CA1073656A - Drilling mud treating agents and method of using same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Monocalcium phosphate containing compounds are employed as drilling mud treating agents to convert deleterious calcium ions present in said drilling muds into water insoluble plant nutrient compositions, and to precipitate suspended cement form said drilling muds.
Such is accomplished by admixing an effective amount of said monocalcium phosphate containing compound with said mud for a period of time of from about 10 minutes to 5 hours for the conversion of said calcium ions and the precipitation of said suspended and dissolved alkaline materials.

Description

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This invention relates to drilling mud compositions.
In one aspect this invention rela-tes to drilling mud treating agents and a method for using same. In yet another aspect this invention relates to novel treating agents for water based drilling muds to improve their disposal properties. In still another aspect this in-vention relates to monocalcium phosphate containing treating agents which convert deleterious calcium ions present in said mud composition into water insoluble plant nutrient compositions and facilitate removal of suspended cement present in said mud compositions prior to disposal of same. In yet another aspect this in-vention relates to a method for removing suspended and dissolved alkaline materials in water base drilling muds and for converting calcium ion in said muds to water in-soluble plant nutrient compositions, said method comprising admixing an effective amount of a monocalcium phosphate containing compound with said mud for an effective period of time for the conversation of said calcium ions and the precipitation of said suspended and dissolved alkaline materials.
Drilling muds have long been used in drilling pro-cesses. Universally, a drilling mud is used in a circulating system with a rotary well drilling mechanism.

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The drillin~ mud is rorced down hole by pumping it down the hollow drill stem through the bit so that it lubricates and cools the blt. Then, the mud is circu-lated back to the surface and into a settling pit. The drilling mud washes out the cuttings which have been made ~rom the hold, and the cuttings are carried outside the drill stem to the surface where the coarse particles are caused to be removed and the mud again used in a continuous circulating process. However, when one has been ~orced to drill through cement much of the cement cuttlng remains suspended in the drilling mud and cannot be settled out, under normal conditions, in the settling pit. If one is to reuse the mud such suspended cement must be removed. However, ln treating such mud, care must be exercised that such treating agents do not destroy the rheological properties Or the mud such as viscosity 3 gel strength and the like. Thus, the drilling mud must have the proper viscosity, that is, be thick enough to carry out the cuttings, but thin enough to be pumped and allow the coarse particles to settle out in the surface mud pits so that the mud may be reused. Further, if one desirbs to dispose of the spent drllling mud the suspended cement creates disposal problems.
Until recent years, a drilllng mud was thought to be usable and practicable if it possessed desi.rable gel strength, viscosity and water loss property, and no one was concerned with the disposal of such drilling muds or fluids. However, disposal of such drilling muds or fluids has gradually bccome an area of prlme importance. ~uch 073~56 has resulted from potential surface pollution. Re-strictions on the disposal of drilling fluids are -becoming more stringent thereby substantially increasing the cost of the disposal of such fluids. The industry -.
is faced with the possibility of additional governmental regulation in regard to the disposal of drilling muds or fluids with the resulted increase in cost. Therefore, much effort has been directed in developing drilling mud treating agents which can readily be employed to remove deleterious substances, such as calcium ions and suspended cement, from the drilling mud prior to dlsposal of same.
A prior art search was conducted on the concept of ..
the invention. Twenty-one patents were reviewed and of these, the following are considered typical.of the prior art:
U.S. Patent 2,935,473 U.S. Patent 2,713,030 U.S. Patent 2,713,031 U.S. Patent 3,079,334 U.S. Patent 3,079,335 U.S. Patent 2,935,473 discloses that excess calcium ion concentration in bentonite base drilling muds is un-desirable as calcium bentonite formed by an excess con-centration results in greater agglomeration of the particles and precipitation resulting in decreased viscosity and gel strengths as well as increased fluid loss. Treatment for such deterioration of drilling mud properties involves addition of a salt such as sodium phosphate which reacts .
with the excess calcium ions to form an insoluble precipi-tate, thus effectivel~ removing the excess calcium ions from the drilling mud environment.

