Acid injection fracturing method

Abstract

The invention provides an acid injection fracturing method. The method comprises the steps that at the front liquid fissure forming stage, an alternative acid injection mode is adopted for fissure fracturing transformation, the alternative acid injection mode comprises the step that 1-5 levels of slugs are alternatively injected into fissures, and each level of slugs are composed of acid liquid and displacing liquid which are injected in sequence. According to the acid injection fracturing method, by combining with technical advantages of fracturing and acidification, through optimization of an alternative injection technology, the relation range of the acid liquid in a fissure fracturing system is enlarged to the greatest extent, and the porosity and permeability of fissure wall rock areimproved; a micro-fissure and branch fissure extension system is expanded and extended, increase of fissure complexity degree and transformation volume is promoted, and the duration time of keeping the flow diversion capacity of the fracturing system is prolonged.

Description

technical field [0001] The present invention relates to the technical field of hydraulic fracturing stimulation of oil and gas reservoirs, more specifically to an acid injection fracturing technology for increasing the volume of fracture stimulation, and in particular to a technology suitable for increasing fracture stimulation in shale and tight sandstone oil and gas reservoir fracturing. Volumetric alternating acid injection fracturing method. Background technique [0002] The increase of fracture stimulation volume is based on the matching of reservoir conditions and fracturing operation conditions. Reservoir conditions include rock brittleness, horizontal stress difference, degree of development of natural fractures, and angle with the direction of maximum horizontal principal stress; the optimization of fracturing conditions is mainly based on the net pressure of main fractures as the objective function. Pressure-related parameters, such as displacement, liquid volume,...

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Problems solved by technology

1) In the case of uncertainty in the evaluation of reservoir parameters, it is difficult to choose a fracture stimulation construction method, and the effect is not ideal: the evaluation of the brittleness index of the fracturing target layer, the two-way horizontal stress difference, and the characteristics of natural fractures are mostly based on core analysis It is difficult to judge the representativeness of the core and the change of reservoir parameters far away from the wellbore, which leads to a certain degree of uncertainty in the characteristics of natural fractures in the reservoir, which increases the volume of fracture stimulation and the degree of complexity of fractures. The purposeful fracturing process design brings many uncertainties

2) The sensitivity of fracture net pressure to construction injection parameters is not strong: in many cases, the effect of increasing the fracture net pressure by adjusting construction injection parameters (such as displacement, liquid volume, construction sand-liquid ratio, etc.) is not obvious. Fracture net pressure increases slightly

3) It is difficult to implement volume fracturing in tight sandstone reservoirs due to the excessive extension of fracture heights: in shale reservoirs, due to the relative development of horizontal bedding fractures / texture fractures, it has a natural shielding effect on hydraulic fracture heights. Under the premise of effective control, low viscosity, large fluid volume, and high displacement fracturing ideas can promote fractures to achieve better steering effects in the horizontal direction; however, tight sandstone reservoirs are relatively undeveloped due to horizontal bedding fractures If we directly refer to the idea of ​​shale gas volume fracturing with low viscosity, large liquid volume, and high displacement, it may cause the fracture height to be excessively out of control, which is completely opposite to the expected goal of horizontal fracture diversion and expansion of the stimulated volume. Effect

At present, in many shale and tight sandstone oil and gas reservoirs, there are problems such as low initial production after fracturing, rapid production decline, and short production stabilization period, which affect the effective development of such reservoirs and the effective production of reserves.

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