The Reconstruction Method of Density Curve of the Tight Limestone Reservoir in Da’anzhai Member

Abstract

The porosity of the tight limestone reservoir in Da’anzhai Member of Sichuan basin is generally less than 3%, and the permeability is less than 0.1×10-3μm2, which belongs to the typical unconventional tight oil reservoir. In the geostress analysis and long horizontal fracturing of the reservoirs in this area, density is an important parameter. It is worth noting that Da’anzhai Member is now in Research Test Stage, in which the new drilling wells are scarce and the logging data are old, there is a general lack of density curve in logging data of Da’anzhai Member. Therefore, the density curve needs to be reconstructed. Considering that the actual characteristics of the rock which can determine the actual geological significance of the reconstructed curve had not been analyzed in the common reconstruction methods, this paper established a new method to reconstruct the density curve. Through the analysis of Geophysical volume model, the density curve can be reconstructed from the response of lithology and pore, the analysis shows:(1) as for limestone, sandstone and mudstone in Da’anzhai Member, the GR and RT curves were the most relevant indicators, and RT curve had a higher resolution of thin layer;(2)as for the response of ultra-low porosity (<3%) in the Da’anzhai Member, AC curve had an effectively reflection, in addition, the RT and AC were the most sensitive curves to the characters of the pore size.Based on the analysis, the density curve was reconstructed by GR, RT and AC curve from the response of lithology and pore under the constraint of the diameter of borehole, and compared with the measured density of core. The contrast showed that the value of reconstructed density curve had the same trend with the measured value, and even in the expanded section of the borehole, the reconstructed density had a better correlation with the core density than the logging density curve. The further calculation of rock mechanics showed that, the density curve reconstructed by this method was suitable for the interpretation of rock mechanics parameters in Da’anzhai Member.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018