Hydrocarbon fluids, such as oil and natural gas, and other desirable formation fluids are obtained from a subterranean geologic formation, i.e., a reservoir, by drilling a well that penetrates the formation zone that contains the desired fluids. Once a wellbore has been drilled, the well must be completed, which involves the design, selection, and installation of equipment and materials in or around the wellbore for conveying, pumping, or controlling the production or injection of fluids.
When the subterranean formation is “soft” or poorly consolidated, small particulates (typically sand) present in the formation may dislodge and travel along with the produced fluid to the wellbore. Production of sand is undesirable since it erodes surface and subterranean equipment, and it must be removed from the produced fluids before they can be processed. In particular, the migrating sand can plug the flow channels in the formation and necessitate other stimulation techniques, such as acid stimulation, to restore the well's performance.
Various methods have been employed to reduce or eliminate the simultaneous production of sand and other particulates with the formation fluids. One common approach has been to filter the produced fluids through a gravel pack that has been placed into the wellbore. Such gravel packs are often retained by a metal screen. The produced formation fluids travel through the permeable gravel pack (and the screen) before entering the wellbore. The sand and other particulates in the produced fluids are blocked by the gravel pack. This technique has been widely used, but it has several disadvantages. Over time, the gravel pack and the screen may be plugged by scale or particles, or badly eroded by the sand and other particulates in the produced fluids. This reduces the effectiveness of the gravel pack and screen and may actually shut down the production if the gravel pack and/or screen becomes plugged with sand or formation fines. Additionally, the presence of the metal screen in the well inhibits reentry of drills and other tools into the wellbore and the metal screen can be difficult and costly to remove.
It is thus desirable to develop so-called screenless completion techniques. These techniques typically involve the injection of a consolidating fluid, such as a resin-based consolidating fluid, through the wellbore and into the formation surrounding the interval of interest. Resin-based consolidating fluids generally include an organic resin, a curing agent, a catalyst and an oil wetting agent. The resin system hardens in the formation, thereby consolidating it. Resin-based consolidation systems may be complicated to apply, especially those involving multiple treatment stages, and the treatment results may be erratic. When the individual components of the consolidating fluid are pumped at different stages into the formation they may or may not come together in the right order, or in the right amounts, or they may not even come into contact at all. And, if they do combine, good mixing of the components is not assured. This difficulty helps explain the erratic and unreliable results that operators have experienced using such multi-stage consolidating fluids.
In an effort to overcome some of the disadvantages of resin-based consolidation fluids, other well treatments have been proposed which use inorganic systems to modify the formation and thereby reduce the production of sand and fines.
For example, U.S. Pat. No. 3,593,796 describes a multi-stage process in which the following components are injected sequentially into the formation: (1) an aqueous solution containing a silicate adapted to wet the fine sand grain particles, (2) an aqueous solution of a silicate-precipitating agent capable of reacting with the silicate in solution (1) so as to form a solidifying material and therein to bind the fine sand grain particles, and (3) a solution containing an oil-wetting agent. This treatment is designed to immobilize the fine particles in the formation and prevent their migration when subjected to subsequent fluid flow. The aqueous solutions of alkaline earth metal salts (e.g., calcium chloride), acidic iron salts, and certain other metal salts can be used as the silicate-precipitating agent.
In another instance, U.S. Pat. No. 3,741,308 describes a method of converting an unconsolidated sand formation into a consolidated, permeable formation by flowing volumes of aqueous calcium hydroxide (or compounds which hydrolyze or react with each other to form calcium hydroxide) through the pores of the unconsolidated formation. The calcium hydroxide solution could be formed by adding sodium hydroxide to a solution of calcium chloride. In the practice of this process the sand particles in the formation become coated with calcium silicates of unknown or indefinite composition, and it is proposed that the coating cements the individual grains together and increases the structural strength of the sand assemblage.
In essentially all multistage consolidation treatments, there is an element of chance in whether the reactants and components will be combined in the formation in the proper order, the proper amounts, or whether they will even come in contact at all in the desired formation interval of interest. The efficiency of mixing or blending is also questionable.
Though some of the above-mentioned techniques have achieved a degree of commercial success, many of them have been hindered by technical and/or cost limitations. It would thus be desirable to provide a method by which unconsolidated sands could be successfully consolidated while also providing an effective technique for establishing suitable communication through the consolidated sands between the formation fluids and the wellbore.