Intermittent pumping sampling method for low-permeability reservoir

Abstract

The invention relates to an intermittent pumping sampling method for a low-permeability reservoir, which comprises the following steps of: calculating a stratum mobility lower limit of continuous pumping sampling of an ultra-low-permeability reservoir, and carrying out intermittent pumping when the mobility is smaller than the stratum mobility lower limit of continuous pumping sampling; obtaining the breakthrough volume of the formation fluid, and simulating inversion to obtain the original invasion depth of the drilling fluid; according to the experimental data, obtaining the initial invasion speed of the slurry filtrate under different original invasion depths, and determining the upper limit of the continuous invasion speed of the slurry filtrate in the pumping sampling process; performing key factor numerical simulation of intermittent pumping to obtain intermittent pumping operation schemes under different conditions and the total operation time of the corresponding operation schemes; determining an optimal pressure recovery ratio; and an intermittent pumping operation scheme and the total operation time of the operation scheme under the continuous invasion speed of the slurry filtrate and the optimal pressure recovery ratio are obtained. According to the scheme, the sampling problem of the ultra-low permeability reservoir can be solved, and the sampling success rate is increased.

Description

Technical Field

[0001] The invention relates to the technical field of reservoir pump sampling, and more specifically to an intermittent pump sampling method for a low-permeability reservoir. Background Art

[0002] Offshore low-permeability reservoirs contain a large amount of oil and gas resources. They are an important part of building an offshore "oil and gas resource supply and security center" and are of great significance for meeting national energy needs and meeting oil and gas security. However, due to the poor physical properties, complex pore structure, and low contrast of fluid response of low-permeability reservoirs, conventional logging is difficult to accurately evaluate the properties of reservoir fluids. At present, the most important and economical means of implementing fluid properties is cable pump sampling technology, which is crucial for reserve evaluation and operational decision-making in the exploration stage.

[0003] Cable formation testing technology is a testing method used to obtain rock properties and fluid information in low-permeability formations. It can reduce the number of wells tested, shorten the drilling cycle, and improve overall efficiency. This technology lowers the logging tool to a fixed position in the reservoir in the well, and uses the pressure difference to drive the formation fluid into the tool, thereby testing and sampling the reservoir. It is very important for evaluation in the exploration stage, and has now become one of the indispensable technologies for offshore exploration reserve evaluation, cost reduction and efficiency improvement.

[0004] In 2020, Zhao Yuanliang and others studied the pump breakthrough mechanism and found that porosity and invasion depth are the two main factors affecting the purity of formation fluids during pump sampling operations. However, no pump sampling operation method has been formed for ultra-low permeability reservoirs. In 2022, Gao Yongde simulated the correlation between porosity, invasion depth and filtrate contamination rate and pumping time for low-porosity and low-ultra-low permeability reservoirs in the Wenchang A Depression in the Pearl River Mouth Basin, effectively guided the selection of probes and improved the operational timeliness of cable formation testing. However, for ultra-low permeability reservoirs with mobility <0.03mD / cP, the pressure drop exceeds the instrument limit, continuous pumping cannot be established, and the success rate of pump sampling is very low.

[0005] In summary, in low-permeability and ultra-low-permeability formations, the continuous pumping sampling method has a low success rate and cannot obtain formation fluid samples, which in turn affects the accuracy of decision-making and evaluation. Summary of the invention

[0006] In order to overcome the problem that the continuous pumping sampling method in the above-mentioned prior art has a low success rate in low permeability and ultra-low permeability formations and cannot obtain formation fluid samples, the present invention provides an intermittent pumping sampling method for low permeability reservoirs, which can improve the success rate of sampling.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: an intermittent pump sampling method for low permeability reservoirs, comprising the following steps:

[0008] Step 1: After determining that the area is an ultra-low permeability reservoir based on regional geological data and reservoir characteristics, calculate the lower limit of the formation fluidity for continuous pumping sampling based on the test instrument. When the fluidity is less than the lower limit of the formation fluidity for continuous pumping sampling, perform intermittent pumping.

