Modeling of the suffosion cavities development in bitumen saturated sandstones of Ashalchinskoye deposit under SAGD technology application

Abstract

The development of the Ashalchinskoye bitumen deposit using steam assisted gravity drainage (SAGD) technology associated is with suffosion processes in bitumen-saturated sandstones layers. Based on model experiments it was shown that influence of the water vapor on bituminous sandstones leads to a decrease in their mechanical parameters. As result of this reaction will decrease of cohesive forces between rock fragments due to the dissolution of bitumen and carbonate cement. The parallel lateral injector and exploitation wells which located in weakly cemented sandstones will lead to dissolution of their cement and destruction of the mineral skeleton to mouldy state. In the conditions of stabilized filtration flowing between paired wells, a part of very fine-grained terrigenous material will be washed out, promoting to formation of suffosion cavities in reservoir layer. Based on existing technological parameters for development of the Ashalchinskoye bitumen-saturated deposit was carried math modeling of this process development. As examples we used two horizontal wells of 200 and 400 m in length, with minimal and maximal flow rates 20 and 34 tons per day, respectively. Estimation of the suffosion cavity size, as well as the time of its formation is carried out taking into account the physical filtration rate of the fluid in the pores of each rock type, which characterizes the degree of cementation of the rock. Mathematical calculations have shown that the development of such sandstone reservoirs in the field of filtration flow between paired lateral wells can lead to the formation of suffosion cavities. The intensity of the cavity development will be determined by the degree of sandstones cementation and technological parameters of exploration system. Mainly suffosion process depends from horizontal well exploration length and recovery rate of formation fluid. Sign of the suffosion cavity beginning formation can be considered the appearance of terrigenous material in hole of exploitation well.