Abstract:

The F oilfield， a deep-water sub-salt oilfield in the Santos Basin of Brazil， is characterized by deep burial， diverse lithology and strong heterogeneity. Unlike commonly-seen porous reservoirs and some large karst cave reservoir clusters in Western China， the reservoirs in the study area are deep-water lacustrine carbonate rocks with small vug size and various fracture types， resulting in extremely unclear seismic responses and wrong interpretations with conventional prediction methods for fractured-vuggy reservoirs. In addition， the massive salt layers overlaying the reservoirs also reduce the resolution of seismic data of well fractured and vuggy parts and pose challenges to the understanding of their distribution pattern through post stack seismic method. To deal with the problem， this study develops a workflow suitable for the seismic prediction of small fractured-vuggy carbonate reservoirs of diversified lithology against a deep-water sub-salt setting based on the development characteristics of fractures and vugs in the study area and a combination of well and seismic data analyses to eliminate the lithologic interference of mudstone and igneous rocks. It features in the optimization of seismic data and a quick responsiveness to geological information conveyed through seismic anomalies by making full use of core， FMI well-logging and production leakage information. Application to the prediction of dissolution pores and vugs has been proven positive as the method is capable of defining the sensitive seismic attributes of fractures and vugs to predict fractures by combining structural stress field and to predict vugs by combining seismic inversion results such as wave impedance， porosity and CGR. The study is of guiding significance to the prediction of lacustrine carbonate reservoirs with fractures and vugs.

Key words: sensitive seismic attribute, seismic inversion, prediction of carbonate fractures and vugs, deep-water sub-salt reservoir, lacustrine carbonates, Santos Basin, Brazil