode are separated by an electrical fiberglass isolator. Control circuitry is used to maintain zero voltage potential difference between the upper part of the tool and the measure electrode. Thus, current is forced to flow into the formation, in a perpendicular way near the pad face. The individual current measurements recorded from each button is a function of the formation conductivity and the voltage applied. These measurements are scaled to resistivity values in order to correlate with conventional resistivity logs. High resolution images are achieved by sampling at a high rate (120 samples per foot) the readings from 144 "buttons" mounted on the 6 pads. Due to the short depth of investigation on this tool (around 0.3 in to 0.5 in, depending on the conductivity of the formation), image log measures the flushed zone (assuming that invasion in the formation occurs).