Conditions of trapped gas accumulations in the course of selective flooding of deposits

Abstract

In the given article the authors have analyzed the mechanism of a gas reservoir trapping in the water-flooded areas of deposits in conditions of water drive occurrence under stratal waters income to the gas-saturated pore volume. It has been found out that the mechanism of trapped gas deposits by raising the level of gas-water contact and selective flooding are fundamentally different by volumes of locked gas, the rate of formation and approach to its production.

It has been found out already at the early stages of research that selective water streams intrude into low-power high-permeable layers by section and the area of deposits reducing formation pressure. They dissect the initial gas-saturated pore volume into several volumes, which are hydrodynamically-trapped in varying degrees. That is, it creates a hydrodynamic macroinhomogeneity of megavolumes accumulations, what is the current effective gas-saturated pore volume amounts about 80-95%, and only 5-20% of the volume occupied by the medium stratum water. Due to the layering (volatility) of the pore space in certain areas of the collector layer there are observed "lithological windows", therefore the above and embedded in the section selective water streams are connected and there is the effect of the cut-off and trapping of significant values of gas by stratum water. It is concluded that it is during the selective stratal waters implementation is spread the negative phenomenon of gas accumulations trapped which may be equivalent by volume to industrial deposits. It is suggested that the trapped volumes of gas formed by selectively flooding are called hydrodynamic-trapped gas accumulations. The conditions of their formation are researched on the basis of studying the processes of selective deposits flooding of Timofeevska, Kotelevsky, Berezovsky and other fields.

On the assumption of characteristics of the hydrodynamic-trapped gas accumulations at the expense of selective flooding it is offered in each case in the sequence to determine unflooded gas-saturated deposits intervals and test them for subsequent extraction of dry gas.