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U.S. Patent 2,713,030 and U.S. Patent 2,713,031 disclose the use of various alkali metal molecularly dehydrated phosphates such as sodium acid pyrophosphate, sodium metaphosphate, tetrasodium pyrophosphate, ana the like, which are characterized by their ability to revert to the orthophosphate form in the presence of water, as additives for drilling mud.
U.S. Patent 3,079,334 and U.S. Patent 3,079,335 disclose that polyphosphates such as sodium tetraphosphate, sodium hexametaphosphate, sodium tripolyphosphate, and other alkali metal polyph ~ hates are added to calcium-based drilling muds.
An object of the present invention is to improve the disposability properties of water based drilling mud compositions. Another object of the invention is to economically improve the useful life of drilling mud compositions by the removal of deleterious calcium ions and suspended materials, such as cement. Another object of the present invention is to provide a drilling mud treating agent which will substantially eliminate pollu-tion problems in the disposal of water based drilling muds. These and other objects and features of the present invention will be apparent to those skilled in the art and by reading of the following detailed description of the invention.
According to the present invention, I have discovered that the disposability properties of water based drilling mud compositions can readily be improved by treating such mud compositions with an effective amount of monocalcium ~C~73656 phosphate containing compounds. By employing such monophosphate containing compounds one can readily convert the deleterious calcium ions present in water based drilling mud compositions into water-insoluble phosphate compounds having plant nutrient properties.
In addition, any suspended cement present in said mud compositions can be precipitated from the drilling mud so that said mud can be reused or readily disposed.
Broadly, such is accomplished by admixing an effective amount of said monocalcium phosphate containing compound with the mud composition being treated for an effective period of time for conversion of the calcium ions present in same and ~or the precipitation of suspended and dissolved alkaline materials.
In the drilling of deep wells, such as oil and gas, by the employment of mud laden drilling fluids as in the , rotary system of drilling, strata of a contaminating character may be encountered in large masses which often supply calcium ions and/or cement to the drilling mud or fluid. Further, many of the mud laden drilling fluids contain calcium ions. As the concentration of calcium ions builds up within the drilling mud or fluid, the rheological properties of such fluid are often altered or destroyed. In addition, the build up of such dele- `
terious calcium i.ons, and/or suspended cement, may create serious disposal problems. Thus, the industry has long been faced with the problem of developing a drilling mud system or drilling mud treating agent in which the rheo-logical properties of the mud are not altered and which will enable the spent drilling mud to be disposed of on ~73~56 the drilling site wlthout determi.nental environ~enta].
effects. ~t has now been discovered that, by incorpora-ting into water based mud systems an effective amount of a monocalcium phosphate containing compound, substantially all of the calcium ions present in the mud system can be converted into water insoluble phosphate containing com-pounds having plant nutrient values. Further, when the drilling mud is ~ound to contain suspended cement, such cement can be removed by the use of an effective amount of sald drilling mud treating agent.
The monocalcium phosphate containing compound em-ployed as the drilling mud additive in the method of the invention can be any suitable compound containing mono-calcium phosphate which is chemically compatible with the water base drilling mud being treated. ~specially de-sirable results have been obtained wherein the drilling mud treating agent is selected from the group consisting of monocalcium phosphate or a mixture of monocalcium phosphate and calcium sulfate. When a mixture of mono-calcium phosphate and calcium sulfate are employed as the treating agent the monocalcium phosphate and calcium sulfate are present in such mixture in an amount o~ from about Ll0~60 to 60-40 weight percentl respectlvely.
The amount of treating agent employed to convert the calcium ions present in the drilling mud to water in-soluble plant nutrient compounds, or to precipitate the suspended cement, will vary widely depending upon the content of calcium ions and/or suspended cement present in the drilling mud. However, it is necessary that at least a stoichiometric amount of the monocalcium phos-phate constituent in the treating agent be maintalned, based upon the concentration of calcium ions encountered .

