TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThrough-tubing carbon-oxygen (C/O) logging is a popular means for reservoir monitoring since a slim logging-insidecasing tool was introduced. The tools are available in 2.5 inch and 1.6875 inch outer diameters. Both the tools log inside of casing to quantitatively determine fluid saturation within the formation. In the absence of any other external information, the C/O technique has limitations when the survey is carried out inside the tubing. However, at times this becomes necessary when the reservoir to be evaluated is covered with both tubing and casing. There has been limited use of the slim logging-inside-casing tool for completions with both tubing and casing. This application has augmented the C/O methods of saturation estimation for measurements made inside the tubing. The present work documents the results of a pulse neutron logging operation carried out for estimation of the remaining oil saturation of a reservoir covered with tubing and casing. Both the inelastic capture and the sigma survey were recorded in this well. Careful planning was carried out for achieving an oil saturation precision of around 7 saturation units. The interpretation of the lithology from both the open and the cased hole logs is discussed. A new method was used for estimating the permeability from the cased hole spectroscopy logs. The saturation profile estimated from the C/O log is integrated with the estimated permeability results. The saturation results are in agreement with field observations and also demonstrate that bypassed reserves can be estimated on the basis of pulse neutron logging carried out inside tubing.

Open hole log evaluation has been traditionally used for formation evaluation purposes and is commonly used for reservoir characterization. Adverse hole conditions precluded use of these services. Under these circumstances, it becomes necessary to acquire the necessary log data after the well is cased for reservoir evaluation. Cased hole logs provide answers with acceptable uncertainty in characterized formations. However, in cased wells, which are not well characterized, the results tend to have a higher uncertainty. In one of the wells in Egypt the operator could not acquire the data in the open hole section because of adverse hole conditions. High quality cased hole data was acquired in the interesting section even in difficult borehole condition (heavy wash outs etc). The measurements are compared with the available open hole data and the responses explained. All the data which could have been acquired in the open hole was acquired in the cased hole with the available cased hole sensors.. Based on the data from the cased hole the bore hole condition at the time of casing the well was predicted. We also demonstrate that gaseous hydrocarbon can be identified from the cased hole epithermal neutron measurements which compared well with the resistivity and the density neutron separation. Reliable matrix density values have been estimated from the cased hole spectroscopy providing a reliable porosity values from the cased hole density. Reservoir parameters have been estimated in the cased hole section. It was possible to devise cost effective planning for completing the well based on these parameters. The ability to provide cased hole measurements helped the operator in avoiding a costly side track. Introduction Open hole formation evaluation from open hole logs has been the standard in formation evaluation for many years. During the last five years we have seen a trend in using some of the open hole services in cased hole for making a meaningful formation evaluation. These measurements have also been strengthened with the addition of tools exclusively for cased hole services. E & P companies always prefer to have the open hole logs for estimating the reservoir parameters. On numerous occasions, the risk of open hole logging is high. It makes economic sense to conduct logging operations after the well has been cased under those conditions. This paper describes the results of the analysis behind casing carried out for one of the operators in Egypt. The operator could not record open hole logs in the zone of interest because of bad bore hole conditions. The alternative was to side track the well so that necessary data can be acquired in the zone of interest. This was not a viable alternative since there was no guarantee that the well condition would improve while drilling the side track. After carrying out a detailed techno economic evaluation it was decided to case the well and run the fairly comphrensice suite of analysis behind casing services (ABC) for detailed formation evaluation. The basic services consist of the cased hole formation resistivty (CHFR(*), cased hole formation density (CHFD*), cased hole formation porosity (CHFP*). In addition to these basic services the client also reorded the DSI* and the ECS* for estimating the sonic slownesses and derivingt the lithology from the spectral measurements respectively. In this article we discuss the comparison of the basic open hole and the cased hole logs are discussed. The petrophysical results from the open and the cased hole are analyzed. A "synthetic density" log was also computed from the continuous grain density estimated from the spectroscopy measurements. There was a good correspondence of the match between the synthetic density and the cased hole density. The CHFP was also used for identification of gas bearing zone from zones and were confirmed by testing results.

