Phase Transformations in Gas Producing Wells of the Kovyktinskoye Gas Condensate Field and Chayandinskoye Oil and Gas Condensate Field (Eastern Siberia)

The main characteristics of the Kovyktinskoye gas condensate field (KGCF) and the Chayandinskoye oil and gas condensate field (ChOGCF) were analyzed: formation temperature and pressure, gas composition, total mineralization and ionic composition of formation water. For the KGCF, the formation gas water content in equilibrium with pure and mineralized water was calculated. Temperature profiles of a typical production well at different gas flow rates were determined and compared with the temperature profiles of the ChOGCF wells. A detailed analysis of phase equilibria in the “water + gas + mineral salts + methanol” systems in the wells was carried out. It was shown that for KGCCF wells in the absence of formation water flow, water vapor condensation in the well tubing does not begin immediately, but at some distance from the well bottom, and water vapor condenses into liquid water. Hydrate formation is possible in the top of the tubing closer to the wellhead. Whereas for the ChOGCF well, the water vapor contained in the gas condenses in the tubing into the hydrate phase, bypassing liquid water. When methanol or water-methanol solution (WMS) is injected to the well bottom, the phase transformation pattern changes. In the tubing of the Kovyktinskoye field wells, methanol initially completely evaporates into the gas phase, and WMS condensation begins higher up the wellbore, prevetning the hydrate formation at the wellhead. In the case of the Chayandinskoye field, methanol injected into the well bottom partially evaporates into the gas phase with simultaneous condensation of water vapor. This process forms diluted WMS, which can intensify the hydrate formation process. In the case when the mineralized formation water flows into the well, the condensation of water vapor from the gas begins immediately at the bottom and the concentration of salts in the liquid phase decreases. For the KGCF, the salt concentration is nevertheless sufficient for self-inhibition of the wells, while for the ChOGCF, additional methanol injection is required. The features of the unstable hydrocarbon condensate formation and changes in its composition along the well tubing of were also analized.