Abstract:
An improved chemical composition and process for cleaning pipe dope from wellbores has been established. The chemical composition is of an aliphatic hydrocarbon and/or esters with a biodegradable water insoluble monoterpene preferably having a flash point (PMCC) greater than 140° F. the mixture then used neat, or in a dispersion of seawater, being used to remove pipe dope from tubing, casing and the like.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates to the treatment of wellbore casing, tubing, drillstring, etc. to remove pipe dope. Pipe dope is a pipe thread sealant. The primary function of thread compounds is to provide sealability, galling resistance, and uniform frictional characteristics while lubricating the thread pattern of drill pipe during make up. 
     The current API MODIFIED pipe dope was introduced in 1955. The API MODIFIED contains lead, zinc, graphite and copper. Other metals such as aluminum flake, brass, bronze, nickel, talc, silica, calcium carbonate and clays have been used in other compounds. The heavy metals, up to 25 percent of the volume provide the sealability with their particle size being in the range of 45 microns. 
     The API 8 round connections are tapered with the primary sealing mechanism being achieved by making up the threads until plastic deformation of the threads occurs. The thread compound must create a film strong enough to maintain a barrier and seal between the two contacting surfaces. If the integrity of the thread compound film was broken down, the bearing stresses and heat created at the point of contact would cause the connection to weld together. The joint would eventually break down due to the tearing of the weld during additional rotation. 
     Unfortunately these thread compounds will effectively seal off pore throats in the formation, gravel pack or even whole perforations. By design, these compounds are resistant to temperature and chemical degradation and are difficult to remove from tubing, and nearly impossible to remove from the confines of a pore throat. 
     The extent of the problem can be illustrated by a typical scenario involving the completion of a 10,000 foot well with 27/8-inch, 6.4 pound tubing. The tubing string would have 322 connections, assuming 31 foot joint length. If an average of two teaspoons of dope per connection were extruded into the string, approximately one quart of dope would end up in the tubing. Considering that the dope is water insoluble and if it were to collect in the bottom of the work string, a total of four feet of tubing could be filled. In addition most completions require several pipe trips involving the re-doping of many of the connections. 
     A common misconception is that pipe dope is removed or is soluble in acid or caustic when a pickle job is conducted. Acid or caustic however has almost no effect on the pipe dope. 
     In the past the pipe dope has been removed by using various solvents such as xylene, toluene and even low flash point terpenes. Because of increasing safety and environmental concerns these chemicals are unattractive. 
     A new composition for cleaning pipe dope from a well system has been developed. The composition includes a terpene hydrocarbon with a flash point of greater than 140° F. mixed with either an oil soluble aliphatic hydrocarbon, an ester with a flash point of greater than 140° F., or mixtures of both oil soluble aliphatic hydrocarbons and esters. The oil soluble aliphatic hydrocarbon component may be a mixture of different oil soluble aliphatic hydrocarbons and, likewise, the ester component may be a mixture of esters. The preferred terpenes are biodegradable monoterperens more preferably alpha-pinene derivatives. The preferred oil soluble aliphatic hydrocarbons have a viscosity of less than 10 cps @ 75° F. Preferred esters are acetic acid esters of C 6  -C 8  branched alcohols. The preferred oil soluble aliphatic hydrocarbons are petroleum napthas. In the preferred mixture the terpene hydrocarbon is from about 90% to about 50% by weight of the composition and the oil soluble aliphatic hydrocarbon, ester, or mixture of both is about 10% to about 50% by weight of the composition. 
     A process has been developed to use the composition mixed with a brine solution such as seawater to remove the pipe dope. Although the composition can be pumped in the well without dilution, it has been found that a dilute solution offers excellent cleaning capability with about 5 to 20 minutes of contact with the area to cleaned with 10 minutes of contact time preferred. The same pump that is used on a rig to pump the cement can be utilized to pump a combination brine and pipe dope cleaning composition. Since the same pumping system is used and the contact time for a dilute solution is only 10 minutes, a significant savings in rig time utilization is achieved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows the chemical structures of d-Limonene, alpha-pinene and some derivatives of alpha-pinene in IUPAC format. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The composition is a blend of high flash point (greater than 140° F.) terpene hydrocarbon with oil soluble aliphatic hydrocarbons or esters with a flash point greater than 140° F. used in the removal of pipe dope. The composition can be pumped neat or in conjunction with seawater. The material is not soluble in seawater but when pumped in turbulent flow the solvent is broken into small droplets. The small droplets are more effective in removing the pipe dope and as a result higher pump rates can be used. The higher pump rate reduces rig operation time by several hours. 
     Pickling of the string can be conducted in several ways. A pump rate of 1 bbl/min has long been established in the industry. The purpose of the pipe dope pickling is to remove the dope. A subsequent treatment (acid pickling) is performed following or in conjunction with the pipe dope pickling to remove scale, rust or other contaminants by use of 5 to 15% HCl. The solvent removes the dope that may be covering the scale to improve the efficiency of the acid treatment. 
     A typical treatment is as follows. Pump a pill consisting of 4 drums (5 barrels) of the pipe dope cleaning composition down the tubing at 1 bbl/min. The preferred composition is about 70% alpha-pinene derivatives, Glidsol 180 manufactured by Glidco and 30% of the preferred aliphatic hydrocarbon, petroleum naptha. When the pill reaches the bottom of the tubing, but before turning the corner, reverse the flow and pump the material out of the string or tubing. This provides a total contact time of 10 minutes. The pump sequence can have a pill of acid, normally 5 to 15% HCl following directly behind the solvent. The HCl is in an aqueous solution of water, seawater, filtered brine or other available aqueous solutions. 
     If the tubing had a volume of 180 bbls, 6 hours would be required to pickle the string. If one pumps at 2 bbl/min (50% dilution of pipe dope cleaning composition in seawater) the time would be cut in half. For a Gulf of Mexico operation at $24,000.00/day current rig cost, the savings would be $3,000.00 and in a North Sea operation with a daily current rig rate of $60,000.00/day the savings would be $7,500.00. 
     EXAMPLE 1 
     Pipe dope is difficult to remove from steel. A test is conducted to see how quickly API MODIFIED COMPLEX pipe dope can be removed from steel. A 400 ml beaker is filled with roughly 250 ml of the fluid to be evaluated. A magnetic stir bar is used to put the fluid in turbulent flow. A steel coupon with approximately 1 inch by 2 inch area covered with about 3/32 inch layer of pipe dope is lowered into the fluid and the cleaning efficiency is measured with respect to time. The solvent tested shows a flash point measured by the Pensky Martin Closed Cup method (PMCC) in the following Table 1 and as noted in other tables herein. 
     
