In nearly all applications, the steady-state models discussed in the previous section are not adequate in describing the water influx. The transient nature of the aquifers suggests that a time-dependent term be included in the calculations for We. In the next two sections, unsteady-state models for both edgewater and bottomwater drives are presented. An edgewater drive… Continue reading Unsteady-State Models
Month: June 2023
Steady-State Models
The simplest model that will be discussed is the Schilthuis steady-state model, in which the rate of water influx, dWe/dt, is directly proportional to (pi – p), where the pressure, p, is measured at the original oil-water contact.5 This model assumes that the pressure at the external boundary of the aquifer is maintained at the initial value pi and that flow to… Continue reading Steady-State Models
Introduction
Many reservoirs are bounded on a portion or all of their peripheries by water-bearing rocks called aquifers (from Latin, aqua [water], ferre [to bear]). The aquifers may be so large (compared with the reservoirs they adjoin) that they appear infinite for all practical purposes; they may also be so small as to be negligible in their effect on reservoir performance. The… Continue reading Introduction
Introduction to Pressure Transient Testing
Pressure transient testing is an important diagnostic tool that can provide valuable information for the reservoir engineer. A transient test is initiated by creating a disturbance at a wellbore (i.e., a change in the flow rate) and then monitoring the pressure as a function of time. An efficiently conducted test that yields good data can… Continue reading Introduction to Pressure Transient Testing
Superposition in Bounded or Partially Bounded Reservoirs
Although Eq. (8.39) applies to infinite reservoirs, it may be used in conjunction with the superposition principle to simulate boundaries of closed or partially closed reservoirs. The effect of boundaries is always to cause greater pressure drops than those calculated for the infinite reservoirs. The method of images is useful in handling the effect of boundaries. For example,… Continue reading Superposition in Bounded or Partially Bounded Reservoirs
Superposition
Earlougher and others have discussed the application of the principle of superposition to fluid flow in reservoirs.3,12,13,14 This principle allows the use of the constant rate, single-well equations that have been developed earlier in this applies them to a variety of other cases. To illustrate the application, the solution to Eq. (8.38), which is a linear,… Continue reading Superposition
Productivity Ratio (PR)
In evaluating well performance, the standard usually referred to is the productivity index of an open hole that completely penetrates a circular formation normal to the strata and in which no alteration in permeability has occurred in the vicinity of the wellbore. Substituting Eq. (8.47) into Eq. (8.49), we get The productivity ratio (PR) then… Continue reading Productivity Ratio (PR)
Productivity Index (PI)
The ratio of the rate of production, expressed in STB/day for liquid flow, to the pressure drawdown at the midpoint of the producing interval, is called the productivity index, symbol J. The productivity index (PI) is a measure of the well potential, or the ability of the well to produce, and is a commonly measured well property.… Continue reading Productivity Index (PI)
Radial Flow of Compressible Fluids, Pseudosteady-State Flow
The differential equation for the flow of compressible fluids in terms of the real gas pseudopressure was derived in Eq. (8.42). When the appropriate boundary conditions are applied to Eq. (8.42), the pseudosteady-state solution rearranged and solved for q yields Eq. (8.48):
Radial Flow of Slightly Compressible Fluids, Pseudosteady-State Flow
Once the pressure disturbance has been felt throughout the reservoir including at the boundary, the reservoir can no longer be considered as being infinite in size and the flow is not in the transient regime. This situation necessitates another solution to Eq. (8.38), using a different boundary condition at the outer boundary. The initial condition… Continue reading Radial Flow of Slightly Compressible Fluids, Pseudosteady-State Flow