Crossflow Effects During an Idealized Displacement Process In a Stratified Reservoir

Abstract

A mathematical model has been used to investigate cross flow effects in a stratified reservoir during an idealized displacement process. A process in which one incompressible fluid displaces completely another incompressible fluid of the same density and viscosity was considered. The reservoir was assumed to be composed of homogeneous layers which are discrete but interconnected. Approximate five-spot flow geometry was simulated by arranging two pie-shaped cylindrical (two-dimensional) wedges in series. Some of the common production methods rely, for their effectiveness, on the fact that the formation consists of isolated strata. This is particularly true of selective plugging and single-zone production- injection methods. The effectiveness of these techniques for several cases in which adjacent strata are in communication has been evaluated. The usual production-injection schemes for fluid injection processes involve using the same completion interval in both the production and the injection wells. The efficiency of this, as well as alternative production-injection procedures has been examined for some cases involving communicating strata. Introduction The performance of many fluid injection projects is marred by early breakthrough and by production of a high percentage of the displacing phase after breakthrough. This channeling effect, if it occurs in reservoirs which have large permeability variations, is often explained on the basis of a model composed of discrete, isolated strata. Corrective or preventive measures based on this same model are also common. The behavior of stratified models has been the subject of considerable study. An excellent review of the early literature was given by Seba. Studies of the depletion performance have since been made for continuous, unrestricted communication between strata and for production from one permeable bed in continuous but restricted communication with an adjacent permeable bed. Model studies of displacement processes in stratified systems with crossflow also have been reported. Finally, methods which account for crossflow have been developed for computing displacement behavior in stratified systems. Most methods for controlling or preventing channeling involve some change in the interval open to production and/or injection. Although many variations of the selective completion problem have been studied in regard to the depletion of a reservoir, little attention has been given to the behavior of a displacement process under similar conditions. Seba used a resistance network model to study the performance of a process in which one incompressible fluid displaces an identical fluid from a linear, stratified reservoir. He investigated the possibility of improving the vertical coverage by limiting the completion interval of the production well. This investigation deals with techniques in which selective completion of the production and/or the injection wells is used in an attempt to control channeling. At one extreme, selective plugging and single-zone isolation (assuming perfect execution) should be successful if the reservoir is actually made up of independent strata. At the other extreme, they can hardly be expected to be successful if the channeling is caused by a mechanism in which stratification effects are negligible even though there are extreme variations in the formation permeability and/or the injectivity profile of the wells is not uniform. By contrast, it is difficult to anticipate the effect that the amount of communication between the beds of a stratified system will have on the efficiency of selective completion techniques. The objective of this study is the quantitative determination of the effect of communication on the behavior of some particular stratified systems which will at least lead to qualitative conclusions. SPEJ P. 229ˆ

Placement Using Viscosified Non-Newtonian Scale Inhibitor Slugs: The Effect of Shear Thinning

“…Flow in layered systems with crossflow has also been studied previously (Root and Skiba 1965;Zapata and Lake 1982;Sorbie et al 1989b;Sorbie et al 1990;Sorbie and Seright 1992).…”

Developing High Resolution Static and Dynamic Models for Waterflood History Matching and EOR Evaluation of a Middle Eastern Carbonate Reservoir

“…It is well recognized that cross-flow has significant impact on sweep efficiency of immiscible displacement in layered reservoirs. The effect of both gravity and viscous forces on cross-flow and sweep efficiency has been extensively studied in the literature (Root andSkiba 1964, Goddin et. al.…”

A Strategy for Attacking Excess Water Production

“…22 For many years, engineers recognized that near-wellbore blocking agents are ineffective in these applications. 73 Even if the blocking agent could be confined only to the high permeability channel, water quickly crossflows around any relatively small plug. The only hope for blocking agents in these applications exists if a very large plug (i.e., that plugs most of the channel) can be…”

“…73 Unfortunately, existing gelants (including the so-called "colloidal dispersion gels") enter and damage all open zones in accordance with the Darcy equation and basic reservoir-engineering principles. 22 Penetration and damage caused to the less-permeable zones is greater for viscous gelants than for low-viscosity fluids.…”