Unblocking method for heavy mud pollution of ultrahigh-pressure gas well

Abstract

The invention relates to the technical field of oil production engineering, in particular to an ultrahigh-pressure gas well heavy mud pollution unblocking method which comprises the steps that the using amount of an unblocking agent is determined according to the pollution condition of a target layer of a fractured polluted well; the plug removal construction comprises two sections of construction operations of a plug removal earlier stage and a plug removal later stage: in the plug removal earlier stage, plug removal liquid is pumped in by adopting low displacement, and the displacement of the plug removal liquid in the plug removal earlier stage is greater than the opening displacement of natural fractures and smaller than the opening displacement of artificial fractures of reservoirs; in the later stage of blocking removal, blocking removal liquid is pumped in through high displacement; in the later stage of unblocking, the discharge capacity of the unblocking liquid is larger than the open discharge capacity of the artificial fracture of the reservoir and smaller than the discharge capacity of construction pressure limiting. According to the method, the using amount of the blocking remover is calculated according to the pollution range, the method of solving near blocking with low displacement in the early stage and solving far blocking with high displacement in the later stage is provided, the blocking removal effect is enhanced, and scientific and technological support and technical guarantee are provided for removing mud pollution of a polluted well after fracturing.

Description

Technical Field

[0001] This invention relates to the field of oil production engineering technology and is a method for unclogging heavy mud contamination in ultra-high pressure gas wells. Background Technology

[0002] The central section of the southern margin of the Junggar Basin, a key area for oil and gas development, is characterized by its ultra-deep, high-temperature, and ultra-high-pressure nature. Currently, most gas wells in this area require fracturing for production. However, during fracturing testing and well completion tubing replacement, high-density drilling mud is prone to leakage, leading to the deposition and accumulation of barite particles in natural fractures, reservoir matrix, and artificial fractures. This results in decreased production and pressure in wells. Therefore, there is an urgent need to establish a targeted reservoir unblocking process and parameter design method to guide the safe and effective unblocking of wells contaminated with drilling mud after fracturing, and to guide the safe and efficient development of similar deep ultra-high-pressure gas wells.

[0003] Conventional reservoir fluid damage primarily stems from contamination caused by drilling and completion fluid leakage into formation matrix pores and natural fractures during drilling and completion. However, there is currently no research data on contamination caused by well-killing mud leakage into matrix pores, natural fractures, and artificial fractures during well-killing and completion string replacement after fracturing. Furthermore, existing unblocking technologies mainly target matrix and natural fracture contamination in unfractured wells, lacking analysis on wells experiencing mud contamination after fracturing and completion string replacement. Therefore, a design method for unblocking mud-contaminated wells after fracturing is needed to remove contamination from seepage channels and improve gas well production capacity. Summary of the Invention

[0004] This invention provides a method for unclogging heavy mud contamination in ultra-high pressure gas wells, overcoming the shortcomings of the prior art and effectively solving the problem of reservoir contamination caused by mud loss after fracturing.

[0005] The technical solution of this invention is achieved through the following measures: a method for unclogging heavy mud contamination in ultra-high pressure gas wells, comprising:

[0006] The dosage of unblocking agent is determined based on the contamination status of the target formation in the contaminated well after fracturing.

[0007] The congestion relief work includes two phases: the initial phase and the final phase.

[0008] In the initial stage of unblocking, a low-flow-rate pump is used to inject the unblocking fluid. The initial flow rate of the unblocking fluid is Q. 前期注入 The following conditions must be met: Q 前期注入 The displacement Q is greater than the opening of a natural crack. 天然裂缝张开 And less than the reservoir artificial fracture opening displacement Q 人工裂缝张开 ;

[0009] In the later stages of unblocking, a high-flow-rate pump is used to inject the unblocking fluid; the flow rate Q of the unblocking fluid in the later stages of unblocking is... 后期注入The following conditions must be met: Q 后期注入 Greater than the reservoir artificial fracture opening displacement Q 人工裂缝张开 And less than the discharge volume Q of the construction pressure limit. 施工限压 .

