Polymers are known to degrade chemically under reservoir conditions. In this paper we simulate the effect of chemical degradation on polymer flooding, using a modified chemical flooding code. We particularly investigate layered reservoirs, in which particularly investigate layered reservoirs, in which vertical crossflow is shown to be the leading oil recovery mechanism. The calculated effects of degradation are explained in terms of the effects of polymer on fluid flow patterns. Results are polymer on fluid flow patterns. Results are presented for different polymer and reservoir types, presented for different polymer and reservoir types, and the effect of non-uniform reservoir temperature on degradation rates is also studied. It is shown that there are a number of types of polymer flood in which the effects of chemical degradation are less severe than might initially be expected.
When a polymer is considered for an improved oil recovery project, it should first be subjected to a number of laboratory screening tests. Such procedures should include polymer injectivity, procedures should include polymer injectivity, adsorption and brine compatibility tests along with a study of its microbial, mechanical and chemical degradation characteristics.
The chemical stability of polymers under reservoir conditions has been identified as one of the most important factors governing the success of a polymer flood. Substantial laboratory investigations polymer flood. Substantial laboratory investigations of polymer stability have been carried out both to gather general data on degradative mechanisms and for specific field applications. Long term stability testing has been carried out on polyacrylamide, xanthan biopolymer and on a range of other polymer types Each of these investigations polymer types Each of these investigations has involved the aging of polymer solution samples with a wide range of additives under different environmental conditions, and the measurement of viscosity and screen factor at times of up to several months.
It has been found that chemical degradation can be particularly significant under conditions of elevated temperature and high salinity. Although the use of various additives can substantially increase polymer stability, chemical degradation will remain an important issue in the planning of polymer floods in the field.
In order to make best use of these careful experimental studies, it is essential to understand how the polymer behaves. This requires us to move substantially beyond simple comparisons of polymer lifetime with the expected timescale of polymer flooding. In this paper it is shown that such comparisons can be very misleading. Instead, a full investigation of the effects of polymer, and polymer degradation, on fluid flow within the reservoir, is needed. It is only then that we can state what degree of polymer stability is required for technical and economic viability.
A chemical flooding simulation model has been developed, which includes calculation of temperature distributions and chemical reactions whose rate may depend on temperature. In this paper, we report the results of numerical studies of polymer flooding using the full facilities of this model. An analysis of the basic incremental oil recovery mechanisms due to polymer is provided in terms of its effect on flow patterns within the reservoir. These mechanisms are patterns within the reservoir. These mechanisms are then used to interpret the results of simulations of floods with polymers of different physical properties, subject to degradation at different properties, subject to degradation at different rates.
Much of the work reported is concentrated on stratified reservoirs, with a high permeability contrast between the different layers, and low water/oil mobility ratios. This is in part because such formations are found in the North Sea. In these cases, polymer might be used to improve waterflooding performance by reducing channelling along the high performance by reducing channelling along the high permeability layers, leading to better sweep of the permeability layers, leading to better sweep of the low permeability layers and a lower watercut. Reservoirs with and without barriers to vertical flow are considered - the distinction is shown to be most important in assessing the effects of chemical degradation. For comparison some results are presented on the impact of polymer degradation in the presented on the impact of polymer degradation in the flooding of homogeneous areal systems.