Two New Chemical Components for Sand Consolidation Techniques

Two New Chemical Components for Sand Consolidation Techniques

Abdel-Alim H. El-Sayed*, Musaed N. Al-Awad & Emad Al-Homadhi, King Saud University, Riyadh, Saudi Arabia,

* SPE Member

Abstract

Sand production problems are encountered

throughout the world and recently detected in Saudi

Arabian oil fields. Therefore an increased emphasis

is being placed on proper initial well completion as

the value of non-renewable oil reserves increases

and cost of remedial work skyrockets. Sand control

by consolidation involves the process of injecting

chemicals into the naturally unconsolidated

formation to provide in situ grain-to-grain

cementation. Techniques for accomplishing this

successfully are perhaps the most sophisticated ones

undertaken in completion work.

Many methods have been suggested to

consolidate the wall of the wellbore for few inches

or feet around the hole. These methods are either

expensive or temporarily. This paper introduces

two new cheep chemical components to be used to

consolidate friable sand formation at temperature up

to 300ºC. The paper introduces these two

components, discusses the physical and

petrochemical properties of the consolidated sand

and the factors affecting this consolidation and

highlight the laboratory process and field

application of these two components.

Introduction

Sand production problems are experienced

in many oil and gas productive formations [1]. They

are most significant in unconsolidated sandstone

reservoirs. Sand influx into the wellbore may lead

to various problems such as erosion of valves and

pipelines, plugging the production liner and sand

accumulation in the separators. Cleaning and

repair works related to sand production plus loss of

revenue due to production rate restriction amounts

to great costs incurred by the industry every year.

Furthermore, undetected erosion of production

equipment may pose a major safety hazard in case

of high-pressure gas wells. Therefore, sand control

has attracted much research effort for more than six

decades [2].

Sand production is explained in several

ways. The most convincing theory attributes sand

production to friction and resultant pressure drop as

well fluid passes through the small pores of the sand

body. If the cementing materials are not strong

enough and that the pressure drop is high, the

individual sand grain is displaced and carried into

the wellboe. Another plausible explanation

considers the fact that the formation compaction as

the bore pressure decreases, and the variations of

the load, tends to shift sand grains and shear the

cementing material. Another strong explanation

highlights the chemical difference between the

water initially present when the sand grains were

first deposited and that water contained in the

aquifer. Water production can actually dissolve a

part of the cementing material between sand grains.

Several methods were proposed and adopted

for the control of sand productions in the past [3-5].

These control methods are intended either to

prevent or reduce the flow of sand particles into the

wellbore during the course of production. Three

processes are employed predominately for the

control of sand production in oil and gas wells.

These methods include mechanical means such as

sand screens, filters, perforated or slotted liners,

gravel packing [3-7]; chemical agents such as

plastic, phenolic, epoxy, furan, and enzymes

consolidations or a combination usually introduced

to the oil industry [8-22]. Certain completion and

production practices are also used to reduce or

totally prevent sand production. Each method has

brought some useful achievements.

Low and high temperature oxidation of

crude oil has been used to test its potential as sand

consolidation material [23-25]. The crude oil reacts

with oxygen through numerous and complex

reactions. These reactions in turn depend upon the

temperature. Low temperature oxidation is found

below 500o C and is characterized by products such

as oxygenated hydrocarbons like aldehydes,

alcohol, ketones, acids and hydro-peroxides with

carbon oxides [21]. Light oils were found to be

more susceptible to low temperature oxidation than

heavy oils, because low temperature increases the

viscosity and density and hence alters the

distillation characteristics of the oil. It also affects

the quantity of the fuel available for combustion

[24].

In sand consolidation, there are two major

factors: The first concerns the placement of a

binding film in the pores. The binding film must

adhere to the surface of sand grains and do not

obstruct the flow of the fluid. The second factor

regards the strength. This is particularly useful in

the design of consolidation method of steam

displacement wells, where temperatures in the

stimulation phase goes up 700oF.

A high temperature sand consolidation

system that is stable to the wellbore temperatures of

372o C was developed [25]. The development

resulted from two improvements in the technique.

