CN107066769B - Efficient acidification design method suitable for ultra-deep layer crack type carbonate reservoir - Google Patents

Abstract

The invention discloses a high-efficiency acidification design method suitable for an ultra-deep layer crack type carbonate reservoir, which sequentially comprises the following steps: (1) calculating injection displacementQ _injThe value range of (A) is,Q _ro≤Q _inj<Q _lim，Q _rois the critical discharge capacity of the re-opening of the natural fracture,Q _limthe upper limit displacement for construction is set; (2) optimized design construction displacementQ _opAnd the amount of acid solutionV _op(ii) a (3) And designing a pumping program. The method considers the mechanical characteristics of the carbonate reservoir natural fracture in the opening process and the acid liquid flow reaction characteristics after opening, combines the reservoir geological characteristics and the engineering conditions, can solve the problem of blindness in the design of the deep plugging removal and acidification construction parameters of the current ultra-deep fracture type carbonate reservoir to a great extent, improves the acidification yield-increasing effect, and saves the acidification economic cost.

Description

Efficient acidification design method suitable for ultra-deep layer crack type carbonate reservoir

Technical Field

The invention relates to a high-efficiency acidification design method for an ultra-deep fracture type carbonate reservoir in the field of petroleum engineering, which ensures that acid liquor can enter a natural fracture to remove internal pollution, enables the natural fracture to become a high-speed channel for crude oil and natural gas to flow into a shaft, and improves acidification yield-increasing effect.

Background

The marine carbonate rock oil gas resource amount of China is about 340 multiplied by 10⁸t oil equivalent, and the detemining rate is only 11%, the exploration and development potential is huge (Xielanlong, Huangchong, Wangxing, China carbonate rock oil and gas reservoir detemining reserve distribution characteristics [ J]Marine oil and gas geology, 2009, (02): 24-30). In recent years, with the shift of marine carbonate exploration targets to deep and ultra-deep layers in China, ultra-deep layer crack type carbonate becomes a key point for exploration and development as a main reservoir type. Such reservoirs typically have low matrix permeability and have natural fractures as the primary channels for oil and gas flow. Working fluid can enter and block natural fractures in the drilling and completion processes, so that the productivity of the oil and gas well is reduced. Whether the flowing ability of natural cracks can be recovered or not is important for realizing the economic and efficient exploitation of the fractured carbonate reservoirs (the Zhoutai, unconventional oil and gas geology [ M)]Geological press 2011).

Generally, aiming at a low-permeability carbonate reservoir, forming an artificial fracture with high conductivity by acidizing and fracturing is an effective modification mode; however, the ultra-deep carbonate rock (taking the Xixia supernatural overlap system as an example) is difficult to crush a reservoir under the existing engineering conditions due to the fact that the buried depth is deeper (not less than 6500m), the pressure coefficient is high (1.4-1.9), and the fracture pressure of a wellhead is high; matrix acidification is the only means for safely, economically and efficiently building and increasing the yield of the reservoirs.

The carbonate matrix acidification is to inject acid into a reservoir with low construction displacement under the condition of not crushing reservoir rocks, and the acid is used for dissolving and corroding rocks in a near-well damage area so as to improve the flow capacity of the near-well damage area. Due to the fact that a non-radial pollution zone is formed by the leakage of drilling and completion working fluid of a fractured carbonate reservoir and the damage radius is large, the deep blockage removal of a natural fracture and the flow capacity recovery of the natural fracture are difficult to achieve through conventional matrix acidification (Guojianchun, Wanghingweng, great Vanhui, abnormal high-stress reservoir transformation theory and technology [ M ]. scientific publishing, 2015).

Aiming at a fractured carbonate reservoir, the technical key of efficient acidification and reconstruction is to remove the damage of natural fracture deep parts caused by the leakage of working fluid in the well drilling and completion process. The core thought is as follows: forcing the natural cracks to be opened again with certain construction displacement, enabling acid liquor to flow along the natural cracks to react so as to form certain effective crack length and acidified crack width of the natural cracks, and finally forming a high-speed oil-gas flow channel (Guojianchun, Lucleng, Xiaoage, conception, leaf and essence, SANGYU, Quchuandi Longzimai group reservoir modification technology for maximally reducing the epidermal coefficient of a gas reservoir [ J ] natural gas industry, 2014, (03): 97-102).