[0009] For example: Taking the Yingqiong Basin as the research target area, combined with regional geological data and reservoir characteristics, it is clear that this block is an ultra-low permeability reservoir. Specifically, the permeability of the Ling 3rd Member reservoir in Baodao District is distributed in the range of 0.1 to 267.67×10 －3 μm 2 The average is 6.02×10 －3 μm 2 , which belongs to low-ultra-low permeability reservoir as a whole. The formation test instrument pump module + probe module combination is preferred. The three commonly used pump modules for cable sampling operations in the area: high-pressure pump module (HP), ultra-high-pressure pump module (XHP), and ultra-ultra-high-pressure pump module (XXHP) are combined with three probe modules with different discharge areas, ultra-large diameter probe, elliptical probe and speed star probe, a total of 9 schemes, which can provide different pumping capacities and adaptability ranges. Calculate the lower limit of the formation fluidity for continuous pumping sampling, determine the fluidity below which intermittent pumping is performed, and clarify the scope of research.

[0010] Calculating the lower limit of formation mobility for continuous pump sampling involves the following steps:

[0011] S1. Determine the initial pump hydraulic pressure: Determine the initial pump hydraulic pressure based on the reservoir characteristics of the target area.

[0012] S2. Determine the flow rate of the pumped fluid: obtain the pump displacement based on the initial pump hydraulic pressure, and obtain the pumped fluid flow rate based on the pump displacement. The calculation formula for the pump displacement is:

[0013] y=-1.2524·10 -17 ·x 5 +1.1166·10 -13 x 4 -3.0068·10 -10 ·x 3 +1.2524

[0014] 10 -17 ·x 2 -1.2525 10 -17 ·x+1.0218

[0015] Where y is the pump displacement; x is the pump hydraulic pressure;

[0016] The formula for determining the pumped fluid flow rate is:

[0017]

[0018] Where POFR is the pumping fluid flow rate; s is the motor speed; D u is the substitution coefficient.

[0019] S3. Calculate the flow pressure based on the flow rate of the pumped fluid.

[0020] The pressure difference between the formation pressure and the flow pressure is calculated according to the flow rate of the pumped fluid, and the flow pressure is calculated according to the pressure difference between the formation pressure and the flow pressure and the formation pressure. The calculation formula for the pressure difference between the formation pressure and the flow pressure is:

[0021]

[0022] Wherein, ΔP is the pressure difference between formation pressure and flow pressure; is the formation fluidity; c s is the probe shape factor.

[0023] S4. Calculate the pressure after the pump according to the flow pressure and pump hydraulic pressure. The calculation formula for the pressure after the pump is:

[0024] P m0 =D u ·P h +P l

[0025] Among them, P m0 is the pressure after the pump; P l is the flow pressure; P h For pump hydraulics.

[0026] S5. Calculate the lower limit of the formation fluidity of the continuous pumping of the pump module and probe module instrument combination and determine the pumping method.

[0027] Step 2: Based on the data of regional historical wells in step 1, the breakthrough volume of formation fluid during the pump sampling process is obtained, and the original invasion depth of drilling fluid is obtained by simulation inversion based on the pump breakthrough volume and porosity.

[0028] The original invasion depth of drilling fluid is obtained by inversion based on the pumping breakthrough volume and porosity of conventional wells. The invasion depth of drilling fluid in low permeability reservoirs ranges from 5 to 17 inches, with an average of 11.8 inches.

[0029] Step 3: Based on the experimental data, the initial invasion velocity of the mud filtrate at different original invasion depths is obtained, that is, the upper limit of the continuous invasion velocity of the mud filtrate during the pump sampling process is determined.

[0030] The static mud invasion rate is obtained by the mud invasion experiment of low porosity and permeability sandstone reservoir without considering the increase of pressure difference. The effective pumping speed is calculated by the total pumping volume and the total operation time.

[0031] Use the different pumping breakthrough volume breakthrough charts to find the total pumping volume for selected conditions.

[0032] The simulated "intermittent" pumping pressure recovery ratio of the oversized probe is 40%, 50%, 60%, 70%, 80%, 90%, the intrusion depth is 8in, 15in, 20in, and the mud contamination rate is 20%, 50%, 80%, and the total operation time under the corresponding conditions is obtained.

