Anisotropic depth imaging with ver-tical transversely isotropic (VTI) models has become the dominant practice in the industry. However, anisotropic parameters for these models continue to be derived by basic practices without the use of tomography. Hanging a single profile of Thomsen's parameters from the water bottom still remains the most common practice. In a simple structural setting, it is usually possible to focus the data and obtain a good image despite having a simple and unrealistic model for Thomsen's parameters. However, depth positioning of such images is usually suboptimal. Better positioning requires more geologically plausible models. In addition, imaging in complex settings may require tilted transversely isotropic (TTI) models.
This paper uses the inventory of three actively managed forest estates located in the Coastal, Central Interior, and Northern Interior forest regions in British Columbia to estimate the cost to produce Carbon credits ($ per Carbon credit) when the harvest is reduced below the baseline level. The financial analysis was conducted over a range of discount rates (0-16%) and the total cost included the opportunity cost due to harvest reduction and the Carbon project cost (the Carbon project initial establishment and validation cost and the ongoing verification cost for two frequencies (1-year and 5-year)). When the opportunity cost was not included, the cost per Carbon credit was similar to previous findings (lower cost per Carbon credit for higher site index (i.e. top height in meters at age 50)). However, when the opportunity cost was included the cost per Carbon credit was higher for higher site indices which corresponded to higher average value per hectare harvested (AVHH) (i.e. timber revenue multiplied by average harvested volume per hectare per year). The reversal of trends is the result of the average timber revenue being higher for higher site indices which resulted in a higher opportunity cost and higher AVHH. The opportunity cost represented 58% to 97% of the cost per Carbon credit. Compared to the 5-year verification, the 1-year verification frequency increased the total cost per Carbon credit by 1% to 22%, with the smallest increase being when the Carbon project cost represented a small percent of the total cost. The estimates for the three forest estates analyzed here represent three points from a larger spectrum, and they identify the cost per Carbon credit over a range of site indices (14.7 to 25.6 meters top height at age 50), AVHH (12.2 to 63.7 thousand $ ha −1 year −1 ), and timber net revenues ($4 to $35 m −3 ). Further research is required to determine if the trends found in this study hold over a more densely populated spectrum.
Anisotropic depth imaging with Vertical Transversely Isotropic (VTI) models has become dominant in the industry.However, anisotropic parameters for these models continue to be derived by very basic practices without use of tomography. Hanging a single profile of Thomsen parameters from the water bottom still remains the most common practice. In a simple structural setting, it is usually possible to focus the data and obtain a good image despite having a simple and unrealistic model for Thomsen parameters. However, depth positioning of such images is usually suboptimal. Better positioning requires more geologically plausible models. In addition, imaging in complex settings may require Tilted Transversely Isotropic (TTI) models. In this case study we construct several anisotropic models using approaches with increasing complexity and evaluate the model impact on image quality and ties to well data. We start with a "new default" model, where a single, smoothed, borehole-calibrated profile is hung from the water bottom, and then we progress to an "intermediate" model where a similar profile with more vertical details is propagated using major geological horizons. We finish with an "elaborate" model, where profiles from several wells are interpolated throughout the model using geologic horizons. We contrast all these models to an "old default" model derived without well calibration. We observe a generally steady improvement in well ties compared to the "old default" model, with the proportionally largest change coming from simple well calibration ("new default" model) and additional uplift coming from incorporating geologic horizons ("intermediate" model). Differences between "intermediate" and "elaborate" models are small, while switching to TTI models clearly helps resolve complex structures in dipping areas. IntroductionIt is well understood that seismic data do not constrain all parameters of an anisotropic velocity field. Therefore, Thomsen parameters are usually estimated from joint inversion of well and seismic data at borehole locations. Profiles derived at wells are extrapolated or interpolated throughout the volume and kept static; whereas, velocity is updated with tomography. It is a general expectation that more accurate and geologically plausible volumes of Thomsen parameters models may lead to better images and improved well ties. We apply different model building practices and quantify their impact on imaging and ties to well data.
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