| Abstract |
For resource extraction projects, exploratory deep wells are drilled, logged and tested to validate commercial production. The collection and analysis of data from these wellbores is necessary to increase the understanding of any reservoir, including those in geothermal work. However, deep drilling is expensive and successful commercial outcomes are risky. Consequently, many operators are reluctant to invest in additional rock analyses, even when their advantages are clear. Implementation of practical and cost-effective data collection procedures is fundamental to reduce investment associated with drilling and testing, but cost and benefit must be balanced. For instance, recording of pressure and temperature is currently a standard for any geothermal deep well. However, the use of common wireline tools and testing programs that include rock material such as cores are rare. This is not surprising considering the additional cost, technical challenges and limited coverage provided by core collection in the wellbore. For instance, a given core sample has high location accuracy (e.g., depth) but results are specific to that exact depth and may not extrapolate to larger areas of the reservoir without integration with wireline results. As a byproduct of drilling, cuttings rock material circulated up the wellbore are typically collected at discrete measured drilling depths and are commonly archived and available for subsequent research. The use of drilling cuttings as a characterization tool has had historical challenges, including lack of depth precision and insufficient accuracy of laboratory measurements. However, although lacking the depth precision of core (cuttings are typically assigned a depth range based on calculated circulation time to reach the surface from the bit), they have the benefit of being inexpensive and are arguably more representative of bulk properties within depth intervals of a reservoir than point data, such as sidewall cores. Here we propose a workflow in support of geothermal resource characterization in deep wells using high resolution cuttings analysis. From acquisition to interpretation, the workflow takes into account unique criteria to assess heat as the source of geothermal reservoirs and its interaction with fluids. The grade of modification to current operations in geothermal wells would have to be technically adequate and perform towards decreasing risk indicators at the wellsite as rig time. Accurate continuous laboratory measurements of properties such as mineralogy, thermal conductivity, and specific heat capacity along with approximation of heat flow and other advanced measurements, would be required for adequate characterization and estimation of the geothermal resource. |