[0033] Step 4: Conduct numerical simulation of key factors of intermittent pumping to obtain intermittent pumping operation plans and the total operation time of the corresponding operation plans under different pressure recovery ratios, different invasion depths and different continuous invasion speeds.

[0034] When simulating the key factors of intermittent pumping, the ultra-large diameter probe is used as the research object, the basic parameters of the model are input and determined, and a numerical simulation grid is established. The pumping process under different porosities and invasion depths is numerically simulated according to the numerical simulation grid, and a breakthrough chart of different pumping breakthrough volumes is established to obtain the sampleable pumping volume of the ultra-large probe under different porosities and invasion depths. Among them, the basic parameters of the model include porosity, horizontal permeability, vertical permeability, invasion depth, formation fluid viscosity, formation fluid density, overbalance pressure, water-based mud filtrate viscosity, and water-based mud filtrate density.

[0035] Step 5: Determine the optimal pressure recovery ratio.

[0036] The total operation time increases with the increase of pressure recovery. According to actual data, the pressure recovery ratio is 40% when the instrument failure rate is less than 10%. When the pressure recovery is less than 50%, the increase in operation time is small, but the low pressure recovery ratio means more frequent switching of pumps, which puts a heavy workload on hydraulic and electronic equipment. When the pressure recovery is greater than 70%, the operation time will increase significantly. Therefore, the optimal pressure recovery is 50% to 70%.

[0037] Step 6: Obtain the intermittent pumping operation plan and the total operation time of the operation plan under the drilling invasion depth and the optimal pressure recovery ratio.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention adopts an intermittent pumping sampling method for low permeability reservoirs, breaks through the continuous pumping operation capacity of the cable pressure sampling instrument, and realizes higher quality offshore low permeability reservoir sampling. By innovating the process and system of the existing equipment process, the sampling process is optimized to break through the instrument hardware capacity limitation. This can improve the accuracy and representativeness of sampling. The sampling technology can break through the original lower limit of sampling fluidity, thereby realizing effective sampling in low permeability reservoirs below 0.1-0.3mD / cP. Compared with traditional tools such as higher-end speed star probes and double packers, the optimized sampling technology can save at least 2 million in a single operation. At the same time, due to the low risk, the uncertainty in operation and the possible losses can be reduced. The optimized sampling technology has been successfully applied to 8 low permeability wells, and the sampling success rate has increased from the original 60% to 90%, playing an important role in the implementation of low permeability reserves and improving the quality and efficiency of operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flow chart of an intermittent pump sampling method for a low permeability reservoir of the present invention;

[0040] Figure 2 is a flow chart of calculating the upper limit of formation mobility for intermittent pump sampling of the present invention;

[0041] Figure 3 This is the relationship between the total operation time and the pressure recovery ratio when the penetration depth is 8in;

[0042] Figure 4 This is the relationship between the total operation time and the pressure recovery ratio at the penetration depth of 15in;

[0043] Figure 5 This is the relationship between the total operation time and the pressure recovery ratio at an intrusion depth of 20in;

[0044] Figure 6 It is a design of a pump sampling scheme for ultra-large diameter probes in ultra-low permeability reservoirs;

[0045] Figure 7 This is the interpretation result of intermittent pump sampling of low-permeability sandstone in a well in the South China Sea. DETAILED DESCRIPTION

[0046] The drawings are only for illustrative purposes and cannot be construed as limiting the present invention. To better illustrate the present embodiment, some parts of the drawings may be omitted, enlarged, or reduced, and do not represent the size of the actual product. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the drawings. The positional relationships described in the drawings are only for illustrative purposes and cannot be construed as limiting the present invention.

