US3410797A - Drilling muds - Google Patents

Description

United States Patent 3,410,797 DRILLING MUDS Raymond W. Walker, Union, and Hugh E. Ramsden,

Scotch Plains, N..l., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Nov. 13, 1964, Ser. No. 411,115 4 Claims. (Cl. 252-85) ABSTRACT OF THE DESCLOSURE Certain organotin dithiophosphate compounds, e.g. dibutyl tin didecyldithiophosphate and stannous bis (didecyldithiophosphate), in water base drilling muds reduce the tendency of the drill pipe to become stuck during drilling.

The present invention relates to improvements in the drilling of wells and, in particular, to improved drilling fluids used in rotary type well drilling processes. More particularly, the invention relates to drilling muds having proper-ties which inhibit or prevent the sticking of drill pipe and drill collars.

In the drilling of wells by the rotary method, a drilling fluid is circulated down the drill string and up the annulus between the drill string and the borehole wall, while the drill string and drill bit attached thereto are rotated. Drilling muds used as the circulating fluid are essentially suspension of solids in water; these solids form the bulk of the mud filter cake. In general, the solids are clays and barite and their relative amounts present in the bulk mud are controllable within limits set by the required mud density. Important functions of drilling muds are: to clean the borehole of chips and cuttings and carry these to the surface; to lubricate the drill bit and drill stem; to form a filter cake to seal and maintain the walls of the borehole and prevent formation damage; to control the pressure on the annulus to prevent blowouts or formation breakdowns and lost returns; to sustain the cuttings in the event of rig shutdown, so that these do not fall to the bottom of the hole and stick the drill pipe; and to protect the surrounding formation in order that the wellbore may thereafter be successfully surveyed by known well-logging methods.

Sticking of drill pipe and drill collars during the drilling of wells is a well-known problem. When drill pipe and drill collars contact the Wall of the borehole, they become imbedded in the fiter cake and a force is created which pushes the pipe and collars against the borehole wall. This force is equal to the product of the area per unit of length of the pipe imbedded in the filter cake, the length of the pipe imbedded, the difference between the hydrostatic drilling fluid column weight and the formation fluid pressure, and the coeflicient of friction between the pipe and filter cake. This type sticking is commonly referred to as differential pressure sticking or wall sticking. Another force which causes sticking occurs from purely mechanical causes. For example, an abrupt change in direction of the borehole may cause bending of the drill pipe and the resistance to this bending may give rise to a sufficiently large force holding the pipe against the borehole wall to cause sticking. Thus, the drill pipe is forced against the borehole wall in some manner and the resistance to movement of the pipe against the mud cake is greater than the pulling forces available, which results in the pipe becoming stuck in the borehole and necessitates an expensive fishing job.

To inhibit or prevent sticking of drill pipe and drill collars, many expedients have been tried. It is common practice to spot oil in the well over the section where the pipe is stuck and this practice often allows the pipe to become loosened. Another practice that reduces, but does not eliminate pipe sticking is to emulsify oil in the drilling mud. To enhance the effectiveness of the oil emulsion muds in this respect, a number of special oils have been tried that are alleged to be better than the commonly used diesel oil or kerosene. Unfortunately, the majority of these special oils, other than certain kerosenes having nonfluorescent properties, introduce into the circulating mud system a fluorescent material that interferes with the eologic evaluation of the formation core and cuttings samples by confusing the oil naturally in the sands with the oil of the circulating mud, and for this reason, their use is drastically restricted.

According to the present invention, it has been found that certain organotin compounds are very effective drillmg mud additives. The organotin compounds to which the present invention is directed may be more accurately defined by the following general formula:

wherein 3 :0 to 3, 1:1 to 3, and y+z= an even integer from 2 to 4. R is an organo radical containing 2 to 18 carbon atoms and selected from the group consisting of alkyl, alkenyl and aralkyl. R is an organo radical containing 2 to 18 carbon atoms and selected from the group consisting of alkyl, alkenyl and aralkyl. R is an organo radical containing 2 to 18 carbon atoms and selected from the group consisting of alkyl, alkenyl and aralkyl.