[0010] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0011] The dosage of the unblocking agent is determined based on the contamination status of the target formation in the fracturing well, including:

[0012] Determine whether the artificial fractures in the target formation of a fracturing well are contaminated;

[0013] When artificial fractures are contaminated, the amount of unplugging agent used includes the amount of unplugging agent V required for unplugging the artificial fractures in the target formation of the contaminated well after fracturing. 人工裂缝 The amount of unblocking agent V required for unblocking matrix pores in the near-wellbore zone 基质 The amount of unclogging agent required for unclogging natural cracks (V) 天然裂缝 .

[0014] The above-mentioned determination of whether the artificial fractures in the target formation of a fracturing well are contaminated includes:

[0015] The artificial fracture throat diameter r is determined based on the relationship between the artificial fracture throat diameter and the pressure difference inside and outside the fracture.

[0016] When the particle size (diameter) R of the weighting agent used in the target layer fracturing operation 加重剂 When kr is greater than or equal to kr, it is determined that the artificial crack is contaminated with a weighting agent, where k is a coefficient.

[0017] The relationship between the diameter r of the artificial fracture throat and the pressure difference inside and outside the fracture is as follows:

[0018]

[0019]

[0020] Where r is the diameter of the artificial fracture throat (m); R is the diameter of the artificial fracture proppant sphere (m); β is the deformation of the artificial fracture proppant (m); P is the pressure difference between the inside and outside of the fracture (MPa); Wf o V1 is the width of the non-deformable, non-embedded support crack, in meters; V1 is the Poisson's ratio of the proppant, dimensionless; E1 is the elastic modulus of the proppant, in MPa.

[0021] The amount of unclogging agent V required for unclogging the above-mentioned artificial cracks 人工裂缝 The following formula is used to calculate:

[0022] V 人工裂缝 = (4 / 3 × π × a × b × w × α) × ρ × ε × M Equation 3

[0023] Where a is the half-length of the artificial fracture (m); b is the half-height of the artificial fracture (m); w is the width of the artificial fracture (m); α is the barite plugging volume correction coefficient, dimensionless; and ρ is the density of barite (g / cm³). 3 ε is an additional coefficient, dimensionless; M is the dosage of unblocking agent consumed per unit weight of barite, m 3 / t.

[0024] The required amount of unblocking agent V for unblocking the matrix pores in the aforementioned near-wellbore zone 基质 The following formula is used to calculate:

[0025] V 基质 =π×d 2 ×h×Φ Formula 4

[0026] Where d is the reservoir base contamination radius, in meters; h is the perforation section length, in meters; and Φ is the average porosity of the target layer, in percent.

[0027] The required amount of unclogging agent V for unclogging the above-mentioned natural cracks 天然裂缝 The following formula is used to calculate:

[0028] V 天然裂缝 = (N×L×H×γ×α)×ρ×ε×M Equation 5

[0029] Where N is the number of natural fractures in the near-wellbore zone, dimensionless; L is the fracture length, m; H is the fracture height, m; γ is the width of the artificial fracture under closed-loop conditions, m; α is the barite plugging volume correction factor, dimensionless; and ρ is the barite density, g / cm³. 3 ε is an additional coefficient, dimensionless; M is the dosage of unblocking agent consumed per unit weight of barite, m 3 / t.

[0030] The initial injection volume of the unblocking fluid pump mentioned above is V. 基质 and V 天然裂缝 The sum of these values, and the injection volume of the unblocking fluid pump in the later stage of unblocking, is V for artificial cracks.

[0031] The above-mentioned natural crack opening displacement Q 天然裂缝张开 Reservoir artificial fracture opening displacement Q 人工裂缝张开 Construction pressure limiting displacement Q 施工限压 It is obtained by the following method:

[0032] The pressure p within the artificially fractured reservoir 人工裂缝张开 Construction pressure limit p 施工限压 The internal pressure p of a natural crack opening 天然裂缝张开 Substituting into the left side of equation 6, we can calculate Q. 人工裂缝张开 Q 施工限压 and Q 天然裂缝张开 ,

[0033]

[0034] Where, p net E is the net pressure within the crack, MPa; E is Young's modulus, MPa; H is the crack height, m; Q is the displacement, m³. 3 / min; μ is the liquid viscosity, mpa.s; L is the crack length, m.

