The Effect Sand Handling Equipment Has On Prop Sand Quality
Authors: Wendorff C.L. , Garbis S.J. 
Published: December 2007

The effect of sand handling equipment on the quality of propping sand has been investigated. Early results have indicated that sand size is not significantly changed on its trip from the supplier to the wellhead. In addition, conductivity tests on 20/40 prop sand indicates some particle size variation from current specifications can occur without causing significant reduction in conductivity.

Introduction

In recent years, the quality of propping sand has become increasingly important. The search for adtional oil and gas reservoirs has caused the industry to explore deeper horizons and expand the development of marginal producers. Both have had an important impact on increasing the use of proppants. Production from deeper zones has taxed the ability of Production from deeper zones has taxed the ability of sand to serve as a prop, resulting in higher strength materials, such as bauxite, being used in critical wells instead of sand. However, sand can be used successfully for propping fractures in wells of moderate depth, provided it is high quality sand. Reservoirs that were considered marginal producers a few years ago are commercial producers today due to the improvements have greatly increased the amount of prop sand used per well. With significantly larger treatments, higher flow capacity of the fracture is needed to give effective drainage. Again, larger amounts of high quality sand have been necessary to achieve this goal.

The search for high quality prop sand has resulted in the production of sand from two sources. The first source is the St. Peters sandstone, which underlies second source is the Hickory sandstone underlying areas of Central Texas. The majority of sand used in propping fractures has come from these two formations. propping fractures has come from these two formations. The quality of sand loaded into rail cars and trucks has long been required to meet minimum specifications. These specifications control particle size within narrow limits and insure freedom from nonquartz contaminants. While the quality of sand at the supplier has been known and controlled for years, the quality of sand at the well site has recently been under closer scrutiny because of the greater need for high quality sand. This has led to several questions:

How should sand be sampled so that samples are truly representative?

How is prop sand affected by the handling and transportation it is subjected to prior to injection into the well

What effect do these changes have on the fracture conductivity of the prop sand?

In order to answer these questions, we followed rail car and truck loads of sand from the supplier to the well site. Samples of sand were taken at each transfer point and analysis of the samples were made to show any changes in particle-size distribution. While the field-sampling program was underway, fracture conductivity testing was done to study the effect particle-size distribution has on sand permeability at increased overburden stresses. permeability at increased overburden stresses. A statistical approach was used in which a baseline particle-size distribution was developed by sampling sand as it was loaded into several rail cars and trucks from a single supplier of 20/40 Hickory sand, Rail cars and trucks from the same supplier were sampled as they were unloaded into sand sites at several different districts storage sites. Districts were chosen which received sand from only one supplier. The last samples were taken as the sand was transferred from the transport into the blender at the well.

SAMPLING AND SIEVE ANALYSIS

In all cases, samples were taken from a moving stream of sand. The scoop and sampler shown in Fig. 1 and described in ASTM C-429-72 were used for sample collection. Both were sufficiently large to collect samples from the full width of the sand stream.