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Bloemenkamp, Richard (Schlumberger) | Zhang, Tianhua (Schlumberger) | Comparon, Laetitia (Schlumberger) | Laronga, Robert (Schlumberger) | Yang, Shiduo (Schlumberger) | Marpaung, Sihar (Schlumberger) | Guinois, Elodie Marquina (Schlumberger) | Valley, Glenn (Schlumberger) | Vessereau, Patrick (Schlumberger) | Shalaby, Ehab (Schlumberger) | Li, Bingjian (Schlumberger) | Kumar, Anish (Schlumberger) | Kear, Rick (Schlumberger) | Yang, Yu (Schlumberger)
While they provide a recognized technical advance for wells drilled with oil-based mud (OBM), OBM-adapted microresistivity images of the last 13 years remain far from the geologic interpretability provided by imagers that operate in a water-based mud (WBM) environment. Recently the use of a high-definition WBM imager has been demonstrated in wells drilled with OBM, but its application has been principally limited to high-resistivity formations with excellent hole conditions or to cases where the drilling fluid has been engineered to favor acquisition.
To fill this gap, a new wireline microelectrical imager has been introduced, engineered from the ground up to acquire high-definition, full-coverage images in any well drilled with OBM. The all-new physics architecture includes a strategy to minimize and eventually eliminate the inevitable contribution of the nonconductive fluid and to optimize the mode of operation in accordance with formation parameters. New tool-specific processing steps complement the standard borehole image processing workflow to render highly representative images of the formation.
Examining the measurement response in detail, via both modeling and real-world examples, demonstrates several favorable characteristics, for example, sensitivity to vertical as well as horizontal features, reduction of shoulder-bed effects, and reduced sensitivity to desiccation cracks.
The novel mechanical architecture includes a new sonde design with significant operational advantages. It conveys a sensor array composed of 192 microelectrodes providing 98% circumferential coverage in an 8-in. borehole. The individual microelectrodes are smaller than those of industry-standard imagers for WBM, each with a surface area of only 10.8 mm2, which provides excellent spatial resolution.
From a field test comprising more than 40 operations in various OBM fluids, high-definition images were acquired in a variety of environments, from high-resistivity carbonates to shales and low-resistivity clastics, demonstrating the robustness and widespread applicability of the new tool. The examples include challenging environmental conditions and they explore the limits of accurate measurement. Comparison with legacy images demonstrates that the new physics of measurement coupled with the high-resolution, high-coverage sensor array has achieved much more than a microimaging step change. The new images faithfully reproduce formation geology with photorealistic clarity and promise to revolutionize the geologic interpretation of wells drilled with OBM.
Abstract 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.
Both structural and stratigraphic features are clearly distinguished from the borehole electrical resistivity images. These detailed images allow evaluations and interpretations and have been proven to be invaluable to geoscientists since they were first introduced more than 15 years ago. By providing high resolution logs of the wellbore, imaging tools are able to resolve not only structural features, but fine scaled stratigraphic details. First and second generation electrical resistivity imaging tools operate only in conductive water-based muds. Tools that operate in non-conductive oil-based muds have been developed in recent years, but they do not have the spatial resolution of the earlier tools. This limitation has now been largely overcome with a novel adaptation of the second generation tools that replaces the micro-resistivity buttons with miniature springloaded scratcher knives that make electrical contact with the formation by cutting through the nonconductive layer on the borehole wall.
Electrical borehole imaging tools are the evolutionary descendents of traditional dipmeter tools, and exponentially increase the value of the information gathered. Instead of 4, 6, or 8 buttons measuring resistivities circumferentially around the borehole, 150 to 196 buttons measure micro-resistivities from which false-colour images of the borehole wall are generated. These higher resolution images can be used for traditional dip and strike information, but also allow for more detailed geological interpretations to be made, both in terms of fine sedimentological features, and in large scale structural trends. Prensky in Lovell et al (1999) traced the advances in borehole imaging technologies from the earliest optical techniques to current wireline and LWD imaging tools. At that time, electrical borehole imagers were limited to obtaining their measurements in wells filled with conductive wellbore fluids. In oil-based mud systems however, the major applications of high resolution imagers, namely reservoir (facies identification) and fracture characterization were dependent upon acoustic imagers. Unfortunately, acoustic imagers suffer from borehole wall artifacts and signal amplitude attenuation from a variety of factors, including eccentricity, solids and weighting materials in drilling muds. Since then, the latest advances in wireline imaging technologies have focussed on obtaining electrical borehole images in wellbores containing nonconductive drilling fluids. Cheung et al (2001) and Lofts et al (2002) presented the industry?s first wireline electrical images taken in a non-conductive wellbore fluid. These tools are physically based upon the respective water-based imaging tools discussed above, but make changes in the pad and electronics to enable them to generate electrical images in non-conductive borehole fluids. These tools measure the Rxo component of the near-wellbore environment by using focussing and measuring currents to generate microlateral conductivity images. This paper presents examples of images using a new tool design in non-conductive mud systems. The key element to obtain micro-resistivity measurements in non-conductive fluids hinges on obtaining electrical continuity between the electrode and the formation. Weatherford?s Oil Mud Imager (OMI*), uses a novel approach to obtain this continuity in the form of knives that cut through mudcake to make physical, and therefore electrical contact with the borehole wall. Field testing of the OMI began in May 2005.