The existing fracture type carbonate reservoir acidizing design method only uses an effective action distance of acid liquor (the distance of the fracture flowing through before the acid liquor is changed from active acid to residual acid is the effective action distance of the acid liquor) as an index to optimize the construction displacement of the acid liquor and the acid liquor consumption (Zhao Qiang, Liu Ping Li, Liu Dong, and the like.) in the fracture type carbonate reservoir matrix acidizing design calculation method, researches [ J ]. the natural gas industry, 2001, 21(4):69-71), and does not judge whether the natural fracture can be reopened under reservoir conditions and engineering conditions.

Efficient acidizing design of ultra-deep fractured carbonate reservoirs includes construction parameter optimization to achieve the dual goals of re-opening natural fractures and improving the flow capacity of natural fractures. The construction parameters to be designed comprise the requirement of the critical re-tensioning discharge capacity Q of the natural crack_roAt the same time, the pressure limiting Q is not exceeded during the construction of the well head_limConstruction displacement Q_opAnd can make the acidified cuticle coefficient S_adThe lowest acid liquor dosage V is achieved_op. The construction discharge capacity and the acid liquor consumption are too small, so that the natural cracks cannot be opened, and the deep blockage removal of the natural cracks cannot be carried out; the construction discharge capacity and the acid liquor consumption are too large, so that the construction risk is increased, and the economic cost is increased. Therefore, a high-efficiency acidification design method for an ultra-deep fractured carbonate reservoir is needed.

Disclosure of Invention

The invention aims to provide an acidification design method for efficient blockage removal of an ultra-deep fractured carbonate reservoir. The method has reliable principle and simple and convenient operation, can directly utilize basic geological parameters of the block and engineering parameters of a target well, conveniently and efficiently develop acidification design, and has wide market application prospect.

In order to achieve the above technical objects, the present invention provides the following technical solutions.

The efficient acidification design method suitable for the ultra-deep layer crack type carbonate reservoir sequentially comprises the following steps of:

(1) calculating injection displacement Q_injValue range of (1), Q_ro≤Q_inj<Q_lim，Q_roCritical displacement for re-opening of natural fractures, Q_limAnd the upper limit displacement of construction is set.

In order to judge whether the natural fracture can be opened in the acidizing process, the compressibility of acid liquor in a shaft, percolation to a reservoir and a reservoir pollution skin coefficient are considered, a shaft pressure building model is established, and a natural fracture re-opening impending model is calculated based on logging information and well body structure dataBoundary displacement Q_ro(ii) a In order to ensure that the pressure of a wellhead does not exceed the construction pressure limit in the construction process, the construction upper limit displacement Q is calculated based on acid liquid system performance evaluation data and well body structure data_lim。

(2) Optimized design construction displacement Q_opAnd the amount of acid solution V_op。

And (4) establishing a radial fracture acidizing simulation model by considering that the natural fracture is a circular fracture around the well hole. Based on the injection displacement range (Q) given in step (1)_ro≤Q_inj<Q_lim) Calculating the effective length r of the natural fracture after acidification under the conditions of different injection discharge capacity and acid liquor dosage_efAnd the width w of the acidified seam_acid. R obtained by calculation_efAnd w_acidCalculating the equivalent borehole radius r after acidizing_aewThen, introducing an acidified epidermis coefficient calculation model, and obtaining Q corresponding to the lowest epidermis coefficient by calculation_injDetermining construction displacement Q_opAnd the corresponding acid solution dosage V_op。

(3) And designing a pumping program.

Based on the preferred Q in step (2)_opAnd V_opIn order to reduce the initial construction difficulty and improve the acid liquor utilization efficiency, a pump injection program is designed by adopting a variable-displacement four-section type stepped injection mode.