[0047] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "long", "short" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limitations on this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0048] The technical solution of the present invention is further described in detail below through specific embodiments and in conjunction with the accompanying drawings:

[0049] Example 1

[0050] Example 1 of an intermittent pump sampling method for a low permeability reservoir, such as Figure 1 As shown, the following steps:

[0051] Step 1: After determining that the area is an ultra-low permeability reservoir based on regional geological data and reservoir characteristics, calculate the lower limit of the formation fluidity for continuous pumping sampling using the test instrument. When the fluidity is less than the lower limit of the formation fluidity for continuous pumping sampling, perform intermittent pumping;

[0052] Step 2: Based on the data of historical wells in the area in step 1, the breakthrough volume of formation fluid during the pump sampling process is obtained, and the original invasion depth of drilling fluid is obtained by simulation inversion based on the pump breakthrough volume and porosity;

[0053] Step 3: Based on the experimental data, the initial invasion velocity of the mud filtrate at different original invasion depths is obtained, that is, the upper limit of the continuous invasion velocity of the mud filtrate during the pump sampling process is determined;

[0054] Step 4: Conduct numerical simulation of key factors of intermittent pumping to obtain intermittent pumping operation schemes and the total operation time of the corresponding operation schemes under different pressure recovery ratios, different invasion depths and different continuous invasion speeds;

[0055] Step 5: Determine the optimal pressure recovery ratio;

[0056] Step 6: Obtain the intermittent pumping operation plan and the total operation time of the operation plan under the continuous intrusion rate of the mud filtrate and the optimal pressure recovery ratio.

[0057] Beneficial effects of this embodiment: The present invention adopts an intermittent pumping sampling method for low permeability reservoirs, breaking through the continuous pumping operation capacity of the cable pressure sampling instrument to achieve higher quality offshore low permeability reservoir sampling. By innovating the process and system of the existing equipment and technology, the sampling process is optimized to break through the instrument hardware capacity limitations. This can improve the accuracy and representativeness of the sampling. The sampling technology can break through the original lower limit of the sampling fluidity, thereby achieving effective sampling in low permeability reservoirs below 0.1-0.3mD / cP. Compared with traditional tools such as higher-end speed star probes and double packers, the optimized sampling technology can save at least 2 million in a single operation. At the same time, due to the low risk, operational uncertainty and possible losses can be reduced. The optimized sampling technology has been successfully applied to 8 low permeability wells, and the sampling success rate has increased from the original 60% to 90%, playing an important role in the implementation of low permeability reserves and improving the quality and efficiency of operations.

[0058] Example 2

[0059] Example 2 of an intermittent pump sampling method for a low permeability reservoir further defines steps 1 to 5 based on Example 1.

[0060] Specifically, in step 1, if Figure 2 As shown in Figure 1, the calculation of the upper limit of formation mobility for intermittent pump sampling includes the following steps:

[0061] S1. Determine the initial pump hydraulic pressure: Determine the initial pump hydraulic pressure based on the reservoir characteristics of the target area.

[0062] S2. Determine the flow rate of the pumped fluid: obtain the pump displacement based on the initial pump hydraulic pressure, and obtain the pumped fluid flow rate based on the pump displacement. The calculation formula for the pump displacement is:

[0063] y=-1.2524·10 -17 ·x 5 +1.1166·10 -13 ·x 4 -3.0068·10 -10 ·x 3 +1.2524

[0064] 10 -17 ·x 2 -1.2525 10 -17 ·x+1.0218

[0065] Where y is the pump displacement; x is the pump hydraulic pressure;

[0066] The formula for determining the pumped fluid flow rate is:

[0067]

[0068] Where POFR is the pumping fluid flow rate; s is the motor speed; D u is the substitution coefficient.

[0069] S3. Calculate the flow pressure based on the flow rate of the pumped fluid.

[0070] The pressure difference between the formation pressure and the flow pressure is calculated according to the flow rate of the pumped fluid, and the flow pressure is calculated according to the pressure difference between the formation pressure and the flow pressure and the formation pressure. The calculation formula for the pressure difference between the formation pressure and the flow pressure is:

[0071]

[0072] Wherein, ΔP is the pressure difference between formation pressure and flow pressure; is the formation fluidity; c s is the probe shape factor.

[0073] S4. Calculate the pressure after the pump according to the flow pressure and pump hydraulic pressure. The calculation formula for the pressure after the pump is:

[0074] P m0 =D u ·P h +P l

[0075] Among them, P m0 is the pressure after the pump; P l is the flow pressure; P h For pump hydraulics.

