Continuous Orientation Measurement Systems Minimize Drilling Risk During Coring Operations

Abstract

Abstract Complex new field developments and in-fill drilling programs have placed extra emphasis on the work conducted by an oil company's geological and petrophysical departments. Core samples retrieved from the wellbore are a key source of data to these groups. Secondary and tertiary recovery projects have placed an extra premium on these core samples being oriented to assist in fracture orientation and measurement of directional permeability and porosity. The traditional survey instrument used to measure the in-situ orientation of a core as it is being cut has been the mechanical film recording system developed for borehole deviation measurement. The use of this system placed certain risks on the drilling operation, as it was necessary to stop drillstring rotation and fluid circulation to make the orientation measurements. Solid state transducers developed for real time directional surveying formed the basis for the development of electronic survey tools as replacements for the mechanical film systems. The transducers used are stable enough to be used in a "continuous" mode within the coring operation, thus negating all risks previously associated with oriented coring. The impact on the coring operation of taking orientation measurements is now zero. This paper seeks to outline the development and application of electronic survey tools for core orientation measurements. Advantages of the continuous method are highlighted, and operational experiences on more than 60 wells worldwide to date are discussed. Background The orientation of a core has, historically, been frowned upon by oil company drilling departments. The best arguments in the world that the geology and petrophysical departments could propose for orienting cores were always countered with the arguments against as proposed by the drilling group. These arguments centered around the tremendous risk placed on the drilling operation. These arguments included:the risk of getting stuck in hole through having to stop rotating and circulating while the orientation pictures were being taken.the likelihood of the core being broken as the core head torqued up after each picture was taken.the increased risk of jamming the core-barrel itself during these stops. P. 341^