[0035] The intra-fracture pressure p of the artificially created fractures in the aforementioned reservoir 人工裂缝张开 The pressure p within the natural crack opening 天然裂缝张开 The result is obtained by calculation using the following formula:

[0036] p 天然裂缝张开 =(σ H -σ h (1-cos2θ) / 2 Equation 7

[0037] p 人工裂缝张开 =σ H -σ h Formula 8

[0038] Where θ is the contact angle, °; σ H The maximum principal stress is σ, MPa; h The minimum principal stress is , MPa.

[0039] This invention provides a method for unclogging heavily contaminated mud wells after fracturing and replacement of the completion tubing. It is applicable to wells contaminated with mud after fracturing. The method determines the contamination range of the well after fracturing, calculates the dosage of unclogging agent based on the contamination range, and proposes a variable displacement method to increase the affected area by "low displacement in the early stage to unclogging near the blockage + high displacement in the later stage to unclogging distant the blockage," thereby enhancing the unclogging effect and providing scientific and technological support for the removal of mud contamination in wells after fracturing. Attached Figure Description

[0040] Appendix Figure 1 This is a schematic diagram of the contamination range of the injection fluid in unfractured wells and fractured wells in Embodiment 11 of the present invention.

[0041] Appendix Figure 2 This is a schematic diagram showing the relationship between the diameter of the artificial crack throat and the pressure difference in Embodiment 11 of the present invention. Detailed Implementation

[0042] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0043] The present invention will be further described below with reference to embodiments:

[0044] Example 1: This method for unclogging heavy mud contamination in ultra-high pressure gas wells includes:

[0045] The dosage of unblocking agent is determined based on the contamination status of the target formation in the contaminated well after fracturing.

[0046] The congestion relief work includes two phases: the initial phase and the final phase.

[0047] In the initial stage of unblocking, a low-flow-rate pump is used to inject the unblocking fluid. The initial flow rate of the unblocking fluid is Q. 前期注入 The following conditions must be met: Q 前期注入 The displacement Q is greater than the opening of a natural crack. 天然裂缝张开 And less than the reservoir artificial fracture opening displacement Q 人工裂缝张开 ;

[0048] In the later stages of unblocking, a high-flow-rate pump is used to inject the unblocking fluid; the flow rate Q of the unblocking fluid in the later stages of unblocking is... 后期注入 The following conditions must be met: Q 后期注入 Greater than the reservoir artificial fracture opening displacement Q 人工裂缝张开 And less than the discharge volume Q of the construction pressure limit. 施工限压 .

[0049] Example 2: As an optimization of the above example, the dosage of the unblocking agent is determined based on the contamination status of the target formation in the fracturing well, including:

[0050] Determine whether the artificial fractures in the target formation of a fracturing well are contaminated;

[0051] When artificial fractures are contaminated, the amount of unplugging agent used includes the amount of unplugging agent V required for unplugging the artificial fractures in the target formation of the contaminated well after fracturing. 人工裂缝 The amount of unblocking agent V required for unblocking matrix pores in the near-wellbore zone 基质 The amount of unclogging agent required for unclogging natural cracks (V) 天然裂缝 .

[0052] In this invention, the near-wellbore zone refers to the contaminated area surrounding the target formation of the contaminated well to be unplugged. It should be noted that the pre- and post-unplugging construction operations in this invention are for target formations where the mud contamination range includes artificial fractures, matrix porosity in the near-wellbore zone, and natural fractures. For reservoirs where artificial fractures are not contaminated, the pre-unplugging construction plan in this invention can also be applied to unplugging matrix porosity and natural fractures in the near-wellbore zone.

[0053] Example 3: As an optimization of the above examples, determining whether artificial fractures in the target formation of a fracturing well are contaminated includes:

[0054] The artificial fracture throat diameter r is determined based on the relationship between the artificial fracture throat diameter and the pressure difference inside and outside the fracture.

[0055] When the particle size (diameter) R of the weighting agent used in the target layer fracturing operation 加重剂When the value is ≥kr, it is determined that the artificial crack is contaminated with a weighting agent, where k is a coefficient. In this invention, k is set to 0.5.

