The density-neutron log combination is a common standard for reservoir evaluation, typically used for porosity and lithology estimation. The measurements require the use of radioactive sources that operators are increasingly trying to avoid, particularly in areas where drilling operations are challenging and the lost-in-hole risk is elevated. This paper introduces a workflow that integrates surface-measurements, i.e., advanced cuttings, with nuclear magnetic resonance (NMR) and acoustic log data to estimate formation-porosity and bulk density and to distinguish different lithologies. We present cases where we integrate the porosity from NMR or acoustic with mineralogical analyses on cuttings to infer matrix density by calculating a weighted average of the mineral densities according to their fractional volume in the rock. Formation fluid density is calculated based on a saturation analysis, with the fluid composition and densities of water and hydrocarbons estimated from downhole fluid sampling. This novel method develops a calculated continuous synthetic bulk density log. Standalone NMR logging can deliver a very accurate, lithology-independent measurement of porosity in oil and water zones. Even though NMR measurements may face challenges in gas-bearing reservoirs, a very accurate porosity can be obtained by integrating NMR and acoustic logging data together with natural gamma ray and resistivity data. An overall comparison of NMR-acoustic porosity to porosities derived from density-neutron and core data within different lithologies shows that the measurements are consistent within +/- 1 porosity unit (pu). To deliver the same set of information as the density-neutron log with standalone NMR, acoustic or an NMR-acoustic log combination, bulk density, and lithology information utilizes the presented workflow integrating the data from surface measurements and downhole logging. The calculated synthetic bulk density logs from the integrated analysis of surface and downhole log data are in good agreement with measured bulk density logs. The presented workflow introduces an alternative to the common density-neutron combination for formation evaluation. It delivers a set of petrophysical properties, such as porosity, bulk density and lithology by integrating NMR with advanced cuttings and fluid analysis without using any radioactive sources in the borehole.

For decades, mud gas data acquired by surface logging has been, and still is, routinely utilized throughout the oil and gas industry for safety monitoring and qualitative reservoir information. Nevertheless, its full potential is not often realized or is highly underestimated. One reason is that current interpretation routines require dedicated personnel and are commonly done offline either daily or sometimes even after the well is already drilled and completed. In this paper the authors present a new real-time approach, significantly supporting real-time operational decision making such as reservoir navigation, formation testing, and completion planning. As of today, mud gas data is used for the identification of fluid contacts and to characterize the hydrocarbon content of geological formations. An offline interpretation has been developed and presented in 2016 by Ritzmann et. al bringing the standard mud gas data into a format that matches a standard petrophysical workflow output. The resulting dataset contains a porosity, saturation and permeability index, matched to the most likely fluid types present in the formation. This method serves as an independent source of information in addition to the commonly used downhole measurements and provides valuable insight where the standard interpretations are in doubt or not decisive. Such scenarios can be, but are not limited to, fluid contacts in mature fields, certain mineralogy masking pay zones or freshwater indicating false pay. Mud gas data is a cost-effective source of information that does not require additional logging tools run in hole. Therefore, this technology is very useful where it is desired to reduce the deployment of additional LWD tools or there is a high risk of tools being lost in hole. This methodology is now available in a real-time, reservoir navigation application and can be monitored while the well is being drilled. Based on the resulting interpretation, sweet spots as well as false detections can be identified, and the well path adjusted accordingly. Additionally, it enables a preliminary insight into potential fluid distribution along the wellbore, helping to optimize logging-while-drilling and wireline pressure and fluid sampling selections. Petrophysical and fluid interpretation can sometimes be very challenging especially in mature fields and complex reservoirs. Therefore, it is crucial to leverage all available data to make the best timely decisions, preferably while the well is being drilled. The authors strongly recommend integration of all available data, as early as possible, to derive the closest interpretation to reality, before landing the well.

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In extended reach and horizontal wells, it is critical to maintain borehole quality and stability to ensure efficient drilling and for the running and installation of completions. Categorising the risk of borehole degradation is becoming an important aspect of the well planning process. The quality of the borehole is affected primarily by geomechanical or drilling practices, which can significantly impact the life cycle and completion expenditure/cost of a well. We show examples of how recently available, high-resolution, acoustic logging-while-drilling (LWD) borehole image logs have enabled detailed characterisation of borehole shape to the extent that we can visualise and analyse all contributors to borehole stability. LWD measurements also enable the use of time-lapse logging; comparing images from the first pass with repeated logging runs at later stages in drilling to look for degradation in conditions of the borehole shape. These data can be used for several new or existing applications that can be split into two main categories: 1. drilling hazards – degrading borehole shape profiles, identification of borehole breakout and washed-out sections and 2. completions hazards – cement volume calculations, identification of trajectory and small-scale irregularities that could impair liner placement. These applications use zonation to describe all ranges in borehole trajectory, borehole shape and image artefact features for coding of the well during or shortly after drilling. This scheme is then combined with a geomechanics-centric integrated risk management workflow which provides an improved well planning process by identifying potential drilling and geological risks in each of the planed well sections. Pre-drill risk identification combined with visual verification of the borehole condition enables quick decision making for drilling and potential de-risking of subsequent wireline logging and completions operations, thereby allowing safe, predictable operations with minimal NPT, from drilling to completions. The enabling technology of high-resolution LWD acoustic imaging has made possible the visualisation of borehole shape features in detail previously not possible in either water or oil-based mud systems.