The New Look in Oil-Mud Technology

DISPERSIBLE COLLOIDS

JAY P. SIMPSON MEMBER AIME BAROID DIV., NATIONAL LEAD CO. Downloaded from http://onepetro.org/jpt/article-pdf/13/12/1177/2213517/spe-150-pa.pdf by guest on 27 September 2021 J. C. COWAN HOUSTON, TEX. A. E. BEASLEY, JR.

Abstract tributed to the general inflexibility of the systems. This inflexibility resulted primarily because one basic component Liquids having oil as the continuous phase long have was used in an attempt to arrive at all mud properties. been recognized as desirable for drilling and completing These oil systems can be compared with the early water under certain conditions. Performance limitations, high base muds. costs and inconvenience of handling, however, have kept these oil muds from becoming accepted for widespread, Water-base mlfds in the early years of drilling depended general use. upon bentonite for rheological properties, suspension of solids and filtration control. As was learned with these As previously used, the muds consisted of a bodying earlier clay-water systems, one basic component cannot agent for oil, or primary emulsifier of water in the oil, and by itself provide all of ideal drilling-fluid properties. Today a series of supplementary additives to modify that principal each water-base drilling-fluid property can be controlled component. In recent years a new approach to oil muds with an exactness that was not believed possible even 10 has been taken. Oil-dispersible colloids have been developed years ago. Water-base muds are prepared to have certain to perform specific functions in oil without dependence properties to serve specific purposes, some examples of upon thickening of the oil or emulsification of water. Such which include the following: the low-solids, low-viscosity, colloids are typified by an organophilic clay for suspen low-filtration fluids for hard-rock drilling; the high-solids, sion of solids and an organic filtration control agent. These low-viscosity, low-filtration, inhibitive muds for shale drill colloids are effective and stable at well temperatures pre ing in areas of abnormal pressure; and the high-viscosity, sently encountered and do not require supplementary ad high-filtration muds that are left in wells between casing ditives. They also are compatible with wetting agents and and tubing. Properties of these muds can be varied over emulsifiers commonly used to provide tolerance for water wide ranges, and the muds can be converted from one and solids in oil muds. type to another as the need arises. The control and vari With the development of independently effective addi ability of water-base muds are possible because of the large tives, oil muds now have much of the control and vari number of additives currently available for performing ability achieved with water-base muds. Field examples specific functions. With the development of new additives demonstrate that oil systems are being used successfully and new technology, oil muds now have achieved a similar for drilling, coring and completing under extreme condi variability in performance, cost and convenience. tions of both low and high temperature and pressure. Field This paper describes the development and performance personnel utilizing ordinary rig equipment can prepare and mechanisms of materials that independently control specific control the oil muds. In areas of concentrated use, liquid properties of oil muds. Also discussed in the paper are mud facilities are providing further economy and con field applications of this new oil-mud technology. venience. Introdnction The Need for Oil Systems Drilling fluids having oil as the continuous phase were Oil systems have been used for many years to protect first conceived and used in the middle 1930's. The value pay zones having productivities that can be impaired by of these oil systems was immediately recognized, particu water-base muds. Completions using oil muds with good larly in providing quicker and easier well completions and filtration control consistently have resulted in greater initial in increasing the initial rate of oil recovery. Oil systems production rates than could be obtained with water-base have not been used extensively in the past because of muds-often saving the time and cost of fracturing, acidiz performance limitations and high costs that can be at- ing, or extensive swabbing. Cores often must be obtained for use in reservoir-evalua Original manuscript received in Society of Petroleum Engineers office tion studies. Oil muds and invert-emulsion muds have been Aug. 7, 1961. Revised manuscript received Nov. 10, 1961. P~per pre sented at 36th Annual Fall Meeting of SPE, Oct. 8-11, 1961, In Dallas. used to provide cores free from water contamination so

DECEMBER, 191\1 SPE 150 Reprinted from the December, 11)61, Issue of JOURNAL OF PETROLEUM TECHNOLOGY 1177 that an accurate measurement of connate water can be Maintenance costs were high for oil systems of the past. made. Water contaminatiDn, always an acute problem, Dften Oil drilling fluids can be used to maintain good hole caused excessive gelling of the bodied oil and water-wetting conditions by preventing hydration, swelling and sloughing of sDlids, necessitating replacement Df the system Dr at of shale. Pipe s~icking and hole enlargement caused by least dilutiDn with new mud. Water cDntaminatiDn Df in shale hydration thus are avoided. This minimization of vert emulsiDns required that mud prDperties be adjusted hole trouble is attributed to low mud-filtration rates and to by adding Dil and an emulsifier. The principal compDnents the sealing of borehole walls by the oil, which prevents in these Dil systems cDuld nDt be added to adjust a single water from soaking the drilled formation. Maintaining good property without affecting mDst Df the Dther mud proper hole conditions results in faster drilling, better cementing ties. Single additives to cDntrol specific mud properties jobs, and the more effective use of packers in drill-stem were not available to prDvide the flexibility and versatility testing operations. needed for IDW-CDSt use.

