MXPA98009614A - Biodegradable well drill fluid free clay and method to use the same flu - Google Patents

Abstract

The present invention relates to: A dry mix additive, which is used to form a well drilling fluid of clay, ie non-clayey, free of inorganic salts, ie not brine, biodegradable and chemically degradable, based in water, which is capable of imparting non-Newtonian, pseudoplasticity and fluid loss controllers to aqueous systems, for use in horizontal directional drilling, which finds utility in the installation of horizontal environmental wells for soil and groundwater recovery . The dry blend comprises (1) from about 80-90 by weight of pre-gelatinized corn starch heteropolysaccharide, and (2) from about 10-20 by weight a synthetic biopeptide, such as xanthan gum treated with a dispersing agent (glyoxal) to facilitate dispersion. Sodium hypochlorite may be added, if desired, to the well drilling fluid to provide resistance to bacterial attack. The dry mix is added either to fresh water or water-based in quantities of 5.44 to 6.804 kg of dry mix to a barrel (137.97 x 10exp-3m3) of water and then used as drilling fluid when drilling horizontal wells for soil recovery and groundwater. Also, if desired, calcium hypochlorite can be circulated through the hole in the well following the drilling operation to accelerate the degradation of the polymers in the well drilling fluid. Following the drilling of the hole in the well, the contaminated formation fluids are removed from the orifice of the well.

Description

FREE-OF-CLAY BIODEGRADABLE WELL DRILL FLUID AND METHOD FOR USING THE SAME FLUID BACKGROUND OF THE INVENTION The present invention relates to a composition which is capable of imparting non-Newtonian, pseudoplasticity, fluid loss controlling, properties to aqueous systems. More particularly, the present invention relates to the formation of a water-based, clay-free, biodegradable, biodegradable drilling fluid for use in horizontal drilling wells for soil and groundwater repair. One of the most common methods for underground environmental recovery, such as the removal of contaminated soil and contaminated groundwater, is to first drill a well bore either vertically or horizontally to the area or boom, and then install an extraction well for extract contaminants using air or fluid to remove contaminated groundwater. Vertical recovery and delivery systems are by far the most conventional approaches for soil and groundwater recovery. Recent advances in horizontal directional drilling have added a new dimension to environmental recovery. "It is convenient to drill horizontal wells instead of vertical wells for various reasons.The conventionally drilled vertical wells are perpendicular to the central axis of the contaminated area, while the horizontal wells can travel parallel to such a central axis. previously required as many as ten or more vertical wells.The geometry of a horizontal well provides a large wellbore area for recovery, thereby improving the efficiency of the recovery process.Moreover, horizontal wells can access the inaccessible area of the well. Another way through vertical wells, such as pollutant sources located below buildings, flooded fields, ponds, and contaminating feathers that have migrated out of place, provide a cost effective and less destructive method for soil and groundwater recovery. The purpose of a method of drilling a well norm Almente is to construct a well bore that can receive a well liner while causing minimal damage to the formation that houses the well's mesh. Damage is commonly referred to as bark damage and can be caused by both physical and chemical changes to host formation. Physical changes generally involve a compaction of pore spaces and the intrusion of foreign particles into the formation of pore spaces. The chemical changes are the dissolution and precipitation of minerals caused by any chemical interaction between the formation of fluids and the drilling fluid. The damage of the skin is not strictly limited to the side of the well drilling. The damage continues in the formation as long as the drilling fluid can travel, generally referred to as "invasion". The degree of invasion of drilling fluid into host formation can cause difficulties during well development. Using fluid to assist in drilling is often referred to as fluid-assisted drilling is the most common and conventional method of horizontal directional drilling (HDD). The main drilling fluid functions in HDD include the transportation of perforated soil or rock cuttings to the surface, cooling and cleaning of the pit auger or cutters of the stretcher cutters, the reduction of friction between the drill pipe and the well drilling , and the stabilization of the well hole, particularly in the formation of soft soil, transmission of hydraulic excavation, and modification of soil. In addition to performing the functions mentioned above, the drilling fluid used in an HDD installation must be environmentally benign and easily processed. A drilling fluid that can be biologically degraded, often referred to as biodegradable, is the most desirable fluid to be used in the environmental directional well installation.

