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The Tyumen formation is the main hydrocarbon-saturated layer of the Krasnoleninskoe oil and gas condensate field located in Western Siberia. This formation is characterized by significantly changing structural dips and represented as thin, interbedded shale and sandstone layers. Such a formation structure complicates the real-time evaluation of formation properties, well correlation and proper well placement. This paper presents the results of horizontal well drilling at the Krasnoleninskoe field using advanced resistivity logging technology.
Advanced resistivity logging technology is used in field operations for various applications. This technology includes logging-while-drilling (LWD), a deep-azimuthal resistivity tool, and sophisticated data interpretation software. The tool performs multi-component, multi-spacing and multi-frequency measurements downhole. The measurement set can be configured individually for each particular geology and application type to ensure effective operations. Next, these measurements are transmitted to the surface, where high-performance multi-parametric inversion recovers formation parameters of interest in real-time. The inversion software enables the processing of any combination of tool measurements and is based on a 1D layer-cake model with an arbitrary number of layers to operate with complex multi-layer formations.
Besides the complex laminated structure of the Tyumen formation, an additional challenge is the low resistivity contrast between the shale and sandstone interlayers. This factor is typical for many West-Siberian fields; it complicates the resolution of interlayers and degrades the evaluation accuracy of their parameters.
To overcome these challenges, a set of deep-azimuthal resistivity tool measurements, suitable to resolve thinly laminated formations, was identified and transmitted uphole while drilling. Real-time inversion was performed in a user-controlled mode to ensure the careful tracking of geology changes. These results enabled operational geologists to monitor the formation properties during the drilling.
Data inversion software ensured the accurate evaluation of formation properties and structural dips estimation in complex conditions of the Krasnoleninskoe field. Structural dips recovered by inversion significantly differed from values observed at offset wells, i.e., 5 to 12 degrees, instead of 0 to 2 degrees. A perfect match between the measured and synthetic resistivity data confirmed high confidence of inversion results. Moreover, there was a strong correlation between the structural dip angles estimated from resistivity data and derived from LWD natural gamma-ray (GR) image. Many of shale and sandstone layers observed in the GR curves were resolved by resistivity inversion.
The depth of the remote layer detection was estimated during the job; it enabled geoscientists to delineate the reservoir volume that contributed to the tool measurements.
This case study describes the first application of advanced resistivity logging technology in a complex laminated formation of the Krasnoleninskoe field. This technology enables the resolution of thin interlayers, evaluation of their properties and estimation of structural dips in real time. These parameters are important for proper well placement and accurate petrophysical interpretation. The presented technology is able to increase the efficiency of oil recovery in the complex laminated formations of the Russian West-Siberian fields.
The maximum possible distance at which a deep or an ultra-deep Azimuthal Resistivity Tool (ART) senses an approaching boundary is considered to be the Distance of Detection (DOD) of the tool. Here, by “deep” ART or DART, we refer to the azimuthal propagation resistivity tools which have a DOD value of up to 15 to 20 feet as advertised. While for the “ultra-deep” ART or UDART tools, their marketed DOD values are of up to 100 feet or more under similar specifications. The DOD is often quoted in an ideal environment, where the tool is parallel to a single high-contrast formation boundary with the tool being situated in the high-resistivity side and a low resistivity formation on the other side of the boundary.
Questions arise when multiple boundaries are present as in most reservoir environments. For example, what is the DOD in a formation with multiple boundaries? Is the target boundary the primary boundary or the boundary of the highest visibility? What is the sensitivity of the measurements to the primary boundary, and to the target boundary if it is not the primary one?
We start by analyzing the DOD Distribution for different types of tools in single-boundary model. Then we implement a DOD study of these tools in multi-boundary formations. Special emphasis is given on the sensitivity of the measurements to a target boundary if it is not the primary boundary. The non-uniqueness of solution is discussed in multi-boundary model where the inversion model may or may not fit the actual geology.
The analyses are based on a fast inversion and sensitivity calculation algorithm specifically designed for the ART measurements. This implementation enables us to process the measurements of commercial azimuthal tools, Ultra-deep azimuthal tools or combination of them. Key features of the algorithm include: 1) fast modeling and inversion algorithms allow us to simulate or process the measurements in real time; 2) Flexible model assumption in inversion, especially for multi-boundary model inversion; 3) Application of constraints on the inversion model based on the geological understanding and information from other measurements.
Examples are given to illustrate the DOD and sensitivity analysis for more realistic reservoir environments with multiple boundaries. Discussions are made on issues of concerns such as the selection of formation model, and the sufficiency of input measurements in inversion.
