Type and Distribution of Carbonate Rock Interlayer and Its Influence on Gas-Water Systems Division-Case Study of the West Inner-Platform Gas Fields in the Amu Darya Basin

The Karlov-Oxford terrace of the west inner-platform gas fields on the right bank of the Amu Darya River in Turkmenistan is located in the sedimentary environment of the restricted platform and the evaporation platform. Based on the analysis of core, logging data, porosity, permeability, and test data, the type, origin and distribution of the Karlov-Ooxford stage interlayer in the western gas field are studied. Generally, the Karlov-Ordonian strata are divided into anhydrite interlayer, dense argillaceous limestone interlayer and argillaceous limestone interlayer. The gypsum interlayer is gypsum rock deposited on the evaporation platform in an arid environment, the dense micrite limestone interlayer is micrite limestone deposited under the relatively low-energy hydrodynamic conditions of the limited-evaporation platform or gentle slope, and the marlite interlayer is lagoon mud deposited under the closed and quiet water body on the limited platform or gentle slope. Due to the influence of the vertical and horizontal distribution of the interlayer, the porosity and permeability conditions and the sealing ability, different gas-water systems may be developed in the vertical direction. These different gas-water systems have been confirmed by the test and logging results. The geological understanding of multiple sets of oil, gas and water systems has greatly improved the reserve evaluation of the gas field, and may delay the invasion of bottom water and edge water in subsequent development wells, which has an important guiding role for the development of the gas field.