Polymer-specific enzymebreaker improves completionefficiency in horizontal wellsAlbert Chan, Phillips Petroleum Co., Plano, Texas; Drew Hembling, Phillips Alaska, Inc., Anchorage,Alaska; Brian Beall, BJ Services Co., Tomball, Texas; Mokhtar Elgassier,* BJ Services Co., Bakersfield,Calif.; and J. Jay Garner, BJ Services Co., Anchorage, Alaska
Bottom line. Phillips Alaska Inc. realized a 400-bopd incremental production increase in Well3K-24, a horizontal well with slotted liner, by using polymer-specific enzymes (PSE) to reducepolymer-related, drill-in fluid damage. Respective contributions from lowering of skin andincreased production efficiency of the lateral length were 150 bopd and 250 bopd.
Field description. Kuparuk Field, which is located on the North Slope of Alaska, beganproducing in 1984. The Kuparuk River formation is made up of Upper and Lower Mem-bers separated by a regional unconformity. The wells referenced in this case study arelocated in one fault block in the Lower Member A sands. The five A sands are of LowerCretaceous age.The sands are overlapping, trending from northwest to southeast.Thicknessesof the sands range up to 80 ft, extending along strike up to 40 mi, and down dip up to 15mi. Sand porosity ranges from 0.2 to 30% and permeability ranges from 25 to 50 md. Watersaturation is about 25%.
The formation depth is approximately 7,000 ft. Reservoir temperature is 170F. Oil inthe fault block has an API gravity of 21.3 and a viscosity of 0.8 to 1.2 cp. Asphaltene con-tent is 8%.
In the A sands, the primary cementing materials are clays supplemented by additionalcementation that results from compaction of authigenic quartz overgrowths on the matrix
Major reserve inc-rease obtained by de-watering high-water-saturation reservoirs
New Dominion, L.L.C. hastaken a bolder approachto developing major newreserves in exhausted oiland gas fields. see page 4
Nitrogen huff andpuff process breathesnew life into old field
Using a nitrogen huff andpuff (cyclic) process, Bre-tagne G. P. increased pro-duction from a matureAppalachian basin reservoirfrom 200 bopd to 500 bopdwith no significant increasein water production.see page 6
Air pulse system for artificial lift reduces costs
In six months of testing atthe Rocky Mountain OilfieldTesting Center (RMOTC), aunique air pulse lifting sys-tem, developed by Petro-leum Asset ManagementCo. (PAMCO), loweredpower consumption for lift-ing fluids in two shallow oilwells by 71%.see page 9
Company-operated, integrated, E&P wastemanagement facilityreduces costs
An integrated, E&P wastemanagement facility hasreduced Patina Oil & GasCorp.s costs for process-ing oil-contaminated soilsand fluids, including tankbottoms. see page 11
Reliable, low costvapor recovery systemsaves money whilehelping the environment
Since 1994, Devon EnergyCorp. has employed theVapor Jet system to cap-ture hydrocarbon vaporsfrom oil and water storagetanks in a West Texaswaterflood operation. see page 12
Pilot test demon-strates how CO2 injec-tion enhances coalbedmethane recovery
Since 1995, BurlingtonResources has beenconducting a pilot testof enhancing coalbedmethane recoverythrough carbon dioxide(CO2) injection.see page 14
September 2000For Independent Producers Supplement to World Oil Magazine
September 2000 Petroleum Technology Digest 1
Fig. 1. Final return permeability after the acid soak was 96% for the lab mud and 83% for the field mud.Treatment was an enzyme soak, followed by an 8% formic acid soak.
grains. The intergranular porosity is very good. Permeability is relativelygood, primarily because of abundance of open intergranular pores, goodconductivity and generally low amounts of pore-occluding authigenicmineral precipitates. The illitic clays are grain-coating and poorly-formed/cemented to the matrix grains, which makes the formation sus-ceptible to fines migration. Polymers are required in drill-in fluids to pro-vide a quality completion.
The problem. Polymers in drill-in fluids invade the near wellboreformation and form filter cake around the wellbore. This can sub-stantially reduce well productivity, especially in horizontal andmultilateral wells. Conventional clean-up methods, mainly oxi-dizers and acid treatments, have limited success in removing thedamage caused by polymer residue. These chemical agentsbleach (sodium hypochlorite), lithium hypochlorite, persulfatesand acidsreact with polymers regardless of the cleavage sitelocation. Therefore, they may react with any available site on a poly-mer chain or, for that matter, with downhole tools and tubular goods.This significantly reduces the chance of efficient degradation ofthe polymer strand.
Furthermore, these agents react with a maximum of two sites per mol-ecule, which causes the agents to spend quickly, especially at elevateddownhole temperatures.The end result of this is a partially degraded poly-mer fragment.These fragments can clog pore throats and slotted liners.These oxidizers and acids also can be incompatible with formation min-erals, producing undesirable side reactions with reservoir fluids.They alsocan cause corrosion in tubulars.
Polymer-specific enzymes (PSE). Enzymes are large, highly specializedproteins that are produced by living cells. They are present in all bio-logical systems and are derived from all-natural systems. Althoughenzymes are not living organisms themselves, they act as catalysts toaccelerate chemical reactions, therefore, they have the unique abilityto remain unchanged and available to promote other reactions for anessentially indefinite amount of time.
Advancements in biotechnology have led to the isolation, purificationand fermentation of PSE complexes to remove the residual polymer dam-age associated with starch-, xanthan- and cellulose-based polymers usedin the drill-in process. Each PSE system has been optimized to improvehydrolyzation of specific polymeric linkage sites along the targetedpolymer chain. Degradation of polymer molecules occurs as the enzymecleaves the polymer along its binding sites, ideally reducing it to sim-ple sugars.These sugars are of low molecular weight, water soluble andeasily flow through the pore matrix along with produced fluids.
Three horizontal completions. Three wells (3K-22, 3K-23, 3K-24) weredesigned as horizontal completions with slotted liners. The wells tar-geted two vertically separated sands, A2 and A3. Completion details foreach well are listed in Table 1.
Prior lab and pressure transient tests confirmed that permeability dam-ageas a direct result of filter cake deposits on the formation face froma dual-polymer drill-in fluid systemwould be a problem. Several con-ventional return permeability tests were run to evaluate filter cakeremoval methods using lab-prepared and actual field samples of thedrill-in fluid in conjunction with Kuparuk field A sand core samples.
Case studies for Independent Producers
Supplement to September 2000 World Oil
Welcome to the Petroleum TechnologyDigest, a joint effort by World Oil and the Petro-leum Technology Transfer Council (PTTC) toprovide independent producers with field-proven solutions to their technical problems. Inthis publication, the editors and PTTC staffpresent several recent case studies of explo-ration, drilling and production techniques thathave been tested successfully in oil and gasfields within the U.S.
These case studies have been solicited anddeveloped by the PTTC. No specific applicationof products or services is endorsed by PTTC.Reasonable steps are taken to ensure the relia-bility of sources for information that PTTC dis-seminates; individuals and institutions are solelyresponsible for the consequences of its use.
The not-for-profit Petroleum TechnologyTransfer Council was formed by the U.S. oil andnatural gas industry in 1994 to accelerate thedissemination of technology to independentexploration and producing companies, and tocommunicate industrys needs to the R&D com-munity. PTTC is funded primarily by the U.S.Department of Energys Office of Fossil Energy,through the National Petroleum TechnologyOffice and National Energy Technology Labo-ratory, with additional funding from universi-ties, state geological surveys, several state gov-ernments and industry donations.
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