CA 02308268 2000-05-05 TITLE OF THE INVENTION Well Treatment Fluid and Method of Manufacture NAME OF INVENTOR Shaun T. E. Mesher Dwight N. Loree FIELD OF THE INVENTION This invention relates to well treatment fluids and their method of manufacture. BACKGROUND OF THE INVENTION Various fluids, including hydrocarbon based fluids, have been used during well treatment operations, which include fracturing, maintenace and drilling operations. Particularly in well fracturing operations, it has been common to use condensates. These condensates have proved useful, but they are relatively expensive. In addition, condensates are often used as hydrocarbon solvents for treating wells to remove contaminants such as asphaltenes and waxes. Use of condensates in well treatment is described in Canadian patent no. 2,090,306. It is difficult to decide when to treat a well with such a solvent to yield optimum results. For environmental concerns, and personal safety during drilling operations it is known to be preferable to use a low BETX fluid, and one of the objects of an aspect of the invention is to produce a low BETX fluid. This invention provides an inexpensive way of making a well treatment fluid, a superior fracturing fluid, a safer alternative to conventional drilling fluids and an improved method of treating a well to improve production. SUMMARY OF THE INVENTION There is therefore provided according to a first aspect of the invention a method of producing a well treatment fluid, the method comprising the steps of: CA 02308268 2000-05-05 2 obtaining a crude oil that has been produced directly from a hydrocarbon bearing formation, the crude oil having hydrocarbons with between one and six carbon atoms and hydrocarbons having more than 20 carbon atoms; and refining the crude oil to remove substantially all hydrocarbons from the fluid where the hydrocarbons have fewer than six carbon atoms and to remove substantially all hydrocarbons where the hydrocarbons have more than 20 carbon atoms. According to a further aspect of the invention, there is provided a method of treating a well, the method comprising the steps of: determining the type of contaminants clogging a well; refining produced fluid from the well to remove heavier ends to produce a treatment fluid; and injecting the treatment fluid into the well. According to a further aspect of the invention, there is provided a method of treating a well, the method comprising the steps of: sampling well fluid in the well at a downhole sample point to produce a downhole sample of the well fluid; sampling produced well fluid from the well at the surface to produce a surface sample of the well fluid; analyzing the downhole sample and the surface sample to determine well fluid contaminants lost from the well fluid in transit between the downhole sample point and the surface; and treating the well with a well treatment fluid based upon characteristics of the lost contaminants. To ensure low BETX in the drilling fluid, it is preferable to remove substantially all hydrocarbons having fewer than seven, eight or nine carbon atoms. When heavier ends are removed it is preferable also to remove substantially all hydrocarbons having more than 16 carbon atoms. Preferably, when a fracturing fluid is desired, the crude oil is refined to have a total of less than 2% by weight hydrocarbons having one, two, three, four, five or six carbon CA 02308268 2000-05-05 3 atoms, and to having total of less than 2% by weight hydrocarbons having more than 16 carbon atoms. According to a further aspect of the invention, the crude oil is refined in two stages, a first stage in which a hydrocarbon fraction of predominantly hydrocarbons having 3-12 carbon atoms is taken and a second stage in which the hydrocarbon fraction is further refined to produce a hydrocarbon fraction with predominantly hydrocarbons having 7-12 carbon atoms. According to a further aspect of the invention, the refining of the crude oil is carried out at a wellsite. According to a further aspect of the invention, there is provided a method of treating a well comprising applying to a well a fluid produced by any one of the methods of producing a well treatment fluid herein disclosed. According to a further aspect of the invention, there is provided well is treated with the fluid during fracturing operations. According to a further aspect of the invention, the well is treated with the fluid during drilling operations. According to a further aspect of the invention, there is provided the fluid produced by any of the methods herein disclosed. According to a further aspect of the invention, the timing of the treatment of a well is based upon the volume of contaminants lost in the well between downhole and surface. According to a further aspect of the invention, the content of the well treatment fluid is selected based on the carbon content of the lost contaminants. These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow. BRIEF DESCRIPTION OF THE DRAWINGS There will now be described preferred embodiments of the invention, with reference to the drawings, by way of illustration only and not with the intention of limiting the scope of the invention, in which like numerals denote like elements and in which: CA 02308268 2000-05-05 4 Fig. 1 is a schematic showing a fractionation apparatus according to the invention; and Fig. 2 is a graph showing ratio of sub-surface sample mass to surface sample mass plotted against carbon number for a sample recovered from a well. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In this patent document, "comprising" means "including". In addition, a reference to an element by the indefinite article "a" does not exclude the possibility that more than one of the element is present. The label CX means a hydrocarbon with X carbon atoms. The label CX+ means hydrocarbons having more than X carbon atoms. Removal of substantially all Y means that the remaining fraction has less than 2% mass fraction of Y. In the method of producing a well treatment fluid according to the invention, the first step is to obtain a crude oil that has been produced directly from a hydrocarbon bearing formation. The crude oil will typically have hydrocarbons with between one and six carbon atoms and hydrocarbons having more than 20 carbon atoms. The presence of C20+ hydrocarbons is usually indicated by a dark colour of the fluid. Various crude's may be used such as the crude's noted in Table 1 below. The next step is to refine the crude oil to remove substantially all hydrocarbons from the fluid where the hydrocarbons have fewer than six carbon atoms and to remove substantially all hydrocarbons where the hydrocarbons have more than 20 carbon atoms. This aspect of the invention focuses the fluid on components having solvent capabilities, rather than formation plugging deficiencies. Refinement to remove C l -C5 yields a fluid with a comparably high BETX. It is preferable to further refine the crude to yield a low BETX fluid. This may be accomplished by refining the fluid to remove substantially all hydrocarbons having fewer than seven carbon atoms, with even further improvements if substantially all C1-C8 hydrocarbons are removed, or substantially all C I -C9 hydrocarbons are removed. C17-C20 hydrocarbons have low solvent capability, therefore it is also preferred to refine the fluid to remove substantially all hydrocarbons having more than 16 carbon atoms. This may be carried out in two stages, as illustrated in Fig. 1. In a first stage, a hydrocarbon CA 02308268 2000-05-05 fraction of predominantly hydrocarbons having 3-12 carbon atoms is taken. The crude oil is injected at feed line 10 into conventional fractionation tower 12, where three cuts are taken. A first cut of C15-C30+ is taken at line 14. A second cut of C10-C25 is taken at line 16. A third cut of C3-C12 is taken at line 18. The fluid (DRILLSOLTM) at line 16 has a GC 5 analysis shown in Table 1, for input Crude A. In a second stage, the hydrocarbon fraction taken at line 18 is further refined in conventional secondary fractionation tower 20 to produce a hydrocarbon fraction (WAXSOLTM fluid shown in Table 1) with predominantly hydrocarbons having 7-12 carbon atoms, produced at line 22, with a C3-C6 cut taken at line 24. Preferably, the crude oil is refined to have a total of less than 2% by weight hydrocarbons having one, two, three, four, five or six carbon atoms, and a total of less than 2% by weight hydrocarbons having more than 16 carbon atoms. The fractionation towers 12 and 20 may be located at a conventional refinery, in a separate facility, or advantageously may be provided at an individual well site, where the fluid may be refined and then used for well treatment operations at that well or nearby wells. It is desirable that the fractionation equipment be sufficiently small to be portable from well to well. The fluid thus produced by the method of the invention may be used for fracturing operations (preferably FRACSOLTM fluid), drilling operations (preferably DRILLSOLTM fluid) or treatment of the well with a solvent (preferably WAXSOLTM fluid). Compositions of these fluids are described in Table 1. The invention also provides a method of treating a well, and also to determine when to perform a well treatment operation, such as application of a solvent, squeezing or fracturing, and what fluid to use. Well fluid in the well is first sampled at a down hole sample point to produce a down hole sample of the well fluid. Apparatus for taking down hole samples (known as a bomb) is well known in the art. The apparatus may be