Oil muds have lower freezing points than water-base Performance muds and are better adapted for use in subfreezing weather. FiltratiDn contrDI and suspensiDn usuaIly could nDt be A properly compounded oil mud does not undergo the obtained without causing high ViSCDsity in oil muds pre high-temperature flocculation, gelation and solidification viDusly used. Since the muds required a gel structure to that limit the use of most water-base muds. suspend sDlids at an elevated dDwn-hDle temperature, the Oil muds have been used to provide greater lubricity of viscDsity was particularly high at the lDwer surface temper the drill string and bit, particularly in drilling directional

ature. Hence, Dil muds were difficult to handle fDr even Downloaded from http://onepetro.org/jpt/article-pdf/13/12/1177/2213517/spe-150-pa.pdf by guest on 27 September 2021 or deviated hole. In areas where differential pressure stick nDrmal temperature gradients. The high viscosity prevented ing is an acute problem when drilling with water-base the remDval Df drilled sDlids Dn a shaker screen, causing muds, oil muds are commonly spotted down-hole to free sDlids to' accumulate and necessitating repeated dilutiDn stuck pipe. Oil muds recently have been used for drilling with new mud while drilling. Drilling was SIDW with these to avoid differential sticking of pipe. Dil systems because the inherently high viscosity caused Oil drilling fluids provide protection of drill pipe against IDW rates Df penetratiDn. The high-viscDsity mud presented hydrogen sulfide and salt water and can be left behind a problem when it failed to fall Dut Df the drill pipe by casing to protect against these contaminants that com increasing trip time. monly cause corrosion in water-base muds. Oil muds in the past have had pDDr temperature sta Oil Systems Used in The Past bility because the sDaps and asphalts used as bDdying agents had melting pDints in the same range as the higher As previously used, oil muds have met some of the bottDm-hDle temperatures encDuntered. As the temperature needs for nonaqueous drilling and completion fluids, but in the drilled hDle increased, excessive sDlvatiDn Df the with only moderate success. These fluids generaIly were variDus additives Dccurred. Once the asphalt became dis designed around a single additive that would body or gel solved in the Dil or the micellar soap structures became the base oil to provide filtration control and suspension of molecular in nature under the influence of temperature, solids. The materials most commonly used to gel the base the oil mud lost its ability to suspend solids and to main oils were high-molecular-weight soaps or oxidized asphalts. tain filtration control. Drilling-fluid properties were controlled by adding mater ials that would alter the soap or the asphalt. Mechanisms of Commonly Used Oil-Base-Mud Additives Efforts to provide muds made from oil that had not been thickened led to the emulsification of water in oil. TO' develop truly satisfactory oil muds, a mDre thorough These muds, having oil as the continuous phase, came to understanding of the additives that functioned best in oil be termed "invert emlusions". The invert-emulsion muds muds over the years was needed. These additives generally have depended primarily upon the emulsification of a could be grouped into three different classes-( 1) bDdying relatively high percentage of water in the oil to provide agents, (2) emulsifiers and (3) wetting agents. Utilizing both suspension of solids and filtration control. Water the experience gained with the old Dil systems and draw emulsification generally was accomplished by using a high ing from technolDgy develDped in Dther fields, a back molecular-weight, alkaline, earth-metal soap as the princi ground regarding the mechanisms of commDnly used Dil pal component. Here again, additives were used to alter mud additives was developed. The fDllowing paragraphs the principal component of the mud. The invert-emulsion briefly describe these additives as they are thDught to muds, however, did offer more positive control of the mud function in oil systems. properties by virtue of the fact that the oil-water ratio could be adjusted to give a wider range of properties.' Bodying Agents Insoluble soaps, asphalts and modified clays have been Cost used as bodying agents fDr straight Dil systems. The insDlu The relatively high cost of oil and invert-emulsion muds ble soaps form various types of micellar structures in the has been the greatest single factor in limiting their use. Dil to produce a stringy type of viscDsity, while asphaltic Muds usually had to be prepared at a mixing plant and materials build viscosity in oils by virture of a high con hauled to the rig site. Unfortunately, locally available centratiDn of solids. On the other hand certain types of crudes or fuel oils were seldom compatible with the oil modified clays build extremely high viscosities with very mud additives and could not be Uied in the mud prepara IDW concentrations of solids. The gelling mechanisms of tion. these modified clays are described in detail by Hauser' and Certain salt solutions were required as the water phase Jordan.' Concentrations of these three general types of in most invert emulsions, and readily available fresh water, gelling agents vs the resulting apparent viscosities in diesel sea water, or brine could not be used. This resulted in oil are shown in Fig. 1. In high-viscosity oils the con loss of time and increased handling costs. centrations of additives needed are considerably lower, 'References given at end of paper. but the relative values are essentially the same.

