To address the increasing number of slim holes being drilled in the range of 5.75 in. to 6.75 in., a mixed-boreholecompensated (MERC) 2-MHz array resistivity tool with a 4.75-in. collar diameter is described for resistivity measurement-while-drilling (MWD) applications. MERC is a unique technique developed to minimize the effects of borehole rugosity. The new MWD array resistivity tool makes multiple MERC phase shift and attenuation resistivity measurements using five transmitter-to-receiver spacings.Five independent MERC phase shift and attenuation measurements are made at 2 MHz. The five phase shift resistivities have similar vertical responses but with increasing radial depths of investigation. The five attenuation resistivities are also vertically similar but coarser and are radially deeper than the phase shift resistivities. This new array resistivity tool effectively exploits the technology and the interpretation methodology recently developed for wireline induction resistivities and the benefits of multispacing probes for formation evaluation. Most of the petrophysical applications developed in conjunction with the wireline resistivity AlT· Array Induction Imager Tool are illustrated from MWD array resistivity logs acquired while drilling.
Statoil has played a key role in testing and development of the new ultra-deep directional resistivity (DDR) logging while drilling (LWD) measurements for high angle and horizontal wells the last 4 years. Inverted resistivity images provide an overview of geological structures and fluid contacts tens of meters around the wellbore. The ultra-deep look around measurements, sensitive to resistivity contrasts up to 30 m away or even more in favorable conditions, are a step change, when it comes to possibility to position the wellbore strategically in the reservoir and to characterize reservoir structure and properties. This paper will present how the new DDR measurements have been applied with success in an operating license on the Norwegian Continental Shelf (NCS). Long horizontal wells in the reservoir sections have been identified as a key strategy to increase recovery. The main benefits from the DDR measurements in the license have been to maximize reservoir exposure by active geosteering, to optimize well placement above oil-water contact, and to increase subsurface understanding which is important input for future well plans.The DDR measurements are already a commercial service with regard to well placement and reservoir landing. Statoil is however also actively pushing for improved reservoir characterization, by coupling geomodels and DDR modeling and inversion software. This paper will also present how standard LWD logs and images can be combined with the DDR inversion results, to build a near-wellbore 3D structural model supporting all available data. This is an important step towards an extended use of the new data not only for well placement, but also for increased subsurface understanding and geomodel update.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractPositioning a horizontal borehole accurately in the reservoir is critical in maximizing the recovery factor. During well planning, the well path is usually optimized based on structural interpretation of seismic surveys, which often lack resolution and accuracy.More detailed measurements, acquired while drilling, can be used to modify the borehole trajectory to improve its position in the reservoir during drilling. A limitation to geological steering is the relatively small volume of investigation of the traditional logging-while-drilling (LWD) sensors, which can typically probe no farther than a meter into the formation. Unpredictable geological events are therefore, in many cases, detected too late to allow proactive geosteering decisions. Furthermore, traditional drilling and surveying methods do not provide the necessary accuracy to position the wellbore at a fixed distance from fluid contacts over a significant horizontal length.An LWD resistivity device was developed with a much larger radial response that allows the detection of lithology features and fluid contacts that are in the tens of meters away from the borehole. This paper describes the principle of measurement of the new deepVISION Resistivity* * tool, introduces the tool prototype, and proposes a method for computing distance from the tool to boundaries using conductivity contrast. Field test examples from the Grane field (offshore Norway) are also presented. * Mark of SchlumbergerThe new deepVISION Resistivity tool has been tested in several horizontal wells and has demonstrated its capability to accurately determine distance to reservoir boundaries and fluid contacts. The results clearly show the tool's potential for applications such as well landing, geosteering, fault throw estimate, reservoir mapping, and reduction in true vertical depth (TVD) uncertainty.
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