In the present invention, the step (1) calculates the injection displacement Q_injThe specific process is as follows:

in order to judge whether the closed natural fracture can be opened under a certain injection displacement, a shaft pressure building model is established (see figure 1): assuming a natural fracture is run through the wellbore, no additional seepage capacity is provided until the fracture is open. The well bore volume is constant, the flow of the acid liquid into the natural fracture and the reservoir is considered as radial flow and accords with Darcy's law, and the improvement of the acid liquid on the permeability of the reservoir in a short time is ignored.

Obtaining bottom hole fluid pressure p by logging and logging information_wReservoir pore pressure p_sRadius r of oil drainage of oil well_ePermeability k of reservoir matrix_mPermeability k after reservoir matrix contamination_dAverage porosity of reservoir phi,Slurry leakage V_lossEffective length of natural fracture r_efAverage natural fracture width w; acquiring the reservoir opening thickness h through well structure data; and obtaining the viscosity mu of the acid liquor through the evaluation data of the acid liquor system performance. And calculating the fluid flow rate Q out of the wellbore according to equation (1)_out(Li Yingchuan oil extraction engineering [ M)]Petroleum industry press, 2009):

in the formula: q_outRepresenting the flow of fluid out of the wellbore, m³/s；

k_mDenotes the reservoir matrix permeability, 10^-3μm²；

h represents reservoir open thickness, m;

p_wrepresents the bottom hole fluid pressure, MPa;

p_srepresents reservoir pore pressure, MPa;

r_erepresents the oil drainage radius of the oil well, m;

r_wrepresents the borehole radius, m;

mu represents the viscosity of the acid solution, mPa & s;

S_drepresenting the pollution skin coefficient of the reservoir without dimension.

Reservoir pollution skin coefficient S in formula (1)_dCalculated from equation (2):

in the formula: k is a radical of_dRepresents the permeability of the reservoir matrix after contamination, 10^-3μm²；

r_dRepresents the reservoir contamination radius, m;

r_ewrepresenting the equivalent borehole radius, m.

Radius of reservoir contamination r in formula (2)_dCalculated from equation (3):

in the formula: v_lossRepresents the amount of slurry leakage, m³；

Phi denotes the reservoir average porosity, dimensionless.

Equivalent borehole radius r in formula (2)_ewCalculated from equation (4):

in the formula: r is_efRepresents the effective natural fracture length, m;

w represents the average width of the natural fracture, m.

Equation (4) is derived from the calculation of equivalent borehole radius proposed by Meyer in 2005 (Meyer B R, Jacot RH. pseudo-state analysis of fine control vertical sections [ C ]// SPE annular Technical reference and inhibition. Society of Petroleum Engineers,2005), in combination with the definition of dimensionless parameter α given by Prats in 1961 (Prats M. effect of vertical sections on pneumatic section-compressive fluidic case [ J ]. Society of Petroleum Engineers Journal,1961: 105. 118. the specific derivation procedure is as follows:

dimensionless parameter α is defined as shown in equation (5):

the equivalent borehole radius calculation method is shown in the formulas (6) and (7):

in the formula: k is a radical of_fDenotes natural fracture permeability, 10^-3μm²；

α denotes dimensionless parameter, dimensionless;

C_fDit shows dimensionless conductivity and dimensionless property.

The non-dimensional conductivity C obtained by driving the formula (5) into the formula (6) and eliminating the non-dimensional parameter α_fDExpression:

the equivalent borehole radius r of the fractured reservoir is obtained by driving the formula (8) into the formula (7)_ewCalculating the formula:

under reservoir contamination conditions, the assumption is made that the natural fracture permeability k in equation (9)_fAnd permeability k of reservoir matrix_mAre all equal to the permeability k after the pollution of the reservoir matrix_dTherefore, the formula (4) can be obtained by simplifying the formula (9).