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1~73~56 in the drilling ~ud composition, the amount Or suspended cement in the drilling mud composition, or a combination of both. Generally, it is desired to maintain the ratio of monocalclum phosphate constituent in said treating agent with the calcium ion concentration and/or cement concentration in a weight ratio of about 1:1 to 5:1, respectively.
As previously stated, the trea~ing agent of the present invention may be employed to removed deleterious calcium ions from any suitable water base drilling mud composition. Likewise, such treatlng agent can be em-ployed to remove suspended cement from any of such water base drilling mud compositions. Such water base drilling mud compositions are well known in the art. Illustrative f such water base systems are the lime mud system the low-lime mud system, and the gypsum mud system. In each system attempts are made to control the calcium ion concentration through the use of an alkali metal hydroxide constituent such as sodlum hydroxide. Further-more, each o~ the drilling mud composltions will contain varying amountSof clay makerial, slaked lime or gypsum, the alkali metal hydroxide, and when desire, other addi-tlves such as mud thlnners and fluid loss additives.
To better illustrate what is meant by water base drilling mud compositlons the followlng examples are re-presentative of the most widely used systems.
Lime Mud Low-Lime Mud Gypsum Mud (Typlcal Formulation) ~Typical Formulation)(Typical tFiorm)ula-20 pounds/barrel 20 pounds/barrel 20 pounds/barrel prehydrated bentonite prehydrated bentonite prehydrated bentonite .
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~L~73~56 Llme Mud Low-Lime Mud Gypsum Mud (Typlcal Formulation) (Typical Formulation) (Typical Formu-lation) 3 pounds/barrel 2 pounds/barrel 5 ppb starch ferrochrom~ ferrochrome lignosulfonate lignosulfonate

2 pounds/barrel NaOH 1 pound~barrel NaOH o.8 pounds/barrel NaOH
5 pounds/barrel 2 pounds/barrel 5 pounds/barrel slaked lime slaked lime CaS04 l pound/barrel l pound/barrel Additional NaOH
starch starch - added to adjust pH to 10.0 Another conventional water base drilling mud system is known aa a gel-caustic mud. In this sytem, prehydrated bentonite is admixed with water and sufficient NaOH added to adJust the pH of the composition. When desired, different base or caustic constituents, such as KOH can be employed in the place of NaOH. When determined desirable, other addi-tives such as mud thinners and fluid loss additives can be incorporated into the gel-caustic mud composition.
In practicing the present invention, it is desirable for one to analyze or calculate the amount of calcium ions and/or suspended cement present in the drill mud to be treated. Such determinations are deslrable to ensure that at least a stoichiometric amount o~ the monocalclum phosphate constituent of the treating agent, based on the amount of calcium ions and/or suspended cement, is incorporated into the drilling mud. As previously stated, the ratio of the monocalcium phosphate constituent of said treating agent with said calclum ions and/or suspended cement is preferably ' ' ''''' . :

~:973~6 maintained in a weight ratio of ~rom about 1:1 to 5:1, respectively. The amount o~ the monocalicum phosphate containing compound may be added in amounts greater than those stated above. However3 no appreciable benefit is produced by such addltional amount.
Once the amount of the above mentioned contaminants has been determined, an e~fective amount o~ the mono-calcium phosphate containing compound is admixed with the mud for an effective period of time to allow con-version of the calcium ion present in the mud into water-insoluble constituents having plant nutrient value, and to allow precipitation of the suspended and dissolved alkaline materlal contaminants present in the mud. The time period required for such admixing can vary widely but will generally range from about 10 minutes to about 5 hours. When desirable, the mud can be treated more than once.
The amount of monocalcium phosphate contalning compound employed can also vary widely. However3 as previously stated, in practicln~ the method o~ the in-vention, the amount of monocalcium phosphate containing compound ls to be employed in at least a stoichiometric amount, based on the concentration o~ calcium ions and dis-solved and suspended alkaline materials presenk in sald mud. Generally, it is desirable to maintain s~id monocalcium phosphate containing compound and said calcium ions and alkaline materials in a weight ratio of about 1:1 to 5:1, respectively. In addition, mud thinners, caustic materials, and other mud additives such as described previously, can be admixed with the treated mud to adJust ' _g_ ~ .