                       TABLE 1______________________________________SOLVENT/   OIL AND   PERCENT CLEANINGFlash point      WATER     EFFICIENCY @(PMCC, °F.)      SOLUBLE   5 min.    10 min.                                15 min.______________________________________Product A  Y/N       57        90    97Terpene    Y/N       86        97    100HydrocarbonGlidsol 180/142d-Limonene A/120      YIN       77        93    100d-Limonene B/122      Y/N       93        1002-ethyl hexyl      Y/N       71        85    97acetate/160Seawater   N/Y       0         0     05% HCl in  N/Y       0         0     0seawater______________________________________ 
    
     The results summarized in Table 1 show the following. The high flash terpene hydrocarbon exceeds the performance of an existing high flash point material Product A which is a blend of d-Limonene and high flash point paraffin oil which suppresses the flash point but lowers the solvent action. The high flash point terpene is comparable to two low flash point d-Limonene materials. Seawater and HCl are ineffective in removing pipe dope. 
     Glidsol 180 is produced by Glidco and is a product of alpha-pinene derivatives. D-Limonene as shown in FIG. 1 is from citrus oil and has been used as a cleaner for various oil field applications. The structure of d-Limonene is known as the terpene hydrocarbon dipentene. Also shown in FIG. 1 is alpha-pinene which can be obtained from the sulfate liquor by product of the Kraft paper process. The alpha-pinene can be chemically modified to form the alpha-pinene derivative structures also shown in FIG. 1 that are similar to d-Limonene. The alpha-pinene derivatives shown on FIG. 1 are exemplary and many other structures are known to those skilled in the art. These structures have similar cleaning abilities, but have been discovered to have distinct advantages in drilling applications in pipe dope removal and wellbore clean up. The flash point of these derivatives is greater than 140° F. making them safe to transport and handle. The flash point of dipentene (d-Limonene) is below 140° F. The use of the alpha-pinene derivatives in combination the oil soluble aliphatic hydrocarbons and esters of the present invention has produced unusual results in cleaning pipe dope. 
     EXAMPLE 2 
     The following Table 2 is a sampling of various types of solvents and the ability to clean pipe dope using the methodology of Example 1. 
     
