| Tongnanba district is a large-scale NNE-NE direction anticline structure belt located at the foot of Micang Mountain in northern Sichuan Basin. Hebachang that belongs to the low fault-fold structural belt of northern Sichuan consists of three secondary tectonic units-Nanyangchang nose, Fuyangba fault block, and Heichiliang faulted nose. The T1J2 unit is one of the major gas pays, and the overlying gypsum rock is the important cap rock in this district.Based on the geologic and logging data, relationships between lithology, physics properties, electric properties and velocities was analyzed, and the math relation between cap rock's property parameter (porosity, permeability, displacement pressure) and wave impedance were statistically fitted. Then multi-parameters prediction was made for the target cap rock by utilizing several geophysical techniques such as fine interpretation technique, wave impedance inversion technique, spectral decomposition technique, seismic coherence technique and AVO technique. Eventually, acquired parameters were used to comprehensively evaluate the sealing ability of the cap rock. According to these parameters, the T1J2 unit has the stratum thickness from 50-230m, gypsum content from 60%-65%, total gypsum thickness from 30-150m, porosities lower than 2.5%, low permeabilities (mostly lower than 1×10-3), and predicted displacement pressure from 1.0～10.0. There is an area with high fracture pressures whose sealing ability is good, while in local areas whose displacement pressures are below 2.0, which indicates their poor sealing ability.According to the comprehensive evaluation, the T1J2 gypsum rock in Hebachang district is favorable for oil & gas sealing, and is capable of sealing large-scale oil & gas pool.
|
PDF Full Text Request