A calculation method for the energy enhancement and permeation distance of tight oil horizontal well fracturing

Abstract

The present invention relates to the technical field of oilfield reservoir transformation, and specifically to a method for calculating the imbibition distance of tight oil horizontal well fracturing energy enhancement. The method mainly solves the problem that the imbibition distance cannot be quantified in the design optimization of tight oil horizontal well fracturing energy enhancement integrated transformation, resulting in a large difference between the post-fracturing capacity prediction and the actual result. The present invention first selects a target well, then determines the well-blocking time by using the well-blocking time formula, and finally determines the target well imbibition distance according to the well-blocking time-reservoir permeability-imbibition distance relationship chart. The present invention is simple and intuitive to operate, can quickly obtain the target well imbibition distance under given conditions, and has guiding significance for the prediction of the post-fracturing capacity of tight oil horizontal wells.

Description

[0001] Technical field: The present invention relates to the technical field of oilfield reservoir transformation, and in particular to a method for calculating the fracturing energy enhancement permeation distance of a tight oil horizontal well.

[0002] Background technology: In recent years, tight oil resources have achieved good results through different fracturing process transformation, but with the continuous increase in the scale of transformation, the problem of declining production capacity has not been alleviated, affecting long-term effective development. Reservoir pore characteristics, energy-enhancing fluid type, fracture spacing, well shut-in time and other factors all affect the effect of tight oil horizontal well fracturing transformation. Through the integrated fracturing and energy-enhancing process mode, the transformation scale is optimized, the energy-enhancing medium is injected, and the well is sealed after fracturing to fully replace the energy-enhancing medium with the crude oil in the pores, increase the pressure diffusion range, replenish the formation energy, and further improve the recovery rate.

[0003] At present, there is no systematic method for calculating the imbibition distance of fracturing energy enhancement, so it is impossible to quantify the reasonable wellbore time and to clarify the relationship between the wellbore time and imbibition distance of different types of reservoirs, resulting in a large difference between the post-fracturing capacity prediction and the actual results.

[0004] Invention content: The purpose of the present invention is to provide a method for calculating the fracturing energy enhancement imbibition distance of a tight oil horizontal well. The method can be applied to different types of tight oil horizontal wells, quantify the target well shut-in time, determine the fracturing energy enhancement imbibition distance under given conditions, and systematically and effectively solve the problem of low accuracy in post-fracturing production capacity prediction, guide the optimization of fracturing schemes, and improve recovery rates.

[0005] The present invention is achieved through the following technical scheme: A method for calculating the fracturing energy enhancement permeation distance of a tight oil horizontal well, comprising the following steps:

[0006] Step 1: Select horizontal wells that need to be imbibed to increase production after fracturing of tight oil reservoirs as target wells;

[0007] Step 2: Optimize the construction scale of the target well through fracturing software simulation and use the well blocking time calculation formula to obtain a reasonable well blocking time;

[0008] Step 3: Determine the target well fracturing energy enhancement imbibition distance under given conditions based on the three-dimensional relationship chart of tight oil reservoir well blocking time-permeability-imbibition distance.

[0009] The target well selection method in the first step is: select a tight oil horizontal well with a "double-peak" pore size distribution in the reservoir core and a large difference between large and small pore sizes as the target well.

[0010] The method for determining the well blocking time t in the second step is: given the target well reservoir porosity φ, permeability K, and crude oil viscosity μ o , fracturing fluid viscosity μ w , interfacial tension σ, diffusion factor C spread , Lc is the target horizontal well fracture spacing, the shut-in pressure ΔP is obtained by small-scale test fracturing of the target well or adjacent wells, and the relationship between the reasonable shut-in time t and the above parameters is established:

[0011]

[0012] According to formula ①, the reasonable well blocking time t of the target well is calculated for different types of reservoir conditions.

[0013] The method for determining the target well fracturing energy enhancement imbibition distance under given conditions according to the three-dimensional relationship chart of tight oil reservoir well blocking time-permeability-imbibition distance in the third step is:

[0014] (1) Establish a formula for the variation of fracture-matrix imbibition distance L with wellbore time t;

[0015]

[0016]

[0017] Where:

[0018] Where: t—well blocking time, G—starting pressure gradient, φ—reservoir porosity, K—reservoir permeability, C spread —Diffusion factor, ΔP—Shut-in pressure, A-Reservoir fluid related parameters, S wf —Water saturation at the imbibition front, S wi —Immobile water saturation, μ w —Fracturing fluid viscosity, μ o —Crude oil viscosity, K rw —Equivalent relative permeability of water phase, K ro —Equivalent relative permeability of oil phase;

[0019] (2) According to formula ②, the imbibition distance L under different permeability K and well blocking time t conditions is determined, and a three-dimensional relationship chart of well blocking time-permeability-imbibition distance is established, namely, the fracturing energy enhancement imbibition distance chart, in which the permeability K is used as the x-axis of the chart, the well blocking time t is used as the y-axis of the chart, and the imbibition distance L is used as the z-axis of the chart.

[0020] The diffusion factor C spread The value is determined by indoor experiments, and the range of values ​​varies for different types of reservoirs. spread The value is 0.7-0.8, tight oil type II reservoir C spread The value is 0.6-0.7, tight oil type III reservoir C spread The value is below 0.6.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention uses a fracturing energy enhancement imbibition distance method to quantify the well-clogging time and imbibition distance of different types of tight oil horizontal wells according to formulas and three-dimensional charts, which can effectively guide the optimization of fracturing schemes and the prediction of post-fracturing production capacity; it has strong controllability, is convenient, simple and intuitive to operate, and can quickly obtain the imbibition distance of the target well under given conditions; the method can systematically and effectively solve the problem of low accuracy in post-fracturing production capacity prediction, guide the optimization of fracturing schemes, and improve the recovery rate.

