| Popis: |
Six horizontal wells were drilled into the Tertiary Chatt Sand reservoir of the Breitbrunn gas field in Bavaria, Germany. The purpose of this campaign was to develop part of the depleted reservoir into a gas storage sand. A detailed geological and petrophysical study was prepared prior to drilling and resulted in the identification of high quality reservoir layers that were targeted by the horizontal wells. Despite the simple anticline structure of the field, geometric drilling was ruled out due to remaining geological and directional uncertainties. The geosteering approach adopted relies on real-time GeoVision Resistivity (GVR·) resistivity images, which were used for the first time ever during this drilling campaign. The image data are compressed downhole and transmitted to the acquisition computer on the rig where they are decompressed and analyzed. The images allow the precise placement of the borehole relative to the geology, which "keeps the bit in the sand". Layer heterogeneity like tight streaks, concretions or patchy porosity can be identified as such, and are not interpreted as a different layer entered by the hole, which would lead to a wrong geosteering decision. Logging-While-Drilling (LWD) azimuthal data are acquired during drilling and also during wash-down passes which follow a bit change. A comparison of these time-lapse data sets can provide invasion profiles through time and around the borehole. |