Examples of suitable compounds include but are not limited to stannous bis(didecyldithiophosphate), dibutyl tin bis didecyldithiophosphate, didecyltin bis diisobutyldithiophosphate, dibenzyltin bis dioetyldithiophosphate, diethyltin didodecyldithiophosphate, butyltin tris dedicyldithiophosphate, tripropyltin dibenzyldithiophosphate. A pgeferred compound is dibutyltin bis didecyldithiophosp ate.

Preparation of the compounds having the above formula may be eflected by any of the methods known to the art. For example, in one such method an organotin halide represented by the following formula:

wherein y, z, y-l-z, and R are as above defined and X is a reactive halogen, such as chloride, bromine and iodine,

is reacted with a salt of dithiophosphoric acid represented by the following formula:

wherein R and R" are as above defined and M is a cation, preferably a metal equivalent of hydrogen. Alkali and alkaline earth metals, such as sodium, calcium, and the like, may be used. Ammonium or amine salts may also be used. The dithiophosphates are prepared by wellknown methods.

The additives ofthe present invention may also be prepared by reacting an organotin oxide represented by the following formula:

wherein R is as above defined, with a dithiophosphoric acid represented by the following formula:

s on

HS I

wherein R' and R" are as above defined.

W-hile various methods of preparing the additives of the present invention have been briefly mentioned, still other methods will be apparent to those skilled in the art and it is intended that all additives having the general formula described above be included regardless of their method of preparation.

The additives of the present invention are added to drilling mud in proportions of about 0.001 to 1.0% by weight, preferably about 0.01 to 0.1% by weight. A most preferred drilling mud contains about 0.05% by weight of the additive of the present invention.

This invention is applicable to all of the clay-type drilling muds normally employed in rotary drilling. Such muds may simply compromise suitable clays dispersed in water or they may contain other added materials such as quebracho, lignin sulfonates and the like. Clay-laden drilling fluids of densities and viscosities that are suitable for rotary drilling generally range in density from about 9 to about 11.5 pounds per gallon. If heavier drilling fluids are needd, finely ground heavy minerals, such as barite, hematite, pyrite or siderite may be added since these materials will contribute high density without unduly increasing the viscosity of the drilling mud.

To evaluate the effectiveness of drilling mud additives in decreasing the tendency for drill pipe to stick, a wellknown Stickometer Test was used to measure the sticking coefficient which is defined for purposes herein as the ratio of the pulling force to the perpendicular force at the time of the measurement. Essentially, the sticking coeflicient is a measure of how strongly pipe becomes stuck in the presence of a given mud system after a certain residence time under a specified perpendicular force.

The sticking coeflicient is defined for purposes herein as the tangential force required to move a plate over the mud filter cake divided by the force normal to the plate. This may be expressed as:

Thus, the sticking coefficient is a dimensionless quantity corresponding to a coefficient of friction; however, unlike coefiicient of friction it is not a constant, but is time dependent and dependent on the thickness and composition of the filter cake as well. However, by testing at constant filter cake thickness and time, the composition remains as the major variable. Differences between the sticking coeflicents of the mud with and without additive are expressed as percent sticking tendency.

In order to demonstrate the utility and efficacy of the present invention, the sticking coeflicient was experimentally determined for drilling muds of various compositions, using the followin technique:

