The key objective of the study is to develop a method for probabilistic estimate of the fluid types in the Achimov reservoirs within the East Urengoy license block where the presence of water-gas zones is common.
Currently, the scientific community is considering various hypotheses for the formation of flooded zones in anticlinal Achimov reservoirs. Our study describes the development of the concept associated with the intrusion of fresh elision waters squeezed out of clay seals into the initially gas-bearing reservoir during the neotectonic movements in the Paleogene time and compression of clay cap horizons of the sedimentary cover. The concept of elision waters intrusion implies the desalination of the source formation water which leads to uncertainties in assessing the fluid types and the need to complicate petrophysical models. A complex petrophysical model has been developed for the conditions of variable salinity of formation waters, implying the integration of electrical and flow models. At the same time, the electric model is a modification of the Archi-Dakhnov model adjusted to variable water salinity. The flow model gives an understanding of the critical saturations depending on the reservoir properties. Within the reasonable limit of salinity variability and calculated critical saturations, an algorithm for estimating the fluid types with the probabilities of “gas”, “gas and water”, and “water” has been developed. In total, these probabilities make up a unity (100%). The results of the probabilistic assessment of the fluid type were verified against the field data received from open-hole DSTs and logging-based inflow composition data. The model implementation across the entire well stock allowed to update the contour of the water-gas zone and analyze the distribution of elision waters within the reservoir.
References
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