|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
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.
Tilsley-Baker, R. (Baker Hughes) | Hartmann, A. (Baker Hughes) | Sviridov, M. (Baker Hughes) | Sanabria, O. (Baker Hughes) | Skillings, J. (Baker Hughes) | Kjølleberg, M. (Statoil Brasil) | Barbosa, J. E. (Statoil Brasil) | Loures, L. (Statoil Brasil) | Pearson, P. Swalf (Statoil Brasil) | Morani, B. (Statoil Brasil)
Abstract Extra-deep reading azimuthal resistivity tools have been deployed in various reservoir settings around the world in recent years in an effort to further improve efficiencies in reservoir development. For many years field development relied on standard and azimuthal propagation resistivity tools with depths of investigation up to approximately 5m, contributing to optimized and pro-active geosteering. While effective at geosteering against adjacent boundaries to maintain position in oil bearing formation, more complex reservoir architectures require data sensing further into the formation to allow a closer correlation with seismic models and provide more complete reservoir mapping. The first extra-deep propagation resistivity tools were developed by employing lower frequency waves, increasing antenna spacing and eventually adding lower frequency azimuthal signals. The new designs greatly increased the depth of detection and also added directional components. However, due to the greater volume of formation being investigated, the deeper readings bring extra complexity and uncertainty to the interpretation process so that innovative inversion software is required to support the tools and produce results that can be used in real-time. The inversion method described in this paper for the interpretation of extra-deep azimuthal resistivities employs a-priori constraints and is user-controlled in order to accurately monitor laterally and vertically changing geology. The examples shown here will demonstrate how inversion results based on a full suite of resistivity measurements have brought benefits to reservoir understanding by deriving sandstone thickness, detecting multiple bed boundaries, locating remote sandstones and remote resistivity plus the relative dip between the tool and the formation. The integration of this data results in better constrained reservoir models and an improved field development strategy. This paper will present the results of wells drilled using extra-deep azimuthal resistivity tools on the Peregrino Field in Brazil. The reservoir comprises complex high energy gravity flows consisting of reservoir units difficult to map due to being below seismic resolution. The sandstones have limited lateral extent and thicknesses ranging from 2m to 25m. Originally developed to improve net sandstone drilled in the Peregrino heavy oil reservoir by allowing a more strategic approach to geosteering, the tool deployment has brought additional benefits in reservoir understanding which impact seismic model interpretation, future well planning, completion strategies and reduce the need of pilot holes.
Abstract Drilling operators very often perform reservoir navigation and mapping using extra-deep resistivity tools. Tool responses depend on formation properties tens of meters away from the wellbore and require sophisticated processing by inversion to provide operators with a multilayer resistivity model. The accuracy and reliability of inversion results are very important and need thorough assessment. We present two new methods of inversion quality control, validate their applicability, and provide a comparative analysis with existing methods on several synthetic and field cases. Deterministic and statistical methods of estimation of resistivity, tool detection, and resolution capabilities are applied to evaluate the quality of inversion results. We discuss tool ability to detect single boundary, depth-of-detection (DOD) and depth-of-reliable-detection (DRD) concepts based on covariance matrix analysis, and introduce a new method of DOD estimation based on resistivity model perturbations, with posterior tool response monitoring. We propose a new statistical resolution analysis method related to response-surface technique and compare its results with other approaches. The applicability of the methods considered is validated by guided inversion for typical job stages (pre-well, real-time, post-well) and applications (landing, reservoir navigation, mapping). Inversion results for extra-deep logging-while-drilling (LWD) resistivity tools are usually shown as a multi-layer resistivity distribution map or picture, without a clear indication of the uncertainty of the structures presented on the picture. The uncertainty of inversion results depend not only on tool specifications (i.e., frequency range, electronic noise level and antennae spacings), but on the complexity of surrounding formations as well. The new method for DOD estimation deals with model complexity and gives several estimates based on different subsets of measurements. Common approaches to inversion result quality control only provide partial reliability indicators, usually around the final inverted model. The suggested resolution analysis method generates a statistic from models assessed during inversion execution, analyses it, and eventually provides the resolution accuracy of formation parameters. The method enables identification and quantification of disconnected uncertainty regions, when they exist, thus ensuring an exhaustive analysis of the parameter space. Based on synthetic and field cases considered, we conclude that understanding of uncertainties associated with reservoir navigation requires the application of several data analysis techniques. Complementary use of data inversion, DOD estimation and resolution analysis yield a comprehensive evaluation of the environment and show the realistic capabilities of the tool. The developed methods enabled the implementation of scenario-oriented workflows that deliver not only the final resistivity model but also its reliability indicators. The paper will show how to interpret and evaluate the quality of inversion results provided by vendors. Two new methods to evaluate the result model extend the capability to analyze uncertainty from several different perspectives. Better understanding of the inversion deliverables with the reliability indicators will help the operators to make more confident decisions during reservoir navigation, or posterior oil field development.
