Infinite Acting and Finite Acting - yohanesnuwara/reservoir-engineering GitHub Wiki

During single-phase-flow in porous media, flow behaves in two conditions: infinite-acting (or unsteady flow) and finite-acting (or pseudosteady flow). Under short time and distance of flow from the outer boundary of reservoir, flow starts with behaving infinite-acting.

Infinite-acting happens when:

• Flow time is of short duration.
• Well drainage area is large, reservoir is large enough.
• Flow transient has not reached the reservoir boundary.

Time to reach finite-acting is t_finite_acting. t_finite_acting is calculated in this way:

• Calculate r_eD = re / rw from Equation 6.14; re: reservoir size, rw: radius of wellbore
• Calculate t_Dw_finite = 0.25 * (r_eD**2) from Equation 6.13.
• Re-arrange Equation 6.13 to calculate t from t_Dw: t_finite_acting = ((poro * mu_oil * ct * (rw**2) * t_Dw_finite)) / (0.0002637 * k ) in oilfield units

Infinite-acting occurs at flow times < t_finite_acting, or automatically flow t_Dw < t_Dw_finite. When flow times >= t_finite_acting, or automatically flow t_Dw >= t_Dw_finite, flow/well/reservoir behaves finite-acting.