The present invention relates to fluids and compositions useful in subterranean operations, and more particularly, to additives and treatment fluids with improved shale inhibition, and associated methods of use.
A treatment fluid may be used in a variety of subterranean operations. As used herein, the term “subterranean operation” is defined to mean any operation that requires the performance of some action or procedure below the surface of the earth, including, but not limited to, actions or procedures performed in the course of recovering oil, gas, and/or other substances from a formation below the surface of the earth. Such subterranean operations also include, but are not limited to, service line and tunneling operations. As used herein, the term “treatment,” or “treating,” does not imply any particular action by the fluid or any particular component thereof, but instead refers to any use related to a subterranean operation in conjunction with a desired function and/or for a desired purpose. For example, a fluid may be used to drill a well bore in a subterranean formation or to complete a well bore in a subterranean formation, as well as numerous other purposes.
Drilling operations may involve any number of different techniques known and practiced in the art. In the most basic sense, rotary drilling operations typically involve attaching a drill bit on a lower end of a drillstring to form a drilling tool and rotating the drill bit along with the drillstring into a subterranean formation to create a well bore through which subsurface formation fluids may be recovered. In another method of drilling, coiled tubing may be used instead of jointed pipe and the drill bit may be rotated using a downhole motor. The process of drilling a well bore typically requires the use of a drilling fluid. Drilling fluids are used, inter alia, to cool the drill bit, lubricate the rotating drill pipe to prevent it from sticking to the walls of the well bore, prevent blowouts by serving as a hydrostatic head to counteract the sudden entrance into the well bore of high pressure formation fluids, and remove drill cuttings from the well bore. A drilling fluid used in connection with drilling a well in a subterranean formation may be any fluid substance (gaseous or liquid) or a mixture of fluids and solids (such as solid suspensions, mixtures and emulsions of liquids, gases and solids).
During drilling of subterranean well bores, it is not uncommon to encounter various strata that comprise reactive shales. As used herein, the term “shale” is defined to mean materials that may “swell,” or increase in volume, when exposed to water. Examples of these shales include certain types of clays (for example, bentonite). Reactive shales may be problematic during drilling operations because of, inter alia, their tendency to degrade when exposed to aqueous media such as aqueous-based drilling fluids. This degradation, of which swelling is one example, can result in undesirable drilling conditions and undesirable interference with the drilling fluid. For instance, the degradation of the shale may interfere with attempts to maintain the integrity of drilled cuttings traveling up the well bore until such time as the cuttings can be removed by solids control equipment located at the surface.
Shale disintegration also may impact “equivalent circulating density” (“ECD”). ECD may be affected by the solids content of the drilling fluid, which may increase if surface solids control equipment cannot remove shale from the drilling fluid. Plastic viscosity (an indicator of size and quantity of solids) is an important parameter that affects drilling rate. Maintenance of appropriate ECD is important in drilling a well bore where a narrow tolerance exists between the weight of the drilling fluid needed to control the formation pressure and the weight of the drilling fluid that will fracture the formation. In such circumstances, minimizing shale degradation may be desirable, inter alia, to control of the viscosity of the drilling fluid. Moreover, degradation of drilled cuttings prior to their removal at the surface may prolong drilling time because shale particles traveling up the well bore can break up into smaller and smaller particles, which can expose new surface area of the shale particles to the drilling fluid and lead to further absorption of water and degradation.
Shale degradation may substantially decrease the stability of the well bore, which may cause irregularities in the diameter of the well bore, e.g., the diameter of some portions of the well bore may be either smaller or greater than desired. In an extreme case, shale degradation may decrease the stability of the well bore to such an extent that the well bore collapses. Degradation of the shale also may interrupt circulation of the drilling fluid, cause greater friction between the drill string and the well bore, and/or cause the drill string to become stuck in the well bore. Accordingly, the complications associated with shale swelling during drilling may substantially increase the time and cost of drilling.
A traditional method of inhibiting shale swelling during drilling to attempt to minimize such complications has been to use an oil-based drilling fluid as opposed to an aqueous-based drilling fluid. However, environmental regulations enacted by numerous countries have limited the use of oil-based drilling fluids.
Another conventional technique used to counteract the propensity of aqueous drilling fluids to interact with reactive shales in a formation involves adding a shale-inhibiting component to the aqueous drilling fluid. As used herein, the term “shale-inhibiting component” refers to a compound that demonstrates a propensity for inhibiting the tendency of shale to absorb water. Amphoteric materials (i.e., substances that may exhibit both acidic and/or alkaline properties) are one type of water-based shale inhibitor that has been used in the past. Amphoteric materials are believed to attach to the shale substrate, thus preventing water ingress. However, amphoteric inhibitors may be environmentally undesirable, especially in heavily regulated areas, because they typically demonstrate low biodegradability and high toxicity. Potassium chloride is another conventional shale-inhibiting component. Although potassium chloride is widely used as a shale inhibitor in the North Sea, it is considered to be only moderately effective at inhibiting shale swelling. Furthermore, potassium chloride can be environmentally unacceptable in other areas of the world, for example, regions such as around the Gulf of Mexico, because its concentration of potassium ions may harm certain types of marine life. Potassium chloride is also disfavored in regions such as the Middle East where wells are drilled in close proximity to aquifers due to concerns that the potassium chloride will contaminate the aquifer. Polyglycols have also been used as shale inhibitors in water-based drilling fluids, but have not demonstrated satisfactory inhibition levels. Partially hydrolyzed polyacrylamides (“PHPA”) have also been utilized in many regions, but these have been found to have undesirable properties in certain circumstances.
Drilling fluids containing silicates are used in the art to manage shale reactivity with aqueous-based drilling fluids. However, silicates do not provide the desired lubricity (i.e., the ability to lubricate equipment used in a drilling operation) for subterranean drilling operations, nor do they effectively reduce the accumulation of shale on equipment that comes into contact with those shales encountered in a well bore. Drilling fluids containing nanoparticles are also used in the art to manage shale reactivity with aqueous-based drilling fluids by, inter alia, providing lubricity and preventing the accretion of shale on drilling equipment. However, these nanoparticles generally do not impart increased hardness to the shale, a property that may facilitate the removal of shale particles from a well bore and/or circulated drilling fluid.