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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 Formation evaluation can become complex when the invading mud-filtrate properties are unusual, variable or unknown like in sodium potassium (Na/K) formate water base mud (WBM) environments. In these situations, computed reservoir properties are adversely affected and become strongly dependent on the formation invasion status. The Permian age reservoir discussed in this paper, consists of highly unconsolidated heterogeneous sandstone sequences, saturated with condensate rich gas. From a drilling engineering perspective, the shales are often unstable, requiring high mud overbalance to maintain hole stability in wells with high inclinations, which resulted in recurrent differential sticking incidents. The use of formate based drilling fluids in this field, gained acceptance over time, primarily to minimize drilling problems. The downside of formate muds, however, is that log data interpretation encounters serious challenges because of the uncertain petrophysical properties of the mud, affecting log measurements in two ways. The first are those effects related to the mud present inside the borehole and surrounding the tool, or so-called environmental effects. The second are those related to the invading mud-filtrate present inside the formation, resulting in pessimistic porosity, mineralogy and permeability estimates. This paper shows how Na/K formate WBM filtrate effects can be identified and eliminated using Logging-While-Drilling (LWD) time-lapse data acquisition and analysis to provide time-independent logs in a manner that renders the logs immune to various mud-filtrate effects. These logs, together with a corresponding new petrophysical model, make it possible to do away with the mud-filtrate petrophysical properties, and to solve for porosity, mineralogy and fluid saturations from standalone nuclear measurements, irrespective of the formation invasion status. Moreover, the results demonstrate how valuable LWD time-lapse data acquisition can be, and that data acquired while drilling – especially resistivity data in this instance – are important to validate this novel formation evaluation interpretation approach.
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.