Schwartz (1969) correlation for optimal gravel size based on the formation grain size distribution depends on which two factors?

Schwartz (1969) correlation for optimal gravel size based on the formation grain size distribution depends on which two factors?

• A. Permeability and porosity
• B. Uniformity of the formation, and velocity through the screen
• C. Grain size distribution only
• D. Fluid viscosity

Answer: (B)

Schwartz’s correlation for choosing gravel size works through two practical controls on how the formation interacts with the gravel pack: how uniform the formation’s grain sizes are and how fast fluid moves through the screen. The uniformity of the formation, often tied to its sorting, sets the typical pore throat sizes and the tendency for fines to migrate into the gravel pack; a uniform, well-sorted formation implies a more predictable pore structure, guiding the gravel size needed to filter without overly restricting flow. The velocity through the screen represents the erosive and transport forces acting on fines; higher seepage velocity increases the risk of fines movement and breakthrough, so the gravel should be sized coarser to resist migration while preserving permeability. Together, these two factors—formation uniformity and through-screen flow velocity—define the optimal gravel size in Schwartz’s framework. Permeability or porosity alone, or relying solely on grain-size distribution, or focusing on viscosity, don’t capture this specific combination the way Schwartz does.

Schwartz’s correlation for choosing gravel size works through two practical controls on how the formation interacts with the gravel pack: how uniform the formation’s grain sizes are and how fast fluid moves through the screen. The uniformity of the formation, often tied to its sorting, sets the typical pore throat sizes and the tendency for fines to migrate into the gravel pack; a uniform, well-sorted formation implies a more predictable pore structure, guiding the gravel size needed to filter without overly restricting flow. The velocity through the screen represents the erosive and transport forces acting on fines; higher seepage velocity increases the risk of fines movement and breakthrough, so the gravel should be sized coarser to resist migration while preserving permeability. Together, these two factors—formation uniformity and through-screen flow velocity—define the optimal gravel size in Schwartz’s framework. Permeability or porosity alone, or relying solely on grain-size distribution, or focusing on viscosity, don’t capture this specific combination the way Schwartz does.