THE COMBINED APPLICATION AND UTILISATION OF CMR™ AND FMI™ WIRELINE TECHNOLOGY IN WONNICH-I

Abstract

Wonnich, a new gas and oil discovery was drilled in July 1995 within exploration permit TP/8 Part 1 in the Barrow Sub-3asin. The well was logged using emerging wireline technology which resulted m significant im­provements in understanding the quality of reservoir rocks, their genesis and post depositiunal alterations. Both the Combinable Magnetic Resonance Imaging Tool (CMR™) and the Formation Micro-Imager (FMI™) data were acquired in the 216 mm hole section of the well. The interval between 2.575 and 2,525 m. which forms the basis of this technology review, comprises an aquifer sandstone which was logged with the CMR tool to inves­tigate the pore size and distribution and to provide a comparison between the CMR porosity and standard porosity derivations. The CMR data presented in this paper was p-ocessed by Schlumberger using the stan­dard sandstone settings. The high resolution, density derived porosity and the CMR porosity showed good agreement in both magnitude and vertical resolution. The aquifer sandstones reached a maximum of 18 per cent porosity with a CMR permeability maximum of 400md between 2,544-2,551 m. The T2 relaxation times distribution in sands, occurs between 33 and 250 ms with the peak and mean coinciding at 100ms. Several shale intervals show T2 attenuation due to hole washout. Utilising both the FMI azimuthal images and the CMR permeability curve it was established that some of the permeability barriers shown by the CMR and 'regular' open hole logs are in fact nodular formation components, rather than beds. These would thus not impact fluid flow and completion design. Further image analysis within the aquifer sands shows that the palaeocurrent direction is northwest, with a southeasterly sediment provenance. The larger scale process signatures within the lower sand are replaced by friction dominated and low energy pro­cesses towards the upper portion of the sand. This fining upwards profile is reflected not only in the GR logs but also in the pore size reductions shown by the CMR T2 relaxation profiles extending the application of these technologies to depositional environment analysis and grain size distribution. Post depositional influences in­clude siderite and clay diagenesis and fracturing associ­ated with aquifer seals.