Setting Retarding Composition for Well Cementing and Recementing

In recent years the need to exploit oil resources at very considerable depths has been observed; this phenomenon has been the cause of multiple problems in the drilling and finishing techniques for oil wells, particularly in the application of slurry for cementing and recementing oil wells, since the internal temperature of the well becomes higher as its depth increases, which causes a faster setting of the slurry and makes its handling more difficult.

In the drilling, finishing and repair operations of oil wells cementing of the casings is employed; this technique is conducted by introducing a cement slurry to the bottom of the oil well through the cementing pipe; the slurry is placed in the annular space between the casing and the well walls, where it sets more or less rapidly, depending on the prevailing temperature.

In order to overcome the disadvantages of the immediate setting of the cement slurry, the applicant has carried out research activities.

In U.S. Pat. No. 3,905,826, having the same assignee as the instant invention, a setting retarding composition is described which has as basic ingredients carboxymethylcellulose, dextrine, borax, and optionally organic salts, and it presents as novel feature the fact that it can be applied with good results at depths of up to 13123.4 ft.

It is, therefore, a purpose of the present invention to provide an improved composition for retarding setting which can be applied with good results at operating depths between 13123.4 and 21325.5 ft.

Another object of the present invention is to provide an improved setting retarding composition that can be applied with stable well depth temperature of the order of 392.degree. F.

An additional object of the present invention is to provide a composition that increases the setting time of cement slurries up to five hours or more.

These objects and others that can be accomplished within the scope of the invention, shall be better understood and observed in more detail from the following specification.

The improved setting retarding composition of the present invention is constituted by the following ingredients:

The inorganic acid selected is boric acid.

In the following examples shown in Tables I through V, there appear the experimental results obtained in the evaluation of a representative composition of the present invention having the following composition:

The tests carried out to evaluate the setting retarding composition comprise: thickening time measurings for casing cementing and recementing at depths between 13780 and 20013 ft., considering a temperature gradient of 37.degree. F./328ft.; rheological properties at 80.degree. and 125.degree. F.; compression resistance in a 24 hour time period; and water loss at 995.4 psi differential pressure and at temperatures of 80.degree. and 210.degree. F.

The performed tests were conducted in accordance with the procedures established by the American Petroleum Institute, as shown in report API-RP-10B "recommended practice for testing oil-well cements and cement additives"; for this type of tests, silica flour, cement, and water without chlorides and additives regularly used for the cementing of wells, including sodium chloride, were employed.

The experimental tests were carried out using silica flour in order to avoid the resistance loss which appears in cement when it is subject to high temperatures, since the retarder is applied at temperatures higher than 210.degree. F.

Among the tests that were carried out to evaluate the retarder there was one to determine the compatibility of the product with Hallad -9 and D-19 water loss reducers. (High molecular weight polymers).

Tables I, II and II.--In these Tables are shown the results of the application tests at different well-depth static temperatures of the setting retarding composition in the cementing and recementing of wall casings, regular and short, using different concentrations of the composition. Also, it can be observed that the slurries prepared with the setting retarder are adequate for casing cementing and recementing at depths between 13780 and 20013 ft.

TABLE IV.--In this table are shown the results obtained when the setting retarder is subject to the filtering and rheological properties tests of slurries prepared with the retarder and 40% of silica flour by cement weight.

In these examples it is shown that the setting retarder retains cement slurry water which enables reduction and even elimination of the use of water loss reducers. The rheological properties determined at 80.degree. F. indicate that the slurries are easy to handle during preparation; properties at 125.degree. F. show their behaviour or performance, that is, once they are placed in the well, it is observed that viscosities and yield points decrease, which causes a reduction of friction losses during displacement of slurry to the annular space.

TABLE V.--In this Table are shown the results obtained when the retarding composition is subject to compression resistance tests in a 24 hour interval. The retarder is used at different concentrations according to the well depth and stable temperature, with mixtures prepared from cement and silica flour.

According to the results shown in the aforementioned Table, it is observed that the mixtures of cement, silica flour and retarder acquire high resistances after 24 hours of their preparation.

TABLE IV.--In the following Table, comparative results are shown of the efficiency of the retarder of the present invention, in comparison with other known retarders, thereby illustrating the properties presented by the new retarder are superior to those of other commercial products (A and B).

According to the retarder performance in the thickening time tests, it is shown that the additive of the present invention can be successfully used at stable well depth temperatures of the order of 392.degree. F.

Also, if concentrations of the retarding additive higher than 4.5% by cement weight are used, the setting of the slurry can be retarded for a period of time longer than five hours, at depths of 20013 ft.

The following can be cited as additional advantages of the retarder of the present invention:

The setting retarder is compatible with products regularly used in the cementing of oil-well casings.

Elimination or partial reduction of the use of water loss reducing agents.

Reduction of friction losses during displacement of the retarder to annular space.

The retarder does not produce foam during slurry preparation; consequently, the use of anti-foaming agents is eliminated.

Finally, it is evident that slurries prepared with silica flour and the retarder can be used safely in the cementing of casings, since they present a resistance higher than 497.7 psi, which are commendable to continue the drilling or finishing of an oil-well.