Gravel for Sand Control: A Study of Quality Control
Authors: Boulet Denis P. 
Published: December 2007

Standard dry sieve analyses were performed on 51 field samples gathered from U.S. Gulf and West Coast locations to determine the size distribution of each sample and to evaluate the extent of out-of-gauge materials. Permeability, acid solubility, and crushing tests also were conducted. Permeability, acid solubility, and crushing tests also were conducted. Most samples contained significant amounts of out-of-gauge materials. Any amount of this material will impair permeability.

Introduction

In poorly consolidated formations, hydrocarbon production often is accompanied by formation-sand production. production often is accompanied by formation-sand production. The method most widely used to control this problem is to use a gravel pack with a wire-wrapped screen or a slotted liner. When designing such an installation, the gravel generally is sized according to the formation-sand size distribution. The concentric screen or liner is later sized to agree with the gravel size.Gravel-pack efficiency relies on bridging, where formation sand grains form bridges on the outside of the packed gravel. Several design rules have been published packed gravel. Several design rules have been published to relate formation sand size to gravel size. Using any available design criteria always results in gravel with a comparatively high permeability. Even after gravel packing, however, several wells did not perform as packing, however, several wells did not perform as expected. Flow seemed to be restricted downhole. Admittedly, this decline can be caused by several factors, including improper gravel sizing because of poor formation samples and poor packing techniques. However, even when applying state-of-the-art packing techniques and when designing with samples from full-size cores, production was not up to expectations.Since all other factors were kept as constant as possible in field operations under close supervision, only possible in field operations under close supervision, only one component (gravel) remained to induce the suspected flow restrictions. Spot checks at the wellsite revealed varying size distributions of commercial gravels. Field samples were gathered later and carefully analyzed. The discovery of significant amounts of out-of-size material in the gravel led to an in-depth permeability study to quantify the material's effects. permeability study to quantify the material's effects. The techniques and results of this laboratory study are presented here, along with recommendations to improve the quality of materials packed into the well. This paper examines gravel mixtures, rather than paper examines gravel mixtures, rather than sand-gravel mixtures; the last case was covered thoroughly by Saucier and Sparlin.

Sieve Analysis

Field operations provided 51 samples of gravel collected at the wellsite just before gravel packing procedures. To obtain as accurate a sample as possible under field conditions, we requested samples of 5-lb (2.27-kg) minimum size. A good sample is always difficult to obtain, even under closely supervised conditions, and is virtually impossible under field conditions. However, we tried to provide the best samples by requesting that sacks of gravel be mixed before sampling. Table 1 lists the various sizes received, as well as the number of samples per size. Each sample was given an identification number and then was sieved using a standard dry sieve analysis. The results appear in Figs. 1 through 3.Fig. 1 gives the sieve analyses for the 20-40 mesh [0.0331 to 0.0165 in. (841 to 419 mum)] and the 40-60 mesh [0.0165 to 0.0098 in. (419 to 249 mum)] gravels.

JPT

P. 164