Generally, drilling fluids will be either clay-based, such as Wyoming bentonite, or clay-free, such as brines and polymer pastes. Although water is a clay-free fluid, water alone does not have the capacity to make the holes drilled from the well hole to the surface. In the drilling fluid class, clay-based fluids have been dominant for years in the field, due to the traditional theory and widely held that the proper viscosity to create a particle carrying capacity in the drilling fluid could be achieved only with a drilling fluid having thixotropic properties, that is, the viscosity must be provided by a material that will have sufficient gel strength to prevent the perforated particles from separating from the drilling fluid when the agitation of the drilling fluid has ceased. In order to obtain the desirable thixotropy or gel strength, hydratable clay or colloidal clay bodies, such as sodium-based bentonite, have been employed. As a result, drilling fluids are usually referred to as drilling "muds". The use of drilling muds has provided the means to satisfy two basic requirements of drilling fluids, namely, viscosity for hole cleaning and gel force for cutting transportation. However, clay-based drilling muds form a filtration cake of iodine in the hole wall of the well, which is difficult to remove during well development. Additionally, the clay particles in clay-based drilling muds can enter the host formation before a mud cake forms and the porosity and permeability of the formation can be reduced. When the permeability of a host formation is reduced, efficiency decreases to remove contaminants from a contaminated soil or groundwater. Yet another serious disadvantage of clay-based drilling muds is that they are not biodegradable and require transportation to an area designated for disposal, thus increasing the cost of the drilling operation. A non-clayey (clay-free) drilling fluid, such as fresh water, avoids many of the clay-based fluid problems, but can cause hydration and disintegration of host formation. However, fresh water with the appropriate additives can provide a drilling fluid with those basic requirements of the drilling fluids. When a clay-free drilling fluid requires relatively high gel strength and viscosity, for example, when used in horizontal directional drilling, it is generally necessary to employ an additive, which may be comprised of a simple compound or a mixture of several compounds to thicken the fluid to the point where it will have the necessary carrier capacity and the cleaning capacity of the appropriate hole. A widely held and accepted theory is that a clay-free drilling fluid should exhibit pseudoplastic properties, that is, the viscosity should be sufficient to prevent the perforated particles from separating from the drilling fluid, when the fluid is under the influence of low cutting forces, such as those found in the annular passage. Materials that can be added to water to create a water-based fluid with pseudoplastic properties are described in the prior art, discussed below. Another requirement for a drilling fluid to drill an orifice, either vertically or directionally, is a low rate of filtration or fluid loss commonly referred to in the oil or gas well drilling technique. It is not enough that a drilling fluid has adequate viscosity and gel strength to prevent perforated cuts from settling when the fluid circulation stops. If the drilling fluid does not have a low filter loss, can result in loss of the drilling fluid to the formation of the host, particularly when drilling through an unconsolidated formation, such as sandy soil. In the article entitled "Fluids Are Key in Drilling Highly Deviated Wells," published in Petroleum Engineer International, Feb. 1988 (pp. 24-26), B. Byrd and M. Zamora described the importance of filtration control to minimize training damage in the drilling of highly diverted wells. A drilling fluid with a low filtration rate allows only a small amount of water to diffuse from the drilling fluid around the formation of the well drilling under the pressure differential that prevails in the well bore. U.S. Patent No. 4,240,915 for Block describes a clay-free, water-based drilling fluid suitable for circulating in a well hole while drilling the hole in the well in an underground formation, which includes water, a water loss inhibitor. , a weight agent and a viscosifying agent, in which the viscosifying agent is an aqueous medium produced by mixing under a high degree of agitation a water-soluble alkali metal aluminate (Na2O »AI2? 3ß3H2O) with an acid compound soluble in water. water selected from the group consisting of an inorganic acid or a salt of a strong acid and a weak base. The aqueous part of the drilling fluid has the aluminum hydroxide agent in an amount sufficient to impart pseudoplastic, non-Newtonian properties to the fluids when the fluids have a pH of at least 8. US Patent No. 4,255,268 to Block describes a water-based, clay-free drilling fluid, to be used to drill hole holes in underground formations having an aqueous mixture of water, a water loss inhibitor, a weight agent and a viscosifying agent, in which the viscosifying agent is a reaction product of ferric hydroxide formed in an aqueous medium by contacting under a high degree of agitation a ferric salt soluble in water, such as ferric chloride (FeCl3) with a water-soluble base, which contains or produces groups hydroxide in water in amounts to cause the hydroxy to ferric ratio to be at least about 3: 1, e.g., Fe (OH) 3. The aqueous phase of the drilling fluid has the ferric hydroxide agent [Fe (OH) 3] therein in an amount sufficient to impart pseudoplastic, non-Newtonian properties to the fluid at a pH of at least 8. US Pat. No. 4,264,455 for Block is directed to a clay-free, aqueous drilling fluid for use to drill bore holes in underground formations having an aqueous system comprising water, a water loss inhibitor, and a viscosifying agent, in which the agent The viscosifier is a reaction product containing hydroxyl-containing magnesium. The hydroxyl-containing magnesium agent of the reaction product is formed in an aqueous medium under high-speed agitation between a magnesium salt, such as MgO, which is substantially soluble in water and a water-soluble base selected from the group consisting of alkali metal oxide, alkali metal hydroxide, alkali metal salt of a weak acid and ammonium hydroxide. The aqueous system of the drilling fluid has the objective reaction product therein in an amount sufficient to impart pseudoplastic, non-Newtonian properties to the fluids when the fluids have a pH above 1 1. U.S. Patent No. 4,366,070 to Block discloses an improved, water-based clay-free drilling fluid that is capable of imparting a high degree of pseudoplastic and fluid loss controlling properties. The composition is a combination of an aluminum hydroxy-containing agent having an assumed molecular formula of AIO (OH) and a cross-linked hydroxyalkyl cellulose reaction product. The composition involves (1) an aluminum agent containing hydroxy formed by mixing in an aqueous solution and low high degree of agitation, a water-soluble basic agent selected from an alkali metal aluminate, alkali metal hydroxide or ammonium hydroxide with a water-soluble acidic agent selected from an inorganic acid, or aluminum chloride, sulfate or nitrate, so that at least one of such agents is a compound containing aluminum; (2) a reaction product formed between a hydroxyalkyl cellulose and a crosslinking agent, the crosslinking agent being present at a concentration equivalent to at least about 1% stoichiometric with respect to the hydroxyalkyl cellulose. U.S. Patent No. 4,428,845 to Block is directed to a composition for imparting both pseudoplasticity and water loss control to aqueous alkaline systems and to the use of such compositions to form an improved, water-based clay-free drilling fluid. The composition is a combination of (1) an aluminum hydroxy-containing agent similar to that described in U.S. Patent No. 4,366,070; and (2) a reaction product formed in an acidic medium between a polyvinyl alcohol with 0.01 to 0.1% of the stoichiometry of a polyaldehyde. Both polyvinyl alcohol and polyaldehyde are synthetic polymers (made by man), as opposed to polymers that occur naturally. U.S. Patent No. 4,473,479 to Block discloses a composition that is capable of imparting a high degree of pseudoplastic and water loss controlling properties to aqueous systems and to the use of such compositions to form a water-based, clay-free drilling fluid. , improved. The objective composition is a combination of a hydroxy-containing aluminum agent similar to one described in U.S. Patent Nos. 4,428,845 and 4,366,070, and a reaction product formed between a hydroxyalkyl and a crosslinking agent. The crosslinked hydroxyalkyl cellulose reaction product is similar to one described in U.S. Patent No. 4,366,070. U.S. Patent No. 3,988,246 to Hartfiel is directed to an improved clay free well drilling fluid, having thixotropic gel properties for use in underground formations, in which the fluid includes water, a viscosifying amount of a heteropolysaccharide produced by the action of bacteria of the genus Xanthomonas in carbohydrates, a stabilizing amount of magnesium oxide (MgO), an organic starch derivative and a soluble brine-forming salt. In some situations a lignosulfonate salt is added to maintain the desirable properties of the well drilling fluid.

