A refined evaluation method for the stress field of the Chang 73 shale oil reservoir of northern Shaanxi

Abstract

Shale oil resources are abundant in the Chang 73 reservoir in the eastern Ordos Basin. The thin interbeds of shale in the Chang 73 section of the Yanchang Formation in the oil-bearing section are developed with solid interlayer inhomogeneity and unclear longitudinal interlayer stress difference. This has resulted in unpredictable high seam extension heights during hydraulic fracturing. Based on the results of the Kaiser experiments, the lithological variability was finely described by combining with downhole core observations, and the longitudinal interlayer stress difference coefficient in the Chang 73 section was finely interpreted by using logging data to evaluate the regional distribution pattern of ground stress in the Chang 73 shale reservoir in northern Shaanxi. After studying 600 wells in north of Shaanxi, it was found that: the maximum longitudinal ground stress variation in the Chang 73 reservoir with a thickness of 30-50 m was 35-55 MPa, the minimum ground stress variation was 30-50 MPa, and the minimum was 30 MPa. The horizontal stress difference in the Chang 73 reservoir north of Shaanxi was 3.2-8.6 MPa. The maximum horizontal stress was high in the northwest and low in the southeast, with high values distributed in Jiyuan and Dingbian areas and low values distributed in Zhidan. The refined evaluation of the ground stress results guides the selection of the fracturing layer and the optimal design of the horizontal well trajectory in the field.