1178 JOURNAL OF PETROLEUM TECHNOLOGY Emulsifiers charge, with the net charge depending on the acidity of Many different types of emulsifiers and combinations the solution. This material, similiar in nature to soaps, of emulsifiers have become available through the years. has a nonpolar hydrocarbon tail (forked) and a strongly Due to cost, availability, or effectiveness limitations, how polar head. Lecithin has been used for years as a disper ever, only a few compounds have found application as sant in printing inks, rubber and paints, its dispersing emulsifiers in invert-emulsion muds. High-molecular-weight mechanism primarily being attributible to its wetting ability. soaps, the oldest and most widely used oil-mud emulsifiers, are used for emulsifying water in oil to control rheological A New Technology Utilizing Organophilic Colloids properties and even filtration in some systems. From the foregoing discussions of the limitations of the The soaps are salts of long-chain fatty acids derived old oil systems and a better understanding of the mechan from naturally occurring oils or fats. Reactions of high isms of the more commonly used oil-mud additives, it is molecular-weight organic acids with monovalent cations readily apparent that there was a need for new organ such as sodium, potassium, or lithium result in water ophilic colloids that would function independently of soluble soaps that preferentially form oil-in-water emul other additives. Examples of such colloids are two syn sions. Reactions of the organic acids with multivalent ions thetic compounds recently developed specifically to pro such as magnesium or calcium result in soaps that pre vide improved oil muds-a nongelling organophilic clay ferentially form water-in-oil emulsions. Emulsions prepared for suspension of solids and a non-asphaltic, oil-dispersible with these multivalent-metal soaps are usually stabilized organic colloid for filtration control. with other additives. Suspension Agent Downloaded from http://onepetro.org/jpt/article-pdf/13/12/1177/2213517/spe-150-pa.pdf by guest on 27 September 2021 Weuing Agents Almost from the conception of rotary drilling, clays Wetting agents have been used extensively in oil systems, have been added to water-base drilling fluids to build vis particularly to combat water contamination and to pre cosity. Incorporation of clay made possible the subsequent vent water-wetting of solids. One widely used class of suspension of weighting materials. As oil-mud systems materials is the phospholipids. A typical member of this developed, weight suspension was obtained by using high class is lecithin, the structure of which is as follows. concentrations of various asphalts or by gelling the oil. Gel-forming organophilic clays also have been used in C17H ..·COO·CH 2 oil-mud systems, particularly as suspension agents for oil I o· base packer fluids.' Relatively small amounts of the oil C17H 3.COO·CH I dispersible clay yielded extremely high gels which were I I useful for suspending weighting material but which were CH,.O·P-O-(CH,) 2-N+(CH ) 3 3 unsatisfactory for drilling fluids because of the resulting o high viscosities. For some time there has been an acute need for a sus Lummus' cites the effectiveness of this additive in oil-base " pension agent that could be added in low concentration to drilling fluids. Lecithin is considered to be an amphoteric oil without significantly increasing viscosity and gel micellar colloid. The phosphate ion carries a negative strength. To fill this need, a nongelling organophilic clay charge and the quaternary amino nitrogen carries a positive has been developed based on earlier work on the synthesis of organophilic clays which develop gel structure in organic 200 liquids. The technologies for the two types are similar. The gel-forming organophilic clays are made by cation GEL- FORMING exchange reactions between onium salts and clays. Clays 100 ORGANOPHILIC which may be used include montmorillonite, hectorite, saponite, attapulgite and illite. These clays have unbalanced 60 crystal lattices and are believed to have negative charges which normally are neutralized by inorganic cations held at the planar surface of the lattice. Some of these clays 0.. are ideal for onium-salt reactions because they have high 030 base-exchange capacities and because the inorganic cations >- t- SODIUM can be replaced with relative ease. (/) SOAP Bentonite, which has montmorillonite as its chief mineral o o component, is commonly used in the preparation of or (/) ganophilic clays. When sodium bentonite is used, an equili > 10 brium reaction takes place to form an organic onium bentonite plus salt.

