High-flow-conductivity acid fracturing method for carbonate rock reservoirs

Abstract

The invention discloses a high-flow-conductivity acid fracturing method for carbonate rock reservoirs, and belongs to the field of reservoir reconstruction technologies. The high-flow-conductivity acid fracturing method includes applying acid fracturing processes for corroding crack by acid fluid and hydraulic fracturing processes for filling the crack with added sand in a combined manner, to be more specific, forming the crack in the carbonate rock reservoirs by the aid of non-reactive ahead fluid and reducing the surrounding temperatures of wall surfaces of the crack; injecting high-concentration acid fluid systems to corrode the wall surfaces of the artificial crack and forming uneven grooves in the wall surfaces of the crack by means of corroding to allow the crack to have certain flow-conductivity after the crack is closed; enabling high-viscosity sand-carrying fluid to carry proppants and flow into crack systems and filling the crack with the high-viscosity sand-carrying fluid to further improve the flow-conductivity of the crack. The high-flow-conductivity acid fracturing method has the advantages that the high-flow-conductivity acid fracturing method is reasonable in design, simple in process and convenient to implement in fields, the high-flow-conductivity crack systems with the acid-corroded crack and crack closing supporting functions can be formed, oil and gas flow resistance can be reduced, the acid fracturing reconstruction effects can be improved for the carbonate rock reservoirs, and the high-flow-conductivity acid fracturing method can be widely used for acid fracturing reconstruction construction for limestone, dolomite and carbonate rock oil and gas reservoirs with mud.

Description

technical field [0001] The invention belongs to the technical field of reservoir transformation, and in particular relates to an acid fracturing method for carbonate rock reservoirs with high conductivity. Background technique [0002] Carbonate reservoirs are one of the most abundant oil and gas resources in the world, and currently about 50% of oil and gas reserves and production come from this type of reservoirs. However, carbonate reservoirs are usually buried deep, with relatively compact lithology, strong heterogeneity, low porosity and low permeability, and require reservoir reconstruction to be developed and utilized. [0003] At present, acid fracturing in carbonate reservoirs is mainly used to increase the production of oil and gas wells, and some blocks combine acid fracturing and sand fracturing in combination with the characteristics of oil and gas reservoirs. Conventional acid fracturing mainly achieves deep penetration of long fractures by controlling acid fl...

AI Technical Summary

Problems solved by technology

However, the rock modulus of carbonate rock reservoirs is usually high, the fracture pressure is high, and the construction during the sanding stage is difficult. At the same time, the construction fluid does not react with the carbonate rock, and it is difficult to communicate with the micro-fracture system inside the reservoir, resulting in sanding. After fracturing, the gas supply volume is limited, making it difficult to sustain high and stable production

In order to combine acid fracturing and sand fracturing technology, cross-linked acid-carrying sand acid fracturing technology has emerged at home and abroad, that is, cross-linking acid system is used to carry sand acid fracturing, but the cross-linking acid is usually cross-linked on the ground, and the acid solution after cross-linking The frictional resistance of the jelly is much greater than that of the fracturing fluid jelly, which makes the construction pressure higher. At the same time, the cross-linked acid is a macromolecular polymer, and it is difficult to break the gel after cross-linking, which seriously damages the reservoir

[0004] U.S. Patent US531003 discloses an acid fracturing method for controlling the height of upper and lower fractures by injecting two kinds of low-density and high-density acid liquid systems. The low-density acid liquid system is injected into the upper oil and gas reservoir around the wellbore to extend the fractures upward. Injecting a high-density acid liquid system into the lower oil and gas reservoirs in the lower oil and gas reservoirs to extend the fractures downward, but this method is a single acid fracturing process, and rock creep after acid fracturing can easily lead to a decrease in fracture conductivity

