This paper describes a study of the variability of measured composition for a single bulk sugarcane bagasse conducted across eight laboratories using similar analytical methods, with the purpose of determining the expected variation for compositional analysis performed by different laboratories. The results show good agreement of measured composition within a single laboratory, but greater variability when results are compared among laboratories. These interlaboratory variabilities do not seem to be associated with a specific method or technique or any single piece of instrumentation. The summary censored statistics provide mean values and pooled standard deviations as follows: total extractives 6.7% (0.6%), whole ash 1.5% (0.2%), glucan 42.3% (1.2%), xylan 22.3% (0.5%), total lignin 21.3% (0.4%), and total mass closure 99.4% (2.9%).

The effectiveness of cell-free rhamnolipid biosurfactant, derived from the culture medium at the end of fermentation was investigated for the removal of two different kinds of oil from contaminated sandy soils. The crude cultivation medium, containing 13.2 g L −1 of rhamnolipids, had a surface tension, interfacial tension and critical micellar concentration of 30 mN m −1 , 2 mN m −1 and 60 mg L −1 , respectively. The evaluation of biosurfactant in the culture medium (BM) and oil concentrations in the removal of oil from different contaminated sandy soil was performed using a statistical experimental design tool. Oil in sandy soil, containing predominantly aromatic or paraffinic hydrocarbons (5 to 10% w/w), was removed by as much as 91 and 78%, respectively, in the presence of reduced amounts of BM (6.3 to 7.9 g L −1 ). The progress of oil removal was monitored for 101 days and results indicated that removal efficiency in sandy soil with aromatic characteristics was relatively stable over the entire period. Based on these studies, it is concluded that use of a BM was effective in reducing oil concentrations in contaminated sandy soil.

Injectivity decline during sea/produced water injection is a wide spreadphenomenon in offshore and onshore waterflood projects. It happens due to solidand liquid particles suspended in the injected water; their capture by the rockresults in the hydraulic resistivity increase. The field injectivity declinehistory is used for characterisation of the formation damage system andconsequent well behaviour prediction. The injectivity index increases M times during the damage-free displacementof oil by water (M is the water-oil mobility ratio). It affects the wellinjectivity prediction during poor quality water injection and changes theresults of injectivity decline curves interpretation. We study the combined effect of the particle suspension injection and of thetotal oil-water mobility variation on well injectivity. An explicit formula forinjectivity decline due to both effects was derived. The effect of the totaloil-water mobility variation on injectivity is particularly significant forcases of heavy oil and relatively low formation damage. The injectivity decline formula derived allows for determination offiltration and formation damage coefficients and filter cake permeability fromthe well injectivity history. Two examples of well data treatment for thedeep-water offshore reservoir A (Campos Basin, Brazil) are presented. Introduction Injectivity impairment during water injection is a wide spread phenomenon inwaterflooding projects that use seawater, produced water or any other poorquality water. Solid and liquid particles from the injected water are capturedby porous media resulting in internal/external cake formation and insignificant injectivity damage1–3. The mathematical model for deep bed filtration in injector vicinity waspreviously developed1,2, and an explicit formula for injectivitydecline was derived. Further, the analogous formula was obtained for externalcake formation1–3. The main result is a piecewise linear dependenceof impedance index (the inverse of injectivity index) on injected water volumefor both deep bed filtration and external cake formation. The injection well vicinity is saturated by oil at the connate waterpresence before the injection, and is filled by the residual oil at thepresence of water after the flood. So, the injectivity index should increase Mtimes during waterflooding4,5 (M is the water-oil mobility ratio).Nevertheless, effects of changing oil/water mobility on injectivity declineduring internal/external cake formation have not been either studied or takeninto account during injector history interpretation. In the current work, an analytical model accounting for formation damage dueto both particle retention and water/oil mobility alteration is developed. Themodel is based on the observation that the formation damage due to particlecapture takes place in the injector's one-meter-radius-neighbourhood where onecould assume the residual oil saturation, while two-phase flow of oil and wateris important outside of this neighbourhood. An explicit formula for injectivityderived allows for well behaviour prediction as well as for formation damagesystem characterisation from the field data on well injectivity. Injectivity decline prediction has been performed for two wells from thedeep water offshore reservoir A (Campos Basin, Brazil) using the analyticalmodel developed, and the values for formation damage parameters, as obtainedwith and without total mobility variation consideration, differ significantly.The difference is particularly high for the cases of heavy oil and relativelysmall formation damage. Injectivity Decline due to Deep Bed Filtration and External CakeFormation Let us discuss one-phase flow of aqueous suspension accounting for particlecapture. Usually the injectivity impairment due to suspended particles happens in twostages: first the injected particles penetrate into a reservoir and arecaptured by reservoir rocks with consequent permeability reduction (deep bedfiltration) and second the particles build up an external filter cake after thecomplete plugging of the inlet cross section by retainedparticles1–3.

