FLUID SUBSTITUTION IN HORIZONTAL CHALK WELLS AND ITS EFFECT ON ACOUSTIC ROCK PROPERTIES - A CASE STUDY COMPARING LOGGING WHILE DRILLING AND WIRELINE ACOUSTIC DATA

摘要

The introduction of new full-wave acoustic logging while drilling (LWD) tools has enabled the acquisition of reliable acoustic data during the drilling process. Maersk Oil and Gas AS has recently run the latest in acoustic LWD technology in wells drilled in North Sea chalk reservoirs. These data were compared to the array acoustic wireline (WL) data. The paper will focus on acoustic data sets acquired in horizontal wells drilled in the chalk reservoir of the Halfdan oil accumulation, offshore Denmark. The reliability of real-time LWD acoustic data from down-hole semblance processing will be assessed in comparison to post-processed memory LWD and WL data, with the aim of developing meaningful realtime quality control indicators. Through comparison of acoustic LWD and WL data acquired during and after the drilling process, respectively, the paper will investigate the effects of mud filtrate invasion on measured slowness values by fluid-substitution modeling. Shear data from WL dipole and the LWD quadrupole tools are compared in this regard. Interpretation of the acoustic LWD data sets is enhanced by additional information from the standard LWD data and LWD density images in combination with the WL resistivity images providing improved stratigraphic and high resolution bed boundary information. These data assist in assessing the influence on the acoustic data of drilling at low angles through a highly, acoustically stratified reservoir.