Specifying the perforation intervals and evaluating the productivity of thin-bedded sands and shales is crucial for well completion cost optimization. This requires the accurate identification of hydrocarbon-bearing sands and their contribution to production. Relying only on borehole-imaging tools to select the productive intervals is not suitable in this lithologic type because of the difficulty of permeability quantification. In this paper we present a technique to integrate the detection of hydrocarbon-bearing sands with water saturation information and an estimation of permeability. Hydrocarbon-bearing sands are detected by high-resolution resistivity from borehole-imaging tools combined with water saturation from openhole logs (OHL), and permeability from nuclear magnetic resonance (NMR) or a modular dynamic tester tool. We use the geostatistical concept of indicators to convert the inputs from these tools into binary data (0 and 1) based on the best selected cutoffs for those inputs, where a value of 1 means that location is good to perforate. The results of this integration are compared to the results from the production logging tool that is sensitive to the laminated sand units for evaluating its actual productivity. The best cutoffs to select for those parameters are in good agreement with the production logging tool results. The result is a set of optimized perforation intervals consistent with all the data. In addition to the certainty percent associated with the selection of perforation intervals. Three gas wells producing from the same formation were used to apply this technique. One of the three wells was used to select the best cutoffs. For the other two wells, we used the same cutoffs to select the best perforation intervals and determine the certainty associated with them. The correct selection of the perforation intervals from the two wells was confirmed with the production testing and production logging results. Introduction High-resolution resistivity (SRES) tools are essential to identify the hydrocarbon-bearing layers in thin-bedded formations. However, hydrocarbon-bearing layers are not necessarily productive layers. Recently it was noticed that exploration and production (E&P) companies are relying on the borehole imaging tools to identify the perforation intervals. However, we have noticed from the production logging results performed across these formations that relying only on one tool to select the perforation interval is not the best approach. We saw the need to integrate different tools to assist in selecting the perforation and assessing the uncertainty associated with this selection. The following parameters have great impact in selecting the perforation intervals in thin-bedded gas reservoirs:The high-resolution resistivity to detect the thin sand bedsThe permeability for the productivity of the sand bedsThe water saturation from conventional openhole log interpretation for the hydrocarbon in place quantification. The objective of this study was to select the perforation intervals based on the integration between these three parameters. Thus, it was important to know how we can integrate these independent parameters with completely different dimensions to select the correct perforation intervals. Since our objective was to select specific intervals for perforation, we used the concept of an indicator1 to get a vertical indicator map for each parameter. An indicator of 1 means the location is a good candidate for perforation, and 0 means it is not a good candidate. The indicator map of each parameter depends on the threshold or the cutoff values selected for each parameter that will be selected based on the production-logging tool for the key well.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractOpen hole log evaluation has been traditionally used for formation evaluation purposes and is commonly used for reservoir characterization. Adverse hole conditions precluded use of these services. Under these circumstances, it becomes necessary to acquire the necessary log data after the well is cased for reservoir evaluation.Cased hole logs provide answers with acceptable uncertainty in characterized formations. However, in cased wells, which are not well characterized, the results tend to have a higher uncertainty.In one of the wells in Egypt the operator could not acquire the data in the open hole section because of adverse hole conditions. High quality cased hole data was acquired in the interesting section even in difficult borehole condition ( heavy wash outs etc). The measurements are compared with the available open hole data and the responses explained. All the data which could have been acquired in the open hole was acquired in the cased hole with the available cased hole sensors.. Based on the data from the cased hole the bore hole condition at the time of casing the well was predicted..We also demonstrate that gaseous hydrocarbon can be identified from the cased hole epithermal neutron measurements which compared well with the resistivity and the density neutron separation. Reliable matrix density values have been estimated from the cased hole spectroscopy providing a reliable porosity values from the cased hole densityReservoir parameters have been estimated in the cased hole section. It was possible to devise cost effective planning for completing the well based on these parameters.The ability to provide cased hole measurements helped the operator in avoiding a costly side track. .

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