U.S. Patent Nos. 4,025,443 and 4,151,096 to Jackson each disclose an additive composition for use in clay-free, non-clay well drilling fluids, including a hydroxyalkyl guar gum and a magnesia stabilizing amount. and a highly infusible magnesium oxide (MgO), or magnesium hydroxide [Mg (OH) 2]. One theory of the effectiveness of these two patents is that very slightly soluble magnesia, which is present in excess of its solubility in the well drilling fluid, provides a basicity reservoir of just the right amount to maintain the pH of the fluid in the range at which guar gum is more stable. Without the addition of magnesia or magnesium hydroxide, guar gum, which is well known to be unstable or degradable in the neutral pH environment, deteriorates rapidly. U.S. Patent No. 4,422,947 to Dorsey et al is directed to a thixotropic, aqueous, clay-based or clay-free well drilling fluid that has improved fluid loss control, desirable flow characteristics and low slate sensitivity for be used when drilling a well. The fluid includes water or a brine base including an effective amount of an additive including (1) a cross-linked potato starch, cross-linked heteropolysaccharide with a cross-linking compound selected from phosphorus oxychloride or urea-formaldehyde, (2) a heteropolysaccharide derived from a carbohydrate by bacteria of the genus Xanthomonas, and (3) a hydroxyethylcellulose. Such well drilling fluid is either clay-based, or clay-free, but is a brine-based solution containing water-soluble salts, such as sodium chloride (NaCl), calcium chloride (CaCl 2) or potassium chloride (KCl). This patent is also directed to a water-loss control additive, liquid concentrate, for use in water-based or brine-based well drilling fluids with the same composition as that in the dry mix additive previously described. However, the liquid concentrate additive according to this patent contemplates that the carrier is either an alcohol or diesel oil. U.S. Patent No. 5,407,909 to Goodhue, Jr. et al is directed to a method for preparing and using a soil stabilizing fluid comprising (1) adding water to a soil cavity; (2) adding PHPA in dry powder in the cavity; and (3) digging to enlarge the cavity while a portion of dry powdered PHPA is in a transient, partially hydrated, swollen state. In summary, the Block patents, as described above, involve a water-free, clay-free drilling fluid for use in drilling well holes in underground formations having an aqueous mixture consisting of water, an inhibition of loss of water and a viscosifying agent. The viscosifying agent described in each of those patents for Block involves an inorganic compound, for example, aluminum hydroxide in U.S. Patent No. 4,240,915, ferric hydroxide in U.S. Patent No. 4,255,268, magnesium hydroxide in U.S. Patent No. 4,264,455 , and aluminum containing hydroxide in each of U.S. Patent Nos. 4,366,070; 4,428,845; and 4,473,479. Those inorganic viscosifying agents are not biodegradable and some of them are not completely soluble in water. Insoluble or fine particles in the water-based drilling fluid, free of clay but not free of solids, can block or restrict flow through host formations, thus reducing the efficiency of environmental recovery by involving water removal underground contaminated underground formations. The water-based, clay-free drilling fluids described in such Block patents are simply not environmentally acceptable for use in the horizontal horizontal well installation for soil and groundwater recovery. Also in summary, the Hartfiel and Jackson patents, described above, involve viscosifying agents derived from heteropolysaccharides, for example, a heteropolysaccharide produced from carbohydrates with Xanthomonas bacteria in U.S. Patent No. 3,988,246 (to Hartfiel), hydroxyalkylene guar gum in US Pat. 4,025,443 and 4,151,096 (both for Jackson); however, none of these viscosifying agents is stable without the addition of an inorganic compound containing magnesium. Hartfiel and Jackson clay free well drilling fluids are likewise not suitable for horizontal horizontal well installation applications. A heteropolysaccharide crosslinked with phosphorous oxychloride and urea formaldehyde is employed as the viscosifying agent in the above-noted patent for Dorsey et. to the. Urea-formaldehyde and its derivatives are known to be environmentally unfriendly substances.

In addition, the dry additive in this patent was intended to be used in a brine-based completion fluid for oil / gas well drilling and completion work, in which the liquid concentrate is dispersed or suspended in alcohol or diesel oil, without neither is suitable for use in environmental horizontal directional drilling, such as environmental well installation. A synthetic, high molecular weight copolymer of polyacrylamide and polyacrylate when mixed with fresh water, provides a viscous polymer solution for use in geoconstruction drilling, such as drilling well and ditching. This type of wellbore stabilizer fluid, free of clay described in the prior art for Goodhue Jr. et al. it does not show those prerequisite properties of a drilling fluid, such as pseudoplasticity and gel force for suspension of cuts and low fluid loss control capacity. The fluid mentioned in this patent provides only fluid viscosity and cohesion to keep the wellbore drilled from collapses. Without exception, the Goodhue et al patent is only applicable to vertical holes of wells with a limited depth of perhaps 76.2 m. the fluid disclosed in US Pat. No. 5,407,909 is simply not suitable for drilling a particularly directional well bore hole hitherto achieved. Moreover, the copolymer of polyacrylamide and polyacrylate is not considered to be a biodegradable polymer. The copolymer, which forms a deformed mass, hydrated in water, adsorbs strongly on the surface of the formation and covers or encapsulates the formation particles. Encapsulation can cause the flow of host formation to break down. As a result, such fluid is not suitable for use in the installation of environmental horizontal wells for soil and groundwater recovery. Therefore, the main objective of the present invention is to provide a stable, pseudoplastic drilling fluid, free of inorganic salts and free of aqueous clay, which does not damage the formations that house the orifice of the well. It is also another object of the present invention to form an aqueous fluid, free of clay, free of inorganic salts, and biodegradable. which shows non-Newtonian, pseudoplastic properties, in order to be able to drill well holes, particularly horizontal or directional well holes, and the like in an efficient manner. In addition, the object of the present invention is to form a drilling fluid, which is substantially stable at ambient environmental conditions of low pH normally found in drilling well holes. It is still another object of the present invention to form a drilling fluid, which is biodegradable, which does not damage the host formations surrounding the drilled well orifice, which does not block the flow path of the formations. Still, the aim of the present invention is to form a drilling fluid which exhibits high gel strength and low fluid loss properties, in order to be able to drill well holes in an unconsolidated formation.

It is also an object of the present invention to provide a drilling fluid additive consisting of a dry blend of a naturally occurring polymer and a biopolymer. When such a dry mix additive is mixed with an aqueous continuous phase including fresh water and / or acidic water with a low pH, it provides a homogeneous drilling fluid having stable viscosity, sufficient for, hole cleaning, adequate gel strength, particularly initial gel strength for suspension of cuts or debris, and control of low water loss, and a very desirable fluid property when drilling in unconsolidated formations, such as sandy soil. It is a further advantage of the present invention that the drilling fluid formulated with the dry concentrate comprising a mixture of polymers is non-toxic and biodegradable. It is a further advantage of the present invention that this water-based drilling fluid, free of clay, biodegradable, pseudoplastic, is very suitable for drilling horizontal horizontal wells for recovery work. These and other advantages and features of the present invention will become apparent upon reading the following disclosure, description and teachings set forth below.

BRIEF DESCRIPTION OF THE INVENTION The objects of the invention are generally achieved by providing a well-drilling fluid, free of clay, free of inorganic salts, comprising either fresh water or acid water, or mixtures thereof, wherein a dry blend comprising from about 80-90 weight percent of a natural polymer and from about 10-20 weight percent of a synthetic biopolymer is incorporated. More specifically, the preferred embodiment of the present invention contemplates the natural polymer comprising a corn starch polymer or a potato starch polymer, or mixtures thereof, and the synthetic biopolymer comprising Xanthan gum treated with a dispersing agent, for example, glyoxal. As a further feature of the present invention, the drilling fluid can be preserved as a commercially available sodium hypochlorite solution, commonly referred to as bleach.

