Information regarding site occupancy of fish that migrate long distances during non-spawning periods together with estimates of recruitment trends for individual populations can be informative for management, especially when individuals from different spawning populations intermix and are sampled/harvested together. Tendencies for individuals from different populations to preferentially occupy specific regions increases vulnerability to anthropogenic and natural disturbances. Using mixed stock analysis (MSA), we estimated population-specific occupancy of lake sturgeon in open-water and nearshore regions of Lake Michigan across a hierarchy of spatial scales. Open-water mixture composition differed between Lake Michigan’s eastern and western basins. Significant heterogeneity in habitat occupancy was also observed at microgeographic scales throughout open-water regions of Green Bay, indicating non-random occupancy to regions proximal to natal streams. Estimates of relative recruitment levels determined from MSA extensions indicated increasing recruitment trends for spawning populations associated with Wisconsin tributaries (Oconto/Peshtigo, Fox, and Menominee Rivers). Our lake sturgeon results demonstrate the utility of genetic data for informing management efforts for spatially-structured, highly migratory species. Similar analyses could prove beneficial for species with similar characteristics.

The comparison of Logging-While-Drilling (LWD) and Wireline (WL) measurements is an ongoing challenge in Formation evaluation quarters. The differences are more often due to the dynamic changes that occur along the borehole wall and near wellbore formation environment, altering the measurement environment during the acquisition of both measurements. In conditions where these alterations are minimal, the LWD and Wireline usually have excellent agreement, while with increasing severity of the wellbore alterations, significant differences can occur between the LWD and Wireline. This paper presents a methodology to profile the dynamic wallcake alterations by utilizing the variations in resistivity of the wallcake and near wellbore environment from time lapse logging-while-drilling and Wireline measurements. Traditionally such dynamic wellbore alterations are quantified with downhole mechanical calipers and ultrasonic acoustic caliper measurements, both of which measure variations in the physical dimensions of the wellbore diameter as a direct indication of wallcake and nearwellbore alterations. Field examples are presented from wells drilled in the Columbus basin, Trinidad and Tobago. The near wellbore alterations are observed to show a strong correlation to the time-lapse resistivity ratios. Logging-while-drilling and Wireline-bulk-density measurements showed good agreement in the sections with minimal near wellbore alterations where the hole maintained near gauge conditions, while significant differences were observed in sections where severe alterations of the near wellbore has occurred and the hole had become under-gauged or over gauged. We also discuss some of the causal factors of the dynamic near wellbore alterations such as wall cake sleek along shale swells, filter cake buildup in permeable formations and hole washouts, and the implications for accurate petrophysical evaluation and reservoir description. The limitations of utilizing the time lapse resistivity method in profiling the near wellbore characteristics are also highlighted. Introduction The demand for real-time formation evaluation parameters has continued to grow and subsequently puts logging-while-drilling measurements in the spotlight as a viable means of drilling, accurately evaluating and at the same time minimizing drilling and conveyance risks to formation targets. After over 60+ years of utilization and application[1] of LWD in the Oil industry, the question still lingers as to whether the LWD measurements are Wireline replacement, or of comparable quality to the Wireline equivalent. This paper seeks to evaluate the comparison of Bulk density measurements on Logging-While-drilling with the equivalent Wireline-Bulk-density measurements. Bulk density measurements on LWD are made with a gamma source and detector system mounted on a rotating sub as part of the drilling bottom hole assembly (BHA), positioned about 15m behind the drilling bit means acquisition is shortly after formation is cut. While on Wireline the Bulk density measurements are made with a similar gamma source and detector system, but mounted on pad device extended against the borehole wall. The Wireline measurements are however made in a time lapse that can vary from several days to several weeks from the time the hole is exposed. In this window of time lapse the wellbore wall and near wellbore environment can undergo complex dynamic alterations that ultimately determine the comparable quality of both the LWD and Wireline Bulk density measurements.

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