DISPERSIBLE COLLOIDS The New Look in Oil-Mud Technology 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.