[0056] Example 4: As an optimization of the above examples, the relationship between the artificial fracture throat diameter r and the pressure difference inside and outside the fracture is as follows:

[0057]

[0058]

[0059] Where r is the diameter of the artificial fracture throat (m); R is the diameter of the artificial fracture proppant sphere (m); β is the deformation of the artificial fracture proppant (m); P is the pressure difference between the inside and outside of the fracture (MPa); Wf o V1 is the width of the non-deformable, non-embedded support crack, in meters; V1 is the Poisson's ratio of the proppant, dimensionless; E1 is the elastic modulus of the proppant, in MPa. All these parameters can be obtained from actual field parameters and laboratory experimental methods.

[0060] After well shut-in following fracturing and testing, the weighting agent particles (usually barite powder) in the kill mud can easily diffuse into the seepage channels and precipitate, causing reservoir contamination. While barite powder can cause precipitation contamination in reservoir matrix pore throats and natural fractures, whether it causes contamination in artificial fractures requires separate assessment. Based on the understanding that fracturing well heavy mud contamination is caused by the precipitation of barite particles in artificial fractures during the kill process, the formation of a strong bridging structure between barite particles and proppant pore throats during the flowback process, and the resulting "easy entry, difficult exit" blockage mechanism, this invention proposes a method for determining whether barite powder contamination occurs in artificial fractures during the shut-in flowback process. This method determines the contamination range based on the contamination mechanism, thereby accurately designing the dosage of unblocking agent.

[0061] Example 5: As an optimization of the above examples, the amount of unclogging agent V required for artificial crack unclogging is... 人工裂缝 The following formula is used to calculate:

[0062] V 人工裂缝 = (4 / 3 × π × a × b × w × α) × ρ × ε × M Equation 3

[0063] Where a is the half-length of the artificial fracture (m); b is the half-height of the artificial fracture (m); w is the width of the artificial fracture (m); α is the barite plugging volume correction coefficient, dimensionless; and ρ is the density of barite (g / cm³). 3 ε is an additional coefficient, dimensionless; M is the dosage of unblocking agent consumed per unit weight of barite, m 3 / t.

[0064] Example 6: As an optimization of the above examples, the amount of unblocking agent V required for unblocking matrix pores in the near-wellbore zone is... 基质 The following formula is used to calculate:

[0065] V基质 =π×d 2 ×h×Φ Formula 4

[0066] Where d is the reservoir base contamination radius, in meters; h is the perforation section length, in meters; and Φ is the average porosity of the target layer, in percent.

[0067] Example 7: As an optimization of the above examples, the amount of unclogging agent V required for unclogging natural cracks 天然裂缝 The following formula is used to calculate:

[0068] V 天然裂缝 = (N×L×H×γ×α)×ρ×ε×M Equation 5

[0069] Where N is the number of natural fractures in the near-wellbore zone, dimensionless; L is the fracture length, m; H is the fracture height, m; γ is the width of the artificial fracture under closed-loop conditions, m; α is the barite plugging volume correction factor, dimensionless; and ρ is the barite density, g / cm³. 3 ε is an additional coefficient, dimensionless; M is the dosage of unblocking agent consumed per unit weight of barite, m 3 / t.

[0070] In this invention, α is 0.25, and the additional coefficient ε is the amount of unblocking agent needed to dissolve barite that is 20% to 40% more than that required in the laboratory, with a value ranging from 1.2 to 1.4.

[0071] Example 8: As an optimization of the above example, the injection volume of the unblocking fluid pump in the early stage of unblocking is V. 基质 and V 天然裂缝 The total injection volume of the unblocking fluid pump in the later stage of unblocking is V. 人工裂缝 .

[0072] Example 9: As an optimization of the above examples, the natural crack opening displacement Q 天然裂缝张开 Reservoir artificial fracture opening displacement Q 人工裂缝张开 Construction pressure limiting displacement Q 施工限压 It is obtained by the following method:

[0073] The pressure p within the artificially fractured reservoir 人工裂缝张开 Construction pressure limit p 施工限压 The internal pressure p of a natural crack opening 天然裂缝张开 Substituting into the left side of equation 6, we can calculate Q. 人工裂缝张开 Q 施工限压 and Q 天然裂缝张开 ,

[0074]

[0075] Where, p netE is the net pressure within the crack, MPa; E is Young's modulus, MPa; H is the crack height, m; Q is the displacement, m³. 3 / min; μ is the liquid viscosity, mpa.s; L is the crack length, m.

