Prediction Of Ordovician Limestone Reservoir In Sha 48 Area Of The Tarim Basin

The burial depth of limestone reservoirs in S48 well field of Tarim Basin is quite deep. Suffering from intensive erosion and multi-stage reformation, the reservoir space is various and complex. This kind of reservoir is characterized by low porosity and permeability, which has strong heterogeneity. The fractures and caves are randomly distributed and they are greatly different in density and scale. As a result, the signal-noise ratio and resolution of seismic data are both low, which makes oil and gas exploration rather difficult. So how to predict the fractures and caves precisely is really important as well as the key of carbonate reservoir exploration.According to features of these carbonate reservoirs in S48 well field, we identified and predicted the distribution and fluid type of the fractures and caves in this area, based on the limestone reservoir as the target zone. At first, on the basis of analyzing reservoirs’ geological features and theory of seismic methods in identifying fractures and caves were studied. The thesis used multiple methods to predict the fracture and cave zones, including coherent analysis, shear-wave split technique, seismic attributes and PP-wave seismic and logging joint inversion. By studying the relationship between fracture-cavity system and amplitude attribute, its features of seismic attributes were concluded. In addition, joint PP and PS inversion were applied. This method can calculate many important attributes parameters to detect the hydrocarbon potential of reservoir, like amplitude ratio between PP-wave and PS-wave, Vp/Vs, Poisson’s ratio. All these results were verified by comparing with drilling and logging data.Through carrying out the above research work, this research focusing on the Ordovician fracture-cavity carbonate reservoir in target area achieved some results and obtained the following conclusions:1. Relatively single or well preserved fracture shows "a string of beads" in pp seismic sections. Amplitude attributes are more sensitive and effective in identifying fractures and caves. Generally, the amplitude attributes are much higher when fractures or caves are filled with fluid.2. The shear-wave split technique is very important to detect fractures. Moreover, it can effectively predict the dominant orientation and intensity of fractures.3. Both PP-wave seismic and logging joint inversion and joint PP and PS inversion are suitable to predict reservoirs like those in target zones. However, the latter are more effective and the results are more reliable, for reason that it cannot only realize mutual authentication by using multi-wave data, but can provide elastic parameters to detect hydrocarbon.