An Optimal Design Method for Improving the Effect of Supercritical Carbon Dioxide Dry Fracturing

Abstract

The invention provides an optimized design method for improving a supercritical carbon dioxide dry method fracturing effect. Through researching and optimizing a more suitable thickener, the performance such as rheological property, sand carrying performance, resistance reduction performance and filtrate loss reduction performance of a supercritical carbon dioxide fracturing fluid system is improved. At the same time, the viscosity of the fracturing fluid system can be greatly improved by the thickener. Through optimizing a suitable proppant material for supercritical carbon dioxide fracturing, the degree of sand coating of fracturing construction is further improved, and the flow conductivity of a fracture is enhanced. According to the method, through optimizing a closed sand-mixing device, the volumetric performance is improved, and the requirement of a site fracturing construction sand volume is satisfied. Through optimizing the construction parameters, injection modes and the like,while a transformation effect is ensured, a sand ratio and a CO2 utilization rate are improved gradually so as to further optimize and adjust a fracturing process, geological damage is avoided as much as possible, deep communication is established, a sweep volume is expanded, fracture support is strengthened, and the effect of supercritical carbon dioxide dry method fracturing reconstruction is improved.

Description

technical field [0001] The invention relates to an optimal design method for improving the effect of supercritical carbon dioxide dry fracturing, and belongs to the technical field of petroleum exploitation. Background technique [0002] In the case of supercritical fluid applications emerging in the petroleum industry, supercritical CO 2 The application of fracturing fluids has gradually been recognized by technicians in the oil and gas industry, and according to their use methods and scales, the following types of liquid CO with different advantages and disadvantages have been formed: 2 Fracturing process. [0003] (1) Supercritical CO 2 Energy storage pre-fracturing process, the process pre-stages small-scale CO 2 , converted to CO 2 The mass ratio is 10-20%. Its advantage is that it can increase formation energy, reduce fracturing fluid loss, promote rapid flowback of fracturing fluid, and reduce damage; its disadvantage is that the pre-CO 2 The scale is small, the ...

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Problems solved by technology

[0003] (1) Supercritical CO 2 Energy storage pre-fracturing process, the process pre-stages small-scale CO 2 , converted to CO 2 The mass ratio is 10-20%. Its advantage is that it can increase formation energy, reduce fracturing fluid loss, promote rapid flowback of fracturing fluid, and reduce damage; its disadvantage is that the pre-CO 2 The scale is small, the affected area is small, and the damage of water-based fracturing fluid to the reservoir and supporting fractures cannot be avoided

[0004] (2) Supercritical CO 2 The whole process with injection fracturing technology, this process adopts the whole process of injecting CO 2 , CO 2 The mass ratio is 30-50%. Its advantage is that it can reduce water-based fracturing fluid fluid loss and promote flowback; its disadvantage is that supercritical CO 2 The scale is small, the affected area is small, and the damage of water-based fracturing fluid to the reservoir and supporting fractures cannot be avoided; this process is mainly used in low-pressure oil and gas reservoirs and weak water-sensitive reservoirs, mainly to improve the flowback rate of fracturing fluid

[0005] (3) Supercritical CO 2 Foam fracturing process, which uses the whole process of injecting CO 2 , CO 2 The mass ratio is 50-70%. Its advantage is that it can reduce fracturing fluid loss, enhance fracture creation ability, and promote rapid flowback of fracturing fluid; its disadvantage is that it cannot avoid the damage of water-based fracturing fluid to reservoirs and propped fractures ; This process is mainly used in low-pressure oil and gas reservoirs and medium-strong water-sensitive reservoirs to reduce filtration loss and pollution

[0006] (4) Supercritical CO 2 The advantage of pre-fracturing + water-based sand-carrying fracturing technology is that it can increase formation energy and reduce fluid loss; at the same time, due to CO 2 The scale is large, the sweeping area is large, and it is beneficial to the formation of complex fractures to increase the volume of stimulation. The water-based fracturing fluid (cross-linked jelly) has a high sand-carrying concentration and a large amount, which is conducive to the formation of high conductivity and stable fractures; its disadvantages It is impossible to avoid the damage of water-based fracturing fluid to reservoirs and supporting fractures; this process is mainly used in tight reservoirs, low-pressure oil and gas reservoirs, strong water-sensitive and strong water-locking reservoirs

[0007] (5) Supercritical CO 2 Dry unsupported fracturing process, which uses CO2 injection throughout the process 2 , CO 2 The mass ratio is 100%, and its advantage lies in the supercritical CO 2 Large-scale, large-scale sweeping area, large volume of stimulation, complex fractures mainly composed of shear fractures, and high conductivity; the disadvantages are that there is no fracture skeleton support, the formation is sensitive to stress and the production time is prolonged, and the fractures are closed and conductive. The flow capacity decreases, and the output declines rapidly

[0008] (6) Supercritical CO 2 The dry sand fracturing process has the advantage of supercritical CO 2 Large-scale, large-scale sweep, large volume of stimulation, and complex fractures mainly composed of shear fractures, which are effectively supported, and the conductivity of the formed fractures has long-term stability; the disadvantage is that it requires high equipment and requires sand There is a risk of sand plugging; this process is mainly used in low-pressure oil and gas reservoirs, strong water-sensitive, strong water-locked reservoirs

[0020] 2) The construction scale and sanding intensity of dry fracturing are limited by the equipment, that is, the sanding scale is limited by the amount of sand added by the closed sand mixer, the sanding intensity is not high, and the sanding method needs to be improved;

[0021] 3) The pressure in the dry fracturing construction system is not stable, that is, the CO 2 The discharge speed of the tanker is different and the pressure in the tank decreases with the construction, resulting in unstable pressure, which affects the construction, and the direct liquid supply is not stable, and there is no buffer equipment;

[0022] 4) Carbon dioxide dry fracturing has low sand-carrying capacity, which limits the conductivity of artificial fractures;

[0023] 5) The supporting equipment is not perfect, and there is no special manifold skid or manifold truck for carbon dioxide dry fracturing

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