[0076] This invention is based on the net pressure p inside the seam. net Calculation formula Calculate the unblocking displacement, let p 人工裂缝张开 p 施工限压 p 天然裂缝张开 equals p net Substituting into equation 6, we obtain Q. 人工裂缝张开 Q 施工限压 and Q 天然裂缝张开 .

[0077] Example 10: As an optimization of the above examples, the intra-fracture pressure p of the artificially opened reservoir fractures 人工裂缝张开 The pressure p within the natural crack opening 天然裂缝张开 The result is obtained by calculation using the following formula:

[0078] p 天然裂缝张开 =(σ H -σ h (1-cos2θ) / 2 Equation 6

[0079] p 人工裂缝张开 =σ H -σ h Formula 7

[0080] Where θ is the contact angle, °; σ H The maximum principal stress is σ, MPa; h The minimum principal stress is , MPa.

[0081] Example 11: The specific implementation process of this method for unclogging heavy mud contamination in ultra-high pressure gas wells is as follows:

[0082] Specific Implementation Method: The specific implementation process of this method for unclogging heavy mud contamination in ultra-high pressure gas wells is as follows:

[0083] S1, Determine the extent of mud contamination after fracturing:

[0084] After fracturing and well shut-in testing, barite powder particles in the kill mud can easily diffuse into the seepage channels and precipitate, causing reservoir contamination. According to literature review, barite powder, a weighting agent, can cause precipitation contamination in reservoir matrix pore throats and natural fractures, but whether it causes contamination in artificial fractures is unknown. Figure 1 (The left image shows an unfractured well, and the right image shows a fractured well.) It can be seen that the contamination of the fluid entering the fractured well includes artificial fractures, and the contamination area is larger than that of the unfractured well. Therefore, before unblocking operations, it is necessary to first determine whether the artificial fractures are contaminated with barite powder during the well shut-in and backflow processes.

[0085] First, the diameter r of the artificial fracture throat is determined based on the relationship between the diameter of the artificial fracture throat and the pressure difference inside and outside the fracture.

[0086] Calculation of support crack throat:

[0087]

[0088] Calculation of proppant deformation:

[0089]

[0090] Where r is the diameter of the artificial fracture throat (m); R is the diameter of the artificial fracture proppant sphere (m); β is the deformation of the artificial fracture proppant (m); P is the pressure difference between the inside and outside of the fracture (MPa); Wf o The width of the support crack that does not deform or embed, in meters; V1 is the Poisson's ratio of the proppant; E1 is the elastic modulus of the proppant, in MPa (all parameters can be obtained from actual field parameters or laboratory experimental methods).

[0091] Based on the above formula, the relationship between the diameter of the artificial fracture throat and the pressure difference is obtained (see...). Figure 2 Based on the relationship between the proppant pore throat diameter and pressure differential, the proppant pore throat diameter during well kill and flowback processes can be quantitatively calculated and compared with the barite particle size.

[0092] Then, based on the particle size R of the weighting agent 加重剂 The diameter of the artificial fracture throat is used to determine whether there is weighting agent contamination in the artificial fracture. The particle size R of the weighting agent used in the target layer fracturing operation is also considered. 加重剂 When the diameter of the artificial fracture throat (r) is greater than or equal to 0.5 times the diameter of the artificial fracture throat, it is determined that the artificial fracture is contaminated with a weighting agent. Taking well Hu102 as an example, if... Figure 2 As shown, during the well control process of Well Hu 102, the pressure difference between the inside and outside of the fracture was 20 MPa, corresponding to a proppant pore throat diameter of 68 μm. At this time, the 30 μm diameter barite particles used during fracturing could freely diffuse into the artificial fracture support area. During the flowback process, the pressure difference between the inside and outside of the fracture was 100 MPa, and the pore throat diameter was 56 μm. At this time, the 30 μm barite particles were prone to precipitate, clump, and cause bridging at the pore throat, resulting in contamination. Therefore, the mud contamination range of Well Hu 102 was determined to be the artificial fracture, the matrix pores in the near-wellbore zone, and the natural fracture range.