Na Bentonite + C14H"NH, Cl~ C,.H"NH, Bentonite + Na Cl. This base-exchange reaction results in the formation of an electrovalent linkage between the nitrogen atom of the organic onium cation and the bentonite structure. The reaction takes place in an aqueous system with a refined bentonite. The insolubility of the onium-bentonite com pound favors the reaction to the right and also makes 5 10 20 40 80 possible easy separation from the water-soluble salt. CONCENTRATION OF BODYI NG AGENT. LB / BBl The hydrocarbon chains of the onium cation are held Fig. I-Apparent viscosity (at 600 rpm) of bodying agents firmly to the surface of the bentonite platelet by attractive in No. 2 diesel oil. forces. X-ray diffraction data show that in this gel-forming

DECEMBER. 1961 1179 clay the normal separation of the platelets at 50 per cent TABLE I-EFFECTIVENESS OF FILTRATION CONTROL AGENT IN VARIOUS OILS relative humidity is approximately 9 0 A. The close spacing AT ELEVATED TEMPERATURES AND PRESSURE is attributed to an overlapping of amine chains. Filtration Filtrate (ml/30 min) Control Agent 125°F, 300°F, Since the attached organic cations render the clay or (Ib/bbl) Type of Oil API 1,000 psi 1,000 psi ganophilic and enable it to disperse in oil systems, it is 15 No.2 Diesel 1.0 5.8 14.0 15- No.2 Diesel 1.0 11.6 not surprising that the suspension properties of the organ 15** No.2 Diesel 1.0 6.4 ophilic clays are dependent on the nitrogen compound 10 No.2 Diesel 1.4 9.6 10 26° Asphaltic Crude 0.0 0.0 2.0 selected, as well as on the chain length of the particular 10 35° Asphaltic Crude 0.0 1.0 3.6 10 40° Paraffin Crude 0.4 10.8 compound. Nitrogen compounds capable of reacting with 10 45 0 Paraffin Crude 0.5 7.6 clays include salts of: aliphatic, cyclic, aromatic and heter 10 35° Asphaltic Crude 0.0 6.5 10% Brine ocyclic amines; primary, secondary and tertiary amines; *Filter Medium: 163-md Brea sandstone core polyamines; and quaternary ammonium compounds. Mon **Filtrates determined after aging samples at 30QoF for 16 hours. ovalent or polyvalent onium compounds work equally well. specifically for oil muds. In many respects this non-asphal Chain length is particularly important in synthesizing tic, oil-dispersible, organic colloid is similar to the non organophilic clays. It has been shown that organophilic gelling organophilic clay previously discussed. Neither class properties are negligible until an amine chain of 10 carbons of material is limited by a melting point. Solvation depends is reached. on the composition and structure of the compound rather Suspension properties depend upon the particular clay than on the type or temperature of the oil. Thus, the colloids can be used effectively in a great variety of oils.

selected; they vary, depending upon the plate-like or rod Downloaded from http://onepetro.org/jpt/article-pdf/13/12/1177/2213517/spe-150-pa.pdf by guest on 27 September 2021 like structure of the clay. Inexpensive and readily available crude oils can be utilized A comparison of suspension and rheological properties to advantage. Table 1 presents data for the filtration con of two modified clays in diesel oil and of bentonite in water trol agent in various types of oil, demonstrating (I) that are shown in Fig. 2. These studies were carried out in the agent functions independently, (2) that it is nonselec cylindrical vessels, and the resulting top oil-or-water tive as to type of oil and (3) that is has excellent perform separation was measured. It should be noted that the ance and stability at high temperature. nongelling organophilic clay provided excellent suspension Although the organic colloid is extremely effective as a properties with very low viscosity and gels. The gel-form filtration control agent, it causes no gelation of the base ing clays-organophilic and hydrophilic-also provided oil. These properties are demonstrated in Fig. 3, emphasiz good suspension properties but with high viscosities and ing that extremely high concentrations can be obtained gel strengths. In another test, the plastic viscosity and before the organIc colloid will contribute significant vis yield point for diesel oil containing an abnormally high cosity. concentration (50 lb/bbl) of the new, nongelling organ In addition to performing its specified function as a ophilic clay were found to be only 14 cp and 33 Ib/lOO filter-loss additive, the filtration control agent makes it sq ft, respectively. possible to obtain oil muds which have rheological proper ties similar to well-deflocculated water-base muds. Fig. 4 Filtration Control Agent shows shearing stress-shear rate curves for unweighted Filtration control additives in general are a class of and weighted invert emulsions tested on a multispeed ro colloids that prevent the drilling mud from filtering into tational viscometer. The muds, containing 60 parts of diesel a permeable formation. Fundamentally, a filter-loss addi oil and 40 parts of water by volume treated with 15 lb/bbl tive for oil systems must possess at least three properties: of a soap-type emulsifier, have a type of rheology generally (1) it must be at least partially insoluble in oil; (2) it exhibited by invert emulsions used in the past. The curves, must be partially soluble or dispersible in the oil; and (3) convex toward the stress axis and approaching the inter if it is to function independently of other solids, it must cept at low rates of shear, show the muds to be essentially disperse to and retain a distribution of particle sizes and pseudoplastic. This is especially true for the weighted mud. shapes adequate for filtration control. The curves indicate very low yield points. Based only on A new filtration control agent has been synthesized the 300- and 600-rpm readings ordinarily measured in the

