Advances in Well Completion Technology
Authors: Sparlin D.D. 
Published: December 2007

Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering.

"You can't hurt a good well." This old maxim of the oil industry should belaid to rest. Some of the most important advances in well completion technologyduring the 1970's were made in formation damage prevention. It behooves us totake advantage of these advances because operators using cleaner completionfluids and better completion practices are making wells with better productionrates practices are making wells with better production rates and lowerpressure drawdowns than ever before. Much of this success in obtaining higherproductivities can be attributed to awareness that formation damage is a realproblem. A hydrocarbon-bearing formation is like a sand filter. A sand filterbecomes plugged as it performs its job of removing solids from a fluid. Afilter made of a typical U.S. gulf coast Miocene sand would have pore sizesranging from 2 to 10 mu m; dirty water pumped through it would be cleanedeffectively. Solids larger than 10 mu m would be stopped right at the surfaceof the sand filter and particles sized from about 0.5 to 10 mu m would betrapped throughout the sand. Only solids smaller than 0.5 mu m might passthrough the sand, but they would be so small that they wouldn't be visible.That filtering process is exactly what happens in wells when fluid is lost to aformation. Solids larger than the pore sizes of the formation are trapped inthe perforations or on the face of the formation. Particles perforations or onthe face of the formation. Particles about the same size as the formation poresare carried out into the formation where they are likely to be trapped. Largersolids may come back out of the well when it is put on production, but many ofthese solids will remain trapped. If the well has been gravel packed, practically all the solids will remain trapped. packed, practically all thesolids will remain trapped. In any case, the permeability of the formation willbe less than if these solids were not present. The problem of formation damageby solids becomes even more apparent when we consider how small perforationsare and how little dirt it takes to fill them completely. About 5 lbm (2.3 kg)of solids will fill 20 average-size perforations. Only 14 bbl (2.2 m3) of waterwith 0.1 wt % solids content will fill 20 perforations with dirt completely.This reasonably perforations with dirt completely. This reasonably assumes thatmost of the dirt is stopped by the formation sand and remains in theperforations as the fluid flows into the formation.

Filter Considerations

One major method to reduce plugging of a formationand perforations with solids is plugging of a formation and perforations withsolids is the use of filters to clean completion and workover fluids. Cartridgefilters are the most common means of removing solids from these fluids. Theyare on most wellsites now and have reduced formation damage greatly, but theyare not a cure-all. Polypropylene filters have proved to be the most reliabletype. Polypropylene cartridge filters are rated usually from 1 to 200 mu m withthe most common ratings being 2, 5, 10, 20, and 50 mu m. This implies thatthese filters will remove all the solids larger than their micron rating. Forinstance, a 2-mu m filter might be expected to remove all particles larger than2 mu m diameter. This is absolutely wrong! At best these filters can removeonly 90% of the solids from a fluid, and solids much larger than the filterrating pass through. Some of the practices that have been found to enhance theability of these filters to remove solids are to (1) use low flow rates throughthe filters, (2) remove the largest solids and the bulk of the solids from thefluids before filtering, (3) stop bypassing of fluids around the cartridges, and (4) change the filters when they begin to plug. The maximum flow ratethrough a set of 16 or 18 filter cartridges should be 1 bbl/min (0.159 m3/min).These are the numbers of cartridges commonly found in one filter unit. Tofilter fluid at higher rates requires either multiple filter units connected inparallel or larger filter containers such as those used by Amoco Production Co.at High Island with 65 cartridges. Production Co. at High Island with 65cartridges. The larger particles and the bulk of the solids should be removedfrom the fluid by settling tanks, shakers with fine mesh screens, mud cleaners, or hydrocyclones. Bypassing of fluids around the filter cartridges is a commonproblem.