Based on the calculation result of the formula (1), calculating the volume change amount Δ V of the fluid in the well bore within the time step Δ t by the following formula:

ΔV＝Δt(Q_inj-Q_out) (10)

in the formula: Δ V represents the volume change of the fluid, m³；

Δ t represents the calculation time step, s;

Q_injindicating injection displacement, m³/s。

Obtaining the volume V of the well bore through well body structure data, and calculating the bottom hole fluid pressure change quantity delta p required by the fluid volume change quantity delta V caused by compression action according to the following formula:

in the formula: Δ p represents the change in bottom hole fluid pressure, MPa;

C_acidexpresses the acid liquid compression coefficient, MPa^-1；

V denotes the wellbore volume, m³。

Based on the calculation result of the formula (11), the bottom hole fluid pressure p at the current time step is calculated from the following formula_w：

p_w＝p_w'+Δp (12)

In the formula: p is a radical of_w，p_w' indicates the bottom hole fluid pressure at the current time step and the bottom hole fluid pressure at the last time step, MPa, respectively.

By performing iterative calculation through the expressions (1) to (4) and the expressions (10) to (12), the current injection displacement Q can be obtained_injDownhole fluid pressure p under conditions_w。

Assuming that the acid percolates into the natural fracture and reservoir before the natural fracture opens, when the downhole fluid pressure p_wGreater than or equal to the normal stress sigma of the wall surface of the natural fracture_nJudging that the natural fracture can be opened again;

p_w≥σ_n(13)

in the formula: sigma_nThe normal stress of the wall surface of the natural crack is MPa.

Normal stress σ of natural fracture wall in formula (13)_nCalculated according to the following formula (Li Yingchuan oil extraction engineering [ M ]]Petroleum industry press, 2009):

in the formula: θ represents the angle of approach, degree, of the natural fracture to the wellbore or hydraulic fracture;

σ_Hrepresents the maximum horizontal principal stress, MPa;

σ_hrepresenting the minimum level principal stress, MPa.

From the low injection displacement Q, expressions (1) to (4) and expressions (10) to (14) are used_inj(value 2 m)³Min) starting to take value, calculating the current injection displacement Q_injDownhole fluid pressure p under conditions_wWhen the bottom hole fluid pressure p_wEqual to the normal stress sigma of the wall surface of the natural crack_nAt this time, the injection displacement Q_injNamely the critical discharge Q of the natural crack re-expansion_ro. Otherwise Q may be increased_injRepeating the above steps until fullFoot p_w＝σ_n。

Obtaining acid liquid density rho and friction coefficient f through acid liquid system performance evaluation data, obtaining oil pipe length L, oil pipe diameter D and transformation section medium depth H through well body structure data, and calculating corresponding injection displacement Q according to formula (15)_injLower wellhead pressure p_t(Li Yingchuan oil extraction engineering [ M)]Petroleum industry press, 2009):

p_t＝p_w+p_F-p_H(15)

in the formula: p is a radical of_tRepresents wellhead pressure, MPa;

p_Frepresents the friction resistance of acid liquor in a shaft, namely MPa;

p_Hrepresents the pressure of the fluid column in the wellbore, MPa.

Friction of acid liquid in well_FCalculated according to equation (16):

in the formula: rho represents acid solution density, kg/m³；

f represents the friction coefficient without dimension;

l represents the length of the oil pipe, m;

d represents the diameter of the oil pipe, m.

Pressure p of the fluid column in the well bore in the formula (15)_HCalculated according to equation (17):

p_H＝ρgH (17)

in the formula: g represents the gravity acceleration, and the value is 9.8N/kg;

h represents the depth in the reconstruction segment, m.

From high injection displacement Q_inj(value 7 m)³Min) begins to take value, and the current injection displacement Q is calculated through the formulas (1) - (4), (10) - (12)_injDownhole fluid pressure p under conditions_wThen, the wellhead pressure p is calculated by the equations (15) to (17)_t. When wellhead pressure p_tEqual to pressure limit p of well head construction_lim(pressure limiting P for wellhead construction_limAcquisition according to wellhead parameters), injection displacement Q at that time_injNamely the wellUpper limit discharge capacity Q for construction_lim. Otherwise Q may be reduced_injRepeating the above steps until p is satisfied_t＝p_lim。

