A volumetric fracturing method for deep shale gas at atmospheric pressure

Abstract

The invention discloses a constant-pressure deep shale gas volume fracturing method. The method includes the steps of (1) evaluation of key reservoir characteristic parameters; (2) fracturing coefficient evaluation and perforation position determination; (3) perforation operation; (4) acid pretreatment operation; (5) optimization of crack parameters and overall construction parameters; (6) acid formulation optimization for intermediate acid injection; (7) first-stage mixed injection construction; (8) second-stage mixed injection; (9) third-stage mixed injection; (10) fracturing construction ofthe next segment after displacement, and repetition of the steps (4), (7) and (9). The method can exploit the deep shale gas reservoir yield increasing potential to the maximum, increase the fracturing success rate and meet the deep shale gas reservoir volume fracturing requirement and is beneficial to application and promotion of the hydraulic fracturing technology.

Description

technical field [0001] The invention relates to the technical field of oil and gas field exploration and development, and furthermore, relates to a volume fracturing method for deep shale gas at normal pressure. Background technique [0002] At present, with the deepening of shale gas exploration and development process, it gradually develops from the shallow layer to the deep layer with a vertical depth of 3500m, and the shale gas resources at a depth of 3500m are huge, so the development prospect of deep shale gas is huge. However, with the increase of vertical depth, the fracturing difficulties are as follows: [0003] 1) The stresses in all three directions increase, especially the increase in the maximum principal stress is relatively larger. Therefore, the horizontal stress difference in the two directions increases, resulting in a decrease in the complexity of fracturing. At the same time, the vertical stress increases faster than the minimum principal stress, which ...

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Problems solved by technology

[0004] 2) As the vertical depth increases, the frictional resistance along the wellbore increases. Under a certain wellhead pressure limit, the displacement of fracturing operation is greatly reduced, so that the geometric size of the main fractures decreases accordingly. Therefore, the amount of proppant added And the construction sand-liquid ratio is correspondingly reduced, which greatly reduces the fracture length and flow conductivity of the main fracture;

[0005] 3) With the increase of temperature and pressure, the shaping characteristics of shale rocks are significantly enhanced. Therefore, it is more difficult to break and extend the main fractures, branch fractures, and micro-fractures connected with branch fractures. Therefore, it is more difficult to form complex fractures. Big

[0006] 4) As the vertical depth increases, the minimum horizontal principal stress increases, the net pressure of the main fracture decreases, and the effective closure stress borne by the proppant increases. Therefore, the conductivity of propped fractures in the main fracture and other small and micro-scale fracture systems decreases. It will quickly break and reduce the conductivity. Once the conductivity of a certain place in the fracture drops to 0, the volume of the corresponding fracture stimulation will also be reduced to 0, so that the effective period of fracturing will be quickly reduced;

In this case, if the original construction strategies such as large liquid volume and high displacement are still used, the fracture height may be out of control, not only the volumetric fracture cannot be realized, but the complexity of the fracture is greatly reduced;

[0008] 6) Deep shale gas is sometimes accompanied by normal pressure conditions, so the difficulty of fracturing is greatly increased

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