[0023] Description of the drawings: Figure 1 This is the target well fracturing energy enhancement imbibition distance L chart; Figure 2 is the different bound water saturation S wi Equivalent relative permeability to water phase K rw , oil phase equivalent relative permeability K ro Relationship curve.

[0024] Specific implementation method: The present invention is further described below with reference to the accompanying drawings and examples:

[0025] A method for calculating the fracturing energy enhancement imbibition distance of a tight oil horizontal well comprises the following steps:

[0026] Step 1: Select horizontal wells as target wells that need to be imbibed to increase production after fracturing of tight oil reservoirs.

[0027] Step 2: Optimize the construction scale of the target well through fracturing software simulation and use the well blocking time calculation formula to obtain a reasonable well blocking time.

[0028] Step 3: Determine the target well fracturing energy enhancement imbibition distance under given conditions based on the three-dimensional relationship chart of tight oil reservoir well blocking time-permeability-imbibition distance.

[0029] Example: Take Well A as an example, the details are as follows:

[0030] Target well selection:

[0031] A tight oil horizontal well A was selected, and the high-pressure mercury injection experiment measured that the core pore size distribution range was 0.02-2.1μm, with a difference of 15-35 times between large and small pore sizes, which is consistent with the "double peak" characteristics.

[0032] Get the time t of the well:

[0033] It is known that the target well is a Class I tight oil reservoir with a reservoir porosity of φ0.12, a permeability K of 1.05 mD, and a crude oil viscosity μ o 6mPa·s, fracturing fluid viscosity μ w is 1 mPa·s, the interfacial tension σ is 0.9 mN / m, and the target horizontal well fracture spacing L c =10m. Since this well is a new well, the pump stop pressure is based on the shut-in pressure of the well in the same block, which is ΔP, 11.2MPa. The diffusion factor Cspread The value is 0.75. After the above parameters are determined, they are put into formula ① to calculate that the well blocking time t is 6.3 days to reach the imbibition balance (see Table 1).

[0034]

[0035] Table 1

[0036]

[0037] Determine the imbibition distance L:

[0038] It is known that the target well was blocked for 6.3 days and the reservoir permeability is 1.05 mD. The three-dimensional relationship chart of blocking time, permeability and imbibition distance is used to determine that the imbibition distance L under this condition is 2.5 m (see Figure 1 ).

[0039] The three-dimensional relationship chart of well blocking time, permeability and imbibition distance is drawn based on the formula of the variation of fracture-matrix imbibition distance L with well blocking time t. The specific parameters are well blocking time t, starting pressure gradient G, water saturation at the imbibition front S wf , bound water saturation S wi , fracturing fluid viscosity μ w 、Crude oil viscosity μ o , porosity φ, reservoir permeability K, diffusion factor C spread , shut-in pressure ΔP are shown in Table 2.

[0040] Water phase equivalent relative permeability K rw , oil phase equivalent relative permeability K ro The value is read from the phase permeability curve (see Figure 2 ), where the reservoir permeability is 1.05 and the irreducible water saturation is 0.4.

[0041]

[0042] In the formula

[0043] Table 2

[0044]

[0045]

[0046]

Claims

1. A method for calculating the energy enhancement and permeation distance of a tight oil horizontal well fracturing, characterized in that: The following steps are involved: Step 1: Select horizontal wells that need to increase production through well imbibition after fracturing of tight oil reservoirs as target wells. The pore size range of the reservoir core is between 0.02-2.1μm, and the pore size distribution shows a "double peak" feature; Step 2: Optimize the construction scale of the target well through fracturing software simulation, and use the well blocking time calculation formula to obtain the reasonable well blocking time. The determination method is as follows: the target well reservoir porosity ∅, reservoir permeability K, crude oil viscosity μ o , fracturing fluid viscosity μ w , diffusion factor C spread , L c is the target horizontal well fracture spacing, the shut-in pressure ΔP is obtained by small-scale test fracturing of the target well or adjacent wells, and the relationship between the reasonable shut-in time t and the above parameters is established: According to formula ①, the reasonable well blocking time t of the target well is calculated for different types of reservoir conditions; Step 3: According to the three-dimensional relationship chart of tight oil reservoir well blocking time, permeability and imbibition distance, determine the target well fracturing energy enhancement imbibition distance under given conditions. The determination method is: (1) Establish a formula for the variation of fracture-matrix imbibition distance L with wellbore time t; Where: Where: t—well blocking time, G—starting pressure gradient, ∅—reservoir porosity, K—reservoir permeability, C spread — diffusion factor, ΔP—shut-in pressure, A—reservoir fluid related parameters, S wf —Water saturation at the imbibition front, S wi —Immobile water saturation, μ w —Fracturing fluid viscosity, μ o —Crude oil viscosity, K rw —Equivalent relative permeability of water phase, K ro —Equivalent relative permeability of oil phase; (2) According to formula ②, the imbibition distance L under different permeability K and well blocking time t conditions is determined, and a three-dimensional relationship chart of well blocking time-permeability-imbibition distance is established, namely, the fracturing energy enhancement imbibition distance chart, in which the reservoir permeability K is used as the x-axis of the chart, the well blocking time t is used as the y-axis of the chart, and the imbibition distance L is used as the z-axis of the chart.

2. The method for calculating the hydraulic fracturing energy enhancement imbibition distance of a tight oil horizontal well according to claim 1, characterized in that: The diffusion factor C spread The value is determined by indoor experiments, and the range of values ​​varies for different types of reservoirs. spread The value is 0.7-0.8, tight oil type II reservoir C spread The value is 0.6-0.7, tight oil type III reservoir C spread The value is below 0.6.

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