Still as another feature of the present invention, the drilling fluid can be chemically destroyed with calcium hypochlorite having at least 65% chlorine available. These and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT The composition of the dry mix additive of the present invention preferably contains a naturally occurring, pre-gelatinized polymer such as corn starch in an amount of 80-90 percent by weight, and an anti-aging agent. -sitting such as a type of Xantana biopolymer in an amount from 10-20 percent by weight.

The starch used to formulate the composition preferably comprises a mixture of two types of amylose polysaccharide, a linear polymer and amylopectin, a highly branched polymer. The biopolymer, such as Xantana gum, mixed with the starch, is surface treated with a dispersing agent, eg, glyoxal, to make the Xantana gum easily dispersible in an aqueous medium, thereby minimizing lumps and "fisheyes". " Both the natural polymer and the synthetic polymer involved in the composition of the present invention are biodegradable. The dry mix additive of the present invention, when mixed with an aqueous medium, provides a water-based, clay-free and biodegradable drilling fluid for use in horizontal directional drilling (HDD), particularly useful in the installation of horizontal wells environmental factors for soil and groundwater recovery, because it does not damage the formation that surrounds the orifice of the drilled well and does not block the flow path of the formation. An amount of from 13.15 to 20.86 kg of the dry mix additive according to the present invention is directly mixed with 328.5 x 10"3 3 of fresh water to make 5.44 to 6.804 kg of polymer mixture per barrel of 137.97 x 10" 3 m3 (kg / bbl) of drilling fluid with the desirable rheological properties of fluid for HDD applications. These desirable rheological properties include a ratio of the deformation point (YP) to the plastic viscosity (PV), YP / PV, not less than 1.3 for better orifice cleaning, a 10 minute gel strength of not less than 0.488 kg per m2 (kg / m2) for suspension and transport of efficient cuts, and a loss of API (American Petroleum Institute) fluid of no more than 15 millimeters (ml) for 30 minutes of filtration time (ml / 30 min) for minimize the loss of perforated fluid to the formation of the host, particularly in an unconsolidated sand floor. The plastic viscosity expressed in centipoises, the deformation point expressed in kg / m2, and the gel strength expressed in kg / m2, are determined by ANSI / API RP 13B-1: Standard Procedure for Field Testing Water-based Drilling Fluids , Section 2-viscosity and gel strength. using a viscometer driven by 1 15 volt motor, such as a FANN 35-A V-G Meter. These three rheological fluid properties: YP / PV ratio (>1.3), 10 minute gel strength (> 10), and API fluid loss (> 15) will serve three of the four criteria employed for the optimization of composition formulation according to the present invention. The main function of the starch in the composition of the present invention is to control the loss of fluid or filtration. The starch dispersed and completely deformed, acts in the drilling fluid as a macromolecular colloid. The hydrated starch molecules attack the wall surface of the well bore and bind the formation particles, thereby reducing the permeability of the formation by clogging the interstices with deformable gel particles. As the result of this coating mechanism, the deformable gel particles effectively prevent the drilling fluid from invading the formation of the host and help maintain a stable open orifice by reducing the formation exposure to the drilling fluid. At the same time, this mechanism helps maintain a stable drilling fluid by minimizing the loss of the aqueous phase to the penetrated formations with the corresponding loss of components dissolved in the fluid. The starch coating mechanism also contributes to the successful drilling operation of the drilling fluid by minimizing the dispersion of solids through the perforated coating cuts, as well as by promoting limited flocculation of perforated cuts. A secondary function of the starch in this composition is the support of the rheological properties of the fluid. As a macromolecular colloid, starch can have a noticeable effect in raising the plastic viscosity values while providing lower increases in the values of the point of deformation. In Example 1, the experimental run 1 listed in Table 1 shows that a drilling fluid of 5.44 kg / bbl, which consists only of starch, such as IMPERMEX, marketed by Baroid Drilling Fluids, Inc. of Houston, Texas , in an amount of 100 percent by weight, the rheological properties of the fluid exhibit a low API filtering of 19 ml / 30 min but a very low deformation point and no gel strength. Drilling fluid containing only starch without the addition of another polymer, such as the biopolymer used in the composition of the present invention, does not have those desirable fluid properties for drilling holes through underground formations. A biopolymer (microbial extracellular polysaccharide) such as BARAZAN-D or BARAZAN-D PLUS, marketed by Baroid Drilling Fluids, Inc. of Houston, Texas, was incorporated into the additive composition of the dry blend of the present invention. The main function of such a biopolymer, for example, a Xanthan-type polymer, is to provide the drilling fluid with gel strength suitable for suspending cuts while drilling. The secondary function of the biopolymer is to intensify the rheological properties of the drilling fluid, which consists of water and hydrated starch. The preferred biopolymer used in the composition, sometimes referred to as a modified XC polymer, is preferably treated with a dispersing agent, eg, glyoxal, to facilitate dispersion in an aqueous medium. The polymer XC is used as a rheology modifier since it increases the viscosity in low shear rate flow rates, such as in a well drilling ring, much more than in the higher shear rate flows, such as in the drill pipe and through the nozzle holes. This can result in better hole cleaning while maintaining optimal borehole hydraulics. A drilling fluid having sufficient viscosity to prevent the perforated particles from being separated from the drilling fluid when under the influence of only a low cutting force, is called pseudoplastic fluid. The effect of the biopolymer on drilling fluid in horizontal well drilling is described in an article entitled "Biopolymer Fluids Eliminated Horizontal Well Problems," by M. Seheult, I. Grebe II, J .E. Traweck, Jr. and M. Dudly; published in World Oil®, January 1990. The XC polymer in the composition, when mixed with water, creates viscosity through a network of poly-polymer chains. XC polymer molecules hydrated with this highly branched network structure attribute excellent cut suspension characteristics. This superior suspension due to macromolecular interaction with cuts, is crucial to keep the hole in the well open, especially in high angle sections, diverted from the hole in the well. Guar gum, an edible carbohydrate polymer, which is useful as a thickening agent, has been used in drilling fluids in several major horizontal well installation demonstrations by the Department of Energy with mixed results. In one case, a drilling fluid based on guar gum was used to drill a directional orifice at a vertical depth of 71.62 m in a formation consisting of Quaternary alluvial deposits, which contain clay, silt, sand and gravel. The installation of pit materials and "tremie" pipes went smoothly until the materials were stuck, subtracting 182.88 m. The material eventually broke. The failed installation indicated that the well hole was not sufficiently clean and stabilized before the installation of the well material. The failure was most likely due to the use of guar gum drilling fluid that did not have the gel strength and carrying capacity to remove enough sand and gravel from the depth of the well hole. The case was documented in the article titled "Environmental Horizontal Well Installation and Performance: Lessons Learned," in Horizontal News, Vol. 1, No. 2 published by Colorado Center by Environmental Management by the Department of Energy, Office of Technology Development. Unlike .guar gum, biopolymers such as XC polymer have been used in water-based drilling fluids as additives to drill highly deviated angle holes successfully in loosely compacted formations. Drilling fluids containing XC polymer which exhibit pseudoplastic properties provide the drilling fluid with sufficient viscosity and gel strength for better hole cleaning and transport of effective cut transport. A biopolymer such as XC polymer is, in general, considered to be an expensive drilling fluid additive. A drilling fluid consisting of only polymer XC 5.44 kg / bbl, such as Baroid's BARAZAN D-PLUS exhibits high rheological properties as one (Run 10) shown in Table 1, but can not be economically viable. Therefore, the cost effectiveness of the composition was added as another evaluation criterion in the addition to those previously defined. The composition of the dry mix additive of the present invention when mixed with an aqueous medium such as fresh water or acid water at a concentration of 5.44 kg / bbl (pounds of dry polymer mixture per 137.97 x 103 cubic meters of water) provides a drilling fluid based on water, free of clay and biodegradable, where the rheological properties of fluid meet the three criteria, ie the proportion of YP / PV equal to or greater than 1.3, 10-minute gei force equal to or greater than 0.488 kg / m2, and API Standard fluid loss equal to or less than 15 ml / 30 minutes; and the fourth criterion, that is, the estimated cost or economic factor equal to or less than $ 1 .00 (dollar) per 0.4536 kg. A "barrel" of drilling fluid, for purposes of the present, is 137.97 x 10"3 m 3 of liquid.The dry mix additive of the present invention is prepared by conventional dry mixing process. It is critical, however it is advisable to obtain a homogeneous mixture by mixing the biopolymer in the natural polymer.According to conventional wisdom, a biocide is frequently added to the drilling fluids., which are subject to bacterial degradation under environmental conditions. Microbial growth can result in a loss of viscosity and therefore fluid functionality. This is frequently the case of a drilling fluid consisting of natural polymers and / or biopolymers. Although the biopolymer used in the present invention is a complex branched heteropolysaccharide and is more resistant to bacterial attack than the natural polymer such as corn starch, the biopolymer is subject to bacterial degradation at a much slower rate. It has been found that with a small addition of commercially available liquid bleach containing 5.25% (home grade) or 12.5% (industrial grade) of sodium hypochlorite, the drilling fluids containing the dry blend of the present invention increase the resistance to bacterial attack. and still maintain the properties of fluids for a prolonged period of time without adding any biocide, which frequently causes some environmental concerns due to their toxicity. It has also been found that a subsequent addition, that is, after the perforation is finished, of dry granular calcium hypochlorite to the drilling fluids containing the dry blend of the present invention, will chemically degrade the polymers in the drilling fluids within. of a few days and consequently, an aqueous solution of calcium hypochlorite is used as a development fluid to create the horizontal environmental well after the well orifice was drilled with the drilling fluids containing the composition of the present invention. The following examples are given to illustrate the invention but should not be considered as limiting thereof. All percentages given are based on weight unless otherwise indicated. All measurements were made in accordance with American Petroleum Institutes Recommended Practice Standard Procedure for Field Testing Water-Based Drilling Fluids identified as API Recommended Practice 13B-1 (RP13B-1) First Edition, June 1, 1990.

