Sand Management

  1. Subsea
  2. Production Facilities
  3. Production Engineering
  4. Erosion Management


Sand management is an operating concept in which traditional sand control means are not normally applied and production is managed through monitoring and control of well pressures, fluid rates and sand influx. Sand management has proven to be an effective tool in North Sea oil and gas production wells.Sand management has proven to be workable, and has led to the generation of highly favorable well skins because of self-cleanup associated with the episodic sand bursts that take place. These low skins have, in turn, led to higher productivity indexes, and each of the wells where sand management has been successful has displayed increased oil or gas production rates.

Furthermore, expensive sand control devices are avoided and the feasibility of possible future well interventions is guaranteed. Different analysis and design tools are necessary for evaluating the sand production probability, for quantifying risk reduction, and for establishing practical operational criteria for safe and optimum production. Such design tools include the capacity to predict:

  • Sand production onset;
  • Sand quantities and production rate;
  • Equipment erosion risks;
  • Conditions of sand transported inside the production flowline.

Another essential tool is sand monitoring technology that allows for realtime quantitative sand influx tracking.

Sand Management Philosophy

Classical sand control techniques, such as gravel packing, use of wirewrapped or expandable screens, frac-and-pack, and chemical consolidation, are based on a sand exclusion philosophy: Absolutely no sand in the production facilities can be tolerated. Alternatively, in the absence of means of totally excluding sand influx, the traditional approach is to reduce the production rate to minimize the amount of entering sand. The most extensive field validation of the reliability and cost effectiveness of sand management is possessed by the Canadian heavy-oil wells. This approach is a combination of techniques that define and extend the safety limits. The too conservative approaches in which no sand is permitted into the production system are avoided or delayed.

The Sand Life Cycle

Risk management requires reliable analysis of the “sand life cycle,” starting with predicting formation conditions onducive to sanding, and ending with the ultimate disposal of the produced material at the surface. These techniques are based on:

  • An extensive data acquisition of the field;
  • Theoretical modeling of the involved physical processes;
  • Active monitoring and follow-up on production data;
  • Well testing to optimize production rates.

Also, the techniques will help the production engineer optimize the design and provide risk assessment throughout the well’s production life.

Sand Detachment

Sand detachment is a mixed hydromechanical process, which releases sandstone fragments from the formation near the well, can be viewed as a mixed hydromechanical process. Many models have been established to predict the sanding initiation conditions. First, due to excessive drawdown or reservoir pressure depletion, the production stratum fails in compression or extension from excessive local stresses at the free surface near the wellbore. Alternatively, sanding may result from formation weakening, perhaps from fatigue effects related to repeated well shut-downs, or from water breakthrough and related capillary or chemical cohesion loss.

Second, the yielded material is destabilized and fluidized by hydrodynamic forces from the fluid flow into thewell. In addition, the force varies with time along with local geometry, so sand cannot flow constantly and is likely to be produced as bursts, which has been verified by small-scale laboratory experiments. Transient pressure gradient effects that result from well shut down and start-up and relative permeability changes are the major reasons for the episodic increases in the sand influx, also these are the best known causes for increased forces acting on the sand in the vicinity of wellbore.

Sand Transport

Once sand is detached, it follows the fluid through the perforations and into the well. Then gravity and hydrodynamic forces will act on the grains and sand fragments. The effects of sand, including the probability of transport to the surface, blocking of perforation tunnels, or settling into the well sump or horizontal well section, depends on the balance of the following factors:

  • Fluid rheology and density;
  • Local flow velocity;
  • Local geometrical obstructions;
  • Sand fragment size;
  • Well inclination.

In particular, sand may sediment and be remobilized later as conditions change (e.g., velocity changes, water cut increases) in long horizontal wells. These events may often be interpreted as sanding because of formationfailure, rather than as a well cleanup process.

Sand Erosion

Sand erosion including the area of tubing, flow lines, and chokes is significantly related to the sand transport process. The kinetic energy of the moving particles is transferred to the steel when they impinge on a surface, causing abrasive steel removal. Generally, sand flow rate and sand fragment velocity are the two main factors determining the erosion risk. For heavy crude fields, the velocity is low and the risk is also low; however, HP/HT gas condensate fields, gas expansion and acceleration near the wellhead dramatically increase the erosion risk. Erosion risk is a major technical and economical constraint because it may lead to severe safety problems. Erosion forces the production rate to be kept below a limit that is considered safe.

Surface Sand Deposition

Once sand passes the wellhead, it passes through the surface lines, or, for subsea wells, through the sea line, to deposit in the separator, which must be cleaned and flushed from time to time according to the expected average sand rate. The oil-contaminated sand that is produced is collected and sent for ultimate disposal. For subsea engineering equipment, it has been dumped into the sea in the past, but this practice is not viewed as an option in future operations.

Sand Monitoring

Sand monitoring is a critical aspect of sand management. Sand monitors are used when erosion problems are suspected. Current sand monitoring methods are discussed next.

