Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
2002-08-12
2004-06-01
Marcantoni, Paul (Department: 1755)
Wells
Processes
Cementing, plugging or consolidating
Reexamination Certificate
active
06742592
ABSTRACT:
The present invention relates to techniques for drilling oil, gas, water, or geothermal wells or the like. More precisely, the invention relates to cementing compositions which are particularly suitable for cementing zones which are subjected to extreme static or dynamic stresses.
In general, a well which is over a few hundred meters deep is cased and the annular space between the underground formation and the casing is cemented over all or part of its depth. Cementing essentially prevents the exchange of fluid between the different layers of formation traversed by the hole and controls the ingress of fluid into the well, and in particular limits the ingress of water. In production zones, the casing—and the cement and the formation—are perforated over a height of several centimeters.
The cement placed in the annular space of an oil well is subjected to a number of stresses throughout the lifetime of the well. The pressure inside a casing can increase or decrease because the fluid which fills it can change or because additional pressure is applied to the well, for example when the drilling fluid is replaced by a completion fluid, or during a stimulation operation. A change in temperature also creates stress in the cement, at least during the transition period before the steel and the cement reach temperature equilibrium. In the majority of the above cases, the stress process is sufficiently slow for it to be treated as a static process; and in some cases the forces can be sufficiently large to damage the casing. The cement is also subjected to other stresses which are dynamic in nature, either because they are produced over a very short period or because they are either periodic or repetitive in nature. Perforating creates an over-pressure of several hundred bars inside a well which is dissipated in the form of a shock wave. Further, perforating creates a shock when the projectile penetrates the cement and that shock subjects the zone surrounding the hole to large forces over a depth of several meters.
A further process, which is now routine in oil well, operations and which creates dynamic stresses in the cement, is the opening of a window in a casing which is already cemented to create a multi-branch lateral well. Milling the steel over a depth of several meters followed by drilling a lateral well subjects the cement to shocks and vibrations which usually damage it irreparably.
The present invention aims to provide novel formulations, in particular for cementing regions of oil wells or the like which are subjected to extreme static or dynamic stresses.
An article presented at the SPE (Society of Petroleum Engineers) annual technical conference and exhibition of 1997, Marc Thiercelin et al. (SPE 38598, 5-8 Oct. 1997)—and French patent application. FR-A 97 11821 of 23
rd
Sep. 1997—demonstrate that the risk of rupture of a cement sleeve depends on the thermoelastic properties of the casing, of the cement, and of the formation surrounding the well. A detailed analysis of the mechanisms leading to rupture of the cement sleeve has shown that the risk of rupture of a cement sleeve following an increase in pressure and/or temperature in the well is directly linked to the tensile strength of the cement and is attenuated when the ratio of the tensile strength R
T
of the cement to its Young's modulus E is increased.
Young's modulus is known to characterize the flexibility of a material. To increase that R
T
/E ratio, it is advantageous to select materials with a low Young's modulus, in other words to select very flexible materials.
One known means for increasing the flexibility of a hardened cement is to reduce the density of the slurry by extending it with water. However, that leads to the stability of the slurry being degraded, in particular with the solid and liquid phases separating. Such phenomena can, of course, be controlled in part by adding materials such as sodium silicate, but the permeability of the hardened cement is nevertheless very high, which means that it cannot fulfill its primary function of isolating zones to prevent fluid migration, or at least it cannot guarantee its long-term isolation. Furthermore, lightened cements have lower strength, in particular lower shock resistance, which constitutes a clear handicap for cements intended for use in zones which are subjected to extreme mechanical stresses such as perforation zones.
In the building field, incorporating particles of rubber into a concrete is known to result in better toughness, durability and elasticity [see, for example, A. B. Sinouci, Rubber-Tire Particles as Concrete Aggregate, Journal of Materials in Civil Engineering, 5, 4, 478-497 (1993)]. Concretes which include rubber particles in their formulation can be used, for example, in highway construction to absorb shocks, in anti-noise walls as a sound insulator, and also in constructing buildings to absorb seismic waves during earthquakes. In such applications, the mechanical properties in particular are improved.
In the field of oil well cementing, it is also known [Well Cementing 1990, E. B. Nelson, Schlumberger Educational Services] that adding ground rubber particles (with a grain size in the range 4-20 mesh) can improve impact strength and bending strength. Such an improvement in mechanical properties has also been indicated in patent publications SU-1384724 and SU-1323699. More recently, United States patent, U.S. Pat. No. 5,779,787 has proposed the use of particles derived from recycled automobile tires in a grain size in the range 10/20 or 20/30 mesh, to improve the mechanical properties of hardened cements, in particular to improve their elasticity and ductility.
In its French patent application number FR-A-98 16104 dated 21
st
Dec. 1998, the Applicant describes lightened oil cements reinforced with flexible particles, of low compressibility, with low density, and with an average particle size not exceeding 500 micrometers (&mgr;m). The density of the flexible particles is less than 1.5 grams per cubic meter (g/cm
3
), preferably less than 1.2 g/cm
3
and more preferably less than 1 g/cm
3
. That results in lightened cement slurries. All of the examples given in French patent application FR-A-98 16104 correspond to a slurry with a density of less than 1.68 g/cm
3
.
Further, in patent application FR-A-98 12538, the Applicant also describes cement slurries with a density of less than 1.70 g/cm
3
comprising 30% to 100% (by weight of cement) of rubber particles, with a grain size of 40-60 mesh with a diameter which is preferably in the range 250 &mgr;m to 400 &mgr;m.
As indicated above, a reduction in slurry density tends to encourage its flexibility and is thus usually desired. However, low density may not be desirable in particular when the pressure is high due to the formation or to the nature of other fluids pumped downstream or upstream of the lightened slurry.
The authors of the present invention have set themselves the target of producing cementing slurries reinforced by flexible or rubber particles with a low density, but with the density of the slurries themselves being normal for cementing slurries for oil wells or the like, i.e., typically in the range 1.7 g/cm
3
to 2.2 g/cm
3
.
According to the invention, the problem is solved by cementing slurries for an oil well or the like comprising an hydraulic binder, dense particles with a density higher than the density of the hydraulic binder and reinforcing particles with a density of less than 1.5 g/cm
3
, preferably less than 1.2 g/cm
3
, constituted by a rubber or a flexible material, of low compressibility and with an average grain size of less than 600 micrometers (&mgr;m).
The flexible particles are constituted by a material with a Young's modulus of less than 5000 mega Pascals (MPa) (preferably less than 3000 MPa, more preferably less than 2000 MPa), i.e., the elasticity of these particles is at least four times greater than that of cement and more than thirteen times that of the silica usually used as an additive in oil well cements. The flex
Le Roy-Delage Sylvaine
Thiercelin Marc
Marcantoni Paul
Mitchell Thomas O.
Nava Robin
Schlather Stephen
Schlumberger Technology Corporation
LandOfFree
Cementing compositions and applications of such compositions... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cementing compositions and applications of such compositions..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cementing compositions and applications of such compositions... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3348577