[0005] Chinese patent CN101353958 discloses a temperature-controlled variable-viscosity acid fracturing method for oil and gas wells. The temperature change from the wellhead to the bottom of the well is used to control the gradual increase in the viscosity of the acid fluid. This method can effectively reduce the wellbore friction and at the same time the acid fluid enters the high-temperature formation After the viscosity increases, the acid-rock reaction rate decreases, but this method still uses a single acid fracturing process to transform the reservoir, and the rock softens and creeps during the acid fracturing process, and it is difficult to form a fracture system with high conductivity

[0006] Chinese patent CN103089228 discloses a cross-linked acid-carrying sand acid fracturing method for argillaceous dolomite on the ground. It mainly uses cross-linking acid-carrying sand to fill cracks for the reduction of fracture conductivity after acid fracturing of argillaceous dolomite. The liquid system is ground cross-linked acid, which has high wellbore friction and high construction pressure. At the same time, the cross-linked acid system is difficult to achieve high sand ratio construction (average sand ratio 11.2%), resulting in too low sand concentration and poor conductivity of acid-etched fractures. insufficient

[0007] Chinese patent CN103590803 discloses a solid acid-acid fracturing process. Firstly, a non-reactive liquid is used to create fractures, and then water-insoluble solid acid at room temperature is injected, so that the solid acid enters artificial or natural fractures and is gradually released through the action of formation temperature and pressure. The acid solution is used to etch the deep part of the formation. The solid acid particles injected in this method can continuously release the acid solution to dissolve the rock formation, but the solid particles themselves do not have the function of supporting fractures. At the same time, this method also adopts a single acid fracturing process. Reservoir, it is difficult to form a fracture system with high conductivity

[0008] Non-patent literature "Application of Cross-linked Acid Fracturing and Sanding Technology in Well Shi 31" (Oil and Gas Well Testing, 2007, Volume 16, Supplement), "Application of Cross-linking Acid and Sanding Acidizing Fracturing Technology in Complex Lithology Reservoirs "(Acta Petroleum Sinica, 2008, Volume 29), "Practice of Crosslinked Acid Fracturing Technology for Dolomite Reservoirs in Jingbian Gas Field" (Oil and Gas Geology and Recovery, 2008, Volume 15) and "Carbonate Rock Reservoir cross-linked acid-carrying sand acid fracturing new technology" (China Science and Technology Papers Online, 2010, Volume 5) all introduced the acid fracturing and sanding design of cross-linking acid-carrying sand after the previous cross-linking acid fracture creation method, but the cross-linking acid used in the above method is all ground cross-linking acid, the friction of the wellbore is relatively high, and the pressure of acid fracturing operation is high. Insufficient flow conductivity of cracks

In addition, the acid fracturing methods introduced in the literature all use cross-linked acid to create fractures. The acid fracturing reaction speed is too fast, the acid fluid loss is large, and the length of acid-etched fractures is limited, making it difficult to form deep acid fracturing.

[0009] Non-patent literature "Cooperative Operation Technology and Advantages of Acidizing and Sanding Fracturing" (Petroleum Drilling Technology, 2009, Volume 37) and "Research and Application of Acidic and Sanding Fracturing Combined Restructuring Technology" (Xinjiang Petroleum Science and Technology, 2012 In 2010, Vol. 22), a pre-acid-sand fracturing method was introduced. Before sand fracturing, a period of gelling acid system was injected, followed by a period of spacer fluid, and then pre-fluid and sand-carrying fluid were injected. , the acid fracturing-sanding composite process adopts pre-acid fracture formation, the acid rock reaction speed is too fast, and it is easy to produce a certain diameter expansion around the wellbore, which increases the acid fluid loss rate and makes it difficult to achieve deep stimulation

At the same time, after the fracturing fluid enters the acid-dissolved and enlarged fractures in the later stage, the filtration loss will increase, and the difficulty of adding sand will increase.

[0010] At present, for the stimulation of carbonate rock reservoirs, especially tight low-permeability, high-pressure carbonate rock reservoirs, there is still a lack of a method that can not only achieve high conductivity of fractures but also carry out deep acid fracturing stimulation.

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