120 LB BARITE/BBL DIESEL OIL 120 LB BARITE/BBL WATER field, however, the calculated yield point for the weighted mud would be quite high. Additions of 10 lb/bbl of the ORGANOPHILIC CLAYS NO (NON (GEL NO filtration control agent will change the invert-emulsion SUSPENDING GELLING) FORMING) SUSPENDING BENTONITE PROPERTIES AGENT 20 lB/BBl 10 lB/BBl AGENT 15 lB/BBl muds just mentioned to systems similar in rheology to PLASTIC VIS. CP 15 21 23 YIELD PT. lBIiOO SO FT 5 15 14 16 100 0' GEL. lBIiOO SO FT 2 12 3 10' GEL. lBIiOO SO FT 5 17 10 14 ... o 120 12 ~.~ 75 ...)-0 , D 100 10 Oil OR WATER ~ ~~ SEPARATION ; 8 ~ ~ 50 :r 80 u: >5 0z oil. - 60 0 ~ 6 ~9 z = 25 o z YIELD POINT

1180 JOURNAL OF PETROLEUM TECHNOLOGY most water-base muds, with nearly linear shear stress-shear Contamination with water containing various electro rate relationships. The changes, which can be attributed lytes is no more of a detriment to the performance of the at least in part to further lowering interfacial tension, are filtration control agent in oil than is contamination with accomplished without weakening the emulsion. fresh water. Properties of the filtration control agent in Use of the filtration control agent has resulted in invert the presence of fresh water and water containing com emulsions having better rheology as drilling fluids because monly encountered materials (i.e., salt, calcium chloride, it permits a lower concentration of soap-type emulsifier magnesium sulfate, gypsum and cement) are not affected to be used than normally would be required. Moreover, appreciably. addition of the filtration control agent lowers the effective Both the suspension agent and the filtration control viscosity of an invert emulsion containing a given concen agent discussed here are compatible with the bodying tration of emulsifier. The lower effective viscosity is evi agents, emulsifiers and wetting agents that have been com denced by slightly lower plastic viscosity and considerably monly used in oil systems. However, the two organophilic lower yield point (as calculated from 300- and 600-rpm colloids can be added to diesel or crude oil with no sup viscometer readings) for an invert emulsion having a high plementary materials to obtain a drilling fluid which has water content. This is shown in Fig. 5 for various diesel excellent suspension, filtration and flow properties. The oil-water ratios in unweighted emulsions. composition and properties of such a mud are shown in The reduced yield point caused by adding the filtration Table 2. control agent does not greatly alter the suspension prop Oil or Invert Emulsion erties of these emulsions, for two reasons. Oil muds, even those carefully prepared to contain no Downloaded from http://onepetro.org/jpt/article-pdf/13/12/1177/2213517/spe-150-pa.pdf by guest on 27 September 2021 1. The true yield point of the invert emulsion was not free water, incorporate water when placed in a well and high before the addition; the value calculated from the used. As a matter of economy and convenience, additives 300- and 600-rpm viscometer readings was high because are used to emulsify the water rather than attempting to of the pseudoplastic nature of the fluid. a.. 2. The organophilic clay has a suspending ability that o does not depend upon the formation of gel structure. ;-40 I- Drilling fluids are commonly contaminated with water ~ 30 o and various electrolytes, and the filtration control agent is I/) highly resistant to such contamination. Properties for ;;; 20 various concentrations of the filtration control agent in 2 I- 10 simple mixtures of water and oil are shown in Fig. 6. As I/) may be noted, the plastic viscosity, yield point and API oCt ~ OL-~L------~------~------~ filtrate changed very little even though the amount of water was varied from 10 to 40 per cent by volume. The A 15 lB/BBl EMULSIFIER I- 25 water in each of the mixtures was fully emulsified because .... A., B 15 lB/BBl EMULSIFIER 10 lB/BBl FilTRATION CONTROL AGENT the filtration control. agent lowered the interfacial tensions g 20 , sufficiently. o 'C 15 lB/BBl EMULSIFIER @ 15 '10 lB/BBl FilTRATION CONTROL AGENT An effective surfactant in its own right, the filtration ~ " 2 lB/BBl SUSPENSION AGENT control agent is particularly well suited to accelerate and ":10 C~ " augment the action of an emulsifier or wetting agent in an ~ B~3~' oil mud. The photomicrographs in Fig. 7 show quite ~ 5 --"3__ ~""... ; .... ~ clearly how the filtration control agent decreases the size ulC OL---L______.-JL- ______-'- ______------...... of the water droplets formed by a modified soap-type ): 50/50 60/40 70/30 80/20 emulsifier in diesel oil. VOLUME RATIO, DIESEL Oil/WATER Fig. 5-Effects of filtration control agent and suspension 60 UNWEIGHTED EMULSION agent on rheological properties of unweighted invert emulsions. 48

