Well log and seismic character of Liuhua 11-1 Field, South China Sea; relationship between diagenesis and seismic reflections

An integrated analysis of log, petrographic and seismic data shows that the seismic reflections of Liuhua 11-1 Field image variations in porosity. Crossplots of velocity versus porosity, density versus porosity, velocity versus density and velocity versus gamma-ray demonstrate that the acoustic impedance contrasts and, consequently, seismic reflections represent the alternation of tight and porous zones. A detailed examination of a continuous core suggests that the majority of porosity is related to a phase of leaching in the deep burial realm that postdates pressure solution. This implies that seismic reflections do not necessarily image depositional surfaces. On the other hand, seismic interpretation of areally more extensive 2-D lines and lithofacies analysis indicate that these diagenetically induced porosity units correspond to depositional events. We conclude that the late diagenetic overprint follows primary depositional bedding and therefore seismic reflections still image the depositional architecture of the carbonate platform.