obtained from for example Alpine Oil Services Corp. of Calgary, Alberta, Canada. Typically a 5-liter sample may be taken. Produced well fluid from the well is then sampled at the surface to produce a surface sample of the well CA 02308268 2000-05-05 6 fluid. It is important to maintain the down hole fluid sample at approximately the same pressure and temperature as the down hole pressure during the analysis of the sample, or to take into account any pressure or temperature differences. To do this, the pressure and temperature of the down hole sample may be measured, and before analysis the down hole sample heated to attain the same pressure and temperature. A small sample is bled off the surface sample for analysis at the down hole pressure and temperature. CS2 is added to the sample to maintain all fluid components in solution. The CS2 is measured accurately to ensure its GC reading can be excluded from the sample analysis. The down hole sample and the surface sample are then analyzed to determine well fluid contaminants lost from the well fluid in transit between the down hole sample point and the surface. This may be carried out as follows. First, an analysis such as gas chromatography identifies the C l - C60 content of each fluid. Next, a ratio of fluid content (down hole sample divided by surface sample) is determined for each carbon number, preferably for heavier weight hydrocarbons, such as C30-C60. This ratio declines slowly with increasing carbon number, as shown in Fig. 2. This is believed to be due to heavier hydrocarbons sticking to the production facilities, including the casing. Between C30 and C60 the slope is fairly constant and may be approximated. For example, the slope in Fig. 2 is about -0.0009667. The amount and type of fluid contaminant lost during production may then be calculated. From this analysis, it may be determined when a well treatment is required, and what kind of fluid to treat the well with. For example, if the slope is steep, it may be desirable to increase heavy end content in the well treatment fluid, or increase the aromatic content. A steep slope also suggests more frequent treatment. After sampling of the fluid at a well, the produced fluid may be refined in the apparatus of Fig. 1 at the well, and then used at time intervals suggested by the analysis to treat the same well (e.g. more frequent treatments where large losses in the hydrocarbon stream are indicated in the analysis of the top and bottom samples). The actual time schedule of treatments is dependent upon the particular well. In addition, depending on what components are seen to be lost from the surface sample, the fluid may be refined to have hydrocarbons likely to hold the lost components in solution. CA 02308268 2000-05-05 7 Table 1 shows mass fraction as determined by gas chromatography for two crudes and three refined fractions. Crude A is Sweet Mobil Harmatton Central 7-12, Crude B is Brazeau feedstock November 1999, both being oil fields in Alberta, Canada, DRILLSOLTM drilling fluid was made by refining Crude A to remove C1-C9 and substantially all C20+, FRACSOLTM fracturing fluid was made by refining Crude B to remove substantially all C1- C6 and substantially all C 16+. WAXSOLTM solvent fluid was made by refining Crude A twice. The first stage was one in which a hydrocarbon fraction of predominantly hydrocarbons having 3-12 carbon atoms was taken. The second stage was one in which the hydrocarbon fraction was further refined to produce a hydrocarbon fraction with predominantly hydrocarbons having 7-12 carbon atoms, yielding a fluid with substantially no C 1-C6 and substantially no C 13+. Table 1 Mass fraction of C1-C30+ for various fluids C# Crude A Crude B DRILLSOL FRACSOL WAXSOL 1 0 0 0 0 2 0 0 0 0 3 0.02 0 0 0 4 0.35 0 0 0 5 2.24 0 0 0 6 2.93 0 0.42 0.05 7 5.37 0 5.01 11.47 8 6.58 0.01 12.39 18.69 9 5.81 0.12 13.45 15.89 10 2.73 6.66 0.63 17.00 15.55 11 3.46 6.52 2.34 12.64 9.32 12 3.07 5.28 6.73 8.84 3.57 13 3.19 5.75 13.58 7.37 1.48 14 3.20 4.67 14.48 4.96 0.09 15 3.23 4.69 15.12 1.05 0.03 16 3.16 4.05 13.99 0.75 0 17 2.26 3.11 8.93 0.33 0 18 3.35 3.46 10.57 0.15 0 19 2.76 3.43 9.32 0.17 0 20 2.17 2.61 1.67 0 0 21 1.99 2.14 0.57 0 0 22 2.10 1.60 0.41 0 0 23 1.97 1.35 0.27 0 0 CA 02308268 2000-05-05 8 24 2.04 1.89 0.16 0 0 25 2.09 1.22 0.13 0 0 26 2.37 0.84 0.07 0 0 27 2.45 1.07 0.04 0 0 28 2.63 0.61 0.02 0 0 29 2.57 0.45 0.01 0 0 30+ 25.92 3.25 0.64 0 0 Benzene 0.36 0 0 0 Toluene 1.61 0 2.41 4.42 C# Crude A Crude B DRILLSOL FRACSOL WAXSOL C81-110 3.69 0.03 5.88 8.84 C91-112 1.41 0.16 2.97 2.77 C5H10 1.20 0 0 0 C61-112 1.72 0 0.37 1.26 C71-114 2.25 0 3.84 6.57 Crude A has 21.31 mass% C 1-C9. 25 Immaterial modifications may be made to the invention described here without departing from the essence of the invention.