Gas Gravity Drainage Under Secondary and Tertiary Conditions in Fractured Reservoirs

Abstract

Variety of gases can be used for injection into reservoirs under conditions varying from immiscibility to full miscibility. Also gas injection has found applications in both secondary and tertiary conditions. The advantage and disadvantage of different combinations of each of the above will depend on the particular context. The reported laboratory work and subsequent simulation work has been done in clarifying the influence of the parameters controling the efficiency of the different processes under gravity drainage conditions. This paper addresses the problem of oil recovery by gas injection under primary condition and of water flooded reservoirs with particular emphasis on the use of lean hydrocarbons gas. A systematic investigation was carried out to highlight the parameters controling such processes. The work comprised of analysing reported laboratory experiments under reservoir conditions and interpretation of these experiments using a compositional simulator. Laboratory experiments included both centrifuge tests and core floods under reservoir conditions. The core displacement was designed to help determine the 3- phase oil relative permeability at low oil saturation. The investigation confirms that tertiary lean gas injection is capable of mobilizing Waterflood residual oil and thus reducing the residual oil saturation. The work also helps to identify the role of 3- phase relative permeability. In addition the role of gas-oil diffusion under tertiary condition is discussed. Moreover, simulations were made to clarify the effect of block boundaries in block-to-block interaction.

Development and Optimization of Gas-Assisted Gravity Drainage (GAGD) Process for Improved Light Oil Recovery

“…Injection under secondary conditions, especially in an unsaturated oil reservoir (without gas cap), firstly results in an initial single-phase oil displacement followed by secondary gas-oil gravity drainage in the gas-invaded zone (Saidi and Sakthikumar, 1993). The secondary gravity drainage is controlled by the spreading coefficient (discussed in Section 3.5.3) and this secondary oil film flow (under positive spreading coefficients) is important for high gravity drainage oil recoveries in water-wet and mixed wet reservoirs.…”

Experimental Study of Gravity Drainage During Gas Injection in Carbonate Rocks

“…Knowledge of this mechanism has been progressively improved since sixties 1 . In fractured oil reservoirs submitted to gas injection; gravity drainage is the main mechanism of oil production from the matrix blocks.…”