Low-viscidity drag-reduction slick water acid liquid for carbonate reservoir bed

Abstract

The invention provides a low-viscidity drag-reduction slick water acid liquid for a carbonate reservoir bed, which contains the following raw materials in percentage by weight: 5-20% of an acid, 1-3% of an alkyl quaternary ammonium salt, 0.5-2% of sodium ascorbate, 0.1-0.5% of an emulsion corrosion retarder, 0.5-1% of citric acid, 1-3% of a discharge aiding agent, and the balance of water, wherein the emulsion corrosion retarder is any one of polypropylene emulsion, polyvinylpyrrolidone emulsion and 2-acrylamido-2-methylpropanesulfonic acid-acrylic acid copolymer emulsion; the acid is any one of hydrochloric acid, formic acid, acetic acid or a bionic acid. The low-viscidity drag-reduction slick water acid liquid provided by the invention has low acid-rock reaction rate and good drag-reduction effect, and can reduce fracture acidizing construction wellhead pressure, so that the slot volume crack wall surface suffers from uniform acid corrosion all along, and the crack system around a well casing is more developed, which is helpful for yield increase. The low-viscidity drag-reduction slick water acid liquid has good corrosion inhibition effect, and can realize on-site large displacement construction.

Description

technical field [0001] The invention belongs to the technical field of oil field acidification, and in particular relates to a low-viscosity and drag-reducing slick water acid solution for carbonate reservoirs. Background technique [0002] The exploration area of ​​lower Paleozoic carbonatite reservoir in Yanchang is about 2.0×10 4 km 2 , is the focus of exploration and development of Yanchang Oilfield in recent years, the main purpose is to increase natural gas production. Carbonate reservoirs are especially suitable for volumetric acid fracturing of fracture networks. With the help of the acid’s dissolution of carbonate minerals, while expanding and extending fractures and caves, the conductivity of seepage channels is increased, and more oil and gas seepage channels are communicated and connected. and oil storage space to achieve the purpose of maximizing production increase. Among them, the dissolution distance of the acid solution, the distribution and intensity of...

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Problems solved by technology

[0003] Since carbonate reservoirs generally have a burial depth of more than 3000 m and high temperature and closure pressure, acid fracturing for carbonate oil and gas reservoirs faces many difficulties: (1) Reservoirs are medium-low porosity and ultra-low permeability reservoirs (2) Fractures are relatively well developed and distributed unevenly; (3) Due to the deep burial and high temperature of the reservoir, the temperature can reach 150°C, resulting in a fast acid-rock reaction speed, which affects the acid erosion distance of fractures It is difficult to achieve deep penetration effectively, and it is difficult to effectively communicate with favorable reservoirs or caves far away from the wellbore; (4) Since the in-situ stress and closure stress of carbonate reservoirs are generally high, fractures are easy to close, In a short period of time, the fracture seepage channels formed by acid fracturing will be closed prematurely and fail (that is, the permeability of fractures will become very small), resulting in the inability of stable and high production of some oil and gas wells after acid fracturing

[0004] At present, two types of substances are mainly used in the acid fracturing process to solve the above problems: (1) high viscosity acid (thickened acid, emulsified acid, gelling acid, etc., the viscosity is generally greater than 30mPa.s) or cross-linked water-based fracturing (2) Use neutral slick water (the main composition of the formula is drag reducer + drainage aid + clay anti-swelling agent). If the rate is too fast, the penetration distance of acid or slick water is short, the corrosion distance of fractures is difficult to extend, and the degree of reconstruction of micro-fracture seepage channels near the wellbore is not sufficient, so that the dissolution of carbonate reservoirs is easy to produce cavities, resulting in the near-wellbore zone. If the stimulation force is too large, it is easy to cause the danger of well wall collapse and deformation of the casing; in addition, the carbonate reservoir is deeply buried and the closure stress is high, so the use of such materials cannot effectively reduce the wellhead pressure. Fractures are easy to close, resulting in short-circuit in the fracture seepage channel, which ultimately affects the seepage capacity of the entire fracture, causing the fracture seepage channel formed by acid fracturing to fail prematurely, which has great limitations in production stimulation

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