Gravel Pack Sizing Criteria - It's Time to Re-Evaluate

Abstract

Correct sizing of Gravel packs for sand retention in Gravel Pack and Frac Pack completions has been a controversial topic for many years dating back to the 1960's. One of the earliest studies completed, and still most often cited, was by Saucier in 1974. Saucier proposed sizing the gravel based on the median size of the formation (d50 * 6). The Saucier criteria is still often used and works well for many applications. In 1998, Tiffin furthered the Saucier work in SPE 39437 and suggested that for some specific formation sands, the gravel could be size as much as 7–8 times the median size of the formation. In both bodies of work, the median size of the formation is really the only formation size parameter that is considered in the gravel pack size selection. In the ensuing years, much has been published regarding sand retention testing, but the criteria for gravel pack size selection has not been updated or addressed. In 2012 Martch et al. suggested a new method which correlated sand retention data to a ratio of the effective formation size and the gravel pack pore size (SPE 151865). In this series of work, the gravel pack pore size is further evaluated using the permeability of the gravel pack and other methods. A new sizing method is proposed which is based on the "effective formation size", (Formation d50 / Uniformity Coefficient) as well as the gravel pack pore size. In this manner, the gravel pack is effectively treated like a screen and the selection of gravel pack size becomes similar to the selection of screen size. The sand retention testing used to validate this selection criteria was performed using both constant drawdown and constant rate test methods. These represent the two most common methods used in the industry. The amount of solids produced, the size of the solids produced, and the initial and final gravel pack permeability are measured and reported for each test.