Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
2002-04-03
2003-09-30
Suchfield, George (Department: 3672)
Wells
Processes
Cementing, plugging or consolidating
C106S789000, C106S790000, C166S293000
Reexamination Certificate
active
06626242
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions and slurries for cementing oil and gas wells as well as to the use of such slurries in those wells, and specifically to compositions and slurries containing blast furnace slag to be used in water-based fluids as hydraulic material, in the absence of set inhibitors, such slurries being storable at ambient temperature.
BACKGROUND INFORMATION
The usual procedure for drilling an oil and gas well comprises drilling the well using a drilling fluid. Then, a casing is introduced in the well and a cementitious slurry is placed in the annulus between the outer portion of the casing and the borehole wall. The purpose of the cementitious slurry is to harden and provide efficient sealing between the casing and the well. The outer shell of hardened cement impedes or inhibits the fluid communication among the various formations penetrated by the well. Besides providing isolation among zones, the cement contacts the casing and provides mechanical support and strength to axial movement through the adherence developed between the interfaces of cement and casing as well as between the interfaces of the cement and the formation.
Besides the proper features of adherence between the cement and the casing and between the cement and the formation, of compatibility between the cementitious slurry and the drilling fluid, of the compressive strength and of the rheological parameters, another important feature is the set time (or hardening time) of the slurry compositions. Normally, slurries contain additives for the control of set time (accelerators and retarders) and rheology-modifying additives.
The set activating additives are used in the cementitious slurries aiming at avoiding long waiting times (up to ca. 24 hours) until the slurry hardens, after the slurry being placed in the desired site of the annulus of the well.
The patent literature is abundant in publications dealing with applications of blast furnace slag together with water based drilling fluids.
Thus, U.S. Pat. No. 5,058,679 teaches the in situ solidification of water based fluids by adding blast furnace slag, additives for controlling the set time, as well as rheology modifiers. After addition for example 50 to 400 lb/bbl slag, the drilling fluid is displaced to the annulus and left to harden. The setting time of the drilling fluid treated with slag may be varied according to the temperature conditions of the well and the requirements for the displacing time. Set times are controlled between around one hour and up to several days for temperatures between 40 and 400° F. (4 and 204° C.).
U.S. Pat. No. 5,409,064 teaches a composition and method for cementing a well by combining ingredients which comprise water and blast furnace slag of particle size between 2,000 cm
2
/g and 15,000 cm
2
/g (200 m
2
/kg and 1,500 m
2
/kg), preferably between 4,000 cm
2
/g and 6,500 cm
2
/g (400 m
2
/kg and 650 m
2
/kg) and an activator which comprises sodium pyrophosphate to form a cementitious slurry; displacing the cement slurry to the well, and allow the cementitious slurry to set.
U.S. Pat. No. 5,447,197 teaches storable cementitious slurries made from cementing hydraulically active material, which may be stored in the liquid state. The slurry is activated when needed for cementing. After pumping the activated slurry to the interior of the well, the properties of the hardened cement are suitable for well cementing. The composition contains a set retarder aiming at maintaining the slurry in the liquid state while stored, and an activator to revert the retardation caused by the retarder.
U.S. Pat. No. 5,547,506 teaches liquid storable cementitious slurries made from hydraulically active cementitious material, a set inhibitor to allow storage of the slurry and an activator to activate the slurry.
A paper published by the Society of the Petroleum Engineers (SPE) no. 36973, of October 1996, teaches a new technology for cementing of slim wells with the aid of Liquid Cement Premix (LCP), such technology having the advantage of providing slurries having a more uniform density while dispensing with the use of expensive mixers in the field.
Conceptually, LCP is a storable cement slurry which may be indefinitely kept in the liquid state so that the set is determined as required. The slurry is a pre-mix of Portland cement or any other hydraulic material containing set inhibitors and other additives. Such system requires the use of an activator, which is added immediately before pumping the slurry to the well. The activator resumes hydration and allows that the slurry sets and develops compressive strength. The LCP properties may be adjusted with the aid of the additives used in conventional cementing operations. The slurry is compatible with all the usual cementing additives. LCP attains the usual densities. Values of compressive strength developed after around 3 hours are suitable for well cementing. The range of useful temperatures extends from ambient temperatures to 450° F. (230° C.).
Thus, the literature teaches cementing slurries which use water based drilling fluids and blast furnace slag as hydraulic material, the slurries being pumped to the well soon after being made. The cementing slurries of the state-of-the-art technique necessarily comprise the use of retarders/activators, this representing the presence of more reagents in the composition, besides higher cost. So, the technique is still in need of compositions and storable cementitious slurries for well cementing which may be stored at ambient temperature, dispensing with the use of inhibitors/activators, such compositions and slurries being provided for by the present invention.
SUMMARY OF THE INVENTION
The storable compositions of cementitious slurries for oil and gas wells of the present invention are based on the presence of blast furnace slag as the hydraulic material as well as on specific amounts of other components of the composition, the compositions and slurries being free of set retarders.
The storable compositions of cementitious slurries according to the present invention comprise:
Of from 200 to 500 lb of blast furnace slag/bbl of slurry (570 to 1428 kg of blast furnace slag/m
3
of slurry);
Of from 0.01 to 13 weight % of activators, based on the weight of blast furnace slag;
The balance being made up of water based fluid,
The composition may still contain other usual additives for cementing and drilling fluid for oil and gas wells.
Contrary to the storable compositions of cementitious slurry of the state-of-the-art technique, the storable compositions of the present invention are formulated in the absence of any amount of set retarders.
In terms of concentration, the compositions are defined as: blast furnace slag, kg/m
3
, the activators, weight % based on the weight of blast furnace slag and the possible additives, weight % based on the weight of blast furnace slag or kg/m
3
.
Water or a water-based drilling fluid or a mixture of same constitute the continuous medium.
Another composition of cementitious slurry according to the invention contains zero percent activators at the time of the preparation, the activators being added immediately before pumping the slurry to the wellbore.
Still another composition of cementitious slurry according to the invention contains a portion of the activators at the moment it is prepared the remaining of the activators being added immediately before pumping the slurry to the wellbore.
In view of the three parameters which control the setting time of the slag-containing cementitious slurries:
physical and chemical properties (surface area, vitrification degree and chemical composition) and concentration of the blast furnace slag;
kind and concentration of chemical activators;
wellbore temperature,
The principle on which are based the compositions of the invention storable at ambient temperature in the absence of set retarders relates to the control of the blast furnace slag and the chemical activators.
It should be understood that the temperature of the wellbore where the slurries wil
Campos Gilson
D'Almeida Arnaldo Rodrigues
De Miranda Cristiane Richard
Petroleo Brasileiro S.A. - Petrobras
Suchfield George
LandOfFree
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