Sand-Control Alternatives for Horizontal Wells
Authors: Zaleski T.E. 
Published: December 2007

"All studies to date indicate that gravel packing is preferred forpacking is preferred for reservoirs with high flow capacity where maximumperformance is desired, in formations with substantial clay materials orformation fines, and where flow along the outside of the screen is undesirable. This technique, however, can be at least 5 and sometimes 10 times moreexpensive than others."

Introduction

The use of horizontal wells is now recognized as a viable method ofdeveloping oil and gas reservoirs. Although drilling technology has madetremendous strides over the past 5 years, a number of design and operationalconsiderations for completions remain relatively unexplored. One topic ofincreased debate is control of sand invasion into horizontal wells completed inunconsolidated formations. Most of the world's horizontal wells have beendrilled into something other than sandstone reservoirs, and only a smallpercentage have targeted truly unconsolidated formations. As the industrybecomes more comfortable with the technology, more of these reservoirs arebeing evaluated for horizontal-well applications. It has been well documentedthat horizontal completions increase production rates, as much as two to fivetimes those of conventional techniques, because more of the producing formationis exposed to the producing formation is exposed to the wellbore. Althoughproductivity improvements are highly sensitive to reservoir parameters, it isbecoming generally accepted that optimum horizontal lengths will be 2,000 to4,000 ft. The length of these completions generally causes the velocity of thefluid at the sand face to be an order of magnitude less than that observed inconventional completions. Because drag forces contribute to sand production, horizontal wells can produce at production, horizontal wells can produce athigher sand-free flow rates than conventional completions in the samereservoir. While it is frequently argued that horizontal wells do not need sandcontrol, the potential for sand production increases significantly as reservesdeplete and rock stresses increase. This is becoming more evident today inseveral major North sea fields with conventional completions. Also, manyunconsolidated formations produce sand for the first time with the onset ofwater production, a typical problem in such areas as the Gulf of Mexico. Operator must decide whether to implement sand control in the originalhorizontal-completion program because of an immediate concern or because thepotential exists for a problem to arise as the well matures.

Openhole Completion Alternatives

Gravel packing is generally regarded as a logical solution to present orpotential sandcontrol problems; however, because of its technologicalcomplexities and high costs, alternative sand-control techniques are frequentlymore attractive. The success of a horizontal-well completion depends onbalancing equipment selection and installation with reservoir objectives, formation parameters, and cost. The design guidelines parameters, and cost. Thedesign guidelines in Table 1 are based on field experience in horizontal andhighly deviated wells. Remember that every reservoir is different, sorecommendations should be customized for individual characteristics rather thanapplied universally. While by far the most cost-effective method, the use ofslotted liners in openhole completions has limited capabilities. Used to agreat extent in Canadian heavy-oil reservoirs, slotted liners are appliedprimarily in coarse-grained formations with low production rates and lowsand-producing production rates and low sand-producing tendencies. Wire-wrappedscreens increase effectiveness in medium- to coarse-grained formations and aretwo to three times more expensive than slotted liners for the sameapplications.

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