C EMICALS1II

Enhanced oil recovery is the term used to describe non-conventional oilrecovery techniques. These techniques are designed to recover more oil out of sub-surface reservoirs than is possible by natural production mechanisms or by theinjection of water and gas. These non-conventional techniques may be divided intothree categories; thermal, miscible and chemical. The categories are not exclusive,since chemical additives may be used to improve the effectiveness of thermal andmiscible techniques.

PRINCIPLE OF MOBILISATION OF OIL BY SURFACTANT

Sand grains ---- _

Water injection

Oil droplet .J

Normal droplet is slightly deformed but still held trapped

Surfactant slug

Enhanced oil recovery by chemical processes involves the injection ofsurfactants and water-soluble polymers into the reservoir. These chemicals impro ethe mobilisation and displacement of the oil remaining in the reservoir, and canachieve the recovery of up to a further 40% of the remaining oil.

The EOR surfactants and polymers available from Shell representimportant advances over currently available products. They offer higherperformance and greater cost-effectiveness. And Shell Chemicals Research, in

. collaboration with Shell's Exploration and Production Laboratories, continues toseek new and improved products for all EOR processes.

Shell's EOR surfactants (brand name ENORDET) are backed by overyears' successful experience in the development and production of syntheticsurfactants. Supply of these surfactants is ensured by Shell's control of feedsutogether with the use of Shell-patented manufacturing technology - for exam; =0.the Shell Higher Olefin Process (SHOP) and the Shell Hydroformulation 1>rY.....,.=(SHF).

IMPROVED DISPLACEMENT BY POLYMER FLOODING

• Viscous oilWater

Producer Injector

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Shell's range of polymers for EOR carry the brand name ENORFLO. Thepolysaccharide biopolymers in the range are the outcome of many years' investmentin biotechnology research and offer superior performance capabilities over existingpolymers, plus substantial development potential.

After careful assessment of their cost and performance compared withalternative available products, Shell Chemicals ENORDET and ENORFLO havebeen selected by Brunei Shell Petroleum for their micellar-polymer field trial.Satisfactory field handling of these products has already been demonstrated.

The technical services that can be made available in support of Shell's EORchemicals include fluids design and formulation, chemical analysis and surfacefacilities engineering.

Shell's experience in worldwide distribution ensures reliable delivery ofproducts, even to the most remote areas.

A night view of part of theSeria field in Brunei. This isone of a number in the worlddesignated for large-scaleexperiments on newtechniques for enhanced oilrecovery,

ENORDETSurfactantsProduct Descriptions

ENORDET LXS - Synthetic alkylaryl sulpho natesENORDET LXS grades are a series of linear alkylxylene sulphonates

designed for use as the primary surfactant in micellar-polymer flooding processes.Traditionally, petroleum sulphonates for enhanced oil recovery have been

obtained as by-products from the oleum treatment of white oils; more recently,direct sulphonation of refinery streams and selected crude oils has been used.However, petroleum sulpho nates have several important disadvantages. Theseinclude: product inconsistency due to variations in feedstock quality and refineryoperation; less desirable polysulphonates; and poor handleability.

ENORDET LXS grades have been developed by Shell Laboratories toovercome these disadvantages. The processes used permit precise tailoring of theequivalent weight according to the applicational requirements. Partially or fullyformulated products can be prepared as high active matter concentrates offeringease of handling and maximum economy of transport. The use of specificationpetrochemical feedstocks with Shell's proven production technology ensures thatthe sulphonates are both cost effective and of a consistent high quality.

Reservoi r conditlons arasimulated in hightemperature core fI.......-.=

ENORDET formulations behave as Newtonian fluids in their concentratedform, and may be designed to possess intrinsic viscosity characteristics when dilutedto injection concentrations. This eliminates any need to add water soluble polymersto the surfactant solution in order to achieve adequate mobility control in thereservoir ahead of the aqueous polymer drive.

ENORDET formulations have been developed which displace over 900/0of residual oil from sandstone cores at temperatures up to 70°C and reservoirsalinities varying from 0.5-12% TDS. Recovery of up to 90% has also beenachieved in low salinity reservoir core flood tests. The formulations aremanufactured and distributed as clear concentrates, with an active matter contentgreater than 80% and viscosities in the range of 100-300 cP at 40°C. One-stepdilution in the oil field with minimum additional handling is thus practicable.