[0093] S2, Determine the dosage of the unblocking agent:

[0094] The contamination in Well Hu102 includes artificial fractures, matrix pores in the near-wellbore zone, and contamination in natural fractures. The amount of unblocking fluid required is the sum of the amounts of unblocking agent needed for all three types of channels, i.e., V. 总 =V 人工裂缝 +V 基质+V 天然裂缝 .

[0095] The pore portion of the reservoir matrix is ​​calculated using the pore volume method: V 基质 =π·d 2 •h·Φ. The average porosity of the matrix is ​​Φ = 3.362%, and the contamination radius is d = 2m. V is calculated... 基质 =28.7m 3 .

[0096] The dosage of crack unblocking agent is calculated using the crack volume method. The dosage for the extended portion of the crack is as follows:

[0097] V 人工裂缝 = (4 / 3 × π × a × b × w × α) × ρ × ε × M

[0098] V 天然裂缝 = (N×L×H×γ×α)×ρ×ε×M

[0099] Well Hu 102 has the following characteristics: natural fracture length = 2m, artificially supported fracture length = 110.2m, fracture height h = 68m, average fracture width r = 0.0005m during construction, barite plugging volume correction factor α = 0.25, and barite density ρ = 4.3g / cm³. 3 The additional coefficient ε = 1.3, and the unblocking dosage M consumed per unit weight of barite is 83m. 3 / t. V is obtained through calculation. 人工裂缝 =392.8m 3 V 天然裂缝 =43.5m 3 .

[0100] In summary, the total amount of unplugging agent required for the unplugging operation of Well Hu 102 is equal to the sum of the amounts used for the matrix and fractures. The designed unplugging fluid volume is 465m³. 3 .

[0101] S3, the congestion relief construction adopts a scheme of "low-displacement initial stage to relieve near-field congestion + high-displacement later stage to relieve far-field congestion":

[0102] Because reservoir contamination includes both artificially created fractures extending over long distances and matrix and natural fracture contamination in the near-wellbore zone, barite powder precipitates in different seepage channels. To improve the unblocking effect and scope, a variable-displacement pumping process was developed based on theoretical calculations and numerical simulations: "low-displacement unblocking of near-wellbore areas in the early stage + high-displacement unblocking of distant-wellbore areas in the later stage." In the early stage of unblocking, the net pressure (i.e., the effective pressure that remains after the pumped unblocking fluid overcomes friction along the flow path, friction at the borehole, friction in the near-wellbore zone, and fracture closure pressure, ultimately acting directly on the rock to create fractures) is controlled to prevent the opening of new artificial fractures and remove blockages in the near-wellbore seepage channels. In the later stage of unblocking, artificial fractures are opened to remove distant blockages, ultimately achieving complete removal of contamination in both the near-wellbore zone and distant areas.

[0103] Initial stage of unblocking: Unblocking fluid is pumped in at a low rate. During the process, the net pressure is controlled to be lower than the reservoir artificial fracture opening pressure to prevent the unblocking fluid from being wasted due to the opening of new fractures. In other words, the unblocking fluid discharge rate in the initial stage of unblocking should meet the following requirement: Q 天然裂缝张开 <Q 前期注入 <Q 人工裂缝张开 .

[0104] In the later stages of unblocking: After the contamination of the seepage channels in the near-wellbore artificial fractures is cleared, increase the flow rate of the unblocking fluid to open the mud-contaminated artificial fractures and clear the contamination of the distal artificial fractures. During this process, it is necessary to ensure that the flow rate of the unblocking fluid is greater than the flow rate required to open the artificial fractures but less than the flow rate required for the construction pressure limit, i.e., Q. 人工裂缝张开 <Q 后期注入 <Q 施工限压 .

[0105] In this embodiment, the construction parameters for well Hu102 are: Q 天然裂缝张开 =0.2m 3 / min、Q 人工裂缝张开 =1.1m 3 / min、Q 施工限压 =2.0m 3 / min, V 基质 =28.7m 3 V 人工裂缝 =392.8m 3 V 天然裂缝 =43.5m 3 .

