Diesel Systems

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  • January 1996 15-1

    Section 15

    Diesel SystemsCementing Technology Manual

    Section 15

    Diesel Systems

    Contents

    Introduction ................................................................................................................................... 15-3Components of the DOC Slurry .................................................................................................... 15-4

    DOC Slurry Weights ............................................................................................................... 15-5Drying of the Diesel Oil in the Field ........................................................................................ 15-5Techniques of Squeezing ........................................................................................................ 15-5DOC-Frac Process .................................................................................................................. 15-6WOC Times ............................................................................................................................ 15-6Summary of Compressive Strength Data on Set DOC Slurries ............................................. 15-6Fluid-Loss Discussion ........................................................................................................... 15-10Recompletion ........................................................................................................................ 15-10

    HYFLO........................................................................................................................................15-11Other Uses and Mixes ...........................................................................................................15-11Sand in DOC Slurries .............................................................................................................15-11Oil-Wetting of Cement in DOC Slurries .................................................................................15-11High Weight DOC Slurries .................................................................................................... 15-12Reasons for DOC Not Setting............................................................................................... 15-13

    Field Mixing Instructions for DOC-10 .......................................................................................... 15-15DOC-10 Surfactant, Diesel Oil Cement ...................................................................................... 15-16DOC-3 Surfactant, Diesel Oil Cement ........................................................................................ 15-17Bentonite - Diesel Oil (BDO) (Gunk Squeeze) ........................................................................... 15-18

    Benonite-Cement-Diesel Oil (BCDO) ................................................................................... 15-20Bentonite Diesel Oil Slurry (BDO)............................................................................................... 15-22Bentonite-Cement-Diesel Oil Slurry (BCDO) .............................................................................. 15-23MOC/One - Selective Water Control Process ............................................................................ 15-24MOC-A Surfactant ...................................................................................................................... 15-26

  • Section 15

    Diesel Systems

    15-2 January 1996

    Cementing Technology Manual

    Notes:

  • January 1996 15-3

    Section 15

    Diesel SystemsCementing Technology Manual

    Section 15

    Diesel Systems

    Introduction

    Using water-cement slurries to shut off unwantedwater in oil wells is well known. The slurry is rela-tively cheap and, where it is immediately successfuland oil production can be regained with a minimumof trouble, its use is recommended. Where the waterslurry is not adequate, that is, where squeeze pres-sures are difficult to develop and huge volumes ofcement are required to obtain the needed results,the use of the DOC slurry should be investigated.When the two types of slurry are compared on theprice-per-volume basis, the DOC slurry is moreexpensive, but experience shows the cost of theDOC squeeze is much less when the price of theentire job is added up. The reasons for this differ-ence are:

    1. Less cement is needed. Sometimes the slurryrequired is a small fraction of the normal vol-ume of a water slurry.

    2. There is less damage to the producingformation.

    3. The ratio of successful applications under verydifficult conditions is much higher.

    DOC is particularly good on channel jobs.

    In spite of all the good results, some troubles re-main. One popular thought is that the DOC slurry isa selective means of shutting off water in an oil well.Many jobs have been performed where no remedialwork was required to regain production, but thesecases were the exception, not the rule. This slurry islike a sponge, and where there is water in the for-mation, whether it be in the oil or the water zone, itwill be sucked into the DOC slurry, and the amountof set cement found opposite any zone is in propor-tion to the quantity of water in the zone.

  • Section 15

    Diesel Systems

    15-4 January 1996

    Cementing Technology Manual

    Components of the DOCSlurry

    1. Diesel oil or kerosene (as water free aspossible).

    Crude oils are not recommended because oftheir varying composition, unknown watercontent, and frequent contamination with emul-sion breaking chemicals. Some can be used, buteach one should be checked before attemptingto mix a slurry.

    2. Standard or premium cement is preferred.

    High early-strength cement can be used, butbecause of its greater surface area and fineness,higher oil-cement ratios must be employed toobtain a pumpable slurry. Retarded oilwellcements give a heavier slurry ( a smaller oil-cement ratio is possible), but these cements arenot necessary because the Portland cementslurry will not set until it contacts water. Inaddition, sets will have lower compressivestrengths. Using POZMIX cement is not recom-mended. Laboratory studies show that waterabsorbed in the slurry is adequate to set regularcement but is insufficient to properly setPOZMIX cement.

    3. The DOC-3 surfactant (Part No. 70.15494)

    a. It permits adding twice as much cement to agiven volume of oil.

    b. The slurry has better pumping characteris-tics, which also helps when it is reversedfrom the well.

    c. The set slurry has a much lower permeabil-ity.

    d. The set slurry has a much higher compres-sive strength.

    One of the good properties the DOC-3 gives to theslurry is the ability of water to come into the slurry.The slurry actually makes a capillary system thatdraws the water into the slurry like a sponge. This isimportant because it means the individual cementparticles are still preferentially water-wet. As aresult, the water-wet mass will stick together andset up hard. The slurry also takes in water, evenwhen there is a zero differential pressure.

    Closely related to the water wetability is the abilityof the slurry to thicken on hitting water. This meanssmall volumes of slurry can do the job, and the

    slurry is particularly good against thief formations.This thickening is not related to a flash set. It ismore comparable to a powder which pours freelywhen dry but sticks together and will not pourwhen dampened with water. If the slurry will notthicken, water will not come into the slurry by capil-lary action.

    Surfactant Diesel Oil Surfactant

    DOC-3 100 0.75

    Table 15-1 serves as a guide for preparing theslurry.

    gal gal

  • January 1996 15-5

    Section 15

    Diesel SystemsCementing Technology Manual

    DOC Slurry Weights

    As shown, the slurry weight varies inversely withthe oil-cement ratio. For a guide, Fig. 15-1 gives acontinuous reading of slurry weight to oil-cementratios based on diesel oil weighing 6.86 lb/gal.

    The main factors that affect DOC slurry weights are:

    1. Water in the oil causes low weights.

    The sensitivity of DOC slurry to water contami-nation of the diesel oil is related to the thicken-ing action of the slurry when it is water-wet.When water contamination is present in thediesel oil, a much less concentrated and lighterslurry is mixed. Contaminated water present toa concentration of 0.5% causes the slurry weightto drop from 16.2 lb/gal to 14.5 or 15 lb/gal.

    This water seems to have many sources and hasbeen traced to the supplier, the tank truckbringing the diesel oil to the location, andHalliburton trucks. Regardless of the source, ithas caused considerable trouble in anticipatingthe volume of oil needed for a job. However, thevariance in slurry weights caused by water inthe oil is even more noticeable where DOC-3 isnot used.

    There is a simple method that can be used todetect water in oil. Drop a small amount of theoil in question on a very hot surface. If water ispresent, there will be considerable sputteringand sizzling as the water is quickly vaporized.A water-free oil will just fume and smoke.

    2. Bentonite in the cement will absorb most of theDOC-3 out of the oil, destroying its dispersingproperties.

    When mixing DOC slurries, make every effort touse dry oil, and mix the slurry as heavy as feasible.Many jobs have been successful with lightweight

    slurries, but there is a better chance of success if aslurry with the highest solids-to-liquid ratio pos-sible is mixed.

    If this slurry was not sensitive to small amounts ofwater, the beneficial effects, such as extreme thick-ening of the slurry when it contacts water, and thesuccess that has been obtained in field applicationswould not be possible.

    Drying of the Diesel Oil in