New Environmentally Friendly Fluid to Remove Mn3O4 Filter Cake

Disclosed is a two-stage filter cake removal composition, and method of use thereof, for use in a wellbore for controlled removal of a filter cake present in a target production zone. The two-stage filter cake removal composition may include an enzyme present in an amount of between about 1% and 10%, and a glycolic acid in amounts of between about 1% and 10% by weight. Optionally, hydrochloric acid may be added to the glycolic acid, in an amount of about 1 and 5% by weight. The two-stage filter cake removal composition, when the enzyme is applied to the filter cake in the target production zone in a first stage and the glycolic acid is applied to the filter cake in the target production zone in a second stage, is operable to remove the filter cake in the target production zone over a predetermined extended reaction time.

DETAILED DESCRIPTION OF THE INVENTION

Although the following detailed description contains many specific details for purposes of illustration, it is understood that one of ordinary skill in the relevant art will appreciate that many examples, variations, and alterations to the following details are within the scope and spirit of the invention. Accordingly, the exemplary embodiments of the invention described herein are set forth without any loss of generality, and without imposing limitations, relating to the claimed invention.

As used herein, the term “drilling fluid” shall be used to collectively refer to a completion fluid or a drilling fluid. As understood in the art, “drilling fluid” shall be used to describe a fluid used to aid in the drilling of a borehole for a well (e.g., a horizontal/multilateral well). The drilling fluid may include a water-based mud (e.g., a dispersed or non-dispersed water-based mud), a non-aqueous mud (e.g., an oil-based mud), and a gaseous drilling fluid.

It has been observed that, in normal operations, the Mn3O4particles of the filter cake are covered with polymeric material (e.g., starch), which significantly reduces the solubility of the filter cake in the organic acids. Therefore, there is a need to remove the polymeric material on the Mn3O4particles of the filter cake to more effectively dissolve or remove the filter cake material in the wellbore. Embodiments of the invention provide for the application of an enzyme (i.e., an enzyme that catalyzes the breakdown of starch into sugars) to remove the polymeric material present on the Mn3O4particles of the filter cake.

Glycolic acid has a unique set of properties that makes it ideal for a broad range of applications. Glycolic acid has a dissolving power that is comparable to lactic acid. Additionally, glycolic acid exhibits low corrosion to most common metals, is environmentally friendly, and biodegrades at a rate of 90% in 7 days.

Embodiments of the invention provide a two-stage filter cake removal composition, and method of use thereof, for use in the wellbore for controlled removal of the filter cake present in the target production zone. Generally, the two-stage filter cake removal composition includes an enzyme and a glycolic acid. The two-stage filter cake removal composition, when the enzyme is delivered or applied to the filter cake in the target production zone in a first stage and the glycolic acid is applied to the filter cake in the target production zone in a second stage, is operable to remove the filter cake in the target production zone over a predetermined extended reaction time. Subsequently, the delivery or application of the two-stage filter cake removal composition is operable to control fluid loss from the wellbore into the target production zone.

Another embodiment of the invention relates to a method for the controlled removal of a filter cake from a target production zone of a wellbore using a two-stage filter cake removal composition. In the method, the two-stage filter cake removal composition is delivered to the target production zone. The two-stage filter cake removal composition contacts the filter cake for a predetermined extended reaction time during which extended time the two-stage filter cake removal composition acts to remove the filter cake and after which predetermined extended reaction time the two-stage filter cake removal composition acts to control fluid loss from the wellbore into the target production zone. In this method, the delivering comprises applying an enzyme of the two-stage filter cake removal composition to the filter cake in the target production zone in a first stage and applying a glycolic acid of the two-stage filter cake removal composition to the filter cake in the target production zone in a second stage.

In accordance with another embodiment of the invention, the glycolic acid is present in an amount of about 10% by weight, preferably in an amount of between about 2 and 6% by weight, more preferably about 5% by weight, and most preferably about 4% by weight. According to an embodiment of the invention, the glycolic acid may also be mixed with hydrochloric acid. When mixed with hydrochloric acid, the glycolic acid is present in an amount of between about 4% and 10% by weight. The hydrochloric acid is present in an amount of between about 1-5% by weight.

Another embodiment of the present invention is a one-stage filter cake removal composition for use in a wellbore for controlled removal of a filter cake present in a target production zone, the one-stage filter cake removal composition comprising a glycolic acid and a hydrochloric acid. In this one-stage filter cake removal composition, when the glycolic acid and the hydrochloric acid are applied to the filter cake in the target production zone in a single stage, the composition is operable to remove the filter cake in the target production zone over a predetermined extended reaction time. This predetermined extended reaction time can be up to 16 hours. In this one stage approach, different acid concentrations may be used than in the two stage approach. For instance, 4% by weight glycolic acid and 2% by weight hydrochloric acid are usually sufficient to yield comparable results as 5% by weight glycolic acid used in a two stage treatment process.

According to an embodiment of the invention, about 10% by weight glycolic acid may dissolve, in a two-stage filter cake removal treatment of the filter cake, about 85% by weight of the Mn3O4-based filter cake after about 18-22 hours of soaking at a temperature of about 250° F. and a pressure of about 250 psi.