Volumetric Methods

Volumetric methods include the following issues:

  • Sand traps can be installed to capture sand at tees or bends usually. However, sand traps are not a real-time method because they need to be disassembled to measure the sand production. These techniques have not proven effective, because the majority of the produced sand is normally not captured. (North Sea experience indicates a recovery of 1% to 10%.)
  • Fluid sampling, including centrifugation for water and sand cuts after the primary separator, includes measurements of bottom sediment and water, which are carried out during appraisal well testing or during normal production. However, this method cannot be guaranteed due to the much remaining in the primary separator.
  • Another method that has been used quite extensively in the Adriatic Sea on gas wells consists of dismounting the sand separator, jetting it clean of all sand, and quantifying all produced solids. However, the accuracy and practicality (i.e., the time and manpower required to dismount, jet, and remount the separator) limit its application.
  • Use of an in-line sand cyclone is a new method used on some North Sea platforms. Sand is effectively separated from the produced fluid and stored in a tank. The load cells or other devices on the tank allow for the measurement of sand accumulation in real time.

Acoustic Transducers

Installed in the flow system, a transducer includes the following items:

  • An impact probe installed in the flow line to detect sand grain impacts;
  • An acoustic collar that can be used to capture the information about impact of the sand grains against the wall of pipe or the choke throat.

Sand Exclusion and Separation

Downhole sand screens and gravel packs are often used to stop sand from entering the production system. Typically, sand screens prevent particles larger than 100 microns from entering the production stream. However, a balance should be struck between reducing the productivity by including a sand screen and having to choke back an unprotected well to avoid excessive sand production. In addition, even very small particles can generate a significant degree of erosion; therefore, sand screens and gravel packs cannot guarantee erosion-free operation. Sand separation can be conducted at three principal levels:

  • The primary separation facility topside;
  • The subsea separation module (for offshore installations);
  • In the downhole separator in conjunction with oil/water separation.

Surface modules include high-pressure horizontal baffle-plate separators, vertical gravitational separators, and centrifugal segregators. These devices can be very effective at protecting chokes in particular. In subsea and downhole separation, water-wet sand will normally be separated by gravity and stored or reinjected. A specially designed sand cyclone or sand centrifuge may be required for oil-wet sand.

References

[1] E.S. Venkatesh, Erosion Damage in Oil and Gas Wells, Proc. Rocky Mountain Meeting of SPE, Billings, MT (1986) 489–497. May 19-21.

[2] N.A. Barton, Erosion in Elbows in Hydrocarbon Production System: Review Document, Research Report 115, HSE, ISBN 0 7176 2743 8, 2003.

[3] American Petroleum Institute, Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems, fifth ed., API- RP-14E, 1991.

[4] Det Norsk Veritas, Erosive Wear in Piping Systems, DNV- RP- O501 (1996).

[5] A. Huser, O. Kvernvold, Prediction of Sand Erosion in Process and Pipe Components, Proc. 1st North American Conference on Multiphase Technology, Banff, Canada, pp. 217–227 (1998).

[6] M.M. Salama, E.S. Venkatesh, Evaluation of API RP 14E Erosional Velocity Limitation for Offshore Gas Wells, OTC 4485, Offshore Technology Conference, Houston, Texas, 1983.

[7] S.J. Svedeman, K.E. Arnold, Criteria for Sizing Multiphase Flow Lines for Erosive/ Corrosive Service, SPE 26569, 68th Annual Technical Conference of the Society of Petroleum Engineers, Houston, Texas, 1993.

[8] M.M. Salama, An Alternative to API 14E Erosional Velocity Limits for Sand Laden Fluids, OTC 8898, pp. 721 –733, Offshore Technology Conference, Houston, Texas (1998).

[9] P.D. Weiner, G.C. Tolle, Detection and Prevention of Sand Erosion of Production Equipment. API OSAPR Project No 2, Research Report, Texas A&M University, College Station, Texas, 1976.

[10] T. Bourgoyne, Experimental Study of Erosion in Diverter Systems. SPE/IADC 18716, Proc SPE/IADC Drilling Conference, New Orleans, 28 February - 3 March, pp. 807–816, 1989.

[11] B.S. McLaury, S.A. Shirazi, Generalization of API RP 14E for Erosive Service in Multiphase Production, SPE 56812, SPE Annual Technical Conference and Exhibition, Houston, Texas, 1999.

[12] S.A. Shirazi, B.S. McLaury, J.R. Shadley, E.F. Rybicki, Generalization of the API RP 14E Guideline for Erosive Services, SPE28518, Journal of Petroleum Technology, August 1995 (1995) 693–698.

[13] B.S. McLaury, J. Wang, S.A. Shirazi, J.R. Shadley, E.F. Rybicki, Solid Particle Erosion in Long Radius Elbows and Straight Pipes, SPE 38842, SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 1997.

[14] J. Tronvoll, M.B. Dusseault, F. Sanfilippo, F.J. Santarelli, The Tools of Sand Management, SPE 71673, 2001, SPE Annual Technical Conference and Exhibition held in New Orleans, Louisiana, 2001.


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