Quantitative prediction model for the depth limit of oil accumulation in the deep carbonate rocks: A case study of Lower Ordovician in Tazhong area of Tarim Basin

Abstract

With continuous hydrocarbon exploration extending to deeper basins, the deepest industrial oil accumulation was discovered below 8,200 m, revealing a new exploration field. Hence, the extent to which oil exploration can be extended, and the prediction of the depth limit of oil accumulation (DLOA), are issues that have attracted significant attention in petroleum geology. Since it is difficult to characterize the evolution of the physical properties of the marine carbonate reservoir with burial depth, and the deepest drilling still cannot reach the DLOA. Hence, the DLOA cannot be predicted by directly establishing the relationship between the ratio of drilling to the dry layer and the depth. In this study, by establishing the relationships between the porosity and the depth and dry layer ratio of the carbonate reservoir, the relationships between the depth and dry layer ratio were obtained collectively. The depth corresponding to a dry layer ratio of 100% is the DLOA. Based on this, a quantitative prediction model for the DLOA was finally built. The results indicate that the porosity of the carbonate reservoir, Lower Ordovician in Tazhong area of Tarim Basin, tends to decrease with burial depth, and manifests as an overall low porosity reservoir in deep layer. The critical porosity of the DLOA was 1.8%, which is the critical geological condition corresponding to a 100% dry layer ratio encountered in the reservoir. The depth of the DLOA was 9,000 m. This study provides a new method for DLOA prediction that is beneficial for a deeper understanding of oil accumulation, and is of great importance for scientific guidance on deep oil drilling.