Identifying the Potential Upside of Hydrocarbon Saturation from Electric Logs

2009 ◽  
Vol 12 (01) ◽  
pp. 53-67 ◽  
Author(s):  
Paul F. Worthington
Keyword(s):  
Reservoir Rock ◽  
Log Analysis ◽  
Well Log ◽  
Screening Process ◽  
Type Curves ◽  
Hydrocarbon Saturation ◽  
Shaly Sand ◽  
Well Log Analysis ◽  
Formation Water Salinity ◽  
Petrophysical Evaluation

Summary Validated electrical type curves, which collectively describe a continuum of conductivity behavior of fluid-saturated rocks, allow the petrophysical evaluation of hydrocarbon saturation to be set within a generic reference framework. As part of this process, the type curves permit pre-existing data from other reservoirs to be examined as potential analogs. Through the type curves, a reservoir rock can be classified in terms of its electrical character, specifically adherence to, or departures from, classical clean-sand (Archie) conditions and, by corollary, the degree of any shale (non-Archie) effects. The classification guides the approach to future core-data acquisition and to well-log analysis. In particular, in non-Archie reservoirs the type curves indicate whether the formation-water salinity is sufficiently high for the application of shaly-sand equations for the evaluation of hydrocarbon saturation or whether recourse should be made to a (customized) pseudo-Archie approach. Thus, the type curves are used to ensure that interpretative algorithms are appropriate to the petrophysical task at hand. The application of the type curves, using initializing log data from seven shaly hydrocarbon reservoirs containing relatively fresh formation waters, has illustrated how petrophysical interpretations away from the key intervals can be screened with minimal supporting information through a pseudo-Archie approach. Comparisons of best estimates of hydrocarbon-filled porosity with previously reported values have indicated a potential volumetric upside in all cases, with hydrocarbon saturations being up to 30 saturation units higher for these complex reservoirs. This outcome is attributed to the generic nature of the screening process, which takes account of the electrical character of a reservoir without any of the procedural constraints that are associated with conventional well-log analysis. To reduce further the risk of underestimating hydrocarbon volumes, a set of equivalence charts has been constructed using basic petrophysical properties. The equivalence charts allow a quick-look recognition of any departures from Archie conditions and thence whether the type curves are likely to be required. The screening process has been synthesized into pragmatic workflows, whose adoption should impart additional quality assurance to the petrophysical evaluation of hydrocarbon volumes.

scholarly journals Reservoir quality evaluation of the Farewell sandstone by integrating sedimentological and well log analysis in the Kupe South Field, Taranaki Basin-New Zealand

2020 ◽  
Author(s):  
S. M. Talha Qadri ◽  
Md Aminul Islam ◽  
Mohamed Ragab Shalaby ◽  
Ahmed K. Abd El-Aal
Keyword(s):  
Water Saturation ◽  
Total Porosity ◽  
Effective Porosity ◽  
Log Analysis ◽  
Reservoir Quality ◽  
Well Log ◽  
Shale Volume ◽  
Diagenetic Processes ◽  
Hydrocarbon Saturation ◽  
Well Log Analysis

AbstractThe study used the sedimentological and well log-based petrophysical analysis to evaluate the Farewell sandstone, the reservoir formation within the Kupe South Field. The sedimentological analysis was based on the data sets from Kupe South-1 to 5 wells, comprising the grain size, permeability, porosity, the total cement concentrations, and imprints of diagenetic processes on the reservoir formation. Moreover, well log analysis was carried on the four wells namely Kupe South 1, 2, 5 and 7 wells for evaluating the parameters e.g., shale volume, total and effective porosity, water wetness and hydrocarbon saturation, which influence the reservoir quality. The results from the sedimentological analysis demonstrated that the Farewell sandstone is compositionally varying from feldspathic arenite to lithic arenite. The analysis also showed the presence of significant total porosity and permeability fluctuating between 10.2 and 26.2% and 0.43–1376 mD, respectively. The diagenetic processes revealed the presence of authigenic clay and carbonate obstructing the pore spaces along with the occurrence of well-connected secondary and hybrid pores which eventually improved the reservoir quality of the Farewell sandstone. The well log analysis showed the presence of low shale volume between 10.9 and 29%, very good total and effective porosity values ranging from 19 to 32.3% as well as from 17 to 27%, respectively. The water saturation ranged from 22.3 to 44.9% and a significant hydrocarbon saturation fluctuating from 55.1 to 77.7% was also observed. The well log analysis also indicated the existence of nine hydrocarbon-bearing zones. The integrated findings from sedimentological and well log analyses verified the Farewell sandstone as a good reservoir formation.

Well Log Analysis for Reservoir Characterization of Famenian Carbonates with Criterion of Texture Heterogeneity

2018 ◽  
Author(s):  
Gulnaz Minigalieva ◽  
Albina Nigmatzyanova ◽  
Tatyana Burikova ◽  
Olga Privalova ◽  
Ruslan Akhmetzyanov ◽  
...  
Keyword(s):  
Reservoir Characterization ◽  
Log Analysis ◽  
Well Log ◽  
Well Log Analysis

Well Log Analysis for Reservoir Characterization of Famenian Carbonates with Criterion of Texture Heterogeneity (Russian)

2018 ◽  
Author(s):  
Gulnaz Minigalieva ◽  
Albina Nigmatzyanova ◽  
Tatyana Burikova ◽  
Olga Privalova ◽  
Ruslan Akhmetzyanov ◽  
...  
Keyword(s):  
Reservoir Characterization ◽  
Log Analysis ◽  
Well Log ◽  
Well Log Analysis

Petrophysical Type Curves for Identifying the Electrical Character of Petroleum Reservoirs