First a controlled amount of catalyst is adsorbed on

the sand, so that consolidation takes place near the

sand grains. This action is useful for obtaining

higher permeability consolidation. The second

improvement comes from the elimination of the

adverse effects of water by driving the reaction to

completion. The resin used, in achieving this

accomplishment, is a very viscous derivative of

furlfuryl alcohol, which requires a dilution to make

it easy to inject. A hydrolyzable ester that reduces

viscosity is employed for dilution.

The screening of these proposed methods

shows that they are either expensive or incapable to

prevent the flow of sand particles into the wellbore.

This work presents the results of testing a byproduct

of steel industry that is defined as slag for potential

use in friable sand consolidation. This byproduct is

a waste and causes an environmental problem, if

dumped on land.

Experimental Procedures

The sand used in this study was brought

from Half Moon beach, Eastern Province, Saudi

Arabia. The sand was sieved using ASTM set of

sieves and shaker. The friable sand was packed in a

Hoek Cell to measure its permeability. The absolute

permeability of the friable sand pack before use

with slag is 0.5 Darcy while the permeability of that

before use with sodium silicate is 1.5 Darcy. These

values are used as a reference for the consolidated

samples.

Preparing Sample with Slag

To prepare consolidated sand samples with

slag, chemical activators (Ca(OH)2 and CaCO3)

have been mixed with water using cement blender

for 10 minutes. Slag has been added to the water

and activator mix at a low rate during blending

rotation to ensure complete mix with the water.

After adding the amount of slag to the mix,

blending process continued for another 10 minutes.

Amount of sand was weighed and added to the slag

mix and blended for another 10 minutes. Cement

moulds were tightened, greased and prepared for

making cubical samples. The slag mix was poured

in the moulds. The moulds were tapped

continuously using electric vibrator to allow any

gasses in the mix to peculate and escape from the

mixture. After ensuring complete gas percolation,

the moulds were covered with aluminum foil, put

into oven and cured for 24 hours. The oven

temperature increased gradually to simulate

wellbore temperature till 95° C and kept constant

for the specified curing time.

After curing time, the samples are picked up,

cooled and dismantled from the moulds. Some

samples were used to evaluate the compressive

strength using Versa Tester machine. Other samples

were used to measure the rock permeability using

Ruska gas permeameter. Finally, other samples

were immersed in kerosene or water to measure

their deterioration in water and oil. The samples

immersed in kerosene and water was kept for 30

days under these fluids, and then they were dried

and tested for compressive strength and

permeability. The amount of activators as well as

slag was changed to find out the optimum

composition to be used for sand consolidation.

Preparing Sample with Sodium Silicate

To prepare consolidated sand samples with

Sodium Silicate, sodium silicate solution has been

added to the dry sand and blended for 10 minutes.

For wet sand, water is added first to the dry sand

and blended thoroughly. After that sodium silicate

is added to the wet sand and blended for 10 minutes

to ensure complete mix. Cement moulds were

tightened, greased and prepared for making cubical

samples. The silicate mix was poured in the

moulds. The moulds were tapped continuously

using electric vibrator to allow any gasses in the

mix to peculate and escape from the mixture. After

ensuring complete gas percolation, the moulds were

covered with aluminum foil, put into oven and

cured for 24 hours. The oven temperature increased

gradually to simulate wellbore temperature until the

specified temperature is reached and kept constant

for the proposed curing time.

After curing time, the samples are picked up,

cooled and dismantled from the moulds. Some

samples were used to evaluate the compressive

strength using Versa Tester machine. Other samples

were used to measure the rock permeability using

Ruska gas permeameter. Finally, other samples

were immersed in kerosene or water to measure

their deterioration in water and oil. The samples

immersed in kerosene and water was kept for 30

days under these fluids, and then they were dried

and tested for compressive strength and

permeability

Results and Discussion

Sand Consolidation Using Slag

For any friable sand consolidation

technique, compressive strength, rock permeability

and rock stability under fluid flow are the major

important factors. Therefore, the work is

concentrated on these factors to evaluate the

consolidation process using both Blast Furnace Slag

(BFS) and Steel Making Slag (SMS). The amount

of slag is changed between 20% and 50% relative to

the amount of water. The amount of calcium

hydroxide and calcium chloride lies between 20%

and 40% of the amount of water added. The amount

of sand is kept constant at 2250 gm for all

experiments.