[0106] During the initial stage of easing congestion, maintain a displacement of 0.2m. 3 / min<Q 前期注入 <1.1m 3 / min, a total of 72.2m was injected. 3 Unblocking fluid (V) 基质 +V 天然裂缝 For the later stages of congestion relief, maintain a displacement of 1.1m³. 3 / min<Q 后期注入 <2.0m 3 / min, a total of 392.8m³ was injected. 3 Unblocking fluid (V) 人工裂缝 ).

[0107] Compared to existing conventional reservoir injection fluid contamination removal design methods, this invention additionally considers the contamination of artificial fractures by well-killing mud and specifically designs a variable-displacement pump injection process of "low-displacement in the early stage to remove near-hole blockage + high-displacement in the later stage to remove far-hole blockage." In the early stage, net pressure is controlled to prevent the opening of new artificial fractures and remove near-wellbore seepage channel blockage; in the later stage, artificial fractures are opened to remove far-end blockage, achieving complete removal of contamination in both the near-wellbore and far-end areas. This method was used to guide field unblocking tests in wells Hu101 and Hu102, with a 100% success rate. After unblocking, the oil pressure increased by 50.3 MPa to 55.6 MPa compared to before the measures, and daily gas production increased by 16.0 × 10⁻⁶. 4 m 3 / d to 18.6×10 4 m 3 / d. As of the end of May 2024, the two wells had cumulatively increased gas production by 5103 × 10⁻⁶. 4 m 3 / d, with a significant effect in relieving congestion.

[0108] In summary, this invention clarifies that heavy slurry contamination in fractured wells is caused by the precipitation and backflow of barite particles in artificial fractures during the well control process, which forms a strong bridging structure with the proppant pore throat, resulting in a "easy entry, difficult exit" blockage mechanism. Based on this mechanism, the contamination range is determined, and the dosage of unblocking agent is precisely designed, achieving the dual goals of maintaining unblocking effectiveness and controlling costs.

[0109] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for unclogging heavy mud contamination in ultra-high pressure gas wells, characterized in that... include: The dosage of unblocking agent is determined based on the contamination status of the target formation in the contaminated well after fracturing. The congestion relief work includes two phases: the initial phase and the final phase. In the initial stage of unblocking, a low-flow-rate pump is used to inject the unblocking fluid. The initial flow rate of the unblocking fluid is Q. 前期注入 The following conditions must be met: Q 前期注入 The displacement Q is greater than the opening of a natural crack. 天然裂缝张开 And less than the reservoir artificial fracture opening displacement Q 人工裂缝张开 ; In the later stages of unblocking, a high-flow-rate pump is used to inject the unblocking fluid; Discharge rate of unblocking fluid Q in the later stage of unblocking 后期注入 The following conditions must be met: Q 后期注入 Greater than the reservoir artificial fracture opening displacement Q 人工裂缝张开 And less than the discharge volume Q of the construction pressure limit. 施工限压 .

2. The method for unclogging heavy mud contamination in ultra-high pressure gas wells according to claim 1, characterized in that... Based on the contamination status of the target formation in the fracturing well, determine the dosage of the unblocking agent, including: Determine whether the artificial fractures in the target formation of a fracturing well are contaminated; When artificial fractures are contaminated, the amount of unplugging agent used includes the amount of unplugging agent V required for unplugging the artificial fractures in the target formation of the contaminated well after fracturing. 人工裂缝 The amount of unblocking agent V required for unblocking matrix pores in the near-wellbore zone 基质 The amount of unclogging agent required for unclogging natural cracks (V) 天然裂缝 .

3. The method for unclogging heavy mud contamination in ultra-high pressure gas wells according to claim 2, characterized in that... Determining whether artificial fractures in the target formation of a fracturing well are contaminated includes: The artificial fracture throat diameter r is determined based on the relationship between the artificial fracture throat diameter r and the pressure difference inside and outside the fracture. When the particle size R of the weighting agent used in the target layer fracturing operation 加重剂 When kr is greater than or equal to kr, it is determined that the artificial crack is contaminated with a weighting agent, where k is a coefficient.