ENORDET AOS - alpha olefin sulphonatesENORDET AOS manufactured from linear SHOP (Shell Higher Olefins

Process) olefins are being developed for use as foaming agents in foam modifiedsteam flooding. Laboratory tests together with encouraging initial field trial resultshave shown that these materials are the preferred additives in this process.

ENORDET Co-surfactantsIn addition to the alkylaryl sulphonates, Shell's range of chemicals for

enhanced oil recovery includes the co-surfactants and eo-solvents used in micellar-polymer surfactant slug compositions. The following classes of product areoffered:

Co-surfactantsENORDET xES grades - commercially available alcohol ethoxysulphates.ENORDET xEO grades - commercially available alcohol ethoxylates.ENORDET xEA grades - alcohol ethoxyacetates, under development.ENORDET xEN grades - alcohol ethoxysulphonates, under development.(x designates the number of ethoxy groups).

Co-solventsC3, C4, C, and mixed C7-C9 alcohols.

Accurate determination ofcore flood produced fluidsaids chemical floodingprocess development.

CHEMICALS

ENORFLO water soluble polymersProduct Descriptions

ENORFLO biopolymers have been developed specifically for use asimproved mobility control agents in enhanced oil recovery. They can beeconomically transported, are easily handled in the oil field, and meet therequirements for viscosity building, injectivity and stability in reservoirs over a widerange of salinity and temperature.

ENORFLO- X - xanthan polysaccharideENORFLO - X is an improved form of the anionic hetero polysaccharide. It

is produced by the fermentation of carbohydrates using novel technology and animproved strain of Xanthomonas campestris.

ENORFLO- X is a highly effective viscosifier. In solution it exhibits shear-thinning, pseudoplastic behaviour. The viscosity of the aqueous solutions is notstrongly affected by changes of pH over the range 4.5-10.0; and satisfactoryviscosities are maintained at temperatures over 70°C.

Filterability is frequently used as a measure of quality and i::l~e~~_ENORFLO- X undergoes significant downstream processing d:urililg~:.:::::Z::T.::-=which ensures excellent filterabilities in low-medium salinity brines. lni'~i-;iCi:performance has been confirmed by long duration core flow tests.

EN0RFLO- X is protected against biological degradation b e CCl~cl1::"::addition of formaldehyde; though alternative biocides can be used. Hoproduct is purified during processing to minimise the risk of microbial gro

ENORFLO- X is available as an aqueous concentrate at polymerconcentrations up to 14070w/v. This permits simple and rapid dilution to injconcentrations. Solutions can be prepared in medium salinity brines.

ENORFLO- X has been developed for moderately low salinity reservoirs.Further modified xanthans are now being introduced for higher salinity (up to 15TDS), and higher temperature (up to 85°C) reservoirs.

Tests which have now been running for more than a year demonstrate thestability of ENORFLO- X under typical reservoir temperatures and pressures.

ENORFLO-S - novel polysaccharideENORFLO- S is a novel polysaccharide developed in Shell laboratories for

use in high salinity reservoir brines.At concentrations suitable for enhanced oil recovery, solutions of

ENORFLO- S show negligible elastic and thixotropic behaviour and no yield stress isobservable. The solutions are highly resistant to irreversible viscosity loss under veryhigh shear conditions. The solution viscosities remain almost unchanged at pH'sranging from 2-12, and are enhanced as salinity rises from 3% to 25% TDS. Thehigh viscosifying power is retained up to 65°C, above which temperature the use ofENORFLO- S is not recommended.

The particular feature ofENORFLO-S is its excellent filterability atsalinities up to 15% NaCl plus 1.5% CaCh. Good injectivity at sea water salinitieshas been confirmed in long-duration core floods. The product is therefore especiallysuitable for use in high salinity, medium-to-low permeability reservoirs.

Tests have indicated that under reservoir pressures, and temperatures up to65°C, ENORFLO-S is stable over a period of at least 12months. Biologicalprotection is achieved by the use of conventional biocides.

Fermentation studies lead tonew improved biopolymers.