sand control or sand management(防砂还是出砂管理)

Sand Controlor Sand Management?,Maurice B. Dusseault,Goals,To develop a basic understanding of sand control and sand management physicsTo understand the basic technical options for sand exclusionTo explore completion and production options other than sand exclusionTo outline a decision-making environment for sand control and sand management,Two Basic Approaches,SAND EXCLUSIONScreened CompletionsScreens, filters, etc.Slotted linersGravel packsFrac-and-packScreenless CompletionsOriented perforationsGradient and rate controlHorizontal wellsOpen holes,SAND MANAGEMENTEncouraging sand influxHeavy oil productionCompletion approachLiving with sand influxSand Management conceptEvolution of an oil wellDeliberate sand clean-upA workover and testing approach for wells,Sand or No Sand?,There now exist three possible routes:A: Totally avoid sand ingressB: Live with low rates of sand ingressC: Encourage sanding to enhance oil ratesA: Total exclusion screens, packs, linersB: Live with some sand better oil rates, but a Sand Management framework is requiredC: Encourage sand has proven highly valuable in heavy oil development in Canada,Decisions, Decisions, Decisions,Quantitative answers based on risk analysis, good data, and experience are required to make the best economic decisions.,Option A: Sand Exclusion,When are total exclusion techniques necessary? (i.e.: when are quantitative predictions needed?)Exclusion must be applied when sand influx consequences are absolutely unacceptable:Usually in high-rate natural gas (high steel erosion)Inadequate facilities to handle the sandHowever, exclusion costs money:Reduced oil production rateCAPEX (e.g. 1M$ for a North Sea gravel pack),Option B: Sand Management,When can we live with “some” sand?When oil rates are thereby enhancedIf sand management costs are modestIf well and facility risks can be managedThere are costs and risks involvedAllowing sand influx is more “risky”Facilities modification requiredConstant surveillance is needed to manage riskProbably inapplicable in high gas rate wells,Option C: Encouraging Sand,When do we want to produce sand?When producing heavy oil (CHOPS)As a completion approach (higher k)As a workover approach (eliminate “skin”)There are costs and risks involved, butNo choice in most cases (no sand-no oil)Sand erosion in heavy oil is minimalPumping problems have been solvedSand management costs 10-25% of OPEX,Sanding and Geomechanics,Sanding is a Rock Mechanics IssueThe important geomechanics factors are:Understanding the physics is vital Completion strategy is vitalWell management is vital,The tensile and shear strength of the reservoirThe in situ stresses and pore pressuresThe hydrodynamic drag forces on the matrixAlteration of rock properties (damage)Alterations of stresses and pressures with time,Economics and Risk,ECONOMIC FACTORSProduction RateEffect of screens on QQ and reduction of p/rCompletion CostsCAPEX for installing gravel packs, screensIntervention NeedsFrequency of workoversScale and fines,RISK FACTORSSand erosion riskSurface facilitiesSafety issuesWell impairment riskPlugging the well? Casing loss? Sand handling requirements Separation, storage, disposal,$-$,What the Industry Needs,A software environment to make intelligent well completion decisions in sanding casesEconomic factors must be incorporatedA method of assessing risk in terms of $Analysis tools to support decision makingHard data on costs and benefitsA repository of practical experience in various areas, environments (e.g. offshore)A clear understanding of the physics,Geomechanics Impact Flow Path,Causes of Sanding,Perforations damage the rock (next slide)Confining stress are reduced ( no friction)Cohesion is destroyed, weakeningThus, seepage forces can pluck grains freeAs “cavity” grows, high shear stresses on the walls lead to weakening and dilationOnce the yielded zone approaches the size of the reservoir thickness, the high v aids the process,Types of Sand Production,Sand clean up after perforating before placing the well on productionEpisodic sand bursts during productionContinuous sand influx (heavy oil in UCS)Fine-grained