Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
2002-02-06
2004-05-04
Suchfield, George (Department: 3672)
Wells
Processes
Cementing, plugging or consolidating
C106S711000, C106S819000, C166S293000
Reexamination Certificate
active
06729405
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to methods and compositions for cementing, and more specifically to methods and flexible cement compositions for cementing in high stress and high temperature environments.
2. Description of Related Art
Cementing is a common technique employed during many phases of wellbore operations. For example, cement may be employed to cement or secure various casing strings and/or liners in a well. In other cases, cementing may be used in remedial operations to repair casing and/or to achieve formation isolation. In still other cases, cementing may be employed during well abandonment. Cement operations performed in wellbores under high stress conditions may present particular problems, among other things, difficulty in obtaining good wellbore isolation and/or maintaining mechanical integrity of the wellbore. These problems may be exacerbated in those cases where wellbore and/or formation conditions promote fluid intrusion into the wellbore, including intrusion of water, gas, or other fluids.
In a wellbore, cement may be used to serve several purposes. Among these purposes are to selectively isolate particular areas of a wellbore from other areas of the wellbore. For example, in primary cementing, cement is commonly placed in the annulus created between the outside surface of a pipe string and the inside formation surface or wall of a wellbore in order to form a sheath to seal off fluid and/or solid production from formations penetrated by the wellbore. This isolation allows a wellbore to be selectively completed to allow production from, or injection into, one or more productive formations penetrated by the wellbore. In other cases cement may be used for purposes including, but not limited to, sealing off perforations, repairing casing leak/s (including leaks from damaged areas of the casing), plugging back or sealing off the lower section of a wellbore, sealing the interior of a wellbore during abandonment operations, etc.
One important objective of a primary cement job is to provide good isolation between producing zones up to the surface and in a manner that will endure through the entire life of the well. No fluid movement, either gas or liquid, is normally desirable at any time through the cemented annulus. In this regard, possible paths for fluid movement in the annulus include the interface between cement/rock and cement/casing and the cement matrix. Cement adherence to the formation and casing is primary affected by cement shrinkage and by stress changes induced by down-hole variations on pressure and temperature, especially inside the casing but also at the formation.
Conventional well cement compositions are typically brittle when cured. These conventional cement compositions often fail due to stresses, such as compressional, tensile and/or shear stresses, that are exerted on the set cement. Wellbore cements may be subjected to shear and compressional stresses that result from a variety of causes. For example, stress conditions may be induced by relatively high temperatures and/or relatively high fluid pressures encountered inside cemented wellbore pipe strings during operations such as perforating, stimulation, injection, testing, production, etc. Stress conditions may also be induced or aggravated by fluctuations or cycling in temperature or fluid pressures during similar operations. Variations in temperature and internal pressure of the wellbore pipe string may result in radial and longitudinal pipe expansion and/or contraction which tends to place stress on, among other things, the annular cement sheath existing between the outside surface of a pipe string and the inside formation surface or wall of a wellbore. Such stresses may also be induced in cement present in other areas of the wellbore in the pipe.
In other cases, cements placed in wellbores may be subjected to mechanical stress induced by vibrations and impacts resulting from operations, for example, in which wireline and pipe conveyed assembly are moved within the wellbore. Hydraulic, thermal and mechanical stresses may also be induced from forces and changes in forces existing outside the cement sheath surrounding a pipe string. For example, overburden and formation pressures, formation temperatures, formation shifting, etc. may cause stress on cement within a wellbore.
Conventional wellbore cements typically react to excessive stress by failing. As used herein, “cement failure” means cracking, shattering, debonding from attached surfaces (such as exterior surfaces of a pipe string and/or the wellbore face), or otherwise losing its original properties of strength and/or cohesion. Stress-induced cement failure typically results in loss of formation isolation and/or wellbore mechanical integrity. This in turn may result in loss of production, loss of the wellbore, pollution, and/or hazardous conditions.
Injection or production of high temperature fluids may cause thermal expansion of trapped fluids located, for example, between a pipe string and a cement sheath, between a cement sheath and the formation, and/or within the cement sheath. Such trapped fluids may create excessive pressure differentials when heated and/or cooled, resulting in cement failure. Thermal cycling (such as created by intermittent injection or production of fluids that are very warm or cool relative to the formation temperature), typically increase the likelihood of cement failure.
In still other cases, mechanical and/or hydraulic forces exerted on the exterior of a cement sheath may cause stress-induced cement failure. Such forces include, but are not limited to, overburden pressures, formation shifting, and/or exposure to overpressured fluids within a formation. Increased pressure differential, such as may be caused when the interior of a cemented pipe string is partially or completely evacuated of liquid, also tends to promote cement failure, especially when combined with relatively high pressures exerted on the exterior of a cement sheath surrounding the cemented pipe string.
In addition, any type of thermal, mechanical or hydraulic stress that acts directly on a set cement composition, or which tends to cause deformation of a wellbore tubular in contact with a set cement composition may promote, or result in, failure of a conventional cement composition.
SUMMARY OF THE INVENTION
Natural fiber-containing cementing systems and methods are provided in which cement slurries may be formulated to provide hardened cement compositions possessing relatively high resilience, elasticity, and/or ductility at relatively high temperatures. In one embodiment, such hardened cement compositions may be characterized as having an increased ratio of flexural strength to compressive strength as compared to conventional cement compositions. As used herein, a “hardened cement composition” means a cured or set cement slurry composition.
The disclosed cement formulations may be advantageously used to cement wellbores in relatively high temperature environments where high stress resistance is required. These include oil/gas, water and geothermal wells in which high stress conditions exist or in which cement will be subjected to conditions of high stress including, but not limited to, those types of wellbores discussed above. Specific examples of such wells include, but are not limited to, wells having slimhole completions, highly deviated or horizontal wells, wells exposed to thermal and/or pressure cycling, high perforation density completions, wells completed in formations subject to relatively high overburden and/or fluid pressures, and wells having junction points between a primary wellbore and one or more lateral wellbores. Such cement systems are typically characterized by the ability to provide the ductility needed to withstand impacts and shocks of well operations and/or stresses induced by temperature and/or fluid production/injection, while at the same time providing relatively high compressive strength.
As disclosed herein, a natural fiber-containing cementing system
DiLullo Gino A.
Rae Philip J.
BJ Services Company
O'Keefe Egan & Peterman, LLP
Suchfield George
LandOfFree
High temperature flexible cementing compositions and methods... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High temperature flexible cementing compositions and methods..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High temperature flexible cementing compositions and methods... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3214245