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Collaborating Authors
Results
The Dynamics of Reservoir Fluids and their Substantial Systematic Variations
Mullins, Oliver C. (Schlumberger-Doll Research) | Zuo, Julian Y. (Schlumberger HPS) | Wang, Kang (Schlumberger BGC) | Hammond, Paul S. (Schlumberger-Gould Research) | De Santo, Ilaria (Schlumberger Geoservices) | Dumont, Hadrien (Schlumberger NAO) | Mishra, Vinay K. (Schlumberger NAO) | Chen, Li (Schlumberger NAO) | Pomerantz, Andrew E. (Schlumberger-Doll Research) | Dong, Chengli (Shell Exploration and Production Co.) | Elshahawi, Hani (Shell Exploration and Production Co.) | Seifert, Douglas J. (Saudi Aramco)
Abstract Downhole fluid analysis (DFA) is used to characterize compositional fluid gradients, and equations of state (EoS) models are used for analysis to delineate reservoir fluid variations, connectivity and other complexities. A series of reservoirs is examined to assess the state of the contained fluids in terms of thermodynamic equilibrium in the reservoir. Substantial, systematic fluid variations are found using DFA. The cubic EoS is used for gas-liquid analysis, and the Flory-Huggins-Zuo EoS and the Yen-Mullins model of asphaltenes are used for analysis of dissolved solid-solution equilibria of reservoir crude oils. โYoungโ reservoirs exhibit large, nonmonotonic variations of fluids (and solids), moderately aged reservoirs exhibit monotonic, yet disequilibrium properties and โagedโ reservoirs are fully equilibrated even when in massive scale. Nevertheless, these old reservoirs retain significant fluid and organic solid variations as a result of sequential fluid-related processes in geologic time. The dynamic behaviors of fluids within reservoirs that account for these variations are obtained by linking a fundamental understanding of petroleum with basic concepts from fluid mechanics. In particular, the location of tar deposition within reservoirs is clarified when formed due to asphaltene instability upon a secondary reservoir fluid charge. Tar deposition can be formed upstructure for rapid gas charge, as is regularly seen in young reservoirs, or can be formed at the oil-water contact for a slower gas charge, as seen in many older reservoirs. The state of the reservoir fluids within the context of geologic time is shown to be tightly coupled to key reservoir concerns for production. Thus, understanding the context of the reservoir within the overall geology and petroleum system can be used to optimize reservoir evaluation. The expanding capabilities of DFA, plus major advances in asphaltene science, have revealed dramatic systematic variations of reservoir fluids and are becoming indispensable for optimization of production.
- Africa (0.93)
- North America > United States > Texas (0.68)
- Europe > United Kingdom (0.67)
- Asia > Middle East > Saudi Arabia (0.46)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying (0.93)
Abstract Compositionally graded reservoirs are now observed routinely, and analysis of the gradients is used to assess reservoir architecture. Typically, the variation with depth of bulk properties of oil, such as GOR or asphaltene content, is measured and analyzed with an equation of state (EoS). The recently developed Flory-Huggins-Zuo (FHZ) EoS predicts asphaltene-concentration gradients in equilibrated reservoirs, and comparisons of those predictions with measured asphaltene concentrations (typically provided by downhole-fluid-analysis logging tools) have been used repeatedly to assess reservoir connectivity. Crude oil is a highly chemically complex system, containing millions of unique chemical compounds, which cannot be fully described by bulk properties alone. Interpretation of bulk-property gradients therefore requires simplifying assumptions regarding petroleum chemistry. For example, the FHZ EoS relies on the assumption that the chemical composition of asphaltenes is constant throughout the reservoir, even though the concentration of asphaltenes varies throughout the reservoir. In this paper we test that assumption by examining the chemical composition of asphaltenes isolated from different locations in a reservoir with a large gradient in asphaltene concentration (15- fold variation in asphaltene content over a 300 ft depth range). Asphaltenes are analyzed with two advanced chemical analyses capable of measuring various aspects of their chemical composition: sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy, which measures the relative abundance of different sulfur species; and surface assisted laser desorption ionization (SALDI) mass spectrometry, which measures the mass of asphaltene nano aggregates. The results of these analyses indicate that the detailed chemical composition of asphaltenes is not graded, validating the assumption of the FHZ EoS and suggesting that it is appropriate for compositional-gradient analysis even in reservoirs with large asphaltene gradients. On the other hand, the cubic EoS, which requires large variation in asphaltene properties to model such gradients, appears to be inappropriate.