Haddad, E.. (Schlumberger) | Wells, P.. (Schlumberger) | Fredette, M.. (Schlumberger) | Toniolo, J.. (Schlumberger) | Mallick, A.. (Schlumberger) | Nguyen, H.. (Schlumberger) | Bammi, S.. (Schlumberger) | Laronga, R. J. (Schlumberger) | Kherroubi, J.. (Schlumberger) | He, A.. (Schlumberger) | Gelman, A.. (Schlumberger) | Jarrot, A.. (Schlumberger) | Fratarcangeli, D.. (Tapstone Energy) | Alcorn, T.. (Tapstone Energy) | Tipton, T.. (Tapstone Energy)
Abstract Microelectrical imaging is a well-known and highly versatile geological and reservoir characterization technique that produces representative and photorealistic images of the formations intersected by a wellbore to form the basis of a thorough and reliable geological interpretation. These images are used to characterize geological structures, natural fractures, faults and interpret sedimentary features and rock facies. This paper introduces the world's first through-the-bit microelectrical imaging tool, also the world's smallest tool in the genre, at 2-1/8 in diameter and 140 lbs. The new tool provides the lowest-cost, lowest-risk method to obtain high-quality images in lateral wells for applications such as fracture characterization of unconventional reservoirs. We present the electrical and mechanical design innovations that enabled repackaging the performance of the industry- standard microelectrical imaging tool into a ‘nano’ format tough enough to withstand the rigors of through-the-bit conveyance, often in laterals that exceed two miles' length. The basic physics of the industry-standard are maintained with some obvious changes to the geometry. A simple and elegant twelve-arm bowspring design maximizes coverage of the borehole wall, while being robust enough to prevent pads from being ripped off downhole, a well-known fault of existing imaging tools in lateral wells. In-pad front-end signal processing of twelve buttons ensures strong signal-to-noise while demanding further innovation in miniaturization. Notwithstanding its diminutive size, the new tool delivers images of 5mm nominal resolution and 76% circumferential coverage in six inch boreholes drilled with water-base fluids. We discuss implications of the new design for the image data processing chain, as development of significant new and tool- specific processing methods was necessary. For example, the irregularity of tool movement in long laterals, the lack of wireline cable depth measurement during logging, and the multiple pad levels necessitated the application of new depth correction techniques that smartly combine physics-based and image-based approaches. On another point, considering the lack of real-time QC during memory acquisition, the data acquisition strategy was designed to provide comprehensive auxiliary data to give the processor maximum flexibility to quality control and correct the signal processing. We review the results of seventy-five jobs conducted in North American unconventional wells, and examine the details of specific case studies. In many specific plays, a growing number of operators recognize the geology—in particular the distribution of natural fractures and faults along the lateral, as the key factor in completion performance. We find that the new and efficiently acquired images are a powerful tool to identify and characterize these features, underlining a strategy to eliminate negative surprises and improve lateral completion performance.
Fratarcangeli, Dean (Tapstone Energy) | Alcorn, Tammy (Tapstone Energy) | McBride, Patrick (Tapstone Energy) | Wray, Andy (Schlumberger) | Haddad, Elia (Schlumberger) | Laronga, Robert (Schlumberger) | Khan, Nasar (Schlumberger)
Abstract While multistage lateral completions, where 100% of stages contribute to production have become commonplace in many cases, inconsistent inflow performance persists when wells are compared either from the point of view of frac execution or production results. It has been shown that such differences may be the result of lateral heterogeneity in reservoir quality (RQ) or completion quality (CQ--mechanical properties). Significant advances have been made over the past five years to characterize lateral heterogeneity (through the acquisition of cost-effective horizontal logging) and utilize this data to modifying the completion strategy. However, in some plays, even when RQ and CQ are well-understood, the positive or negative influence of geology (for example, tectonic natural fracturing) may overprint everything else the operator might do to optimize well performance. Characterizing natural fractures, structural complexity (such as faulting) and lateral facies changes are all challenges best addressed through the acquisition of high-definition micro-electrical borehole images. Unfortunately, this technology has historically been considered cost- and risk-prohibitive for most unconventional operators to acquire in horizontal wellbores. However, through the successful introduction of a new full-bore, high-definition micro-electrical imager, conveyed through the bit, a solution to these concerns is finally available in a format that meets the requirements of operators for low cost and low risk exposure, while maintaining full well control. The following case study from the Anadarko Basin, Oklahoma, U.S.A. demonstrates how high-definition through the bit borehole image data, acquired in a single and efficient horizontal run through the bit, is being used to: identify facies variations that can control formation mechanical behavior on hydraulic fracturing, more accurately model local structure & the wellbore position in the stratigraphic section and also, fully characterize tectonic natural fractures for the purposes of targeting them, avoiding them and simulating their interaction with the completion. This enhanced geological understanding is being used independently or in combination with supplemental through the bit measurements to mitigate completion uncertainties and optimize well performance.