Seismic response and prediction of fracture-cavity system in carbonate reservoir:A case study in the Ka-1 field

The weathering crust in carbonate rocks, which usually suffered from multi-period polycycle karstification and structure deformation, is heterogeneous reservoirs that are rich in pores, fractures and caverns.The reservoirs,diversified in scale, space configuration and complex in buildup, are difficult to be predicted and described. The observations in ultrasonic models, which reflected the seismic response characteristics of caverns and fractures in the condition of ideal, opened out that the former behaves the short strong reflect energy, the later the seismic clutter facies. A majority of fracture-cavity systems, included irregularity in shape and close in scale, appear the clutter facies in the background of reflection. In terms of the clustering technique for strong amplitude and the discontinuity detecting technique for clutter reflective facies, the two typical response characteristics can be recognized from seismic data in Ka-1 field. At the same time, the abnormal are further confirmed to correspond with the possible karst fracture-cavity reservoirs in geology cause of formation by dint of the assistance methods such as the pole-structure compensation technique and waveform clustering analysis about seismic micro-facies. The cross-verification of the estimated results makes clear that the karst fracture-cavity reservoirs in Ka-1 field are soft and located in the flatness region from well Z1 to Z11. The conclusion is also confirmed by two wells out of abnormal, which are located the high positions of two structural traps and are poor reservoirs.