Hartmann, Andreas (Baker Hughes) | Vianna, Armando (Baker Hughes) | Maurer, Hans-Martin (Baker Hughes) | Sviridov, Mikhail (Baker Hughes) | Martakov, Sergey (Baker Hughes) | Lautenschläger, Ulrike (Baker Hughes) | Antonsen, Frank (Statoil) | Olsen, Per Atle (Statoil) | Constable, Monica Vik (Statoil)
Extra-deep resistivity has been used successfully since 2004 in Norway for reservoir navigation relative to distant bed boundaries. The need for improved reservoir understanding and geosteering decisions in complex heterogeneous reservoirs has led to the development of a new extra-deep azimuthal resistivity (EDAR) tool. Inversion results of deep azimuthal resistivity measurements are bridging the gap between traditional logging-while-drilling (LWD) measurements and seismic data, and can image reservoir architecture during drilling tens of meters away from the borehole. It is possible to delineate multiple geologic layers directionally away from the borehole with resistivity contrasts without probing the layers directly. The non-unique nature of inversions leads to questions about the reliability and accuracy of the inversion results.
This paper will present measurement and inversion results from an airhang test and a land-based drilling facility, testing the tool and interpretation methodology by comparing results with known geometry. During the airhang test, the tool was suspended at specified distances to a water surface to verify the response. The measured response from this test matched the expectations very well. A field test at a drilling site was conducted to check the performance in a realistic downhole setting. The well was landed horizontally in the target zone using the new EDAR system. The verification step determined the ‘true’ top boundary, which was accomplished by sidetracking from the original hole and penetrating the target top at a point previously interpreted from the resistivity data. The verification tests will be discussed in detail, in addition to a general overview of the hardware and interpretation comprising the measurement.
Tilsley-Baker, Richard (Baker Hughes) | Antonov, Yuriy (Baker Hughes) | Martakov, Sergey (Baker Hughes) | Maurer, Hans-Martin (Baker Hughes) | Mosin, Anton (Baker Hughes) | Sviridov, Mikhail (Baker Hughes) | Klein, Katharine Sandler (Statoil Brazil) | Iversen, Marianne (Statoil Brazil) | Barbosa, José Eustáquio (Statoil Brazil) | Carneiro, Gabriel (Statoil Brazil)
Summary The relatively recent development of azimuthal-resistivity measurements enables proactive geosteering within complex reservoirs. The tools enable determining the distance (up to 5 m in ideal conditions) and the azimuthal direction to a resistivity boundary. In ideal conditions, the well is inside a high-resistivity layer and the shoulder bed is low resistivity, giving geologists warning of approaching adjacent conductive beds. When the tool is in a low-resistivity layer, the depth of detection of an adjacent high-resistivity layer is much smaller. In these situations, it is often not possible to use the tool for effective geosteering. An extradeep-resistivity tool has been used for several years in Norway and has been introduced in the Peregrino Field in Brazil. It operates at lower frequencies than the shallower reading tools, has large transmitter/receiver spacings, and a depth of detection up to 25 m. This tool was deployed in addition to the conventional directional-resistivity instrument. The new application in Brazil was supported by inversion software (still in development) to enable possible interpretation of the geology within the tool range. The inversion results provide information that can help identify adjacent reservoir layers while in the target zone and measure the thickness of the reservoir layer being drilled. Examples are presented from one well where the extradeep resistivity provided early warnings and additional information that helped to steer the well successfully and maximize reservoir coverage. The extradeep measurements from the tool also provide valuable reservoir understanding and knowledge for future well-planning purposes.