particles migration through the formation matrixDeliberate sand clean-up activities during initial completion or during a workoverNew sand influx late in the well life,Perforation Clean-Up,Perforating damages the formationGenerates crushed and disaggregated sandOften in the form of an emulsionClean-up is designed to remove this sandSwabbing (generating high p/r, F) Build-up of p, then sudden drawdownFlushing produced sand to surfaceBut! - Real-time measurements are difficult, and field control almost impossible,Damage From Perforating,intact,weakened,“remolded”,shearstress,normal stress,strengthplots,loss of tensile strength,well,weakening,Using a Mohr-Coulomb strength plot to illustrate damage,perforation,Fines Migration,The matrix stays intact, but small interstitial clay and mineral grains are mobilized by:High local gradients at pore throatsGeochemical alterations (waterflood, DT)Fines tend to block the well, plug screensQ, p/r , & more fines are mobilizedSerious fines problems tend to lead to many workovers, chemical solutions (acids)“Living with” fines is an attractive solution,Fines Production,Throat blockage,Fines mobilized by:D geochemistryDp (drag force)sand strains,clays,grains,Fines are less than 1/20th mean grain size,Continuous Sand Influx,Used in CHOPS (Cold Heavy Oil Production with Sand, m 50 20,000 cP)A valuable, low-risk production strategy in UCS with viscous oils and gas in solutionEntire matrix is produced (not only fines)Typical rates are from 0.25 to 10% sand by volume of the dead liquidsSanding increases well productivity, eliminates fines or asphaltenes blockagesMust cope intelligently with sand,Continuous Sand Production,Yielded and channeled zone generated by large-scale sanding,Heavy oil UCS,As much as 10% sand by volume liquids,Intermittent Sand Bursts,Occurs in poorly consolidated sands, perforated high rate oil and gas wellsBursts are “self cleaning” events, and tend to remove near-well flow impediments (“skin”)Beneficial effects on Q, fewer interventionsLower CAPEX for well completionsHigher risks because of episodic sand influxFacilities must be designed to handle sand,Sand Bursts,Sanding in high rate oil wells in poorly consolidated sandstones comes in “bursts”,A burst may be from a few kg to as much as 100 kg,mini-bursts,time,sand rate,g/m3,10-100 min,sharp rise time,slow decay,Bursts may occur every few days to every few weeks,Clean-Up and Well Tests,Deliberate aggressive clean-up carried out on wells suffering from productivity lossesPressure build-up (skin assessment)Aggressive drawdown to generate sand burstsPeriod of productionBuild-up again, drawdown, produceRepeat 3-4 times and study skin dropThis methodology carries little risk, only time, and in the right candidates, Q,Late Well Life Sanding,Caused by stress changes from depletionSand fabric is damaged by high sCohesion is reducedCaused by phase changes (capillarity effect)Water influx so that Sw increases locallyCaused by operators trying to maintain QoilIncrease in Dp, sanding triggeredAn oil well in a UCS changes its behavior over its life time, soWell management strategy changes needed,Problems With Sanding,Wellbore sand flow and blockage risks Erosion of downhole screens, devicesErosion of surface goods and safetySand separation technology issuesSand disposal or sand clean upParticular horizontal well issuesBlocking at the toe (sand dunes in low parts)Difficult and costly cleaningWe can handle some but not a lot of sand,The Seepage Force on Grains,The hydrodynamic or seepage force,F,Free flow in perforation channel,porous medium flow,p,Seepage Force = F = sAwp/l,p + Dp,p + Dp,p + Dp,The pressure gradient leads to a seepage force that destabilizes individual sand grains or groups of grains,F,Hydrodynamic Drag (I),Also called “seepage force”Results from Dp, is proportional to gradientA = cross-sectional area of grain or “chip”w = a measure of grain diameters = a shape factor to account for geometriesGradient is directional (vector), F is coaxial to the gradient direction,Hydrodynamic Drag (II),To reduce force, reduce the gradient!At a grain or fragment level, this is very difficult to quantify rigorouslyThe