The Application Of Phase-controlled Inversion In Prediction Of Carbonate Reservoirs In The Central Tarim Basin

Tarim basin, especially the central Tarim area, is becoming one of the most attractive areas for hydrocarbon exploration in China. The deeply buried marine carbonate reef-bank reservoirs deposited in the central Tarim Basin are characterized by serious heterogeneity and relatively thinner thickness, obviously controlled by sedimentary facies, which has resulted in many difficulties in differentiating these reservoirs by conventional inversion methods. So, this paper presents a phase-controlled inversion. Firstly, seismic facies models are constructed by comparing the differences of the seismic response characteristics of the reef-bank reservoirs. In this process, macro-seismic phase division is similar to sedimentary facies in operation, but the difference of seismic reflection features is highlighted in the division of the small-scale seismic phases. According to the plane and spatial distribution of different seismic facies, we can count seismic and drilling sample data corresponding to different seismic facies. On the basis of the phase-controlled model, geostatistical inversion can then be applied to precisely predict the spatial distribution of the carbonate fracture-vug reservoirs. What differs from the conventional seismic inversion method is that this phase-controlled inversion has used the cluster analysis of seismic and well data involved in inversion to obtain a more reliable variogram of the impedance and lithology. This procedure has greatly improved the accuracy from a minimum of approximately 75% to a maximum of approximately 90% and geological rationality of the inversion.By the application of phase-controlled inversion in Tazhong NO.1 gas field, the conclusions are drawn as the following three aspects:① Phase-controlled inversion can improve the model’s predictive precision of the reservoirs because it can synthesize the single geophysical inversion problem into an associated inversion problem and decrease the variation of the parameters that describe the single inversion problem during inversion process.② Given randomness of the geologic structures, the combination of the geostatistical theory and seismic facies can effectively improve the seismic longitudi resolution to make the inversion results more applicable to real geologic situations. ③ Due to heterogeneity caused by fractures and pore spaces within carbonate reservoirs, the phase-controlled inversion, integrating logging, and test data can accurately determine favorable reservoirs’ development zones and spatial locations to provide a basis for horizontal well design and rolling exploration.