- North America > United States (1.00)
- Europe (1.00)
- Asia > Middle East > Saudi Arabia (0.68)
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.46)
- Reservoir Description and Dynamics (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene (1.00)
- Facilities Design, Construction and Operation > Flow Assurance > Precipitates (paraffin, asphaltenes, etc.) (1.00)
A High-Resolution LWD Resistivity Imaging Tool โ Field Testing In Vertical And Highly Deviated Boreholes
Prammer, Manfred G. (Martin Scientific LLC) | Morys, Marian (Halliburton) | Knizhnik, Sergei (Halliburton) | Conrad, Chris J. (Halliburton) | Hendricks, William E. (Halliburton) | Bittar, Michael S. (Halliburton) | Hu, Guoyu (Halliburton) | Hveding, Frode (Halliburton) | Kenny, Keith (Halliburton) | Shokeir, Ramez M. (Halliburton) | Seifert, Douglas J. (Saudi Aramco, Reservoir Description Division, Expec Bldg) | Neumann, Peter M. (Saudi Aramco, Reservoir Description Division, Expec Bldg) | Al-Dossari, Saleh (Saudi Aramco, Reservoir Description Division, Expec Bldg)
ABSTRACT An advanced logging-while-drilling (LWD) tool has been introduced that combines laterolog-type resistivity measurements, high-resolution resistivity imaging and an "at-bit" resistivity indicator in a compact collar length of 11โ13 ft. The laterolog measurements are compensated by using two opposed transmitters and correspond to diameter of investigations of 12 to 30 in. These measurements are presented as calibrated resistivity images with resolution limits of 0.5โ1 in., depending on sensor aperture size and environment. The full-imaging approach to resistivity logging is particularly well suited for exploratory and appraisal drilling in high-angle and horizontal wells, where beddings with high relative dip angles are prevalent. In these situations, the petrophysical interpretation and reserve computation based on non-imaging, i. e. circumferentially averaging, resistivity measurements require extensive corrections due to bed boundary effects. These corrections in turn are typically based on dip angle estimates from bore hole images. An integrated approach to laterolog resistivity measurements and resistivity images offers an exacter approach to these problems. The tool's petrophysical relevance is further enhanced by providing near-equivalent measurements in 4-3/4 in. and 6-3/4 in. collar diameters. In both tool versions, nine current-sensing electrodes are arranged in a redundant scheme, providing simultaneous laterolog and imaging data. Transmitters and receivers form multiple pairs with spacings of 10 in., 30 in. and 50 in. In addition to these sensors, the electrical current on the collar towards the bit is monitored; this measurement being particularly significant in real-time geo-steering applications. The paper presents the principles of operation of these tools, their key design parameters and the tool and environmental parameters that influence log responses. LWD log examples from vertical and highly deviated bore holes are discussed and compared to wire line electrical imaging logs. Further topics include the calculation and the visualization of complex resistivity profiles and the standard compensation and environmental correction procedures. The achievable image resolution is discussed as well as the environmental parameters that impact detection and resolution limits. INTRODUCTION Resistivity bore hole imaging is an essential element of modern formation evaluation, particularly in high-angle (HA) and horizontal (HZ) wells and/or in complex lithologies. Logging-while-drilling (LWD) in conductive muds is an attractive plat form for electrical imaging devices due to the azimuthal scanning nature of drill string rotation and the rather slow rate of penetration. With suitable instrumentation and processing, the environment can provide for uniform azimuthal sampling and dense "vertical" sampling, with the drawback that a certain (and variable) amount of standoff between sensor and formation is unavoidable. Thus, LWD electrical imaging always incurs a stand -off-vs.-resolution compromise. The first commercially viable LWD laterolog was introduced by Gearhart Industries (Gianzero et al., 1985). Its principle of operation was based on an earlier idea by Arps (Arps, 1967). Based on '80s technology, the Gearhart tool had a single, uncompensated "lateral" reading and also introduced the so-called "axial" or "bit" current indicator. The interpretation of the latter measurement strongly depends on the distance of the tool to the bit and also on formation resistivity and resistivity contrast.
- North America > United States (1.00)
- Europe (0.87)
- Asia > Middle East > Saudi Arabia (0.46)
- Geophysics > Seismic Surveying > Borehole Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)