Design, Field Testing, and Application of a New Through-The-Bit Fullbore Microelectrical Imaging Tool in Unconventional Reservoirs of North America

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.