Through the steps, the injection displacement Q can be obtained_injWith a lower limit of critical discharge Q of natural fracture re-expansion_roThe upper limit is the upper limit of the construction discharge capacity Q_limI.e. Q_ro≤Q_inj<Q_lim。

In the invention, the construction discharge Q is preferably designed in the step (2)_opAnd the amount of acid solution V_opThe specific process is as follows:

assuming that the natural fracture is a circular fracture around a borehole (see fig. 2), neglecting the loss of acid fluid on the wall surface of the natural fracture, a radial natural fracture acidizing model suitable for the method is obtained according to a flow reaction model of the acid fluid in the natural fracture under a Cartesian rectangular coordinate system proposed by Dong in 2000 and subjected to coordinate change (Dong C, Zhu D, hillAD. modeling of the accessing process in natural fracture [ J ]. SPEjournal,2002,7(04): 400-.

In the formula: x represents the coordinate of the length direction of the natural fracture, m;

z represents the coordinate of the height direction of the natural fracture, m;

p represents the acid flow pressure, MPa;

c represents acid solution concentration, kg/m³；

t represents the acid injection time, s;

k_grepresenting the mass transfer coefficient of acid liquor under the condition of formation temperature, m/s;

β shows the ability of acid to dissolve reservoir rock at formation temperature without dimension.

When equations (18) to (20) are subjected to polar coordinate transformation, an acid liquid mass conservation equation (21)), a mass transfer equation (22)) and a slit width dynamic change equation (23)) in the longitudinal direction of the natural fracture slit under the condition of a radial coordinate system can be obtained as follows:

the initial conditions are as shown in formulas (24) and (25):

p(r)＝0 t＝0 (24)

C(r)＝0 t＝0 (25)

the boundary conditions of the model are as shown in equations (26) to (28):

p(r_f)＝p_s(27)

C(r_w)＝C_i(28)

in the formula: r represents the distance from any position of the natural fracture to the center of the borehole, m;

C_idenotes the initial concentration of acid solution, kg/m³；

K in formula (23)_gβ is obtained from the acid liquor system performance evaluation data.

Acid solution injection amount V_injFrom the current condition of injection displacement Q_injAnd the acid injection time t is calculated as follows:

V_inj＝Q_inj×t (29)

in the formula: v_injRepresents the amount of acid solution injected, m³。

The numerical solution is carried out on the established acid liquid flow reaction model expressions (21) to (29), and the current injection displacement Q can be obtained_injAnd the effective length (effective action distance of acid liquid) r of the natural fracture under the condition of acid injection time t_efAnd the width of the acidified seam w_acidSubstituting the equivalent radius into the formula to obtain the equivalent wellbore radius r after acidizing_aew：

In the formula: r is_aewRepresents the equivalent wellbore radius after acidizing, m;

r_efrepresents the effective natural fracture length, m;

k_drepresents the permeability of the reservoir matrix after contamination, 10^-3μm²；

w_acidDenotes the post-acidification seam width, m.

Equation (30) based on the fracture type reservoir equivalent borehole radius r_ewThe calculation formula (equation (9)) evolves.

Under the conditions of acidizing measures taken against natural fractures, the following assumptions are made: permeability k of reservoir matrix in formula (9)_mEqual to the permeability k after contamination of the reservoir matrix_d(ii) a Permeability k of natural fracture_fEqual to the permeability k of the natural fracture after acidification_afThe average width w of natural cracks is equal to the width w of acidified cracks_acid. Therefore, the formula (31) can be obtained by taking the assumed parameter into the formula (9).

In the formula: k is a radical of_afDenotes the permeability after acidizing of the natural fracture, 10^-3μm²；

Permeability k after acidification of natural fracture_afFrom the width w of the acidified seam_acidAnd (3) calculating according to the cubic law to obtain:

the equivalent borehole radius r after acidification can be obtained by substituting formula (32) for formula (31)_aewAnd (4) calculating a formula.

