Sand Production or ‘Sanding’ is the failure of the producing formation, followed by the flow of failed rock into the wellbore. Very often the flow of failed rock can come to the surface and into surface facilities. Particularly for high rate gas wells, sanding is a major safety issue and the produced solids can erode both downhole and surface flow lines.

The formation fails due to one or more effects:

  • • shear (e.g., high stresses, low wellbore pressure, low rock strength);
  • • tensile (e.g., high flow rate, perm damage at the cavity surface); and
  • • erosion (e.g., high seepage forces).

Models and Analyses for Sanding Problems

There are a number of alternatives for performing a geomechanics sanding analysis based upon the available data and experience. At OFG, we work with our clients and their data to determine the best, fit-for-purpose technique for a given project:

  • • Phenomenological models (correlations, field observations);
  • • Field assessment of sand production potential and remedies;
  • • Analytical  models (conservative);
  • • Semi-empirical (getting better, need  calibration);
  • • Numerical analysis of thick-walled cylinder (TWC) tests; and
  • • Numerical analysis of perforation stability considering a full hydro-geomechanical coupled (uncoupled) model.

Avoiding Sanding, Sand Control or Sand Management?

Sand production can often be prevented – at the loss of production and reserves. Alternatively, techniques can be employed (gravel packs, frac & packs and screens) that control sand production by placing a physical barrier to sand production, but, typically, at the loss of production and reserves. Alternatively, the sand can be managed – produced and disposed when erosion potential can be controlled. Solids Management options, then, include:

  • • Gradient (pressure/production) control to reduce sanding risk;
  • • Selective perforation and/or oriented perforation;
  • • Gravel packs, screens, filters, slotted liner installation, and expandable liners;
  • • Frac for sand control – Frac-&-pack;
  • • Horizontal wells, with lower pressure gradients;
  • • Formation impregnation methods (i.e., resin squeeze); or
  • Sand Management (rather than exclusion) providing:
    • • Higher rates of production; and
    • • Lower completion costs
  • Note that under Sand Management, many wells will develop an increasingly “negative skin” (higher PI) often requiring a redesign the wellhead assembly. In addition Sand Management requires the establishment of sand handling at the surface and the monitor of sand influxes to minimize risk.
Oilrig - Oilfield Geomechanics
Massive solids production from a well, as shown here, is an infrequent challenge. The more insidious challenge is posed by small-volume, infrequent formation solids production that can erode downhole or surface flow lines.

Near-Wellbore - BHP-Drawdown - Oilfield Geomechanics
A common sand production evaluation tool is a Safe BHP-Drawdown plot, shown here, where sanding potential (colored intervals) is shown as a function of bottomhole pressure (y-axis), reservoir pressure (x-axis) and rock strength. Other potential sanding factors include perforation orientation, fluid flow rates, and the timing/onset of water production.

Downhole sand exclusion techniques (frac packs, screens, slotted liners) add a pressure lose to the system – which affects well production. In some cases, allowing for solids production and handling the solids volume at the surface represents a possible alternative.