EXAMPLE 1 Runs 1 to 10 It is important to optimize the distribution of the weight percentage of the two polymers in the composition of the present invention, in order that the dry mix additive, when added to fresh water, will provide a drilling fluid based on water with maximum effectiveness. The optimization was conducted by determining the rheological properties of the fluid from a series of the polymer pastes, each containing 5.44 kg / bbl of a dry mix additive consisting of the two polymers (one natural, one biopolymer) with distribution of variant weight percentage. A polymer, hereinafter referred to as polymer 1, selected for optimization, is a corn starch under the trade name IMPERMEX, which is marketed by Baroid Drilling Fluids, Inc. in Houston, Texas. Another polymer, hereinafter referred to as polymer 2, selected for optimization, is a biopolymer with a trade name of BARAZAN D-PLUS, which is also marketed by Baroid Drilling Fluids, Inc. in Houston, Texas. The total weight percentage of the two polymers in each composition should generally be equal to 100% of the mixture. Table 1 (Runs 1 to 10) lists the rheological properties of the fluid of each polymer paste for optimization. Table 2 summarizes the optimization results and shows which polymer pastes with the rheological properties satisfy the three predetermined evaluation criteria - YP / PV ratio (> 1 .3), gel strength of 10 minutes (> 0.488 kg / m2), and loss of API fluid (> 15 ml / 30 minutes), and with the economic value, satisfy the fourth criterion - cost (> $ 1 .00 / 0.4536 kg). The results of the optimization conclude that the preferred weight percent range of polymer 1 (I MPERMEX) should be from 80-90 percent by weight, and for polymer 2 (BARAZAN D-PLUS) the percentage by weight range should be from 10-20 percent by weight.