7365S, gel strength, pH, and other rheological Properties.
In order to more fully describe the invention the following Example ls set forth. However~ it is to be understood that such Example is provded ~or illustra-tive purposes only, and it will be appreciated by those skilled in the art that numerous modificati~ns may be made in equivalent materials and conditions without de-parting from the scope of the present invention.

EXAMPLE I
A series of experiments were conducted on a gel-caustic mud composition to determine the e~fect of alkaline material, such as cement, on the rheological properties of such composition, and the effectiveness of monocalcium phosphate containing compounds in the removal of such suspended and/or dissolved deleterious materials. The mud sample investigated was mixed in a 5 barrel equivalent lot using 20 pounds per barrel prehydrated bentonite, 0.02 pounds per barrel sodium hydroxide and tap water. The tap water contained a total salt content of approximately 582 mg/l.
The rheological properties of the mud composition were determined on a FANN Model 35 viscometer. The mud compo-sitions were at room temperature, approximately 75 F, during such measurements. The amount of dissolved and suspended alkallne materials in the mud composition was then determined by titrating a sample of the gel-caustic mud with 0.02 N H2S04 to the phenolphthalein end point.
Upon completion of the measurements as to the dissolved and/or suspended alkaline materials in the original mud composition, the mud was contaminated with 1 pound per , .~
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barrel Ca(OH)2 to simulate cement contamination of the mud. Measurements were then made on the con.taminated mud to determine its rheological properties and the amount Or dissolved and suspended alkaline materials present the`rein.
The contaminated mu~ sample was then treate~. with .
2 pounds per barrel of fertilizer grade monocalcium phosphate for 2 hours at ambient temperature.
Measurements on the treated mud were then made to 10- determine the effectiveness of monocalcium phosphate in removing suspended and/or dissolv~ alkaline materials, e.g. cement.
~ The measurements on the treated mud indicated that the monocalcium phosphate was effective in removing a substantial quantity of suspended and/or dissolved alkaline materials, However, since no thinner agents were employed in the makeup of the original gel-caustic mud composition it was determined that it would be pre-ferable to lower the gel strength of the treated mud.
There~ore, I pound per.barrel of ~errochrome lignosulfo-nate and 0.1 pounds per barrel o~ NaOH were lncorporated into the monocalclum phosphate treatèd mud. Measurements . were then made on the resulting mud composition to de-termine its rheologlcal properties and the amount of dissolved or suspended alkaline material present therein.
The results of the various sequential measurements on the gel-caustic mud compositlon are tabulated in . Table I. - -.

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TABLE I

Untreated Cement Monocalcium Thinner Mud Contaminated Treated Treated Mud Mud Mud pH 9.55 12.56 8.16 9.57 Apparent Viscosity11 31 20 10 (600 rpm reading/2) Plastic Viscosity 9 7 13 Yield Point 4 48 13 3 0 Gel 4 15 8 10 Min. Gel 13 16 36 4 PM ' 2.5 0.56 0.73 *PM ~ Amount of dlssolved and/or suspended alkaline material.

~ _ _ ...... _ . . . . . _ EXAMPLE II
A serles o~ experiments were conducted on a gel-caustic mud composltion formulated according to the procedures of Examples I. The rheological propertles and amount of suspended and~or dissolved alkaline materials were determined using a FANN Model 35 viscometer and by ti~rating a mud sample with 0.02 N H2 S4 to the phenolphthalein end point, respectively. Upon completion of the measurements reclted above the mud was contaminated with 1 point per barrel (a OH)2 to simulate cement contaminatlon. Measure-ments were made on the contaminated sample, the results of such being reported in Table II hereinafter. The contaminated mud sample was then treated with 3 pounds per barrel monocalcium phosphate, o.38 pounds per barrel NaOH and 1 pound per barrel ferrochrome lignosulfonate. The treatlng agent, as previously discussed3 is the monocalclum phosphate, the sodium hydroxide and ferrochrome lignosulfonate being employed to ad~ust the pH

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and lower the gel strength of the treated mud composition.
Measurements were then made on the treated mud compositlon, these results being tabulated in Table II.

