In the gravel pack design for an artificial pack tube well, the pack-aquifer ratio ($P-A$ ratio) is defined as:
Options:
(A) Ratio of the 50% size of the gravel pack material to the 50% size of the aquifer material ($D_{50\text{ pack}} / D_{50\text{ aquifer}}$)
(B) Ratio of the effective size $D_{10}$ of the pack to $D_{60}$ of the aquifer
(C) Ratio of the screen slot size to aquifer porosity
(D) Ratio of well diameter to gravel pack thickness
Answer Key:
A
Step-by-Step Solution & Explanation
The standard gravel pack criteria (e.g. USBR / Walton criteria) define the Pack-to-Aquifer ($P-A$) ratio based on the $50\%$ size ($D_{50}$): $P-A\text{ ratio} = D_{50\text{ pack}} / D_{50\text{ aquifer}}$, typically recommended between 4 and 6.