According to an embodiment of the invention, about 4% by weight glycolic acid mixed with 1% by weight of hydrochloric acid may dissolve, in a one-stage filter cake removal treatment of the filter cake, about 90% by weight of the Mn3O4-based filter cake after about 18-22 hours of soaking at a temperature of about 250° F. and a pressure of about 250 psi.

In accordance with an embodiment of the invention, the enzyme includes an enzyme that catalyzes the breakdown of starch into sugars to remove the polymeric material present on the Mn3O4particles of the filter cake for more effectively dissolving or removing the filter cake material in the wellbore. According to an embodiment of the invention, the enzyme includes an amylase enzyme present in an amount of between about 1% and 10% by weight. The amylase enzyme may include, for example, an α-amylase enzyme, a β-amylase enzyme, or a γ-amylase enzyme. In a preferred embodiment, the enzyme of the two-stage filter cake removal composition is an α-amylase enzyme present in an amount of about 10% by weight. In some embodiments, a stabilizer can be added to the enzyme composition.

In accordance with certain embodiments of the invention, the enzyme is applied to the filter cake in the target production zone for a first predetermined period of time based on one of a characteristic of the filter cake, an enzyme type, concentration of the enzyme, and the thermal stability of the enzyme. For example, the enzyme may be applied to the filter cake for a first predetermined period of time of up to about 24 hours, preferably for about 16-24 hours, and more preferably about 20 hours.

In accordance with certain embodiments of the invention, the glycolic acid or glycolic acid and hydrochloric acid composition is applied to the filter cake in the target production zone for a second predetermined period of time. For example, the glycolic acid or glycolic acid and hydrochloric acid composition may be applied to the filter cake for a second predetermined period of time of up to about 24 hours, preferably for about 16-24 hours, and more preferably about 20 hours.

In accordance with certain embodiments of the invention, the concentrations of the enzyme, the glycolic acid, and the hydrochloric acid are based on one or more factors, including, but not limited to, the reservoir temperature, formation mineralogy and composition, filter cake characteristics and composition, enzyme activity, and thermal stability.

EXAMPLES

The examples described below show certain exemplary embodiments of the filter cake removal composition of the present invention, as described herein. As shown in Table 1, water-based drilling fluids primarily weighted with Mn3O4and a small amount of CaCO3particles to control a leak-off rate were prepared to demonstrate the efficacy of the filter cake removal composition, in accordance with certain embodiments of the invention, for dissolving or removing filter cake material in a wellbore. Xanthan, starch, and polyanionic cellulose (PAC-R) polymers were added to the mud to control fluid loss and rheological properties of the drilling fluid. Potassium hydroxide (KOH) was added to adjust the pH of the drilling fluid. Sodium sulfite (Na2SO3) was added to the drilling fluid as an oxygen scavenger.

Table 2 summarizes the main properties of the prepared manganese-tetraoxide-based drilling fluid shown above in Table 1.

According to various embodiments of the invention, glycolic acid is effective for dissolving Mn3O4particles and the Mn3O4-based filter cake. For example, as shown in Table 3, glycolic acid effectively dissolves Mn3O4particles. A 4% by weight composition of glycolic acid dissolved Mn3O4particles with up to 76% by weight at 190° F. Adding 1% by weight of hydrochloric acid to 4% by weight of glycolic acid increased dissolved solids to 99%. The effect of 4% by weight of glycolic acid on manganese ion concentration is further shown inFIG. 1.

Certain embodiments of the invention provide a two-stage filter cake removal composition for controlled removal of a filter cake present in a target production zone. As previously discussed above, Mn3O4particles in the filter cake may be covered with polymeric material (e.g., starch), which significantly reduces the solubility of the filter cake in organic acids. In order to remove the polymeric material, embodiments of the invention provide a two-stage filter cake removal composition which includes the application of an enzyme in a first stage and the application of a glycolic acid in a second stage.

Experimentation demonstrated that an amylase enzyme in an amount of about 10% by weight and a stabilizer in a first stage soaking of about 20 hours followed by glycolic acid (10% by weight) dissolved 88% by weight of the filter cake at about 250° F. (121° C.) and 300 psi, after soaking the filter cake in the organic acid for about 16 hours (seeFIG. 3).

Experimentation demonstrated that glycolic acid (4% by weight) and hydrochloric acid (1% by weight) dissolved 87% by weight of the Mn3O4-based filter cake after 18 hours of soaking time at about 250° F. (121° C.) and 300 psi, in a one-stage treatment process, as shown inFIG. 4.

Samples also showed that the retained permeability was 100%, as shown inFIG. 5. The limestone samples shown inFIG. 5were Indiana limestone cores (LM) and the sandstone sample was a Brea sandstone core (SS). The Indiana limestone were cut from a block with an average porosity 23 vol % and an average permeability of 3-5 mD. The Brea sandstone core had an average porosity of 15 vol % and an average permeability of 50-60 mD. The SS sample, and LM samples 1 and 2 were treated with 10 wt % glycolic acid. LM sample 3 was treated with 5% glycolic acid.

Embodiments of the present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

Unless defined otherwise, all technical and scientific terms used have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Although the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereupon without departing from the principle and scope of the invention. Accordingly, the scope of the present invention should be determined by the following claims and their appropriate legal equivalents.