TABLE II

Untreated Cement Contaminated Treated Mud Mud Mud pH 9.64 12.61 9.33 Apparent Viscosity 1132 9 (600 rpm reading/2~
Plastic Viscosity 9 6 8 Yield Point 4 51 2 O Gel 4 17 10 min. Gel 13 16 PM * ~.0 2.9 o.6 * PM ~ Amount o~ dissolved and/or suspended alkaline material.

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EXAMPLE III
An experiment was conducted on a gel-KOH mud composition to determine its rheological properties, the e~ect of alka-line materlal, such as cement, on its rheolbgical properties, and the effectiveness of a monocalcium phosphate containing compound in the removal o~ suspended and/or dissolved alkaline materials. The mud sample investigated was prepared in a 5 barrel equivalent lot using 20 pounds per barrel prehydrated bentonite, 0.02 pound per barrel potassium hydroxide and tap water. The tap water contalned a total salt content of approximately 582 mg/l.

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The rheological properties o~ the mud composition and amount o~ dissolved and/or suspended alkaline materials present in same were then determined using a FANN Model 35 viscometer and the-titrating procedure of Example I. The mud sample was then contaminated with 1 pound per barrel Ca (OH)2. Measurements were then made on the contaminated mud sample to determine the amount of dissolved and/or suspended alkaline material present therein and the effect of such materiaIs on the rheological properties of the mud composition.
The contaminated mud sample was then treated with 3 pounds per barrel monocalcium phosphate and o.6 pounds per barrel.potassium hydroxide. The potassium hydroxide was used solely for ad~usting the pH of the treated mld composition. Measurements were made on the treated mud to determine the effectiveness of the monocalcium phosphate in removing dissolved and/or suspended alkaline materials.
The results of such measurements are set forth in Table I:rI.

TABLE I r I
Untreated Cement Contamlnated Treated Mud Mud Mud pH 9.25 12.l51 9.51 Apparent 11 32 11 Viscosity .
(600 rpm reading/2) Plastic 9 7 9 Viscosity Yiel.d 4 50 4 Point a Gel 7 16 '.

~36~6 TABLE Ill cont.
UntreatedCement Contaminated Treated Mud Mud Mud , 10 min. 13 14 9 Gel PM * 3.2 0.7 * PM ~ Amount of dissolved and/or suspended alkaline material.

EXAMPLE IV
Experiments were conducted on a gel-lignosulfonate caustic mud composition to determine the effect of alkaline material, cement, on the rheological properties of such a mud composition, and, the effectiveness of monocalcium phosphate contalning compounds in the removal Or such alkaline materials. The mudsam~e investigated was mixed in a 5 barrel equivalent lot using 20 pounds per barrel prehydrated bentonite, 2 pounds per barrel ferrochrome lignosulfonate, l pound per barrel sodium hydroxide and tap water. The tap water contained a total salt content Or approximatély 582 mg/l.
The rheologlcal propertles Or the mud composition and the amount of dissolved and/or suspended solids pre-sent in said mud composition were determined using a viscometer and by titrating as set rorth in Example I.
After the deslred measurements on the mud composition were obtained, the mud was contaminated wikh two pounds per barrel Ca(OH)2, such simulating cement conkamlnation.
Measurements were then made on the contaminaked mud to determine its rheological properties and the amount of --15-- .

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dissolved and suspended alkaline materials present therein.
The contaminated mud sample was treated with 6 pounds per barrel of fertilizer grade monocalcium phosphate.
Measurements were made on the treated mud to determine the effectiveness of monocalcium phosphate in removing sus-pended and/or dissolved alkaline materials. The results of the sequential measurements on the gel-lignosulfonate-caustic mud composition are tabulated in Table IV.

TABLE IV
Untreated Cement Contaminated Treated Mud Mud Mud ., _ . . , _ . . _ .
pH 12.51 12.71 9.4 Apparent Viscosity 9 ll 15 (600 rpm reading/2) Plastic Viscosity 8 10 14 Yield Point 1 2 3 0 Gel l l l 10 min. Gel l 9 2 M ~.l 9.8 3.0 *PM - Amount of dissolved and/or suspended alkaline material.

