Patent Application
20120103609
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Embodiments relate to compositions and methods for treating subterranean formations, in particular, compositions and methods for cementing subterranean wells.
During the construction of subterranean wells, it is common, during and after drilling, to place a tubular body in the wellbore. The tubular body may comprise drillpipe, casing, liner, coiled tubing or combinations thereof. The purpose of the tubular body is to act as a conduit through which desirable fluids from the well may travel and be collected. The tubular body is normally secured in the well by a cement sheath. The cement sheath provides mechanical support and hydraulic isolation between the zones or layers that the well penetrates. The latter function is important because it prevents hydraulic communication between zones that may result in contamination. For example, the cement sheath blocks fluids from oil or gas zones from entering the water table and polluting drinking water. In addition, to optimize a well's production efficiency, it may be desirable to isolate, for example, a gas-producing zone from an oil-producing zone. The cement sheath achieves hydraulic isolation because of its low permeability. In addition, intimate bonding between the cement sheath and both the tubular body and borehole is necessary to prevent leaks.
Optimal cement-sheath placement often requires that the cement slurry contain a retarder. Cement retarders delay the setting of the cement slurry for a period sufficient to allow slurry mixing and slurry placement in the annular region between the casing and the borehole wall, or between the casing and another casing string.
A wide range of chemical compounds may be employed as cement retarders. The most common classes include lignosulfonates, cellulose derivatives, hydroxycarboxylic acids, saccharide compounds, organophosphonates and certain inorganic compounds such as sodium chloride (in high concentrations) and zinc oxide. A more complete discussion of retarders for well cements may be found in the following publication—Nelson E B, Michaux M and Drochon B: “Cement Additives and Mechanisms of Action,” in Nelson E B and Guillot D. (eds.): Well Cementing (2nd Edition), Schlumberger, Houston (2006) 49-91.
Certain types of retarders have been blended with other compounds to extend their useful temperature range, improve cement-slurry properties, or both. For example, the useful temperature range of certain lignosulfonate retarders may be extended to more than 260° C. by adding sodium tetraborate decahydrate (borax). Sodium gluconate may be blended with a lignosulfonate and tartaric acid to improve the rheological properties of the cement slurry. Thus, a myriad of retarders and retarder blends exist which may be applicable to a wide range of subterranean-well conditions.
Cement-retarder technology for well cements is sophisticated; however, as exploration and production operations continue to move into environmentally sensitive areas, especially offshore locations, the population of retarders that may be used is increasingly limited. Government regulations frequently require well operators to restrict themselves to chemical products that have low toxicity and do not bioaccumulate.
It thus becomes more and more challenging to develop efficient cement retarders (and other types of additives) that can meet these ecological criteria. Despite the valuable contributions of the prior art, there remains a need for cement retarders that conform to environmental regulations.
Embodiments allow improvements by providing biodegradable, low-toxicity retarders.
In an aspect, embodiments relate to well-cementing compositions.
In a further aspect, embodiments relate to methods for retarding a cement slurry.
In yet a further aspect, embodiments relate to methods for cementing a subterranean well.
At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. In addition, the composition used/disclosed herein can also comprise some components other than those cited. In the summary of the invention and this detailed description, each numerical value should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary of the invention and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended that any and every concentration within the range, including the end points, is to be considered as having been stated. For example, “a range of from 1 to 10” is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific, it is to be understood that inventors appreciate and understand that any and all data points within the range are to be considered to have been specified, and that inventors possessed knowledge of the entire range and all points within the range.
As stated earlier, there is a need for cement retarders that are biodegradable and do not bioaccumulate. Surprisingly, the inventors discovered that hydrophobins satisfy, at least in part, the goals described above.
The term “hydrophobin” shall hereinafter refer to a protein or polypeptide of the general structural formula shown below.
