TX 75083-3836, U.S.A., fax 01-972-952-9435.Where tensor resistivity data is available it can significantly improve the geological models used for geosteering. Incorporation of this data can predict anomalies not seen on simple models, which may be interpreted incorrectly resulting in unnecessary wellbore deviations, and loss of reservoir penetration. Examples of these effects, and their magnitude, will be used to demonstrate the importance of incorporating electrical anisotropy in the models.
In order to maximize recoverable reserves in both new marginal satellite developments and bypassed oil in mature fields it is vital that a horizontal wellbore is optimally positioned within the reservoir. Recent innovations in drilling technology, three dimensional (3-D) visualization and logging while drilling (LWD) sensors have been integrated into a Reservoir Navigation Service focusing on maximizing the value recovered from every geosteered well. Introduction Standard geosteering techniques based on layer cake resistivity response modelling1,2,3 have proven to be inadequate for the complex geology of the North Sea. To effectively geosteer these fields a range of innovative techniques have been devised to achieve optimal wellbore placement. In this paper we review four recent successful geosteering projects illustrating the key benefits of developing project specific solutions as summarised below.Integration of the earth model into the wellplanning and wellsite geosteering process significantly reduced time and cost involved. The use of wellsite 3-D visualization assisted the entire asset team in realising the goals of the project.Near bit Formation Evaluation sensors4 were used to characterize formation dip and ensure effective navigation within the reservoir utilizing the improved steerability of Rotary Closed Loop Steerable (RCLS) drilling systems.5Advanced processing and unique interpretation of LWD propagation resistivity data confirmed fracture identification in a fractured chalk reservoir prior to completion6.Four horizontal wells were accurately placed within a 3 to 10ft thick zone for a carbonate reservoir gas storage project by geosteering on effective porosity. These case histories are used to demonstrate how geosteering in complex North Sea reservoirs requires field specific techniques to be developed for both the planning and successful execution of a project. Earth Model Integration into Planning and Drilling Wellplanning Conventional wellplanning techniques require the Geoscience team to select a number of targets defined by their location in 3-D space. The Drilling team then attempt to construct a wellplan satisfying these targets which also takes account of necessary engineering limitations such as torque and drag, dog leg severity (DLS), the practical limitations of proposed drilling tools and completion requirements. To achieve a wellplan that is acceptable to both Geoscience and Engineering needs, an iterative process requiring numerous adjustments is commonly used before a definitive wellplan is approved. To improve efficiency and reduce time and costs involved in generating an approved wellplan it is necessary to develop a service integrating wellplanning into the 3-D earth model. A recent proposal from a North Sea operator required the Directional Drilling / LWD contractor to construct a 3-D faulted geological model centred on a proposed horizontal well. Once an accurate model had been built and verified then the well was planned from the reservoir upwards based on the geological objectives supplied by the operator. The objectives were defined as stratigraphic well position within the Brent sequence for a specific fault block, e.g. in fault block 3 the well should remain in the Ranoch formation as opposed to conventional wellplanning where a geometric target is specified (Fig. 1).
Outcrop analogues are very helpful in generation of the reservoir depositional model but are restricted in their application to formation evaluation. They represent a missed opportunity, in particular in the interpretation of high angle and horizontal (HA/HZ) well log response. In our vision they give us access to the depositional controls on vertical and lateral petrophysical rock properties variations as well as actual geometry of the geological bodies; both matters are critical for confident formation evaluation in HA/HZ well setting. The primary objective of this study is the integration of geological answers and petrophysical information to construct forward models of our high technology LWD datasets. We assign a major significance to the visual comparison of the rock picture and a simulated tool response, supported by a detailed petrophysical analysis. We initially used the Ainsa 1 Pyrenean deepwater turbidite outcrop with the petrophysical properties of analogous offshore West Africa reservoirs. Across-channel geological complexity (thin layering and low NTG in marginal part; pinch-outs, amalgamations and rock property variation in the axial part) is valuable to demonstrate improved strategies of interpretation solutions in channel to lobe turbidite settings. Steps to forward model the LWD data include many of today's reservoir characterization procedures: sedimentological description, lithofacies to petrofacies associations, core and field scale 3D petrophysical properties simulation, upscaling, true resistivity matrix generation and resistivity anisotropy evaluation. Forward modeling of tool response accounts for different measurement natures, geometries and DOI's (from meters in resistivity to cm in radioactivity, images and magnetic resonance). The range of the results acquired shows that basic LWD suites often do not provide an accurate result in a heterogeneous environment. For example, in our case water saturation is overestimated by around 30% total through improper use of the classical data. Our study highlights that reservoir parameterization in the presence of all scales of heterogeneities, sand mixtures and thin laminations is enhanced through proper application of gamma ray, resistivity, density, neutron and NMR for the pore volumetrics and imaging for the geobody shaping. Using the approach to a contrasted West Siberian field case with inherent low resistivity contrast and invasion of WBM demonstrates further interpretational challenges. The work ultimately permits a more confident selection of logging suites and subsequent improvement in application of the acquired data to formation evaluation in high angle and horizontal well situations. Introduction Well log data has a rich and diverse history of successful application in hydrocarbon exploration and production activities. Historically vertical well drilling of minimally dipping formations has prevailed and naturally wireline logging tool design was optimised for this condition. The objective of tool design was based on balancing the ideal of reading virgin formation properties (beyond the ‘damaged’ zone) yet maintaining sufficient vertical resolution to adequately define the geological and petrophysical properties of the rock levels under investigation. With sufficient resolution the vertical well case is rich in information for the vertical dimension as it passes through the geology yet the dataset is more limited in characterising the horizontal change in formation properties away from the wellbore. This is largely due to the restricted depth of investigation of the logging devices as well as the lower variability of the geological depositional processes in the near wellbore horizontal area.
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.