Carbonatization of terrigenuos reservoirs of the Pokur formation of Senomanian stage in the northern West-Siberian region: factors of occurrence and nature of distribution

The article observes publications devoted to postsedimentation carbonatization in terrigenous reservoir rocks. The widespread occurrence of this phenomenon in many hydrocarbon deposits and a significant decrease in porosity caused by filling the void space with carbonate cement constitute the relevance of the issue under study. The problems of formation of fluid-resistant rocks in the reservoir, which can influence the redistribution of fluid flows during the development of the deposit, are considered. It is noted that there is no generally accepted methodology for identifying and predicting the distribution of these intervals based on the interpretation of geophysical methods of well survey, as well as the impossibility of differentiation based on seismic data. The problems of predicting the distribution of carbonatization are considered using the example of the studied field X in the Pur-Taz oil and gas region of Western Siberia, where the presence of carbonatization in the form of thin interlayers, solid intervals with varying degrees of cementation, and also in the form of nodules is noted. The facies association of carbonatization with the most sandy reservoirs of coastal-continental environments has been established. The effect of carbonation on filtration-capacitance properties is calculated. The absence of a relationship between the intensity of carbonatization and the proximity of discontinuous faults based on the materials of the deposit under consideration has been revealed. It is established that the carbonatized interlayers extend no more than the first tens of meters. Using the example of other deposits, we focus on the need to consider for carbonatized intervals in petrophysical, geological, and hydrodynamic models. It is shown that the presence of carbonatization is a risk for fluid breakthrough both due to natural fracturing and after hydraulic fracturing. From this point of view, the study of carbonatized intervals and their distribution in the reservoir volume allow increasing the predictive capabilities of hydrodynamic models, taking into account filtration processes in a lithologically heterogeneous reservoir.