TABLE 1 OPTIMIZATION OF TWO POLYMER COMPONENTS Corrida 1 8 Polymer 1,% by weight 100 95 92 90 88 85 82 80 Polymer 2,% by weight 0 5 8 10 12 15 18 20 Paste, kg / bbl 5.44 5.44 5.44 5.44 5.44 5.44 5.44 5.44 Rheolatoic properties of the paste 600 rpm 16 31 42 49 56 66 76 78 300 rpm 9 21 30 35 41 49 58 60 Plastic viscosity, cP 7 20 12 14 15 17 18 18 Deformation point, 0.097 0.536 0.878 1 .024 1 .268 1 .561 1 .952 .. 2.04 kg / m2 Gel of 10 sec. 0 3 7 9 12 16 20 21 min gel 0 4 8 12 15 20 25 27 YP / PV 0.3 1 .1 1 .5 1 .5 1.7 1 .9 2.2 2.3 Filtering (API), ml / 30 min 19 1 1 1 1 12 12 15 14 12 Cost, $ / 0.4536 kg 0.22 0.38 0.47 0.53 0.6 0.69 0.79 0.85 Polymer 1, such as IMPERMEX from Baroid Polymer 2, such as BARAZAN D-PLUS TABLE 2 DETERMINATION OF THE PREFERRED COMPOSITIONS Run 1 2 3 4 5 6 7 8 9 10 Polymer 1, < Me by weight 100 95 92 90 88 85 82 80 50 0 Polymer 2, c Me by weight 0 5 8 10 12 15 18 20 50 100 Criteria YP / PV (= 1 .3) No Yes Yes Yes Yes Yes Yes Yes Yes Yes 10 min gel No No No Yes Yes Yes Yes Yes Yes Yes (> 0.488kg / m2) API filtering (> 15 ml / 30 No Yes Yes Yes Yes Yes Yes Yes No No min) t Cost (= $ 1 /0.4536 kg) Yes Yes Yes Yes Yes Yes Yes Yes No No EXAMPLE 2 Runs 1 to 13 It has been found that the dry mix additive of the present invention, when acidic acid with pH of the solution below 7.0 is added to aqueous medium, provides a water-based drilling fluid, free of clay and biodegradable with the rheological properties of fluid that meet the evaluation criteria. Table 3 (Runs 1 1 to 13) illustrates 5.44 kg of dry mix per barrel with the preferred composition of the dry mix added to two aqueous solutions with pH of the solution adjusted to pH values of 4.1 (Run 12) and 2.2. (Run 1 1) with sulfuric acid. The rheological properties of the fluid of these two acid pastes were compared with those of the paste at the same concentration with the pH of the solution of 8.6 (Run 13). Table 3 shows that the rheological properties of fluid even in an acidic environment such as pH 2.2, still meet those predetermined evaluation criteria. The composition of the present invention is useful for use in horizontal directional drilling, particularly in an environment with acidic contaminants.

TABLE 3 EFFECT OF THE pH OF THE SOLUTION ON THE RHEOLOGICAL PROPERTIES OF THE FLUID OF THE PASTAS, CONSISTING OF 5.44 kg / bbl EACH OF THE DRY MIXTURE OF THE PRESENT INVENTION Corrida 1 1 12 1 3 Fresh water, bbl 1 1 1 pH adjusted 2.2 4.1 8.6 Present invention, kg / bbl 5.44 5.44 5.44 Rheological properties 600 rpm 76 59 56 to 300 rpm 55 42 41 PV, cP 21 17 15 YP, kg / m2 1,659 1.22 1,268 YP / PV 1.6 1.5 1.7 10 min gel, kg / m2 0.634 0.732 0.732 Filtration (API), ml / 30 min 7 15 12 EXAMPLE 3 Runs 14 to 16 It was found that the water-free, clay-free drilling fluid consisting of the dry mix additive of the present invention is biologically degraded through a microbial attack. It can also be chemically destroyed with the addition of calcium hypochlorite solution. The calcium hypochlorite used for the degradation study is a solid solid oxidant containing 65% available chlorine. Table 4 (Runs 14 to 16) shows the results of the addition of varying amounts of calcium hypochlorite to the aqueous pastes, each containing 3.62 kg per barrel (kg / bbl) of the dry mix additive of the present invention. The addition of calcium hypochlorite caused the rheological properties of the pulp fluids to decrease with respect to the time after mixing. The decrease in the rheological properties of the fluids is due to the degradation of the polymers in the composition through an oxidation reaction. ft TABLE 4 DEGRADATION OF THE COMPOSITION OF THE PRESENT INVENTION BY SODIUM HYPOCHLORITE EXAMPLE 4 A water-free, clay-free drilling fluid containing the dry mix additive of the present invention was tested under a field application in Clarke County, Georgia. The project involved the drilling of a 261.82 m directional well with a horizontal section of 182.88 m, and the installation of a high density polyethylene well net of 176.78 m at a vertical depth of 20.42 m. The horizontal well is going to be used to recover in situ groundwater from petroleum hydrocarbons. The area through which the hole was drilled horizontally consisted of two types of formation: gravel and sand (soft) unconsolidated, and gneiss biotic (hard) without acclimatization. The paste, which consisted of the composition of the present invention, v / z, 80-90% starch and 10-20% Xanthan gum, was chosen as the preferred drilling fluid for use in this horizontal directional environmental well installation , because the drilling fluid shows the following properties suitable for the application: high viscosity at low cutting speeds (pseudoplasticity) to transport solids under a variety of ring conditions, the high gel force profile for maximum cut suspension, and low API filtration rate for minimal fluid loss, particularly in unconsolidated gravel and sand. Another reason why the drilling fluid of the present invention was preferred is because the drilling fluid is a clay-free paste, which does not form a wall cake that tends to clog the tracks, and also prevents contaminants from The plume is pumped out of the contaminated area. A pilot hole with a diameter of 25.08 cm was drilled to a total measured depth of 77.41 m at an angle of 18.9 ° with a drilling fluid based on bentonite. The clay paste (bentonite) was replaced with the biodegradable, clay-free drilling fluid of the present invention while constructing an angle at a total vertical depth of 20.42 m. Approximately 70 barrels of the drilling fluid of the present invention at 5.44 to 6.804 kg / bbl were prepared on the surface. After 15 to 20 minutes of circulation, the bentonite paste in the well bore was replaced with the drilling fluid of the present invention. The polymer paste that returns to the sludge tank transported at least 30% of the total drilled solids. The remaining 182.88 m of the horizontal section of the hole was drilled with the polymer paste of the present invention at a maximum deviation of 92.4 °. The drilling fluid has the rheological properties of the fluid as follows: Present invention, kg / bbl 5.44 to 6.804 Viscosity of the tunnel, second / fourth 65 to 70 Plastic viscosity, cP 15 to 20 Deformation point, kg / m2 1 .268 to 1 .708 Gel of 10 seconds, kg / m2 0.585 a 0.732 Gel of 10 minutes, kg / m2 0.732 to 0.976 Proportion YP / PV 1.73 to 1.75 Loss of API fluid, ml / 30 minutes 8.5 to 12 While perforating the horizontal section of the hole, the penetration rate was reduced due to the change from unconsolidated soil formation to a hard biotite gneiss rock. The cuts, coming from an agitator equipped with two sieves, mesh 24 and 30 respectively, appeared to be free of the drilling fluid. Unlike cuts joined with clay particles or sticky synthetic polymers, such as when the clay paste of the high molecular weight synthetic polymer paste is used as the drilling fluid, the cuts suspended in the drilling fluid of the present invention did not absorb much of the active polymers in the paste. The cuts appeared clean, as they would have been rinsed with water or they would never have been exposed to the drilling fluid. The active polymers in the drilling fluid of the present invention provide the paste with viscosity for hole cleaning and gel strength suitable for transporting cuts, but did not cover the surface of the cuts as firmly as it is compared to a weighty synthetic polymer. high molecular The perforation continued horizontally without difficulty and the maximum thrust pressure remained below 56.24 kilograms per square centimeter (kg / cm2). The drilling operation was completed after the 28th union of the drill pipe was pushed. The actual measured depth of the hole was 262.79 m with a horizontal section of 185.31 m. After the pilot was finished as planned, the drill string was removed from the hole and the installation of the horizontal well began. The installation of the horizontal well involved thirty junctions of 6.096 m of H DPE slotted mesh of 15.24 cm in diameter in the horizontal section of the drilled hole (185.31 m) and another twenty joints of 6.096 m of the HDPE pipe of the same diameter in the inclined section of the drilled hole (77.41 m). No difficulty was encountered during the installation of the well. The development of the well took place immediately after the completion of the installation of the horizontal well. The first pumping test was carried out with the anticipation of a maximum flow velocity of 95.55 x 103 m3 per minute. Surprisingly, a real flow velocity of 197.1 x 10"3 m3 per minute was obtained after 12 hours of pumping time.To ensure the minimum amount of residual polymers remaining in the well bore, an aqueous solution was used. calcium hypochlorite as a means to degrade the remaining polymers chemically, even though it is known that the active polymers in the composition of the present invention are biodegradable.Another pumping test was performed after the hypochlorite solution was circulated. Calcium through well drilling Groundwater contaminated with gasoline was removed and pumped out of the hole to a designated tank on the surface of the land for recovery The project was considered a success.