36 (!) z 20 t 60/40 :3is : ~ 24 PLASTIC 10 ...: :s IIJ "\ V I SCOSITY • CP 0 '------T"______-;. ______3.-- ____.,..390/10 ______-;3 II: l8/88l EMULSIFIER II: 12 IIJ 10 lB/BBl FilTRATION CONTROL AGENT I- IIJ 0 ::IE 0 ~ 300 14 PPG EMULSION :;:

I/) 240 I/) IIJ II: lB/BBl EMULSIFIER l- 180 I/) lB/BBl FilTRATION CONTROL AGENT 120 ~

00 200 300 400 500 600 SHEAR. RPM FilTRATION CONTROL AGENT. lB/BBl Fig. 4-Effect of filtration control agent on shear stress Fig. 6-Effect of filtration control agent on rheological ami shear rate relationship of unweighted and weighted filtration properties of oil-water mixtures-volume ratios invert emulsions. of diesel oil to water = 90/10 and 60/40, as indicated.

DECEMBER. 1961 1181 NO 2 lB/BBl 10 lB/BBl

FilTRATION CONTROL FILTRATION CONTROL FILTRATION CONTROL Downloaded from http://onepetro.org/jpt/article-pdf/13/12/1177/2213517/spe-150-pa.pdf by guest on 27 September 2021 AGENT AGENT AGENT Fig. 7-Photomicrographs of invert emulsion containing various concentrations of filtration control agent show the effect of the agent on the size of emulsion droplets-scale = 1.5 microns/ division. (Base fluid-O.6-bbl diesel oil, O.4-bbl water and 15 lb/ bbl emulsifier. Magnification = 450X.) react it chemically. In spite of the fact that oil muds in Field Applications of the New Technology actual use generally contain emulsified water, a sharp dis The availability of independently effective, temperature tinction usually has been made between oil muds and stable, organophilic colloids has removed many of the invert-emulsion muds. Whereas water was the most detri limitations previously associated with oil muds. One of mental contaminant of oil muds, it was a necessary com these limitations. was the high initial cost. Today it is ponent of invert-emulsion muds. The two types of mud possible to select single additives that perform specific were prepared from different basic components and ex functions in a base oil. For example, in areas of normal hibited different mud properties. pressure but low formation temperature, a crude oil or The distinction made in types of oil muds can be bunker fuel that has a naturally low filtration rate can be contrasted to the approach taken with water-base muds. treated with small concentrations of an organophilic clay Increasing the percentage of emulsified oil in a water-base to provide suspension properties. mud from 3 to 15 or even 30 per cent by volume is not In other areas, where low-pressure formations are cn considered a drastic change from one type of mud to an countered and only filtration control is needed, small con other. The mud properties usually can be maintained about centrations of the filtration control agent will provide an the same, utilizing the same mud materials as before the economical oil system. A recent well in Lea County, change in oil content. It is significant that the oil content N. M., is an example of the low initial cost of the oil can be selected to achieve the desired result-for example, muds now available. An invert-emulsion mud was pre a low percentage of oil to assist in recovering cutting pared to drill-in and complete approximately 100 ft of a samples in a low-solids brine mud, or a high percentage water-sensitive sand below 14,000 ft. The total cost of of oil to give less hydrostatic head. Now that oil-mud preparing and maintaining this mud was only $8.30/bbl. materials are available which emulsify water thoroughly Locally available crude oil and brine were used and the and which perform equally well whether the water content mud was prepared on location with no special equipment. is extremely low or very high, a desired water content for Not only are low initial costs possible with the new an oil mud can be selected for optimum performance or oil-mud additives, but extremely low maintenance cost economy-just as oil content is selected for water-base also are attainable. Open-hole displacements of water-base muds. A distinction between an oil mud and an invert muds with the new oil muds, for example, can require emulsion mud, therefore, is no longer really necessary or little or no conditioning. In one well an invert-emulsion even very meaningful when using organophilic colloids mud was desired to drill through a salt overhang in the such as the suspension agent and filtration control agent Vermilion Bay field of South Louisiana. Previous attempts previously discussed. using water-base muds had resulted in hole enlargement, solids build-up and rig time lost in mud conditioning. A