EXAMPLE V
- .._ _ An experiment was conducted on a gel-lignosulfonate KOH
mud composition to determine the effect Or alkallne material, e.g. cement, on the rheological properties of such a mud composition, and, the effectiveness of monocalcium phosphate containing compounds in the removal of such alkallne materials.
The mud sample investigat~ was mixed in a 5 barrel equivalent . ' iL~73656 lot using 20 pounds per barrel preh~drated bentonite, 2 pounds per barrel ferrochrome lignosulronate, 0.9 pounds per barrel potassium hydroxide and tap water.
I`he tap water contained a total salt content of approxi-mately 582 mg/l.
The rheological properties of the mud composition and the amount of dissolved and~or suspended solids present in said mud composition were determined using a viscometer and titrating as set forth in Example I. Once the desired measurements on the mud were obtained, the mud was con~

taminated with two pounds per barrel Ca(OH)2, such simulating cement contamination. Measurements were then made to determine the amount of suspended and/or dissolved alkaline materials present in the mud and the rheological properties of the contaminated mud. The sample of con-taminated mud was then treated with 6 pounds per barrel fertilizer grade monocalcium phosphate and 0.32 pounds per barrel KOH. The potasslum hydroxide was employed solely as a means of ad~usting the pH of the treated mud composition. Measurements were made on the treated mud to determine the e~fectiveness o~ monocalcium phosphate in removing cement type materials. The results o~ all the sequential ~easurements are set forth in Table V.
TABLE V

Untreated Cement Contaminated Treated Mud Mud Mud ;
pH 12.07 12.71 9.5 Apparent Vis- 9 14 14 cosity (600 rpm

3 reading/2) , .

i~7~ 6 TABI,E V cont.

Untreated Cement Contaminated Treated Mud Mud Mud Plastic Viscosity 8 12 12 Yield Point 1 4 3 O Gel 10 min. Gel 1 54 6 PM * 1.6 7- -3 *PM ~ Amount of dissolved and/or suspended alkaline material.

From the above data, as deplcted in each of Examples I through V, it is readily apparent that monocalcium phosphate containing compounds are an effective treating agent for the removal of dissolved and/or suspended alkaline materials, such as cement. The removal of such alkaline material not only results in a spent mud composition having improved disposal properties, but, also allows one to clean spent drilling mud compositions so that same may be reused.

Having thus described the invention, I claim:

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Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for removing suspended and dissolved alkaline materials in water base drilling muds and for converting calcium ion in said muds to water insoluble plant nutrient compositions, said method comprising admixing with said mud monocalcium phosphate, or a mixture of monocalcium phosphate and calcium sulfate containing about 40 to about 60 weight percent mono-calcium phosphate, in an amount sufficient to provide at least a stoichiometric amount of monocalcium phosphate based on the concentration of calcium ions and of dissolved and suspended alkaline material present in said mud composition, for a period of time of from about 10 minutes to about 5 hours effective for the conversion of said calcium ions and the precipitation of said suspended and dissolved alkaline materials.

2. The method of claim 1 wherein said monocalcium phosphate containing compound is employed in an amount to maintain said monocalcium phosphate constituent and said calcium ions and said alkaline materials in a weight ratio of about 1:1 to 5:1, respectively.

3. The method of claim 1 which includes the steps of admixing an effective amount of mud thinner and caustic material to the mud composition after treatment of same with said monocalcium phosphate containing compound to adjust the gel strength and pH
of the treated composition as desired.

4. The method of claim 2 where said mud is treated with a mixture containing about 68 weight percent monocalcium phosphate, about 23 weight percent ferrochrome lignosulfonate and about 9 weight percent sodium hydroxide, said mixture being employed in an amount of 10 weight percent to 50 weight percent based on the weight of said monocalcium phosphate constituent as related to the amount of alkaline materials present in said mud subjected to treatment.