Method for calculating turning fracture initiation pressure in shale refracturing
A fracture initiation pressure and repeated fracturing technology, which is applied in the field of unconventional oil and gas stimulation, can solve problems such as uncontrolled extension direction, excessively large fracture branches, failure to break rocks, etc., and achieve the effect of precise guidance plans and opinions
Active Publication Date: 2018-01-19
SOUTHWEST PETROLEUM UNIV
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Problems solved by technology
The extension of hydraulic fractures and the injection of fluid disturb the in-situ stress field of the reservoir, and the stress interference between fractures makes the stress state of fractures more complicated. Therefore, a theoretical method is needed to reasonably calculate the initiation pressure of diverted fractures during refracturing. Provide important parameters for the optimal design of refracturing. However, in the existing technology, there is no complete calculation method that can directly obtain the initiation pressure of the diverted fracture during refracturing. On-site construction can only be based on experience and real-time downhole measurements. parameters to estimate the pressure value, but the pressure value obtained in this way is prone to be too large or too small. When the pressure is too high, it is easy to cause the crack branch to be too large, and the extension direction is not controlled. If the pressure is too small, the rock-breaking effect cannot be achieved. Effect
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[0073] The geological parameters and construction parameters of a typical shale gas reservoir in southern Sichuan were collected, as shown in Table 1:
[0074] Table 1 embodiment parameters
[0075] Input parameters
parameter value
Rock Young's modulus E(GPa)
18
Rock Poisson's ratio ν, dimensionless
0.2
Minimum horizontal principal stress σ h (MPa)
55
Maximum horizontal principal stress σ H (MPa)
60
Hydraulic fracture length L hf (m)
50
Natural crack length L nf (m)
10
Hydraulic fracture height h f (m)
50
Number of discrete fracture elements 2N, dimensionless
40
Angle between hydraulic fracture and natural fracture, (°)
60
Displacement of hydraulic fracture q(m 3 / min)
3
Fracturing fluid viscosity μ f (mPa·s)
9
Natural crack tensile strength S t (MPa)
0.5
[0076] The above-mentioned data is calculated by adopting a calculatio...
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The invention discloses a method for calculating turning fracture initiation pressure in shale refracturing. The method comprises the following steps of: 1, collecting parameters of fractures, inputting the parameters into a computer to form a fracture system, dispersing the fracture system into 2N fracture units through the computer; 2, substituting the fracture units in the step 1 and related fracturing parameters according to a calculation formula, and calculating system fluid pressure distribution of the fracture units; 3, under the condition of achieving a balance, establishing a dispersed fracture unit stress balance equation through influences, on rock deformation, of pressure distribution points; 4, coupling fluid flow in the fracture system with fracture deformation through the fracture unit pressure distribution and a stress balance condition, and calculating an induced stress acting on the dispersed fracture unit; and 5, calculating turning fracture initiation pressure through the induced stress obtained in the step 4. The invention innovatively discloses the method for calculating turning fracture initiation pressure in shale refracturing, and the method can be used forinstructing fracturing construction.
Description
technical field [0001] The invention belongs to the technical field of unconventional oil and gas stimulation, in particular to a method for calculating the initiation pressure of shale repeated fracturing and steering fractures Background technique [0002] Shale gas reservoirs are unconventional reservoirs with extremely low porosity and permeability. Volume fracturing of horizontal wells activates natural fractures to form complex fracture networks, which can greatly increase the production of shale gas single wells and realize industrial production. In the process of production, the effective stress of the reservoir increases with the decrease of pore pressure, which intensifies the closure of hydraulic fractures, greatly reduces the conductivity of hydraulic fractures, and causes a sharp decline in gas well productivity. In addition, some shale gas wells did not achieve ideal stimulation effects after fracturing due to cognitive and operational reasons. At this time, r...
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IPC IPC(8): G06F17/50
Inventor 赵金洲任岚黄静吴雷泽李丽
Owner SOUTHWEST PETROLEUM UNIV
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