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To meet the increasing energy demand of the world and with the advent of new technologies, operators have been drilling increasingly challenging hydrocarbon pockets to increase recovery of existing assets. New technologies have been developed to achieve a higher degree of accuracy in well positioning and ministering the aspiration supporting the objectives of producing from otherwise impossible targets. Total E&P Angola, operator in Block-17 in offshore Angola, had launched the CLOV development over four fields: Cravo, Lirio, Orquidea and Violeta, located approximately 140 km from Luanda in water depths ranging from 1050 m to 1400 m. With a focus to develop a highly faulted compartment of the Orquidea field, the ORQ-554 well was planned through a series of faults to achieve the desired drainage length within the unconsolidated channel sands of the Oligocene reservoir. The lack of drilling information for the compartment along with poor seismic resolution of the highly faulted structure owed a high level of uncertainty of ±30 m true vertical depth (TVD) in positioning the well and thus the well could miss the target reservoirs if not calibrated with respect to the structure. The above challenges, in addition to uncertainty in the reservoir position, orientation, and overall geological structure, were necessitated a technology that could bridge the gap between conventional logging and seismic data. A new directional electromagnetic (EM) logging-while-drilling (LWD) service with a radial depth of investigation on the order of ±30 m has been introduced to allow early detection and mapping of the approaching reservoir with sharper resolution than obtained with seismic measurements and to add important new pieces to the reservoir characterization puzzle. The multilayer inversion coupled with deeper depth of investigation, allowed for the marriage in of seismic and borehole data, leading a more effective and productive wellbore. This paper will highlight why deep directional resistivity is a step change for doing proactive well placement of highly deviated wellbores as well as for gaining a larger-scale reservoir understanding. Based on the BHA design, the tool was able to provide a resistivity map of the reservoir up to 20m away from the wellbore, detecting multiple layers to improve understanding and in turn support the characterization of the reservoir beyond seismic structural and near-wellbore petrophysical information. In addition, the improved reservoir delineation resulted in more accurate geological models, reserve estimates, and potential improvements to the completion design.

Since the introduction of the first micro-electrical imaging tool in 1986, wireline resistivity images have proven to be an invaluable tool for geological and petrophysical formation evaluation in wells drilled with conductive water-base drilling mud (WBM). However, until recently, wellbore images acquired in non-conductive mud had been met with some less success due to poor borehole coverage, relatively low image resolution and electrical artefacts. In 2014, an OBM-adapted imaging tool was introduced. The new tool was designed to provide improved resolution and borehole coverage as well as geological representativeness of the images. From an operations perspective, the tool sonde and hardware were designed to increase robustness and ease of logging for field engineers, and to improve operational efficiency and reduce rig time in consideration of high spread rates for deep-water drilling rigs and the overall high costs of deepwater wells. The sonde design with two sets of pads supported by spring loaded arms allow both logging down and logging up of the tool to minimize logging time. Unlike previous imaging tools, pads are applied to the formation using spring load and not pad pressure, in order to minimize stick-slip of the tool. Pads are fully gimballed, are free to tilt, and rotate around the pad axis to enable maximum contact with the borehole wall. As for the measurement physics, a high frequency current is sent into the formation which reduces the non-conductive mud electrical impedance. Amplitude and phase of this current are measured and used in the processing to create an electrical impedivity measurement. In order to cover the full range of formation resistivities, two frequency ranges are used. After acquisition, a "composite" processing technique is used in which amplitude and phase measurements from the two frequencies are processed to generate a final impedivity image that is a function of formation resistivity and dielectric permittivity. The case study presented in this paper is an Oligocene-Miocene age deep-water turbidite deposits on the passive margin of West Africa, and comprises a complex of channels and sheet sands with localized intense faulting, and tilting due to salt tectonics and diapirism. The high-resolution image enabled highconfidence classification of geologic features. The variety of geologic features ranges from fine-scale laminations and syn-depositional micro-faults with displacement of a few centimeters to variable-scale injectite features and erosive surfaces. Also, a wide variety of formation textures that represent turbidite channel and levee facies are observed, and include coarse-grained basal conglomerates, rip-up clasts and large clay clasts, debrites, dewatering and flame structures, dish structures, internal injectite structures, pyrite nodules/streaks, and deformed facies. The high resolution image can be used for a wide range of quantitative image analyses such as net pay computation, textural attribute extraction, as well as other quantitative and semi-quantitative interpretations. Today, with more than 13 case studies in West Africa and more than 250 worldwide, the image quality from this new formation imaging technology shows a great deal of improvement over previous generations of non-conductive mud imagers. The ultrahigh-resolution images from the new imaging service enables a wide spectrum of interpretations that can be directly incorporated to enhance the reservoir model and reduce geological and petrophysical uncertainties.

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