Xn—C1—X1-50—C2—X0-5—C3—X1-100—C4—X1-100—C5—X1-50—C6—X0-5—C7—X1-50—C8—Xm
where X may be any of the 20 naturally occurring amino acids (Phe, Leu, Ser, Tyr, Cys, Tip, Pro, His, Glm, Arg, Ile, Met, Thr, Asn, Lys, Val, Ala, Asp, Glu and Gly). Each X may be the same or different. The indices next to X indicate in each case the number of amino acids, C represents cysteine, alanine, serine, glycine, methionine or threonine subject to the proviso that at least four of the amino acids identified by C are cysteine, and the indices n and m are independently natural numbers in the range of 0 to 500 and preferably in the range from 5 to 350 and preferably in the range from 15 to 300.
Hydrophobins occur naturally on filamentous fungi, but may also be synthesized artificially. They have a marked affinity for interfaces and are therefore may be useful for coating surfaces. The coating may usually be hydrophobic. Without wishing to be bound by any theory, it is thought that hydrophobins form a hydrophobic coating on cement particles, thereby inhibiting contact between water and the cement-particle surfaces, and resulting in a retarding effect.
In an aspect, embodiments relate to well-cementing compositions that comprise an inorganic cement, water and a retarder comprising at least one hydrophobin protein. The composition may be pumpable. Those skilled in the art will recognize that a pumpable cement slurry usually has a viscosity lower than 1000 mPa-s at a shear rate of 100 s−1.
In a further aspect, embodiments relate to methods for retarding an inorganic cement slurry. Water is added to a hydraulic cement, thereby producing a slurry. At least one hydrophobin compound is added to the slurry. The slurry may be pumpable. Those skilled in the art will recognize that a pumpable cement slurry usually has a viscosity lower than 1000 mPa-s at a shear rate of 100 s−1.
In yet a further aspect, embodiments relate to methods for cementing a subterranean well. An inorganic cement is provided, to which water is added to form a slurry. At least one hydrophobin compound is added to the slurry, and the slurry is placed into the well. The slurry may be pumpable. Those skilled in the art will recognize that a pumpable cement slurry usually has a viscosity lower than 1000 mPa-s at a shear rate of 100 s−1. Those skilled in the art will recognize that embodiments of the methods may relate to either primary or remedial cementing. In addition, those skilled in the art will recognize that the composition may be pumped through various tubulars including (but not limited to) drillpipe, casing and coiled tubing. The cementing procedure may be the traditional one during which the cement composition is pumped downward through tubulars, and upward inside the annulus between the tubulars and the borehole wall, or between the tubulars and another tubular string. Or, the “reverse-cementing” procedure may be employed, during which the cement composition is pumped downward through the annulus.
In embodiments, the size of the hydrophobin is preferably between about 100 and 350 amino acids, and more preferably between about 100 to 150 amino acids. The hydrophobin concentration in the cement slurry is preferably between about 0.001% and 1.0% by weight of cement, more preferably between about 0.05% and 1.0% by weight of cement, and most preferably between about 0.1% and 0.5% by weight of cement.
The inorganic cement may comprise one or more members of the list comprising Portland cement, calcium aluminate cement, fly ash, blast-furnace slag, lime-silica blends, geopolymers, Sorel cements, chemically bonded phosphate ceramics, zeolites and cement-kiln dust. Of these, Portland cement is preferred.
The cement compositions may further comprise more additives such as (but not limited to) extenders, fluid-loss additives, lost-circulation additives, additives for improving set-cement flexibility, self-healing additives, gas-generating agents, antifoam agents, dispersants and anti-settling agents.
The following example serves to further illustrate the invention.
Three Portland-cement slurries were prepared with the following base-slurry composition: Class H cement, 0.2% polypropylene glycol antifoam agent by weight of cement, and 38.8% water by weight of cement (BWOC). The slurry density was 1970 kg/m3 (16.4 lbm/gal). Hydrophobin retarder was added at the following concentrations: 0%, 0.1% and 0.5% by weight of cement. The hydrophobin was as disclosed in Wohlleben W et al.: “Recombinantly Produced Hydrophobins from Fungal Analogues as Highly Surface-Active Performance Proteins,” Eur Biophys J., 39 (3) February 2010: 457-468.
Thickening time tests were performed in a pressurized consistometer at 52° C. (125° F.) and 35.6 MPa (5160 psi), according to the standard procedure described in ISO Publication 10426-2. The results, presented in Table 1 and
