Tech Paper: Mapping the Bakken with Azimuthal Gamma Ray

New, cost-effective measurement allows for better unconventional well placement in difficult-to-interpret situations

This paper defines current geosteering practices in the Middle Bakken formation using conventional gamma-ray detectors and discusses the use of a new azimuthally sensitive gamma-ray sensor for more accurate well placement in the target formation.

Two wells were drilled in the Middle Bakken formation using both a conventional gamma-ray detector and a new azimuthally sensitive gamma-ray sensor equipped with an inclinometer to provide continuous inclination. Because omnidirectional gamma-ray measurements can be ambiguous, especially when markers have similar gamma-ray readings, azimuthal gamma-ray wellbore images were used to infer the relative stratigraphic movement of the drilling assembly through the formation.

The two lateral wells presented in this study were drilled entirely inside the target zone between the objective gamma-ray markers. Both real-time and memory data were analyzed using borehole imaging software. Relative and true formation dip angles were calculated after estimating the best depth-of- image. The use of azimuthal gamma-ray images made it possible to determine if the wellbore was moving up or down stratigraphically. A more accurate geological correlation based on the image interpretation, together with an enhanced survey using continuous inclination, made it possible to map the top and base Middle Bakken surface locations. A comparison was established with laterolog resistivity images from the same area that were of higher resolution and higher cost, validating the use of azimuthal gamma-ray for dip calculation.

The azimuthal gamma-ray measurement provides insight into stratigraphic well placement beyond what can be determined from omnidirectional measurements. Data acquired from the gamma-ray image, when combined with enhanced directional-survey measurements, can help to further refine geosteering decisions and reduce uncertainty in wellbore placement.

This paper presents an application of a new, low-cost measurement to allow for better unconventional well placement in difficult-to-interpret situations. As this technique is more widely applied, it may lead to a step change in how lateral wellbores are positioned stratigraphically to increase reservoir exposure.
Click below to view further details and download the technical paper (PDF).

Download SPE-183150



Source: International Petroleum Technology Conference, 14-16 November, Bangkok, Thailand

Authors: Susana Gutierrez Carrilero (Halliburton) | David Hinz (Halliburton) | Gordon Moake (Halliburton) | Timothy Parker (Halliburton) | Dan Carson (Petro-Hunt, LLC.)


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