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Collaborating Authors
Results
Porosity partitioning and flow unit characterization from an integration of magnetic resonance and borehole image measurements.
Pal, Aditi (Schlumberger Asia Services Limited) | Seth, Kapil (Schlumberger) | Guru, Udit Kumar (Schlumberger) | Tiwari, Rajiv Ranjan | Dasgupta, D. (Oil & Natural Gas Corp. Ltd.)
Abstract The petrophysical evaluation of carbonate reservoirs in terms of predicting the hydrocarbon potential is trivial. However, it is difficult to correctly predict the fluid flow in the absence of proper characterization of the different flow units encountered in these reservoirs. The process of identifying the flow units becomes non-trivial in the presence of extensive diagenesis process affecting the original depositional texture. The conventional triple combo logs gives an average response when logged against diagenetically altered zone thus overlooking or under-estimating diagenetic features occurring in micro scale. It becomes imperative to look at both micro and macro scale heterogeneity for evaluation of such reservoirs, which has a direct impact on the production, and water injection scheme of such reservoirs. The NMR data and image based secondary porosity estimation recorded in this well were used for partitioning the porosity into micro, meso and macro porosity. Borehole image logs have been interpreted in terms of defining the connectivity of the features seen on the image. This is then used to define a high-resolution connectivity index. An integrated approach using the NMR and the image is being proposed to identify such high permeability streaks that can explain the production performance or the water injection behavior at a later stage of development of the field. Based on the porosity partitioning technique an improved permeability estimate is made. The production results confirm the findings of this study. Introduction In order to link log data to the hydraulic properties of carbonate reservoirs, the oil industry is seeking better methods for characterizing the carbonates. This lead to the development of a method of carbonate rock classification keeping in mind the following key objectives and needs. Robust permeability analysis from logs Understand reservoir productivity by studying the linkage between log data to hydraulic properties of the carbonate reservoir Permeability prediction from logs is always difficult since no logging tool is available which can make direct continuous permeability measurements. Logging tools, instead, measure a surrogate for it such as a textural estimate from bore hole imaging logs or a pore size estimation from NMR logs. The interplay of multiple properties of the rock such as pore size distribution and texture influence the permeability to the extent to which pore throats are plugged with cement or other materials Numerous studies have shown that there is no direct relationship between the porosity and the permeability of the carbonate system. To understand the permeability of the reservoir a pore classification method may have to be resorted which can explain the production behaviour. The pore system classification would also help in designing a water injection program for such reservoirs. This study uses an integrated approach using the NMR and the micro-resistivity bore hole images for identifying and quantifying the secondary porosity and their impact on the permeability. This technique was validated from the dynamic behaviour of a well and shows promise in understanding the performance of the water sweep at the later stage of field development.
- Asia > Middle East (0.69)
- North America > United States > Texas (0.46)
- Geophysics > Seismic Surveying > Borehole Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- North America > United States > Texas > Permian Basin > Wolfcamp Formation (0.99)
- (22 more...)
Abstract Through-tubing carbon-oxygen (C/O) logging is a popular means for reservoir monitoring since a slim logging-inside-casing 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. Introduction Pulse neutron logging (PNL) is the primary means of identifying unswept and bypassed hydrocarbons in producing oilfields all over the world. In the past operators were often forced to exercise the high cost option of pulling the completion string in order to run the carbon-oxygen logs. This was necessary because no logging tool was rated for saturation evaluation inside tubing or other special completions such as blast joints. PNL are of two kinds. Pulse neutron capture or PNC, which have been available for many years in 1 11/16 inch (42 mm) outer diameter. The interpretation from this tool suffers from reduced sensitivity in low or variable water salinity environments. Pulse neutron spectroscopy logs (PNS) measure the ratio of the carbon and the oxygen and are insensitive to water salinity. The PNS tools are available in both 1 11/16 inch as well as 2.5 inch OD. PNS tools can typically record both the capture and the spectroscopy. The PNC logs are relatively insensitive to the steel bore hole contents because they mainly respond to the thermal neutron capture die away time in the rock formation surrounding the bore hole which is compensated by a time based processing system, but PNS logs on the other hand record a spectrum which comes simultaneously from both the bore hole and the formation and respond to carbon and oxygen atoms in both regions. Several cases have been recorded where saturation results were approximate because the tool was used to log outside it's domain of specifications. As a result of this limitation, successful interpretation was limited to intervals where the C/O response could be calibrated in a known environment. There has been limited characterization of the PNS tools in the tubing and casing environment. As a result of these characterizations the limit of the PNS tools have been extended to cover the completions of tubing and casing. PNS tool was recorded in one of the wells in the Zeit Bay, in Egypt. The zone to be investigated was covered with tubing and casing. Due to non-availability of the work over rig the tubing could not be pulled out and the PNS tool was run inside the tubing. The tool was run both in the capture and the spectroscopy mode. This paper discusses the results of the campaign. The validation of the results has also been discussed.
- North America > United States (0.68)
- Africa > Middle East > Egypt (0.52)
- Research Report (0.34)
- Overview > Innovation (0.34)
- Africa > Middle East > Egypt > South Sinai Governorate > Lagia Field > Nukhul Formation (0.99)
- Africa > Middle East > Egypt > Gulf of Suez > Gulf of Suez Basin > Kareem Formation > Shagar Member (0.99)