In-situ stress analysis in the Chang 7 reservoir of northern Shannxi region

Abstract

The Shaanbei Chang 7 shale oil reservoir in the Ordos Basin develops vertically with multiple lithologic superimpositions. The interlayer stress of sand-mud-shale thin interbeds is different, and the stress within the small layer is variable, resulting in high hydraulic pressure fractures and short extension distances. The effective retrofit volume did not meet expectations. Based on the in-situ stress of key layers tested by the Kaiser in-situ stress test, the in-situ stress distribution law of vertical multi-interbedded layers with different lithologies was obtained by finely interpreting the single-well in-situ stress logging results, combined with the geological, structural and sedimentary characteristics of the block, established a three-dimensional in-situ stress regional model of complex lithologic reservoirs based on fine geological bodies, simulated the regional in-situ stress distribution law of sand-mud-shale multi-thin interbedded lithology, and mastered the geological The spatial lateral and vertical differences of the stress field. The calculation results show that the overall three-dimensional stress of the block is σV>σH>σh, the maximum principal stress range of the longitudinal upper interlayer is 35∼58 MPa, the minimum principal stress range is 28∼55 MPa, and the horizontal stress difference range is 6∼8 MPa, the stress value of sandstone in the lateral upper layer is greater than that of shale and that of mudstone, and the difference of horizontal stress in the vertical direction increases with the increase of depth. By analyzing the in-situ stress distribution of different interlayer depths and bedding lithologies, it provides parameter guidance for the fracturing design of complex lithologic reservoirs in the Chang 7 Member in northern Shaanxi, Ordos Basin.

Keywords

• Ordos Basin
• In-situ stress test
• Three-dimensional in-situ stress field
• Fracturing design