Copyright 2012, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Russian Oil & Gas Exploration & Production Technical Conference and Exhibition held in Moscow, Russia, 16-18 October 2012. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract In petroleum exploration, reservoir navigation is used for reaching a productive reservoir and placing the borehole optimally inside the reservoir to maximize production. For proper well placement, it is necessary to calculate in real-time parameters of the formation we are drilling in, and the parameters of formations we are approaching. Based on these results, a decision to change the direction of drilling could be made. Modern logging while drilling (LWD) extra-deep and azimuthal resistivity tools acquire multi-component, multi-spacing, and multi-frequency data that provide sufficient information for resolving the surrounding formation parameters. These tools are generally used for reservoir navigation and real-time formation evaluation. However, real-time interpretation software very often is based on simplified resistivity models that can be inadequate and lead to incorrect geosteering decisions. The core of the newly developed software is an inversion algorithm based on a model of transversely-isotropic layered earth with an arbitrary number of layers. The following model parameters are determined in real time: horizontal and vertical resistivities and thickness of each layer, formation dip, and azimuth. The inversion algorithm is based on the method of the most-probable parameter combination. The algorithm has good performance and excellent convergence due to its enhanced capability of avoiding local minima.
ABSTRACT Laboratory and field data have shown that sedimentary formations can exhibit a surprising amount of induced polarization (IP) effect in the presence of clay, pyrite, or graphitic carbon. The effect can be so strong that the quadrature signal of induction data can be pulled toward the negative direction in an appreciable manner, causing an adverse effect in standard data processing and interpretation of induction data. On the other hand, the strong IP effect makes it possible to determine the dielectric constant at induction frequencies neglected in standard data processing techniques. A pixel inversion-based processing technique enables simultaneous determination of resistivity and dielectric constant in dipping formations using both the in-phase and quadrature signals of induction data. The resistivity log created by the processing can be used in the same way as a standard induction resistivity. The dielectric constant log, a separate output from induction data, provides a different perspective into reservoirs. It introduces an opportunity for novel petrophysical applications, for example, approximating a continuous maturity index of kerogen in unconventional reservoirs, and estimating cation exchange capacity (CEC) of shaly sand formations. The technique is a combination of the maximum entropy and the Occam inversions, which makes the iterative process converge rapidly over a wide range of initial models for resistivity and dielectric constant. The processing considers layering and dipping of the formation systematically by means of a planar-layered model that can dip at a relative dip angle of up to 75°. With this approach, the resistivity and dielectric constant logs obtained are free of layering and dip effects, which often appear in the form of polarization horns or overshoots at large relative dip on standard logs. Using the quadrature signal overcomes the ambiguity of resistivity estimation caused by the strong skin effect in conductive formations. This enables the unique determination of resistivity and dielectric constant over a broad range of formation resistivities with only single array data. The nonuniqueness cannot be resolved without joint use of both shallow and deep arrays in standard data processing. In addition, the large depth of investigation of the quadrature signal makes the inverted resistivity and dielectric constant more representative of the undisturbed zone than the resistivity obtained using only the in-phase signal. The new processing technique has been applied to more than 20 wells for which induction logs were available. Results suggest that the strong IP effect is present in many well-known formations, with the dielectric constant ranging from thousands to hundreds of thousands. Results also confirm the superior quality of the resistivity obtained with the new processing over that of a standard processing technique in a variety of situations. The results from several field cases are analyzed in conjunction with elemental spectroscopy data to shed light on the correlation between a large dielectric constant and clay, pyrite, and kerogen containing graphitic-like carbon structures.
An inversion-based workflow has been developed for resistivity anisotropy and formation dip evaluation using deep directional resistivity and conventional array resistivity measurements in vertical and deviated wells with inclinations up to 60°. The inverted anisotropic resistivity profile can be used in reservoir characterization, to identify low resistivity pay, large scale formation dips, and to aid in refining the model of the overburden thereby improving Controlled Source Electromagnetic measurement interpretation.
The workflow includes inversion-based calibration of harmonic resistivity responses. The measurements are processed in a parallel multi-step workflow based on parameter sensitivities to avoid noise propagation into less sensitive parameters. The workflow is validated on synthetic anisotropic Oklahoma formation models for a range of inclination angles from 0° to 60°. Furthermore, the processing of field data from a vertical well has shown very good agreement with the wireline triaxial induction-derived anisotropic resistivity profile acquired in a nearby well.
Presentation Date: Wednesday, September 27, 2017
Start Time: 3:05 PM
Presentation Type: ORAL