Implications of Water-Alternate-Gas Injection, for Profile Control and Injectivity (1990)

Implications of Water-Alternate-Gas Injection, for Profile Control and Injectivity S.B. Gorell S.B. Gorell Shell Development Co. Search for other works by this author on: This Site Google Scholar Paper presented at the SPE/DOE Enhanced Oil Recovery Symposium, Tulsa, Oklahoma, April 1990. Paper Number: SPE-20210-MS https://doi.org/10.2118/20210-MS Published: April 22 1990 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Gorell, S.B. "Implications of Water-Alternate-Gas Injection, for Profile Control and Injectivity." Paper presented at the SPE/DOE Enhanced Oil Recovery Symposium, Tulsa, Oklahoma, April 1990. doi: https://doi.org/10.2118/20210-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Improved Oil Recovery Conference Search Advanced Search SPE MemberAbstractSimulation results are presented which demonstrate that Water Alternate Gas (WAG) injection should not be expected to improve Vertical distribution of solvent, relative to continuous slug injection, for tertiary processes in non-communicating layered systems. These results are explained by considering the way in which fluid mobilities within, and between, different layers vary with time. WAG injection reduces the effective mobility of fluids in the highest permeability layer compared with continuous injection. However, it also reduces the mobility of the fluids in all the other layers, which can actually increase the fraction Of CO2 entering the highest permeability layer with WAG. Profile control with WAG should not be expected whenever the effective fluid mobility during solvent injection is higher than during water injection.The effect of compressibility on follow-up water injectivity reductions are also considered. Reduced water injectivity can result from the high compressibility of CO2 and the redistribution of pressure profiles when the injectant is changed from CO2 to water. While this redistribution is occurring, the local injection pressure gradient, and therefore the injectivity, is lower than one would calculate if compressibility were ignored. Differences between pressure and rate constrained injection schemes and the effects of slug size are also discussed.IntroductionIt is well known that continuous injection of low viscosity miscible agents, such as carbon dioxide, can result in early breakthrough and poor sweep efficiency. Water-Alternate-Gas (WAG) injection has poor sweep efficiency. Water-Alternate-Gas (WAG) injection has been suggested to alleviate some of these problems. The general idea is that multi-phase flow of CO2 and water should reduce the effective mobility of CO2 and improve sweep efficiency. Unfortunately, problems with scaling small slug volumes makes it difficult to problems with scaling small slug volumes makes it difficult to experimentally test how well WAG will perform. Analytical modeling i s also troublesome due to the cyclical nature of the process. To avoid these problems, much of the concepts about WAG are based on experimental and analytical modeling of solvent-water co-injection. In fact, early efforts to simulate field-scale WAG processes explicitly modeled co-injection. Although co-injection represents the small slug limit, it is not the process being implemented in the field. This paper addresses implications for WAG implemented as explicit alternate slugs. In particular, the results of field-scale simulations are presented where questions about the vertical distribution of CO2 (profile control) and water injectivity during WAG injection are considered.It is often argued that Water-Alternate-Gas (WAG) injection benefits relative to continuous slug injection because it provides profile control in heterogeneous layered reservoirs, such as those found in West Texas. Injected fluids tend to flow preferentially through high permeability layers, bypassing layers with low permeability. WAG permeability layers, bypassing layers with low permeability. WAG injection is supposed to lower the effective mobility of the fluids in the high permeability layers, thus diverting fluid into other layers. Although profile improvement during WAG injection has been conjectured, it has yet to be confirmed through either field examples or simulation studies. This paper documents simulations for tertiary CO2 injection in a 3-dimensional non-communicating layered system which do not demonstrate profile control with WAG. The results show that vertical distribution of CO2 is dominated by permeability constrasts; flow into each layer is essentially proportional to the fraction of the overall system KH and almost independent of WAG ratio.P. 371 Keywords: wag, water injection, mobility, waterflooding, wag injection, fluid mobility, modeling & simulation, water injectivity, vertical distribution, compressibility Subjects: Reservoir Fluid Dynamics, Improved and Enhanced Recovery, Flow in porous media, Waterflooding This content is only available via PDF. 1990. Society of Petroleum Engineers You can access this article if you purchase or spend a download.