Tectonic fracture prediction for lacustrine carbonate oil reservoirs in Paleogene formations of the western Yingxiongling area, Qaidam Basin, NW China based on numerical simulation

Fractures are widely developed in lacustrine carbonate reservoirs in the Oligocene Lower Ganchaigou Formation of the western Yingxiongling area and their distribution trend is unclear. Based on well logging, formation testing, rock mechanics parameters obtained by logging interpretation, and the paleotectonic stress obtained by acoustic emission experiments, finite element numerical simulation is used to restore the tectonic stress of the typical section and target layer plane models in the late Himalayan period in the study area. The fracture distributions of the section and the plane are quantitatively predicted and their distribution trends are summarized. The results show that the tectonic compression at the end of the Neogene was strong in the study area. Under the effect of the paleotectonic stress field, the fracture development degree of the upper member of the Lower Ganchaigou Formation is generally high. Fractures mainly developed in the fault zones and their surroundings, the hanging wall of the Shizigou fault, and the abnormally high-size area of tectonic stress intensity in the northern and middle tectonic zones of the presalt carbonate reservoirs. The fracture distribution is mainly affected by faults, lithology, structural parts, and tectonic stress intensity. The predicted favorable development areas of fractures can be considered favorable exploration positions in the deep layers of the study area. This study can provide a guide for the deep oil–gas exploration in the study area and a feasible method for predicting the sweet spots of this type of tight reservoir.

Graphical abstract

Using the finite element numerical simulation, the geological models for the lacustrine carbonate oil reservoirs are established. The tectonic stress field of theirs is restored. Combined with the comprehensive fracture index evaluation, the fracture development degree parameters are constructed to realize the quantitative prediction of the fracture distribution.