Equivalent well bore radius r after acidizing_aewSubstituting into the following formula (evolved from formula (2)) to obtain acidified epidermal coefficient S_ad：

In the formula: s_adThe index of the acidified epidermis is expressed without dimension.

Based on the injection displacement Q calculated in step (1)_injThe different Q values are calculated in sequence by the calculation methods provided by the equations (21) to (33)_injAnd V_injAcidified cuticle coefficient under conditions S_ad. Final optimization of acidified cuticle coefficient S_adInjection displacement Q corresponding to the lowest value_injAnd acid liquor injection amount V_injAs construction displacement Q_opAnd the amount of acid solution V_op。

In the invention, the pump injection program is designed in the step (3), and the specific process is as follows:

in order to reduce the initial construction difficulty, further improve the utilization efficiency of acid liquor and increase the width of a natural crack in a near-wellbore area, a pump injection program is designed by adopting a variable-displacement four-section type stepped injection mode:

in the first stage, 10% V of acid is injected_opThe injection displacement is usually 1-2 m³The specific view is determined according to the pressure of a wellhead;

in the second stage, 30% V of acid is injected_opThe injection displacement is increased to Q from the first stage injection displacement_opChanging the step number A;

in the third stage, 30% V of acid is injected_opAnd the injection displacement is the construction displacement Q of the optimized design_op；

The fourth stage, 30% V of acid is injected_opInjection displacement of Q_opAnd decreasing to the first stage injection displacement and changing the step number A.

Wherein in the second and fourth stagesThe injection time of each step is equal, and the acid quantity V of each step is injected_pDetermined by the total acid amount in the stage and the number of injection steps:

in the formula: v_pRepresents the amount of acid injected per step, m³；

A represents the number of implant steps, dimensionless.

The number A of the second and fourth stage change steps is 3-5, and is determined according to the site construction pressure.

Compared with the prior art, the invention has the following beneficial effects:

the construction parameters designed by the invention consider the mechanical characteristics of the natural fracture opening process of the fractured carbonate reservoir and the acid liquid flow reaction characteristics after opening, and simultaneously combine the geological characteristics of the reservoir and the engineering conditions, so that the problem of blindness in the design of the deep plugging removal and acidification construction parameters of the current ultra-deep fractured carbonate reservoir can be solved to a great extent, the acidification yield increase effect is improved, and the acidification economic cost is saved.

Drawings

Fig. 1 is a schematic diagram of a wellbore pressure build-up model.

FIG. 2 is a schematic view of a radial natural fracture acidizing model.

FIG. 3 is a bottom-of-well pressure versus wellhead pressure calculation for different injection displacements.

FIG. 4 shows the amount of acid injected at 100m³The effect of acid output under conditions on the effective length and width of the natural fracture after acidizing.

FIG. 5 is a graph showing the effect of acid injection and acid dosage on epidermal coefficient.

Detailed Description

The invention is further illustrated with reference to the accompanying drawings and examples of field applications.

The embodiments are intended to be illustrative and explanatory of the invention and do not limit the scope of the invention.

The efficient acidification design method is suitable for the ultra-deep layer crack type carbonate reservoir, and comprises the following specific processes:

the completion depth of an open hole completion vertical well of a certain carbonate gas reservoir is 7512m, and 79m of slurry is lost in the well drilling process of 7332-³. And judging the natural fracture development layer section according to the logging information, and acidizing and unblocking the natural fracture of the section. Relevant parameters for this well are shown in table 1.

TABLE 1 physical data of reservoir, fluid parameters, and well structure data of the well

A is calculated according to the formulas (1) to (4) and the formulas (10) to (14) in the step (1) based on the data in the table 1, and the natural fracture re-opening critical discharge Q of the well_roIs 3.5m³Min; calculating the upper limit displacement Q of the wellhead construction according to the expressions (1) to (4), the expressions (10) to (12) and the expressions (15) to (17)_limIs 5m³Min; the bottom and top pressure calculations for different displacement conditions are shown in figure 3.

