Seismic While Drilling, Seisbit R&D Project (2005-2006). Pressure analysis by using SWD amplitude data (ID 4.2). Project Eni-Agip/OGS

This report describes the research done in the framework of the Seisbit RD Project, ID 4.2. The amplitude of the Seimic While Drilling (SWD) drill-bit signal is analyzed and related to drilling pressure conditions. The analysis is based on bit-displacement model algorithms, which calculates penetration and bit forces for prescribed drilling conditions. The equations allow us to calculate the expected SWD signal amplitude in relation to rate of penetration and other drilling parameters, and to relate the differential borehole-formation pressure curves to the signal amplitude as well to the sigma-log curves calculated by conventional mud-logging monitoring methods. A case history is analyzed using the data of a well sited in Southern Apennine in Italy, where the drilling and pressure conditions are related to a complex geology being in a thrust fault area interested by several tectonic phases. The amplitude of the drill-bit signal depends on several parameters and complex conditions involving linear and non-linear effects. The drill-bit displacement model (Poletto and Bellezza, 2006) is used to calcolate synthetic SWD seismograms in a zone where overpressure are present and continuos monitoring of the drilling conditions and adjustment of the drilling mud are required. The method shows relations between amplitude of the drill-bit signal, rate of penetration and pressure.