4. The method for unclogging heavy mud contamination in ultra-high pressure gas wells according to claim 3, characterized in that... The relationship between the diameter r of the artificial fracture throat and the pressure difference inside and outside the fracture is as follows: Where r is the diameter of the artificial fracture throat (m); R is the diameter of the artificial fracture proppant sphere (m); β is the deformation of the artificial fracture proppant (m); P is the pressure difference between the inside and outside of the fracture (MPa); Wf o V1 is the width of the non-deformable, non-embedded support crack, in meters; V1 is the Poisson's ratio of the proppant, dimensionless; E1 is the elastic modulus of the proppant, in MPa.

5. The method for unclogging heavy mud contamination in ultra-high pressure gas wells according to any one of claims 2 to 4, characterized in that... Dosage of unclogging agent V required for artificial crack unclogging 人工裂缝 The following formula is used to calculate: V 人工裂缝 = (4 / 3 × π × a × b × w × α) × ρ × ε × M Equation 3 Where a is the half-length of the artificial fracture (m); b is the half-height of the artificial fracture (m); w is the width of the artificial fracture (m); α is the barite plugging volume correction coefficient, dimensionless; and ρ is the density of barite (g / cm³). 3 ε is an additional coefficient, dimensionless; M is the dosage of unblocking agent consumed per unit weight of barite, m 3 / t.

6. The method for unclogging heavy mud contamination in ultra-high pressure gas wells according to any one of claims 2 to 5, characterized in that... V, the amount of unblocking agent required for unblocking matrix pores in the near-wellbore zone 基质 The following formula is used to calculate: V 基质 =π×d 2 ×h×Φ Formula 4 Where d is the reservoir base contamination radius, in meters; h is the perforation section length, in meters; and Φ is the average porosity of the target layer, in percent.

7. The method for unclogging heavy mud contamination in ultra-high pressure gas wells according to any one of claims 2 to 6, characterized in that... Dosage V of unclogging agent required for unclogging natural cracks 天然裂缝 The following formula is used to calculate: V 天然裂缝 = (N×L×H×γ×α)×ρ×ε×M Equation 5 Where N is the number of natural fractures in the near-wellbore zone, dimensionless; L is the fracture length, m; H is the fracture height, m; γ is the width of the artificial fracture under closed-loop conditions, m; α is the barite plugging volume correction factor, dimensionless; and ρ is the barite density, g / cm³. 3 ε is an additional coefficient, dimensionless; M is the dosage of unblocking agent consumed per unit weight of barite, m 3 / t.

8. The method for unclogging heavy mud contamination in ultra-high pressure gas wells according to any one of claims 2 to 7, characterized in that... The initial injection volume of the unblocking fluid pump is V. 基质 and V 天然裂缝 The total injection volume of the unblocking fluid pump in the later stage of unblocking is V. 人工裂缝 .

9. The method for unclogging heavy mud contamination in ultra-high pressure gas wells according to any one of claims 1 to 8, characterized in that... Natural crack opening displacement Q 天然裂缝张开 Reservoir artificial fracture opening displacement Q 人工裂缝张开 Construction pressure limiting displacement Q 施工限压 It is obtained by the following method: The pressure p within the artificially fractured reservoir 人工裂缝张开 Construction pressure limit p 施工限压 The internal pressure p of a natural crack opening 天然裂缝张开 Substituting into the left side of equation 6, we can calculate Q. 人工裂缝张开 Q 施工限压 and Q 天然裂缝张开 , Where, p net E is the net pressure within the crack, MPa; E is Young's modulus, MPa; H is the crack height, m; Q is the displacement, m³. 3 / min; μ is the liquid viscosity, mpa.s; L is the crack length, m.

10. The method for unclogging heavy mud contamination in ultra-high pressure gas wells according to claim 9, characterized in that... The intra-fracture pressure p of artificially opened fractures in the reservoir 人工裂缝张开 The pressure p within the natural crack opening 天然裂缝张开 The result is obtained by calculation using the following formula: p 天然裂缝张开 = (σ H - σ h )(1 - cos2θ) / 2 Equation 7 p 人工裂缝张开 =σ H -σ h formula 8 Where θ is the contact angle, °; σ H The maximum principal stress is σ, MPa; h The minimum principal stress is , MPa.

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