B, based on the data in the table 1 and the calculation result in the A, carrying out numerical solution on the equations (21) to (29) by adopting a finite difference method according to the step (2), and obtaining the corresponding effective length r of the natural fracture under the conditions of different discharge capacities and different acid quantities_efAnd the width w of the acidified seam_acidWherein is 100m³Using different discharge capacities under the condition of acid amount to correspond to r_efAnd w_acidAs shown in fig. 4;

c calculating the difference r from the formulas (30) to (33) in the step (2) based on the data in Table 1 and the calculation results in B_efAnd w_acidCorresponding acidified epidermis factor S_ad。

D according to the calculation results of the mesoderm coefficients (figure 5) in C, respectively and preferably designing the construction discharge capacity Q_opAnd design acid liquor dosage V_op① designed construction discharge capacity Q_op: acidified epidermis factor S_adDecreases significantly with increasing displacement, but 5m³The pressure of the well head corresponding to min is very close to the pressure limiting of the well head, and 4.5m is selected in consideration of construction safety³Min as Q _op② design acid liquor dosage V_op: at 4.5m³Acidified epidermis coefficient S under/min condition_adDecreases with increasing acid solution dosage, but exceeds 200m³The later reduction amplitude is not obvious, and 200m is selected in consideration of economic factors³As V_op。

E adopts the construction displacement Q recommended in D_opAnd the amount of acid solution V_opAnd (4) designing a pumping program through the step (3). The pump injection program is specifically designed as follows:

in the first stage, the amount of acid injected is 20m³Injection displacement of 2m³/min；

In the second stage, the amount of acid injected is 60m³The injection displacement is 2m³The/min is increased to 4.5m³Min, the number of steps is changed to 4, and the acid amount of the steps is 15m³；

In the third stage, the amount of acid injected is 60m³And the injection displacement is 4.5m of optimally designed construction displacement³/min；

The fourth stage, the amount of acid injected is 60m³The injection displacement is controlled to be 4.5m³Min is decreased to 2m³Min, the number of steps is changed to 4, and the acid amount of the steps is 15m³。

The construction displacement and the acid liquor consumption determined by the invention are successfully implemented on site of the well, and the yield of the well is tested to obtain 83.7 multiplied by 10 after acidification⁴m³And d, the elevation is 2.3 times higher than that of the adjacent well S2, and the efficient transformation of the reservoirs is successfully realized through the method.

Claims (2)

1. The efficient acidification design method suitable for the ultra-deep layer crack type carbonate reservoir sequentially comprises the following steps of:

(1) calculating injection displacement Q_injValue range of (1), Q_ro≤Q_inj<Q_lim，Q_roCritical displacement for re-opening of natural fractures, Q_limFor the construction upper limit displacement, the concrete process is as follows:

critical discharge Q for re-opening of natural crack_roMeter (2)The calculation is by the following formula:

ΔV＝Δt(Q_inj-Q_out)

p_w＝p_w'+Δp

in the formula: q_outRepresenting the flow of fluid out of the wellbore, m³/s；

k_mDenotes the reservoir matrix permeability, 10^-3μm²；

h represents reservoir open thickness, m;

p_wrepresents the bottom hole fluid pressure, MPa;

p_srepresents reservoir pore pressure, MPa;

r_erepresents the oil drainage radius of the oil well, m;

r_wrepresents the borehole radius, m;

mu represents the viscosity of the acid solution, mPa & s;

S_drepresenting the pollution skin coefficient of the reservoir without dimension;

Δ V represents the volume change of the fluid, m³；

Δ t represents the calculation time step, s;

Q_injindicating injection displacement, m³/s；

Δ p represents the change in bottom hole fluid pressure, MPa;

C_acidexpresses the acid liquid compression coefficient, MPa^-1；

V denotes the wellbore volume, m³；

p_w，p_w' separately representing the bottom hole fluid pressure at the current time step and the bottom hole fluid pressure at the last time step, MPa;

from low injection displacement Q_injStarting to take value, calculating the current injection displacement Q_injDownhole fluid pressure p under conditions_wWhen the bottom hole fluid pressure p_wEqual to the normal stress sigma of the wall surface of the natural crack_nAt this time, the injection displacement Q_injNamely the critical discharge Q of the natural crack re-expansion_ro；