geometry must be specifiedGradients fluctuate locallyIt is independent of velocity for Darcy flowTurbulence can change drag forceOther complicating factors can arise in practiceThus, some “continuum approach” is neededDebate continues on which method is best,Conditions Around a Tunnel,convergent flow,spalling,damagedrock,F,F,sq,sr,seepage force,Rock matrix,Rock matrix,Perforation tunnel,Perforation Tunnel,r = 0,Zone of highest seepage force,Damaged zone (low c),Intact formation,Convergent flow region,Flow lines,Cased, cemented well,Rock Strength Considerations,If rock is very weak in cohesion, drag forces overcome the tensile strength at a free faceIf the rock is weak in shear, higher stresses caused by drawdown can lead to shearing and loss of strength (cohesion damage)Changes in H2O saturation destroys capillary cohesion (which acts as a tensile strength)If rock strength can be preserved, or even enhanced, sanding risk can be reduced,Rock Strength,shearstresst,normal stress - s,Mohr-Coulombplot of stresses,Rock strength,strong rock,weak rock,c1,c2,Y1,Y2,Good cohesionPoor cohesion,2,1,4,3,1,1,4,Sanding and Rock Strength,UCS UnConsolidated Sandstone, is the usual sanding rock (+ Chalks)The strength of sand is related to its density and the amount of cohesion (cementation)Straining destroys cohesion and also can lead to shearing, dilation, weakeningIf a UCS remains well-confined by stresses in all directions, it can resist thisThus, good confining stress - s3 - is positive,Rock Strength (I),It is possible to reduce sanding risk by increasing the strength of the rockIncrease the cohesionIncrease the confining stressReduce the shear stressMany sand exclusion methods are based on these three basic conceptsFor example:Fracturing increases the confining stress - s3Silicate injection increases the cohesion,Rock Strength (II),Methods to increase the strength include:Resin treatment of weak layers, squeezesPlacing gravel-packs to maintain s3Use Frac-and-pack & other fracturing meth-ods to re-stress the sand and maintain s3Maintain high water-flood pressures to avoid increasing t, reducing s3, or losing cohesionUse expanding screens to maintain s3,Weakening of Sand,Drilling damage can reduce cohesion and cause dilation near the boreholePerforation damage can generate a large zone in which the cohesion is destroyed and the rock “granulated”Too aggressive production can trigger disruption of fabric, weakened zoneDepletion can change stressesThermal shocking, high p injection others?,Strengthening Weak Sands,Add cohesion, restress, minimize damageCohesive methodsRestressing methods,Resin injection, several approachesSilicate injectionResin-coated sand use in fracturing and Frac-Pack,FracturingFrac-Pack methodsRadical ideas (expand a steel liner in the wellbore?),Scale Effects in Sanding,The stability of a cavity or weakened zone is a function of its radiusSmall radius . successful archingLarge-radius . arching less likelyIf cavity grows, unstable sanding more likelyHowever, large cavities also have lower exit gradients so F is lower!Clearly an optimization issue (how large?),Perforation Opening,Scale effect is important as wellSmall openings have a better chance to develop a stable arch behind casingLarge openings will tend to always have the arch collapse under seepageHow big? Roughness, packing density, angularity, are important (unquantified),poor arching better arching,Scale Effects, Opening,6D,perfhole,casing,Scale Effects, Tunnel,stable,unstable,Perforating and Sanding,Do you want to reduce the risk of sanding?Use small diameter entry portsSand will form stable arches behind the casingSmaller diameter, the more stable the archUse deep penetration chargesLarger flow area, lower local gradientsSmaller tunnel diameter, greater stabilityReduce perforation densitySmaller damaged zones that do not overlapOriented perforations in the stress field,Reality of Analysis,Uncertainty prevails in geo-problemsTrue “predictive” analyses are impossibleDeterministic analyses are to “explore” sensitivity, improve understandingUltimately, a risk-based approach is essential, but still totally lackingEmpirical correlations and “calibration” of models are used to improve predictability, and this is a “type” of risk analysis,Sand Exclusion Completions,Open-hole completion (-Y-Q analysis)OH Gravel-pack or slotted liner, no cementConventional perforated casing with:No sand exclusion devices or controlGradient or rate control to reduce sand riskScreen in the casingARCO-frac, Frac & Pack, resin sand.Gravel pack, inside or outsideResin, furan, other consolidation methods,highercost, lower risk,Resin Squeeze,Low k bed poor contactIntermediate k, OKHigh k, deep penetration,Chemical Consolidation,Epoxy, furan treatment, silicate injection AdvantagesLow risk if successfulDisadvantagesCostly to place in long and horizontal wellsHeterogeneity causes placement problemsFlow rate reduction will occurFines, scale, asphaltenes can still block the wellShell uses epoxies in Nigeria,Selective Resin Squeeze,Resin into troublesome zone,Packer,Packer,Used in wells on Sand Management if one seriously troublesome zone must be isolated,Slots, Screens, Wire-Wrapped,Cement,Cement,Open holeSlotted liner,Liners are susceptible to scale and plugging,Openings are sized and shaped using various empirical criteria,Open-Hole & Liners, Screens,Placement of a sized (slotted) filter linerAdvantagesEasy to place in long open holesGood sand exclusion is providedDisadvantagesLiner can collapse (formation often does)Slotted liners often plug and develop scaleErosion of liners is commonAs always, reduction in PI usually develops,Screens Inside Cased Holes,Casing & tubing,Carefully sized screen is placed inside perforated cased well,Screens are prone to scale, erosion, and plugging with fine-grained minerals, but intervention is relatively easy,Screens, Slotted Liners, Filters,Physical exclusion of the particlesAdvantagesSome fines can still flush throughReduces sanding risk to almost zeroDisadvantagesNot usually a selective process Usually reduces PI and susceptible to erosionProvides a substrate for chemical scalePore throat plugging not eliminatedInterventions can be extremely costly,Fracturing Methods,Increase in s3,Fracture propped by resin-coated sand,Fracturing Using Zone Exclusion,Increase in s3,Fracture propped by resin-coated sand,Very weak, high-k sand,Resin-coated sand,Sand not perforated,Propped Fracture Approaches,Re-stress borehole with fracture & proppantAdvantages“Locks” sand by increasing s3, stops influxDisadvantagesAs usual, PI often suffers (positive skin)Difficult in inclined wells (tortuosity effect)Premature tip screen-out during placementFracture containment and placement controlProppant flow-back (use resin-coated sand),High Proppant Fracturing,bottomhole pressure,virgin reservoir pore pressure,time (constant pumping rate),least principal stress,Proppant concentration,Treatment pressures,vertical stress,“Frac-and-pack”,!,High Rate Fractures,proppant forced between casing and rock, sometimes called the halo effect, verified in 1999,Selective Perforating,Sensitive zone left unperforated; now, it cannot produce sand,Often bad zone is high k zone as wellWell models cannot handle thisFull numerical model neededEconomic analysis is required,Formation cross-flow,Selective Perforating,Avoid weak zones likely to cause problemsAdvantagesRelatively effective and economicalDisadvantagesWeakest zone often highest permeability zoneTools to assess PI effect poorly developed yetProblematic in homogeneous reservoirsRock strength assessment is needed,Phasing of Perforations,Which phasing to use?,Spacing of Perforations,Fewer perforations:Higher p/r at each perf = greater sand riskNo overlap of damage zones = less sand risk,More perforations:Lower p/r at each perf = less sand riskOverlap of damage zones = greater sand risk,Oriented, Phased Perforations,Phased perforations in the best orientationsAdvantagesUseful in cased cemented wells, reduces riskDisadvantagesOrientation tool for perf placement requiredSand probability assessment models are poorFull in situ stress mapping is neededField validation remains in its initial stagesReduces but does not eliminate sanding risks,Perforation Strategy,Use 180 phasing in the direction where stresses on perforation tunnel are