The stickometer consists of a stainless steel cylindrical pressure vessel about 3" in diameter and 4" high. This vessel has a centrally located drain hole in the bottom. A core sand filter (porous sandstone) about 2" in diameter and 1" thick is positioned centrally in the pressure chamber over the drain hole. A stainless steel torque plate, which is about 2" in diameter and /8" thick and equipped with a diameter stem about 3" in length, graduated in intervals, is positioned on top of the core sand filter. The mud slurry (sample) is poured in the vessel to within of the top. The cover is placed on the vessel, with the graduated stem extending through the top and the cover is tightened. Five hundred psi nitrogen pressure is maintained on the mud sample. The depth of the torque plate is recorded and the plate is immediately released from the core filter surface. The pressure keeps the plate at its top position. The pressure forces water out of the slurry and builds up a mud deposit on the core filter. After the mud cake has built to thickness, the torque plate is held against the mud cake until it sticks to it. The first torque reading is taken five minutes after the torque plate has stuck to the mud cake. Readings are taken at these intervals: 5-10-15-20-30-45 and each succeeding 15 minutes up to and including 2 hours, the point at which comparisions of sticking tendency are made. Torque readings are then taken with a torque wrench which fits to the top of the torque plate stem.

The sticking coefficient is calculated by the following:

Sticking coefiicient=torque reading 0.00095 The sticking coeflicient of the additive-containing mud is compared with the mud value without additive and the percent reduction sticking tendency is obtained.

Tests conducted with various compositions showed that for best results a drilling mud containing an additive of an organotin compound of the present invention must be present.

A typical base mud is one composed of about 68.5 gm. bentonite clay (Aquagel), 100 ml. water, 11.5 gm. ferrochromlignosulfate (Q-Broxin), 3.5 gm. sodium hydroxide, 1230 gm. barites (Baroid), and 146 ml. kerosene.

A drilling mud was prepared having the above-described typical composition. The sticking tendency of this mud was measured using the above-described Stickometer Test. Various compounds, including additives of the present invention, were added to the base mud and the respective sticking coefiicients were determined. The results of this series of tests are shown in Table I.

TABLE I Percent Sticking Reduction Coetliclent Sticking Tendency Drilling Mud-no additive. 0.065 Drilling Mud plus 0.5% dibutyl d dithiophosphate 0. 044 32-33 Drilling Mud plus 0.05% dibutyl tin didecyldithiophc sphate 0. 044 32-33 Drilling Mud plus 0.0 dibutyl tin didecyldithiophosphate 0. 050 21-22 Drilling Mud-no additive 0. 084 Drilling Mud plus 0.02% dibutyl tin dialkyl dithiophosphate 0. 076 0-10 Drilling Mud plus 0.1% stannous bis(didccyldithiophospliate) 0. 064 27-28 Drilling Mudno additive. 0. 082 Drilling Mud plus 0.1% stannic tetrakis (didecyldithiophosphate) 0.081 0 In the preparation of this compound the dialkyl dithiophosphoric acid was a mixture of C4 and C dithiophosplioric acids.

Results in Table I show that of the various additives tested only the organotin compounds of the present invention significantly reduce the sticking tendency of the base mud.

What is claimed is:

1. A water base drilling mud comprising water and clay to which has been added a small amount, sufficient to reduce the sticking of drill pipe in a bore hole during drilling when using said drilling mud, of an organo tin compound selected from the group consisting of stannous bis (didecyl dithiophosphate) and dibutyl tin didecyl dithiophosphate.

2. A drilling mud as defined by claim 1 wherein said compound is dibutyl tin didecyldithiophosphate.

5 6 3. A drilling mud as defined by claim 1 wherein said 3,047,494 7/1962 Browning 252-8.5 compound is stannous bis(didecyldithiophosphate). 3,219,580 11/1965 Stratton 2528.5

4. A drilling mud as defined by claim 1 wherein said small amount is in the range of about 0.001 to 1.0 wt. OTHER REFERENCES Percent 5 Rosenberg et 21]., Increased Drill Bit Life Through Use References Clted of Extreme Pressure Lubricant Drilling Fluids, article UNITED STATES PATENTS in Journal of Petroleum Technology, vol. 11, August 2,364,283 12/1949 Freuler 252 32.7 1959 195 to 2,786,812 3/1957 McDermott 2s2 32.7 2,959,544 11/1960 Smith et a1. 252-32.? 10 HERBERT GUYNN pr'mary Emmmer