2007 ◽  
Vol 10 (06) ◽  
pp. 711-729 ◽  
Author(s):  
Paul Francis Worthington
Keyword(s):  
Water Saturation ◽  
Early Stage ◽  
Well Logs ◽  
Log Analysis ◽  
Well Log ◽  
Formation Water ◽  
Water Conductivity ◽  
Core Data ◽  
Water Saturated ◽  
Petrophysical Evaluation

Summary A user-friendly type chart has been constructed as an aid to the evaluation of water saturation from well logs. It provides a basis for the inter-reservoir comparison of electrical character in terms of adherence to, or departures from, Archie conditions in the presence of significant shaliness and/or low formation-water salinity. Therefore, it constitutes an analog facility. The deliverables include reservoir classification to guide well-log analysis, a protocol for optimizing the acquisition of special core data in support of log analysis, and reservoir characterization in terms of an (analog) porosity exponent and saturation exponent. The type chart describes a continuum of electrical behavior for both water and hydrocarbon zones. This is important because some reservoir rocks can conform to Archie conditions in the fully water-saturated state, but show pronounced departures from Archie conditions in the partially water-saturated state. In this respect, the chart is an extension of earlier approaches that were restricted to the water zone. This extension is achieved by adopting a generalized geometric factor—the ratio of water conductivity to formation conductivity—regardless of the degree of hydrocarbon saturation. The type chart relates a normalized form of this geometric factor to formation-water conductivity, a "shale" conductivity term, and (irreducible) water saturation. The chart has been validated using core data from comprehensively studied reservoirs. A workflow details the application of the type chart to core and/or log data. The analog role of the chart is illustrated for reservoir units that show different levels of non-Archie effects. The application of the method should take rock types, scale effects, the degree of core sampling, and net reservoir criteria into account. The principal benefit is a reduced uncertainty in the choice of a procedure for the petrophysical evaluation of water saturation, especially at an early stage in the appraisal/development process, when adequate characterizing data may not be available. Introduction One of the ever-present problems in petrophysics is how to carry out a meaningful evaluation of well logs in situations where characterizing information from quality-assured core analysis is either unavailable or is insufficient to satisfactorily support the log interpretation. This problem is especially pertinent at an early stage in the life of a field, when reservoir data are relatively sparse. Data shortfalls could be mitigated if there was a means of identifying petrophysical analogs of reservoir character, so that the broader experience of the hydrocarbon industry could be utilized in constructing reservoir models and thence be brought to bear on current appraisal and development decisions. Here, a principal requirement calls for type charts of petrophysical character, on which data from different reservoirs can be plotted and compared, as a basis for aligning approaches to future data acquisition and interpretation. This need manifests itself strongly in the petrophysical evaluation of water saturation, a process that traditionally uses the electrical properties of a reservoir rock to deliver key building blocks for an integrated reservoir model. The solution to this problem calls for an analog facility through which the electrical character of a subject reservoir can be compared with others that have been more comprehensively studied. In this way, the degree of confidence in log-derived water saturation might be reinforced. At the limit, the log analyst needs a reference basis for recourse to capillary pressure data in cases where the well-log evaluation of water saturation turns out to be prohibitively uncertain.

Assessment of gas hydrate using pre-stack seismic inversion in Mahanadi Basin, offshore eastern India

2021 ◽  
pp. 1-42
Author(s):  
Maheswar Ojha ◽  
Ranjana Ghosh
Keyword(s):  
Gas Hydrate ◽  
Rock Physics ◽  
Type Equation ◽  
Seismic Inversion ◽  
Log Analysis ◽  
Well Log ◽  
Seismic Section ◽  
Bottom Simulating Reflector ◽  
Hydrate Saturation ◽  
Well Log Analysis

The Indian National Gas Hydrate Program Expedition-01 in 2006 has discovered gas hydrate in Mahanadi offshore basin along the eastern Indian margin. However, well log analysis, pressure core measurements and Infra-Red (IR) anomalies reveal that gas hydrates are distributed as disseminated within the fine-grained sediment, unlike massive gas hydrate deposits in the Krishna-Godavari basin. 2D multi-channel seismic section, which crosses the Holes NGHP-01-9A and 19B located at about 24 km apart shows a continuous bottom-simulating reflector (BSR) along it. We aim to investigate the prospect of gas hydrate accumulation in this area by integrating well log analysis and seismic methods with rock physics modeling. First, we estimate gas hydrate saturation at these two Holes from the observed impedance using the three-phase Biot-type equation (TPBE). Then we establish a linear relationship between gas hydrate saturation and impedance contrast with respect to the water-saturated sediment. Using this established relation and impedance obtained from pre-stack inversion of seismic data, we produce a 2D gas hydrate-distribution image over the entire seismic section. Gas hydrate saturation estimated from resistivity and sonic data at well locations varies within 0-15%, which agrees well with the available pressure core measurements at Hole 19. However, the 2D map of gas hydrate distribution obtained from our method shows maximum gas hydrate saturation is about 40% just above the BSR between the CDP (common depth point) 1450 and 2850. The presence of gas-charged sediments below the BSR is one of the reasons for the strong BSR observed in the seismic section, which is depicted as low impedance in the inverted impedance section. Closed sedimentary structures above the BSR are probably obstructing the movements of free-gas upslope, for which we do not see the presence of gas hydrate throughout the seismic section above the BSR.

Conventional Well Log Analysis

1985 ◽  
pp. 19-29
Author(s):  
Mihir K. Sinha ◽  
Larry R. Padgett
Keyword(s):  
Log Analysis ◽  
Well Log ◽  
Well Log Analysis
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