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Antonsen, Frank (Statoil) | Barbosa, Jose Eustaquio Pampuri (Statoil) | Morani, Beatriz (Statoil) | Klein, Katharine (Statoil) | Kjølleberg, Marie (Statoil) | McCann, Andrew (Statoil) | Olsen, Per Atle (Statoil) | Constable, Monica Vik (Statoil) | Eidem, Morten (Statoil) | Gjengedal, Jakob Andreas (Statoil) | Antonov, Yuriy (Baker Hughes) | Hartmann, Andreas (Baker Hughes) | Larsen, David (Baker Hughes) | Skillings, Jon (Baker Hughes) | Tilsley-Baker, Richard (Baker Hughes)
Statoil faced significant well placement challenges while drilling the first development wells on the Peregrino field, offshore Brazil, resulting in lower sandstone contact and production than expected. Efficient drainage from the gravity flow sandstone on this heavy oil field requires a high level of sandstone contact. The need for a deeper azimuthal LWD-measurement was identified as necessary for Peregrino to increase sandstone content in the horizontals by improving the ability to steer within relatively thin sandstone bodies, or to identify and drill neighboring thicker sandstone bodies above or below the well trajectory.
Statoil started a technology collaboration project with Baker Hughes in 2011 to accelerate the development of an extra-deep azimuthal resistivity measurement to address the Peregrino well placement challenges. The first wells utilizing the new LWD technology were drilled in 2012, and the technology has been applied in more than 20 wells on Peregrino so far. This valuable experience is currently transferred to fields on the Norwegian Continental Shelf (NCS).
The extra-deep azimuthal resistivity (EDAR) tool enabled Statoil to avoid pilot holes for stratigraphic control and landing, and to enhance the proactive geosteering within the complex Peregrino reservoir sandstone, resulting in increased reservoir exposure and production. The extra-deep look-around measurements, sensitive to contrasts 20 m from the wellbore or more in favorable conditions, is bridging the gap between traditional wellbore measurements and seismic data; by integrating these data types, interpretation of the reservoir structure and geometry can be refined, resulting in better constrained reservoir models and an improved field development strategy.
This paper presents examples of extra-deep resistivity measurements from reservoir sections drilled on Peregrino to illustrate the technology development, well placement experiences and learnings pertaining to real-time interpretation and geomodel updates. The initial experiences from the Norwegian Continental Shelf will also be presented to explain how the technology works in various geological settings.
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.
Larsen, David Selvåg (ENI Norge AS) | Hartmann, Andreas (ENI Norge AS) | Luxey, Pascal (ENI Norge AS) | Martakov, Sergey (ENI Norge AS) | Skillings, Jon (ENI Norge AS) | Tosi, Gianbattista (ENI Norge AS) | Zappalorto, Luigi (ENI Norge AS)
Abstract Goliat is an ENI Norge-operated oil field located in the Arctic Barents Sea, 85 km NW of the city Hammerfest (Fig. 1). The Goliat reservoirs have a complex structural setting characterized by a large number of faults and a relative high structural dip towards the flank of the structure. This challenging combination calls for horizontal production wells for effective drainage. The Goliat field consists of several proven hydrocarbon reservoir units, but as of the date of this abstract, only Kobbe producers have been drilled. The Kobbe Formation is of Middle Triassic age and is divided into two main subgroups; the Upper Kobbe represents essentially a prograding deltaic system with mouth bars and tidal influenced lobes. In the Lower Kobbe, the system shifts into a more proximal, heterogeneous fluvial setting where sand bodies have limited lateral continuity. One particular challenge is that the well design requires the 8½-in. reservoir section to be initiated in the overlaying Snadd shale. To minimize shale exposure in the landing section aggressive build-up rates are employed, decreasing the length needed in shale. However, a steep approach may lead to deeper penetration in upper Kobbe sandstone, which can result in unwanted intra-shale drilling. Therefore, the key to successful well placement is the early detection of the reservoir top and the accurate mapping of the reservoir sand architecture remote to the wellbore. One way to successfully navigate a complex reservoir like Goliat is to use extra-deep azimuthal resistivity (EDAR) which can detect stratigraphic boundaries up 30m away from the wellbore in optimal resistivity environments (Hartmann, 2014). The development of advanced multi-component inversion modelling techniques (Sviridov, 2014) enhances the interpretations of resistivity data and can accurately provide real-time information regarding reservoir geometry. On Goliat, the EDAR service provided the capability to detect the top of the reservoir at about 20 m true vertical depth (TVD) and nearly 100 m MD before entering the reservoir, enhancing accurate wellbore landing. Extra-deep measurements also helped reduced the uncertainty in fault detection, where related throw can be estimated based on the displacement of boundaries. The use of a measurement with increased depth of detection (DOD), combined with advanced multi-component inversion while drilling techniques and real-time 3D visualization of data and reservoir model were vital to ensure the successful placement of the well. Real-time mapping of the reservoir geometry was key to optimize reservoir exposure.
Ronald, Andy (BP Exploration Ltd) | Rabinovich, Michael (BP Exploration Ltd) | Ward, Mary (BP Exploration Ltd) | Gordon, Miriam (BP Exploration Ltd) | Bacon, Robert (BP Exploration Ltd) | Tilsley-Baker, Richard (Baker Hughes, a GE company) | Wharton, Paul N. (Baker Hughes, a GE company) | Mosin, Anton (Baker Hughes, a GE company) | Martakov, Sergey (Baker Hughes, a GE company)
The benefits of extra deep azimuthal reading logging-while- drilling (LWD) resistivity tools have been well documented previously in several papers which outlined the advantages of using these types of data to avoid the need for pilot holes and unplanned side-tracks. Typically, the focus of these tools is to land-out the well in a particular target sand and to then maximise net sand length in the well bore.
This paper will demonstrate additional benefits that these types of measurements can offer which include; reducing seismic depth uncertainty whilst increasing the confidence of the reservoir boundaries; and providing more information on the depositional architecture of the reservoir to aid integrated subsurface description. Cost savings can also be realised using these measurements, not only by mitigating pilot holes and unplanned sidetracks, but by increasing the confidence of a geological model during drilling thereby allowing an increased drilling ROP and eliminating costly delays e.g. waiting on interpretation of biostratigraphic data to enable well planning updates to occur.
Finally, this paper will look at the importance of ensuring pre-job modelling is accurate and representative of the types of formations to be drilled, provides alternative scenarios to the reference case model and how case sensitivities can be used to provide models that match the realised outcome, increasing confidence in the results and speeding up the geosteering decision making process.
This work was performed in an offshore Tertiary deepwater turbidite formation, comprising a system of stacked, confined and unconfined sands with complex fill patterns and multiple incision surfaces. The well consisted of 4 individual target sands that dipped to the north and displayed an offset stacking pattern with two sands targeted at the crest and two additional sands down dip. As the downdip target sands were previously unpenetrated, seismic depth uncertainty was large resulting in an opportunity to run extra deep azimuthal resistivity measurements to ensure that the sands could be located and drilled to maximise net sand length in the reservoir section.
High angle wells drilled in turbidite formations can be challenging to geosteer because of the unpredictability of the structure of the formations themselves and because the boundaries between net and non-net intervals are often not distinct due to anisotropic effects. The ability of extra deep directional LWD resistivity tools to remotely detect hydrocarbon bearing reservoir and image the formation boundary when approaching helps to reduce the geological risk. The data from these tools can be quickly and accurately applied to a model which leads to better and more timely decisions that can decrease rig time, reduce costs and increase the probability of drilling a successful well.
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.