The objective of this paper is to couple wellbore and surface production facilities models with reservoir simulation for a shale reservoir that contains dry gas, condensate and oil in separate containers. The goal of this integration is to improve liquid recoveries by dry gas injection and gas recycling.
Methods published up to now to investigate possible means of improving recovery from shales have concentrated on laboratory work and the reservoir itself, but have ignored the surface and wellbore production facilities. The coupling of these facilities in the simulation work is critical, particularly in cases involving condensate and oil reservoirs, gas injection and recycling operations. This is so because a change in pressure in the reservoir is reflected almost immediately in a change in pressure in the wellbore and in the surface installations.
The development presented in this paper considers multi-stage hydraulically fractured horizontal wells. Dry gas is injected into zones that contain condensate and oil. Gas stripped from the condensate production is re-injected in the condensate zone in a recycling operation.
The study leads to the conclusion that liquid recoveries can be maximized by utilizing continuous and huff and puff gas injection schemes. In general, huff and puff injection provides better results in terms of production and economics. Molecular diffusion is found to play a crucial role in continuous gas injection operations. Conversely, the effect of this phenomenon is negligible in huff and puff gas injection. This research demonstrates that proper design of wellbore and surface installations, including for example downhole pumps and compressors, is important as they play a critical role in the performance of production and injection operations, and in maximizing recovery of liquids from shale reservoirs.
The novelty of the methodology developed in this paper is the coupling of models that handle surface facilities, wellbores, numerical simulation including oil, condensate and dry gas reservoirs, gas injection and gas-condensate recycling operations. Essentially the shale containers, wellbore and surface facilities are ‘talking’ to each other continuously. To the best of our knowledge this integration for shales has not been published previously in the literature.