Mechanics Of Sand Production And The Flow Of Fines In Porous Media
Authors: Selby Rawya J. , Ali S.M. Farouq 
Published: March 2010

Formation damage in producing reservoirs has been frequently associated with the migration of fines in tile reservoir pores, which leads to pore plugging and permeability impairment. Sand production, encountered when producing from unconsolidated shallow sands, has been recognized to result in many operational and equipment problems.

In this paper the results of laboratory experiments investigating the mechanics of the movement of fines and sand flow into the wellbore are discussed. From linear flow experiments, it is shown that the flow of fines in porous media is influenced by the initial amount of fines present in the formation the fluid flow rate the size and shape of sand grains, and the size and density of fines. Experiments in a radial flow model simulating a wellbore and surroundings reveal that sand production is affected by the overburden pressure applied, the flow rate and the size and shape of sand grains. Two-phase flow experiments were carried out in a Berea sandstone core, using Hamilton Lake erode and either2% or 30% NaCI brine. These experiments show that the relative permeabilities to oil and brine drastically decrease due to fines migration, when the salt concentration in the brine is increased.

Introduction

The flow of fines in porous media has long been recognized to cause formation damage and permeability impairment. Fines have been defined by Muecke(l) as small, loose solid particles present in the pore spaces of consolidated or unconsolidated formations. When these particles are entrained in the fluids flowing toward the well, they can accumulate at pore constrictions, thus plugging the pore channels and causing large reductions in permeability.

The movement of sand into the wellbore when producing from shallow, unconsolidated formations, has been known to cause production loss and well damage. Sand flow into the well results in sand bridging in the casing and tubing, which may lead to the obstruction of fluid flow. Sand production can result in. casing and liner failure due to reservoir compaction, and equipment damage due to abrasion and erosion.

The purpose of this paper is to study the mechanics of flow of fines and sand production, which may lead to prevention of permeability impairment and better sand control methods. In particular, the conditions which lead to the production of fines or sand are investigated, and the effect of fines migration on two-phase flow is briefly examined.

Results obtained from three types of laboratory experiments are discussed: linear flow experiments to study the flow of fines, radial flow experiments to investigate sand production, and two-phase flow experiments to examine the effect of fines migration on relative permeability. The experimental conditions investigated include the fluid flow rate, the grain size and shape of the sandpack, the size and density of fines, and the overburden pressure.

Flow of Fines

Numerous studies investigating the flow of fines were initially conducted in the water filtration area. Clarification studies examined the influence of sand bed parameters such as depth, porosity, grain size and grain shape, as well as water and suspension characteristics, on filter performance.