Guest Editorial: The Uncertainty in Subsurface Position of Your Wellbores Should Concern Managers and Geoscientists

_ Wellbore surveying has advanced significantly from the breakthrough understandings on errors in the 1980s to the application of aerospace technology with advanced error modeling and correction. Unfortunately, a huge gap exists between modern wellbore survey capability and the application of these tools and techniques for proper wellbore positioning and subsurface asset modeling. This gap causes oil and gas companies to carry large unnecessary risk and realize significant loss of asset value throughout the field and well life cycle. Inadequate Practices Are Too Common Concerns that should seriously worry C-suite managers in oil and gas companies are numerous. - Many oil companies lack the required wellbore position uncertainty knowledge in their drilling programs to reliably intercept with a relief well in the event of a blowout, despite their blowout contingency plan (BOCP). The consequences could result in operator bankruptcy. - Inadequate wellbore position uncertainty from poor wellbore surveying practices negatively impacts subsurface models. Many times, this imposes “ghost” faults, creates unreliable wellbore-to-wellbore formation and pressure correlations, both of which negatively impact reservoir development and delivery (thus calculations of 1P, 2P, and 3P reserves). - Unrealistic drilling expectations of trying to hit the “bull’s-eye” or small cross sections for drilling targets with wellbore position uncertainties that far exceed the target dimensions—a technically impossible task. - Borehole surveying that focuses on the calculation of ellipsoids of position uncertainty for wellbore collision avoidance during drilling and ignoring the application of these uncertainty ellipsoids through the reservoir for geology and reservoir modeling. Furthermore, many companies do not address the measured depth errors of drillstrings, wirelines, and drilling techniques, thereby increasing uncertainty of true vertical depths (TVD) which are not actually “true.” These depth errors are generated from many sources including, but not limited to, along-hole drag, pipe/wireline stretch, internal pipe pressure, inappropriate survey spacing, and, especially in geothermal drilling, borehole temperature. - Drilling engineers typically lack the depth of education to apply the appropriate tools and practices to achieve the required position uncertainties and need the support of subject-matter experts (SMEs). These experts exist in some major oil companies and are usually participants in the Industry Steering Committee on Wellbore Survey Accuracy (ISCWSA), also known as the SPE Wellbore Position Technical Section (WPTS). Oil and gas companies without these experts must rely on SMEs in their wellbore surveyor suppliers, necessitating a knowledgeable buyer capability. - Traditional wellbore survey tabulations passed from surveyors to drilling and onto subsurface traditionally show the lateral position and TVD to two decimal places. This is despite the uncertainty of these positions being in the order of tens of feet (or meters). This practice misleads the end users of the wellbore position data into believing they are mapping with unrealistic certainty and would have earned me a “F ” grade on a university lab report.