In this paper, gravel-pack pore size is evaluated further by use of the permeability of the gravel pack and other methods. A new sizing method is proposed that is based on the effective formation size and 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.
Use of a coarser-grained material to stop the production of a finer-sized formation sand in oil wells has been practiced for decades. The selection of the coarser-grained sand has usually been performed on the basis of a multiple of one or more of the smaller particle sizes in the formation material, with the goal being that the formation material will bridge on the larger gravel-pack particles without reducing flow capacity or allowing excessive solids production.
This paper presents an alternative approach to testing and selecting gravel sizes in which the size of the formation material is addressed by using an effective size of the formation grains defined as the median grain size (d50) divided by the uniformity coefficient (d40/d90) and the gravel pack is described by the apparent pore size of the gravel. This approach allows laboratory performance testing for solids production, size of solids, and retained permeability to be compared directly for gravel-pack completions and for screen-only completion. These data are especially useful in the selection of the completion method for horizontal wellbores. Testing methods have been modified so that gravel-pack tests can be performed by both constant-drawdown and constant-rate methods.
A summary of previous important studies investigating gravel-size-selection methods is provided in the complete paper....
Re-Evaluation of Gravel-Pack-Sizing Criteria
10 September 2016