EXAMPLE 5 The drilling fluid of the present invention was still used in another field test application related to horizontal environmental wells installed in Hamilton, Mississippi. The project involved the installation of five horizontal environmental wells with well screens of approximately 137.16 to 152.4 m each to extract the saline water, which was leaking from a pond that maintained 4942.1 to 7413.15 m2 in a marshy area under a dike . The actual vertical depth of each well is approximately 9,144 m below the dike. The drilling fluid of the present invention, v / z, 80-90% natural starch and 10-20% Xanthan gum, was chosen as the drilling fluid to drill these continuous well bores because the drilling fluid of the present invention was used successfully in several previous applications similar to this one. The dry mix additive of the present invention provides a biodegradable drilling fluid to efficiently drill the hole of the horizontal directional well and does not block the pore spaces of the host formation. After the drilling fluid of the present invention was mixed in a tank of 150 barrels at 5.44 to 6.35 kg / barrel of the dry mix additive, a 22.22 centimeter pilot hole was drilled using Digit Track as the guidance system. At the entrance and exit (1 12.77 m) clay was drilled and the horizontal section consisted of coarse to medium sand. At the time of drilling at 144.78 meters, the depth measurement (MD) signals were lost and it was thought that the batteries in the probe ran out. The drill pipe was removed and the batteries in the probe were changed. The lower orifice assembly (BHA) and the drill pipe were sent back to the hole without pumping. This indicated that the hole drilled with the drilling fluid of the present invention remained open without unconsolidated sand. Drilling continued with marking at 266.7 m MD. The hole was enlarged to 41.91 centimeters without any problem. The 17.78-centimeter product line (SCHUMASOIL H DPE VHB-3) was gently pulled into a 25.4 cm HDPE carrier pipe in 2.5 hours. Fifty barrels of fresh water with 0.1 13 kg / bbl of calcium hypochlorite were pumped into the line to destroy the polymer combination of the present invention. The 25.4-centimeter HDPE carrier pipe was unlocked from the 17.78 product line and pulled out with a bulldozer in approximately 4 minutes. The contractor drilled this well with an American Augers DD-70 equipped with a 150-barrel mixing tank with a slate separator agitator, 2 cone sandders on a 120-mesh linear stirrer, and 9 cone desiccators on a linear agitator 120 mesh. This provides excellent solids control. Approximately 39,237 m3 of sand were separated from the drilling fluid. The sand was extremely dry without any gummy residue. Apparently he was free of the drilling fluid. Approximately one hour after the 25.4 cm carrier pipe was removed from the hole, the well began to flow at 13.14 x 103 m3 per minute outside the mesh elevator on the inlet side (elevator the mesh elevator was below the level of water in the holding pond). According to the calculation by the consultant in charge, the hydraulic conductivity of the host formation did not change (decreased) after being exposed to the drilling fluid. The results indicated that the drilling fluid of the present invention does not alter the porosity or the permeability of the formation.

The invention can be incorporated into other specific forms without departing from the spirit or essential characteristics thereof. The above embodiments are to be considered, accordingly, in all respects, as illustrative and not restrictive, of the scope of the invention being indicated by the appended claims, rather than by the foregoing description, and all changes that are within the scope of the invention. The meaning and range of equivalence of the claims are, therefore, to be included in it.

Claims (43)