TABLE 2-01L MUD FORMULATED WITH ORGANOPHILIC single-stage displacement of a medium-pH tannin-treated COLLOIDS mud was made at 5,558 ft in 2,523 ft of open hole. Composition: Table 3 shows the properties of the invert-emulsion mud DiMel Oil, bbl ...... 0.83 Filtration Control Agent, Iblbbl ...... IS immediately after the displacement. Over 2,200 ft of mas Suspension Agent, Ib/bbl ...... 10 sive salt and 519 ft of hard limestone ultimately were Barite, Ib/bbl ...... •...... 270 drilled, with little treatment required to maintain the mud Properties: properties. Mud Weight, Ib/gal ...... 12.0 Plastic Viscosity, cp ...... _.. .. _...... ___ . 28 Yield Point, Ib/lOO sq It ...... 6 Low viscosities, to permit the screening of drilled solids, Initial Gel, Ib/lO sq ft ...... _...... 2 are typical of the new oil muds. As illustrated in Table 4, 10·Min Gel, Ib/lOO sq It ...... 6 API Filtrate, mi ...... 1.2 these muds generally require little or no dilution with new Filtrate, 3000 F-500 psi, ml ...... 6.4 Setlling ...... None mud. A low-viscosity invert emulsion was used to drill

10URNAL OF PETROLEUM TECHNOLOGY through approximately 600 ft of shale and sand in the TABLE 5-RATES OF PENETRATION FOR DRILLING WITH INVERT EMULSION IN SOUTH TIMBALIER AREA, LA.' South Timbalier area of offshore Louisiana using a 6-in. Interval Drilled (It) rock bit. During this interval absolutely no maintenance 3,111 to 10,021 10,021 to 12,568 treatment was needed. Note that the viscosity, yield point Bit Size, in. 12 1/. 8 1/, and even the high-temperature filtrate did not vary sig Mud Density, Ib/gal 10.6 to 12.4 12.4 to 14.2 Drilling Days 6 5 nificantly. footage Dri lied 6,910 2,547 Rotating Hours 117 61 Another unique feature of the new oil muds is that Avg. Penetration Rate, ft/hr 59 42 rheological, suspension and filtration properties can be *Mud prepared on location using emulsifier, filtration controlled at any temperature now encountered. Milligan control agent and suspension agent. and Weintritt6 demonstrated the performance and stability 0 of an invert emulsion at 400 P. The suspension and filtra more fire-resistant than straight oil systems. Weintritt and tion control properties at these high temperatures are as Stearns10 have thoroughly treated the subject of fire good as with any present-day water-base mud. An invert resistant invert-emulsion muds-which they termed emulsion mud was used to drill high-pressure, high "snuffer-type" fluids. The data presented in their paper temperature formations in Terrebonne Parish, La. This suggest that a minimum of 30 per cent water in the emul mud was used to displace a water-base mud, to drill a sion will necessitate only such fire precautions as are cement plug, to drill a 5¥<1-in. hole down to 16,570 ft and customary when using a water-base mud containing emulsi to set a 4Vz -in. liner to the bottom-all without trouble. fied oil. The water-base mud had been displaced because of re Field personnel utilizing rig equipment Downloaded from http://onepetro.org/jpt/article-pdf/13/12/1177/2213517/spe-150-pa.pdf by guest on 27 September 2021 curring difficulties with differential pressure sticking of can prepare and maintain the new oil muds. In areas of concentrated use, pipe and liner. however, liquid-mud facilities are providing further econ The new oil-mud additives also provide low-viscosity omy and convenience. muds which permit good penetration rates. Tabulated in Table 5 are average rates of penetration for an offshore Louisiana well at two different intervals with different bit Conclusions sizes and mud densities. An average penetration rate of Recent technological advances have removed many of about 50 ft/hr was experienced, but in some sections of the performance and economic limitations of oil muds, the hole the rates approached 90 ft/hr. The mud funnel but the technology is still in its early stages of develop viscosity usually was 50 to 60 seconds. Drilled