Method and system for predicting under-salt lake facies limestone reservoir under condition of few wells

Abstract

The invention relates to an under-salt lake facies limestone reservoir prediction method and system under the condition of few wells, and the method comprises the steps: obtaining post-stack seismic data, carrying out the time depth calibration through combining with drilling information, dividing an under-salt lake facies limestone reservoir into an isochronous interface and a secondary isochronous interface, and constructing a stratum position frame through the isochronous interface and the secondary isochronous interface; seismic attributes are calculated, facies zone division of subsalt lake facies limestone reservoir sedimentary facies is carried out based on the seismic attributes and the sequence interface body, and a plurality of virtual well points are arranged on different facieszones; extracting a longitudinal wave speed of the virtual well point, establishing a nonlinear mapping relationship from the longitudinal wave speed to a transverse wave speed and a density parameter by utilizing a BP neural network, calculating the transverse wave speed and the density parameter according to the nonlinear mapping relationship, generating a model data body in combination with astratigraphic horizon framework, and performing low-pass filtering on the model data body to obtain a low-frequency model; and inverting the model to obtain a limestone reservoir structure. Accordingto the method, the multiplicity of solutions caused by manual interpretation of a sequence interface is avoided, the established low-frequency model better conforms to the geological characteristics of lacustrine limestone, and the reliability of an inversion result is higher.

Description

technical field [0001] The invention relates to a method and system for predicting sub-salt lacustrine limestone reservoirs under the condition of few wells, and belongs to the technical field of geological exploration. Background technique [0002] The salt-bearing basins on the passive continental margins on both sides of the South Atlantic Ocean are rich in oil and gas resources, and the exploration potential of sub-salt lacustrine limestone formations is great. Because the sedimentary facies of sub-salt lacustrine limestone changes rapidly, develops alternately with igneous rocks, and has complex lithology and strong spatial heterogeneity, it is necessary to carry out reservoir prediction to identify lacustrine limestone reservoirs. [0003] At present, seismic inversion technology is mostly used to identify and predict underground reservoirs. Seismic inversion is based on seismic inversion theory, with known geological laws and drilling and logging data as constraints,...

AI Technical Summary

Problems solved by technology

For sub-salt lacustrine limestone reservoirs, the reliability of the low-frequency model construction method is low. There are two reasons: First, the spatial distribution of lacustrine limestone is "blocky" and has strong spatial heterogeneity It is quite different from the "layered" strata of conventional clastic rocks. The isochronous interface commonly used in actual production to characterize large-scale tectonic movements cannot realize the "blocky" feature characterization of limestone, and the geological The framework is difficult to constrain the spatial distribution of geological bodies; Second, the number of wells drilled in the exploration stage is very small, and the conventional low-frequency model calculation method of "layer control well interpolation" lacks well control. The common solution in the industry is to use velocity models and rock physics Statistical laws transform the low-frequency model of elastic parameters, but the high-steep deformation of the gypsum-salt layer causes the complex seismic wave field under the salt, and the accuracy of the velocity model under the salt is low, which affects the representation of the geological body under the salt by the low-frequency model

Therefore, conventional low-frequency model building methods are not suitable for seismic inversion of sub-salt lacustrine limestone reservoirs

Images