Alkaline consumption

Calcium and/or magnesium sulphates can originate from dry deposition of aerosols, from deposition of dust or from sulphur-containing rocks in the catchment. Since carbonate seems not to be the only calcium and magnesium source, the alkalinity consumption calculated earlier must be considered as an overestimation. 

Polymeric forms of the coagulants (e.g., polyaluminum chloride) are rather useful because they require lower alkalinity consumption and the concomitant lower production of sludge. Once the colloids are destabilized, slow stirring can also help them merge and form relatively large aggregates called floes (hence the name flocculation) that are separated from water by settlement and filtration. In some cases, these floes can be attached to purposefully generated gas bubbles and separated by flotation. 

Almost all chemical EOR applications have been in sandstone reservoirs, except a few stimulation projects and a few that have not been published have been in carbonate reservoirs. One reason for fewer applications in carbonate reservoirs is that anionic surfactants have high adsorption in carbonates. Another reason is that anhydrite often exists in carbonates, which causes precipitation and high alkaline consumption. Clays also cause high surfactant and polymer adsorption and high alkaline consumption. Therefore, clay contents must be low for a chemical EOR application to be effective. 

Shen and Chen (1996) put the alkaline consumption in this order gypsum > montmorillonite > kaolinite > illite > anorthosite (plagioclasite) > microclinite > quartz > mica > dolomite > calcite. These orders are consistent with the general trend. 

A pilot pattern should be chosen so that the injected fluid is well controlled within the pattern. Otherwise, the fluid may be lost through directional flow channels. Then any interpretation or evaluation of the pilot performance would be difficult. When evaluation wells are drilled, cores should be taken in a closed-loop method so that reservoir conditions are maintained. These cores are used to evaluate alkaline consumption, measure relative permeabilities, and so on. Formation evaluation tests are conducted at evaluation wells. Finally, simulation models (sector models) are built to integrate all the data taken to evaluate the alkaline flooding performance. 

Alkaline consumption by chemical reaction and ion exchange is mainly due to the existence of clays. Thns, clay content shonld not exceed 15 to 25%. Formation permeability shonld be greater than 100 md. 

The interaction between alkali and polymer, to be discussed in this section, includes alkaline effect on polymer viscosity, polymer effect on alkafine/oil IFT, and alkaline consumption in alkaline-polymer systems. 

Laboratory test results show that alkaline consumption in an alkaline-polymer system is lower than in the alkaline solution itself. The reason is probably that polymer covers some rock surfaces to reduce alkali-rock contact. In an alkaline-polymer system, alkali competes with polymer for positive-charged sites. Thus, polymer adsorption is reduced because the rock surfaces become more negative-charged sites (Kmmrine and Falcone, 1987). Mihcakan and van Kirk (1986) observed that alkaline consumption in a radial core is smaller than that in a linear core. 

Alkaline-polymer can reduce polymer adsorption and alkaline consumption... 

NaaCOs—were used to compare IFT reduction, emulsification, alkaline consumption, and aLkaline-polymer interaction. The results were as follows ... 

NaOH Strong emulsification, low IFT, narrow range of optimum concentrations, high aLkaline consumption, and quick polymer hydrolysis so that it was difficult to control. 

Na2SiOy Strong emulsification, low IFT, medium alkaline consumption, and flocculation occurred after a long reaction with polymer. 

One natural core was used to compare the performance of waterflood (W), AP flood, and ASP flood. The recovery factors for W, AP, and ASP were 50%, 69.7%, and 86.4%, respectively. These core flood tests were history matched, and the history-matched model was extended to a real field model including alkaline consumption and chemical adsorption mechanisms. A layered heterogeneous model was set up by taking into account the pilot geological characteristics. The predicted performance is shown in Table 11.3. In the table, Ca, Cs, and Cp denote alkaline, surfactant, and polymer concentrations, respectively. After the designed PV of chemical slug was injected, water was injected until almost no oil was produced. The total injection PV for each case is shown in the table as well. The cost is the chemical cost per barrel of incremental oil produced. An exchange rate of 7 Chinese yuan per U.S. dollar was used. From... 

A number of laboratory investigations were made into different aspects of consumption of sodium hydroxide and sodium orthosilicate in alkaline flooding of petroleum reservoirs for enhanced oil recovery. One investigation studied the role of reversible adsorption and of chemical reaction v en petroleum reservoir sands are contacted with alkaline solutiais. Another investigation studied the effect of flow rate on caustic consumption by means of a series of flow experiments through reservoir sand packs. A third series of high rate flow experiments studied changing alkaline consumption with time. 

Table I also gives the alkaline caisunnption of some minerals and sands obtained by treating 10 grams of sample with excess 1 5% sodium orthosilicate after 5 and 62 days. Although the experimental conditions such as ccxicentraticxi type of alkaline chemicalsr torperature particle size used by different investigators varied the results clearly show that with longer time of contactr alkaline consumption will increase.

In comparing sodium hydroxide and sodium orthosilicate solutions of the same concentration the alkaline consumption for sodium orthosilicate was significantly lower than that for sodium hydroxide. For example, the alkaline consumption of TRIMS Ranger sand was 9.2 mec lOOg sand for 1.0% sodium orthosilicate vhile the consumption was 25.1 meq/lOOg for 1.0% sodium hydroxide. Thus sodiuti orthosilicate seems to be superior to sodium hydroxide for alkaline flooding. 

Alkaline Chemical Sand Alkaline Consumption (ineq/lOO g)... 

During the early 1980 s, soon after the first version of the PAAF process was introduced, a second version was proposed for the PAAF process, which incorporates a single blend slug of alkaline and polymer chased by a fresh polymer slug. The main idea behind the second version of the PAAF process is to employ the capability of polymer adsorption on the rock surface to mitigate the alkaline consumption. ... 

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