solids re ment and all of the problems associated with oil muds covered at the shaker were in the form of hard cuttings obviously have nof been solved. that were easily removed. A No. 12 screen was replaced However, the new additives and the new technology with a No. 18 screen, and a regular rig de-sander was discussed in this paper have achieved many of the original used to minimize solids build-up during this fast drilling. objectives of oil muds while eliminating many of their Although self-potential and resistivity logs cannot be disadvantages. As the new technology is applied in the taken in the nonconductive oil muds, new types of logging field and as new additives are developed through con techniques have been developed simultaneously with the tinued research, it is foreseeable that oil muds will meet development of nonaqueous drilling muds. Today a va and even exceed the performance, variability and economy riety of logs are available for use in nonconductive fluids. characteristics now associated with water-base drilling and Doll' describes an induction logging method that measures completion fluids. the conductivity or resistivity of the strata traversed by the borehole. Radioactive logging tools such as the gamma References ray-neutron log also are useful in oil muds.' Tixier, Alger and Doh' describe a sonic logging apparatus which oper 1. Brandt, G. W., We in tritt, D . .T. and Gray, G. R.: "An Ir,, ates on a two-receiver system and which also is inde proved Water-in-Oil Emulsion Mud", Jour. Pet. Tech. (March, 1960) XII, No.3, 14. pendent of the hole size or the drilling mud. 2. Hauser, E. A.: U. S. Patent 2,531,427 (Nov. 28,1950). The fire hazard presented by oil muds is now better 3 . .Tor dan .T. W.: "Organophilic Bentonites I", Jour. Phys. alld understood. Invert-emulsion muds have been found to be Coll. Chem. (Feb., 1949) 53, 294. 4. Lummus J. L.: Canadian Patent 569,930, Pan American Pe troleum Corp. (Feb. 3, 1959). TABLE 3-PROPERTIES OF INVERT EMULSION IMMEDIATELY AFTER OPEN-HOLE DISPLACEMENT OF FRESH WATER-VERMILION BAY FIELD, LA. (CASING 5. Hauser, E. A.: U. S. Patent 2,531,812 (Nov. 28, 1950). DEPTH = 3,000 FT, OPEN-HOLE = 2,500 FT) 6. Milligan, D. J. and Weintritt, D . .T.: "Filtration of Drilling Mud Density, Ib/gal .. 11.1 Retort Analysis: Fluids at Temperatures Above 300°F", Paper No. 926-e-F Funnel Viscosity, sec ...... 43 Water, vol % 22 presented at Spring Meeting of the Southern Dist. Div. of Plastic Viscosity, cp...... _ 24 Oil, vol % 58 Production of API (March 8-10, 1961). Yield Point, Ib/100 sq It ...... 4 Solids, vol 0/0 20 7. Doll, H. G.: "Introduction to Induction Logging and Applica API Filtrate, ml .... 0.0 Oil-Water Ratio ...... 73/27 tion to Logging of Wells Drilled with Oil-Base Mud", Trans., Filtrate, 250° F-500 psi, ml 1.6 AIME (1949) 186,148. Mud Composition: 20-lb Emulsifier, lO-lb filtration Control Agent and 3.5·lb Suspension Agent. 8. Brannon, H. R., .Tr.: "Spectral Gamma-Ray Logging", TrailS., AIME (1956) 207, 30. 9. Tixier, M. P., Alger, R. P. and Doh, C. A.: "Sonic Logging", TABLE 4-PROPERTIES OF INVERT-EMULSION MUD USED TO DRILL IN SOUTH Trans .. AIME (1959) 216, 106. TIMBALIER AREA, LA., WITH NO MAINTENANCE TREATMENT' Date 10. Weintritt, D . .T. and Stearns, R. 0.: "The Baroid Oil-Base 5/5 5/6 5/8 Emulsion Mud", Baroid News Bull. Oan.-Feb.-March, 1961) 13,10. Depth, It 12.575 12,840 12,920 13,220 *** Mud Density, Ib/gal 16.5 16.5 16.6 16.6 Funnel Viscosity, sec 56 58 59 65 Plastic Viscosity, cp 47 44 56 60 Yield Point, Ib/100 sq It 20 25 25 21 API Filtrate, ml 0.0 0.0 0.0 0.1 EDITOR'S NOTE: PICTURES AND BIOGRAPHICAL SKETCHES Filtrate, 200°F-500 psi, ml 3.8 3.8 3.8 4.0 OF JAY P. SIMPSON, J. C. COWAN AND A. E. BEASLEY, JR., *Drilling shale and sand with 6-inch rock bit. Mud prepared on location using emulsifier, filtration control agent and suspension agent. APPEAR ON PAGE 1210.

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