During the sea/produced water injection, the permeability decline occurs, resulting in well impairment. Solid and liquid particles dispersed in theinjected water are trapped by the porous medium and may increase significantlythe hydraulic resistance to the flow. Impairment of injectors by injected/reinjected water of a poor qualitypresent a serious problem for development of oil fields submitted towaterflooding. Similar problems occur in environmental engineering. Propagation ofbacteria, viruses and contaminants in ground water reservoirs present seriousenvironmental concerns. Design and planning of environmental protectionmeasures should be based on reliable mathematical modelling. The particle transport in porous media is determined by an advective flow ofcarrier water and by hydrodynamic dispersion in micro heterogeneous media. So, the particle flux is a total of advective and dispersive fluxes. Transport ofparticle suspensions in porous media is described by the advection-diffusionequation and by the equation of particle capture kinetics. The conventionalmodel for deep bed filtration accounts for hydrodynamic particle dispersion inmass balance equation but does not consider impact of dispersive flux inretention kinetics. In the present study, the model for deep bed filtration accounting forparticle hydrodynamic dispersion in both mass balance and retention kineticsequations is proposed. The travelling wave solution was found for the blockingfunction type of filtration coefficient (that becomes zero after the depositreaches some critical value). This critical value can be determined from theparticle breakthrough time. Introduction Deep bed filtration of particulate suspension in porous media takes placeduring water injection into oil reservoirs, in the processes of drilling mudpenetration into a reservoir causing formation damage, in produced waterdisposal in aquifers, during bacteria, virus and contaminant transport inground water, during industrial filtering, etc.1–3. The basicfeatures of the process are advective and dispersive particle transport andparticle capture by the porous medium. The reliable prediction of well impairment and oily water propagation isbased on mathematical modelling. The basic equations for deep bed filtration accounting for advectiveparticle transport and kinetics of particle retention and ignoring hydrodynamicdispersion have been developed essentially following the filtration equationproposed by Iwasaki4. A number of predictive models were presentedin the literature1–3,5,6. The equations allow for various analyticalsolutions that have been used for treatment of laboratory data and predictionof porous media contamination and clogging1,3,7,8. Nevertheless, particle dispersion in heterogeneous porous media issignificant for both small and large scales9. The typical sandcolumn size in laboratory experiments is small, so the Peclet number isrelatively low. The typical dispersivity value for large scales is high, soPeclet number may also reach low values. Therefore, several deep bed filtration models account for dispersion ofparticles3,8,10–13. A detailed description of such early work ispresented in the review8. The models account for particle dispersionin mass balance for particles but ignore the dispersion flux contribution intothe retention kinetics. Recent study14 shows that the deep bed filtration model, accounting for dispersion in both equations of mass balance and of capturekinetics, exhibits more realistic behaviour for steady state flows than thetraditional model8,10–13. In the current paper, the travelling wave flow regime was found for themodel that accounts for dispersion in both mass balance and retentionkinetics14. The travelling wave regime exists only for a blockingtype of filtration coefficient that becomes zero after the deposit reaches somecritical value. The critical value can be found from the wave breakthroughtime. The solution obtained can be used for prediction of particle propagation inreservoirs and for interpretation of laboratory coreflood data.