1. CLAIMS 1 . A clay-free drilling fluid, free of inorganic salts, based on water for use in drilling and recovering environmentally contaminated soil formations, comprising fresh water as the continuous phase of said drilling fluid and a dry mixture added to said fresh water, said dry mix including a natural polymer comprising from about 80-90 weight percent of the mixture and a synthetic biopolymer comprising from about 10-20 weight percent of the mixture.
2. 2. The drilling fluid according to claim 1, wherein said dry mix is added to said fresh water in quantities of 5.44-6.804 kg of dry mix per barrel of 137.97 x 103 m3 of fresh water.
3. 3. The drilling fluid according to claim 1, wherein said natural polymer comprises a heteropolysaccharide.
4. 4. The drilling fluid according to claim 3, wherein said heteropolysaccharide comprises pre-gelatinized maize starch.
5. 5. The drilling fluid according to claim 1, wherein said synthetic biopolymer comprises Xanthan gum.
6. The drilling fluid according to claim 1, wherein said natural polymer comprises a heteropolysaccharide of pre-gelatinized corn starch and said synthetic biopolymer comprises Xanthan gum.
7. 7. The drilling fluid according to claim 5, wherein said Xanthan gum has been treated with a dispersing agent.
8. 8. The drilling fluid according to claim 7, wherein said dispersing agent comprises glyoxal.
9. The drilling fluid according to claim 1, wherein said drilling fluid has a deformation point to plastic viscosity ratio of at least 1.3, a gel strength of 10 minutes of at least 0.488 kg / m2 and a Fluid loss of no more than 15 millimeters per 30 minutes of filtration measured at 7.03 kg / cm2.
10. 10. The drilling fluid according to claim 1, wherein said fluid exhibits pseudoplastic, non-Newtonian characteristics. eleven .
11. A clay-free drilling fluid, free of inorganic salts, based on water, for use in drilling and recovering environmentally contaminated soil formations, comprising acidic water as the continuous phase of said drilling fluid and a dry mixture added to said acidic water said dry mix including a natural polymer comprising from about 80-90 weight percent of the mixture and a synthetic biopolymer comprising from about 10-20 weight percent of the mixture.
12. 12. The drilling fluid according to claim 1, wherein said dry mixture is added to said acid water in quantities of 5.44-6.804 kg of dry mixture per barrel of 137.97 x 103 m3 of acidic water.
13. 13. The drilling fluid according to claim 1, wherein said natural polymer comprises a heteropolysaccharide.
14. 14. The drilling fluid according to claim 13, wherein said heteropolysaccharide comprises pre-gelatinized maize starch.
15. 15. The drilling fluid according to claim 1, wherein said synthetic biopolymer comprises Xanthan gum.
16. 16. The drilling fluid according to claim 1, wherein said natural polymer comprises a pre-gelatinized corn starch heteropolysaccharide and said synthetic biopolymer comprises Xanthan gum.
17. 17. The drilling fluid according to claim 16, wherein said Xanthan gum has been treated with a dispersing agent.
18. 18. The drilling fluid according to claim 17, wherein said dispersing agent comprises glyoxal.
19. 19. The drilling fluid according to claim 1, wherein said drilling fluid has a deformation point to plastic viscosity ratio of at least 1 .3, a gel strength of 10 minutes of at least 0.488 kg / m2 and a fluid loss of no more than 15 millimeters for 30 minutes of filtration measured at 7.03 kg / cm2.
20. 20. The drilling fluid according to claim 1 1, wherein said fluid exhibits pseudoplastic, non-Newtonian characteristics.
21. 21. A clay-free, water-based drilling fluid for use in drilling and recovering environmentally contaminated soil formations, comprising either fresh water or acid water as the continuous phase of said drilling fluid and a dry mixture added to said water of continuous phase, said dry mix including a natural polymer comprising from about 80-90 weight percent of the mixture, a synthetic biopolymer comprising from about 10-20 weight percent of the mixture and an effective amount of sodium hypochlorite to increase the resistance of the polymers in said mixture to bacterial degradation.
22. 22. The drilling fluid according to claim 21, wherein said dry mix is added to said continuous phase in amounts of 5.44-6.804 kg of dry mix per barrel of 137.97 x 103 m3 of continuous phase water.
23. 23. The drilling fluid according to claim 21, wherein said natural polymer comprises a heteropolysaccharide.
24. 24. The drilling fluid according to claim 23, wherein said heteropolysaccharide comprises pre-gelatinized maize starch.
25. 25. The drilling fluid according to claim 21, wherein said synthetic biopolymer comprises Xanthan gum.
26. 26. The drilling fluid according to claim 21, wherein said natural polymer comprises a pre-gelatinized corn starch heteropolysaccharide and said synthetic biopolymer comprises Xanthan gum.
27. 27. The drilling fluid according to claim 26, wherein said Xanthan gum has been treated with a dispersing agent.
28. 28. The drilling fluid according to claim 27, wherein said dispersing agent comprises glyoxal.
29. 29. The drilling fluid according to claim 21, wherein said drilling fluid has a deformation point to plastic viscosity ratio of at least 1 .3, a gel strength of 10 minutes of at least 0.488 kg / m2. and a fluid loss of no more than 15 millimeters per 30 minutes of filtration measured at 7.03 kg / cm2.
30. 30. The drilling fluid according to claim 1, wherein said fluid exhibits pseudoplastic, non-Newtonian characteristics.
31. 31. A dry mix for use in a water-based drilling fluid, comprising: a natural polymer comprising about 80-90 percent by weight of the mixture; and a synthetic biopolymer comprising from about 10-20 percent by weight of the mixture.
32. 32. The dry blend according to claim 31, further comprising therein, an effective amount of sodium hypochlorite to increase the resistance of the polymers in said mixture to bacterial degradation.
33. 33. The dry blend according to claim 31, wherein said natural polymer comprises a heteropolysaccharide.
34. 34. The dry blend according to claim 33, wherein said heteropolysaccharide comprises pre-gelatinized maize starch.
35. 35. The dry blend according to claim 31, wherein said synthetic biopolymer comprises Xanthan gum.
36. 36. The dry blend according to claim 31, wherein said natural polymer comprises a pre-gelatinized corn starch heteropolysaccharide and said synthetic biopolymer comprises Xanthan gum.
37. 37. The dry mix according to claim 36, wherein said Xanthan gum tha has been treated with a dispersing agent.
38. 38. The dry mixture according to claim 37, wherein said dispersing agent comprises glyoxal.
39. 39. A method for drilling and recovering an environmentally contaminated soil formation, comprising: drilling a well hole in a ground formation using a drilling fluid, comprising either fresh water or acid water as the continuous phase of said drilling fluid and a dry mixture added to said continuous phase water, wherein said dry mix includes a natural polymer comprising from about 80-90 weight percent and a synthetic biopolymer comprising from about 10-20 weight percent of the mixture.
40. 40. The method according to claim 39, wherein said dry mix also includes an effective amount of sodium hypochlorite to increase the resistance of the polymers in said mixture to bacterial degradation.
41. 41 The method according to claim 39, including the additional step, after drilling said well hole, of discharging said well orifice with an aqueous solution containing calcium hypochlorite in amounts of approximately 0.1 13-0.226 kilograms of granular calcium hypochlorite. dry per barrel of 137.97 x 10"3 m3 of water
42. 42. The method according to claim 41, wherein said calcium hypochlorite has 65% available chlorine concentration
43. 43. The method according to claim 39, including the additional step of removing fluid from the contaminated formation from said well orifice. SUMMARY A dry mix additive, which is used to form a clay free well drilling fluid, ie, non-clayey, free of inorganic salts, that is, not of brine, biodegradable and chemically degradable, based on water, which is capable of imparting non-Newtonian, pseudoplasticity and fluid loss controlling properties to aqueous systems, for use in Directional horizontal drilling, which finds utility in the installation of horizontal environmental wells for soil and groundwater recovery. The dry blend comprises (1) from about 80-90 by weight of pre-gelatinized corn starch heteropolysaccharide, and (2) from about 10-20 by weight of a synthetic biopolymer, such as Xanthan gum treated with a synthetic agent. dispersion (glioxai) to facilitate dispersion. Sodium hypochlorite may be added, if desired, to the well drilling fluid to provide resistance to bacterial attack. The dry mix is added either to fresh water or acid water in quantities of 5.44 to 6.804 kg of the dry mix to a barrel (137.97 x 10'3 m3) of water and then used as a drilling fluid when drilling horizontal wells for recovery of ground and groundwater. Also, if desired, calcium hypochlorite can be circulated through the hole in the well following the drilling operation to accelerate the degradation of the polymers in the well drilling fluid. Following the hole drilling in the well, the contaminated formation fluids are removed from the hole in the well.