Construction upper limit discharge capacity Q_limIs calculated by the following formula:

p_t＝p_w+p_F-p_H

p_H＝ρgH

in the formula: p is a radical of_tRepresents wellhead pressure, MPa;

p_Frepresents the friction resistance of acid liquor in a shaft, namely MPa;

p_Hrepresents the pressure of the liquid column in the shaft, MPa;

rho represents acid solution density, kg/m³；

f represents the friction coefficient without dimension;

l represents the length of the oil pipe, m;

d represents the diameter of the oil pipe, m;

h represents the middle depth of the reconstruction section, m;

from high injection displacement Q_injStarting to take value, calculating the current injection displacement Q_injDownhole fluid pressure p under conditions_wAnd p_tWhen wellhead pressure p_tEqual to pressure limit p of well head construction_limAt this time, the injection displacement Q_injNamely the upper limit discharge capacity Q of the wellhead construction_lim；

(2) Optimized design construction displacement Q_opAnd the amount of acid solution V_opBy the following formula:

V_inj＝Q_inj×t

in the formula: v_injRepresents the amount of acid solution injected, m³；

Q_injIndicating injection displacement, m³/s；

t represents the acid injection time, s;

r_aewrepresents the equivalent wellbore radius after acidizing, m;

r_efrepresents the effective natural fracture length, m;

k_drepresents the permeability of the reservoir matrix after contamination, 10^-3μm²；

w_acidRepresents the seam width after acidification, m;

S_adthe acidified epidermis coefficient is shown, and the dimension is not increased;

k_mdenotes the reservoir matrix permeability, 10^-3μm²；

r_wRepresents the borehole radius, m;

r_drepresents the reservoir contamination radius, m;

based on injection displacement Q_injSequentially calculating different Q values_injAnd V_injAcidified cuticle coefficient under conditions S_adPreferably the acidified epidermal coefficient S_adInjection displacement Q corresponding to the lowest value_injAnd acid liquor injection amount V_injAs construction displacement Q_opAnd the amount of acid solution V_op；

(3) Designing a pumping program, namely designing the pumping program by adopting a variable-displacement four-section type step injection mode:

in the first stage, 10% V of acid is injected_opAnd the injection displacement value is 1-2 m³/min；

In the second stage, 30% V of acid is injected_opThe injection displacement is increased to Q from the first stage injection displacement_opChanging the step number A;

in the third stage, 30% V of acid is injected_opAnd the injection displacement is the construction displacement Q of the optimized design_op；

Fourth stage, 30% of acid is injected％V_opInjection displacement of Q_opDecreasing the injection displacement to the first stage and changing the step number A;

wherein the injection time of each step in the second and fourth stages is equal, and the acid amount V is injected into each step_pDetermined by the total acid amount in the stage and the number of injection steps:

in the formula: v_pRepresents the amount of acid injected per step, m³；

A represents the number of injection steps without dimension, and the value of A is 3-5.

2. The efficient acidizing design method suitable for ultra-deep fractured carbonate reservoirs according to claim 1, wherein the natural fracture re-expansion critical displacement Q_roIn the calculation of (2), the flow rate Q of the fluid out of the wellbore_outCalculated by the following formula:

in the formula: k is a radical of_mDenotes the reservoir matrix permeability, 10^-3μm²；

h represents reservoir open thickness, m;

p_wrepresents the bottom hole fluid pressure, MPa;

p_srepresents reservoir pore pressure, MPa;

r_erepresents the oil drainage radius of the oil well, m;

r_wrepresents the borehole radius, m;

mu represents the viscosity of the acid solution, mPa & s;

S_drepresenting the pollution skin coefficient of the reservoir without dimension;

k_drepresents the permeability of the reservoir matrix after contamination, 10^-3μm²；

r_dRepresents the reservoir contamination radius, m;

r_ewrepresents the equivalent borehole radius, m;

r_efrepresents the effective natural fracture length, m;

w represents the average width of the natural fracture, m.

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