                       TABLE 2______________________________________      Flash                Percent Cleaning      Point  Oil    H.sub.2 O                           Efficiency            °F.                     Solu-                          Solu-     10   15Solvent  Class   (PMCC)   bility                          bility                               5 min                                    min  min______________________________________EXXSOL   AHC     221      Y    N    37   68   91D-110SHELLSOL AHC     142      Y    N    77   97   100142 HTISOPAR M PAHC    177      Y    N    12   30   46EXXATE   E       151      Y    N    78   97   100700PINE     TE      200      Y    N    26   55   77ESTEREASTMAN  GE      212      Y    Y    28   44   72DBDOW DPMA GE      186      Y    N.sub.SM                                6    9   15DOW EB   GE      150      Y    Y     3    6   11______________________________________ AHC  Alphatic Hydrocarbon PAHC  Paraffinc Aliphatic Hydrocarbon E  Esters TE  Terpene Ester GE  Gylcol Ether EXXSOL D110  Petroleum Naptha, Exxon Chemical SHELLSOL 142 HT  Petroleum Naptha, Shell Oil ISOPAR M  Isoparaffinic Hydrocarbon, Exxon Chemical EXXATE 700  Acetic Acid Ester of C.sub.6 -C.sub.8 branched alcohols also known as Oxoheptyl alcohol, Exxon Chemical EASTMAN DB  Diethylene Glycol Monobutyl ether, Eastman Chemical DOW DPMA  Dipropyl Gylcol Monomethyl Ether Acetate, Dow Chemical DOW EB  Ethylene Gycol NButyl Ether, Dow Chemical 
    
     EXAMPLE 3 
     A test on blends of an aliphatic hydrotreated hydrocarbon in removing API MODIFIED COMPLEX. The test procedure was the same as that in Example 1. The terpene hydrocarbon was Glidsol 180. 
     
                       TABLE 3______________________________________SOLVENT/     PERCENT CLEANING(X/Y + RATIO BY        EFFICIENCY @WEIGHT)      5 min.      10 min. 15 min.______________________________________SHELLSOL 142 HT        77          97      100Terpene      86          97      100Hydrocarbon (TH)TH/AH 90/10  80          93      100TH/AH 80/20  88          100TH/AH 70/30  91          100TH/AH 60/40  77          97      100TH/AH 50/50  70          95      100______________________________________ 
    
     These data show that maximum efficiency was achieved at a ratio between 80/20 and 60/40 terpene/aliphatic hydrocarbon. In commercial operations a preferred blend is 70/30 terpene/aliphatic hydrocarbon. 
     EXAMPLE 4 
     A test was conducted on a 70/30% by weight, TH/AH blend mixed with seawater in removing API MODIFIED COMPLEX pipe dope at 75° F. The rest of the test procedure was the same as that in Example 1. 
     
                       TABLE 4______________________________________      PERCENT CLEANING      EFFICIENCY @SOLVENT      2.5 min.                5 min.    10 min.                                15 min.______________________________________20% in seawater        48      87        97    10040% in seawater        67      90        10060% in seawater        70      94        10080% in seawater        72      97        100100% TH/AH   84      90        100______________________________________ 
    
     EXAMPLE 5 
     A test was conducted on a 70%/30% by weight TH/AH blend mixed with seawater in removing API MODIFIED COMPLEX pipe dope at 110° F. The rest of test procedure was the same as that in Example 1. 
     
                       TABLE 5______________________________________      PERCENT CLEANING      EFFICIENCY @SOLVENT      1 min.  2.5 min.  5 min.                                10 min.______________________________________20% in seawater        38      75        10040% in seawater        47      88        10060% in seawater        61      91        10080% in seawater        58      94        100100% TH/AH   47      81        100______________________________________ 
    
     The data in Examples 4 and 5 show the improved cleaning of the seawater blends over the neat solvent procedure. The drop of in performance between 60 and 100% solvent indicates the improved performance of droplets in turbulent flow. 
     EXAMPLE 6 
     A test was conducted to determine the effectiveness of Exxon D-110 a petroleum naptha aliphatic hydrocarbon with the preferred terpene, Glidsol 180. The test procedure was the same as Example 1. 
     
                       TABLE 6______________________________________       PERCENT CLEANINGSOLVENT       5 min.    10 min. 15 min.______________________________________Glidsol 180 (TH)         86        97      100EXXON D-110 (AH)         38        69      91TH/AH by weight %90/10         93        10080/20         94        10070/30         87        97      100______________________________________ 
    
     EXAMPLE 7 
     A test was conducted on an ester and the preferred terpene hydrocarbon Glidsol 180. The test procedure was the same as Example 1. The ester is Exxate 700 which is an acetic acid ester of C 6  -C 8  branched alcohols. 
     
                       TABLE 7______________________________________       PERCENT CLEANINGSOLVENT       5 min.    10 min. 15 min.______________________________________Glidsol 180 (TH)         86        97      100EXXATE 700 (E)         78        97      100TH/E by weight %90/10         94        10080/20         93        10070/30         91        100______________________________________ 
    
     The results with the ester are slightly better than the SHELLSOL HT, however the cost of the ester is significantly more. Also, 2-ethylhexylacetate can be used. 
     It is apparent that there has been described herein a chemical composition and process for effectively removing pipe dope from a well drilling system. Various changes and alterations may be made in the practice of the chemical composition and process by those skilled in the art without departing from the spirit of this invention. It is intended that such changes be included within the scope of the appended claims. The present description is intended to be illustrative and not limit the present invention.