[0076] S5. Calculate the lower limit of the formation fluidity of the continuous pumping of the pump module and probe module instrument combination and determine the pumping method.

[0077] Specifically, in step 2, the original invasion depth of the drilling fluid is obtained by inversion based on the pumping breakthrough volume and porosity of conventional wells. The invasion depth of the drilling fluid in the low permeability reservoir ranges from 5 to 17 inches, with an average of 11.8 inches.

[0078] Specifically, in step three, the continuous invasion speed during the pumping process is determined according to the original invasion depth of the mud.

[0079] The static mud invasion rate is obtained by the mud invasion experiment of low porosity and permeability sandstone reservoir without considering the increase of pressure difference. The effective pumping speed is calculated by the total pumping volume and the total operation time.

[0080] Use the different pumping breakthrough volume breakthrough charts to find the total pumping volume for selected conditions.

[0081] The simulation of the oversized probe "intermittent" pumping pressure recovery ratio is 40%, 50%, 60%, 70%, 80%, 90%, the invasion depth is 8in, 15in, 20in, and the mud contamination rate is 20%, 50%, 80%, and the total operation time under the corresponding conditions is obtained, such as Figure 3-Figure 5 shown.

[0082] Specifically, in step 4, when simulating the key factors of intermittent pumping, Figure 6 As shown in the figure, the ultra-large diameter probe is taken as the research object, the basic parameters of the model are input and determined, and a numerical simulation grid is established. According to the numerical simulation grid, the pumping process under different porosities and invasion depths is numerically simulated, and a pumping breakthrough volume breakthrough chart is established to obtain the sampleable pumping volume of the ultra-large probe under different porosities and invasion depths. Among them, the basic parameters of the model include porosity, horizontal permeability, vertical permeability, invasion depth, formation fluid viscosity, formation fluid density, overbalance pressure, water-based mud filtrate viscosity, and water-based mud filtrate density.

[0083] Specifically, in step five, the total operation time increases with the increase of the pressure recovery degree. According to actual data, the pressure recovery ratio is 40% when the instrument failure rate is less than 10%. When the pressure recovery degree is less than 50%, the increase in operation time is small, but the low pressure recovery ratio means more frequent switching of the pump, which puts a heavy workload on hydraulic and electronic equipment. When the pressure recovery degree is greater than 70%, the operation time will increase significantly. Therefore, the optimal pressure recovery degree is 50% to 70%.

[0084] Example 3

[0085] A practical application of an intermittent pump sampling method for low permeability reservoirs. It has been verified and applied in 8 exploration wells of the Hainan Branch of China National Offshore Oil Corporation, and while further reducing the lower limit of cable formation testing, effective formation samples were obtained.

[0086] In a well logging of Hainan Branch of China National Offshore Oil Corporation, the pressure flow rate was less than 0.03mD / cp, and a three-dimensional radial probe was used for pumping operation. Figure 7 As shown in the figure, intermittent pumping was used for pumping, with a cumulative pumping time of 220 min, 3 L of pumped fluid, and formation gas samples were successfully obtained.

[0087] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. An intermittent pump sampling method for low permeability reservoirs, characterized in that: The steps include: Step 1: After determining that the area is an ultra-low permeability reservoir based on regional geological data and reservoir characteristics, calculate the lower limit of the formation fluidity for continuous pumping sampling using the test instrument. When the fluidity is less than the lower limit of the formation fluidity for continuous pumping sampling, perform intermittent pumping; Step 2: Based on the data of historical wells in the area in step 1, the breakthrough volume of formation fluid during the pump sampling process is obtained, and the original invasion depth of drilling fluid is obtained by simulation inversion based on the pump breakthrough volume and porosity; Step 3: Based on the experimental data, the initial invasion velocity of the mud filtrate at different original invasion depths is obtained, that is, the upper limit of the continuous invasion velocity of the mud filtrate during the pump sampling process is determined; Step 4: Conduct numerical simulation of key factors of intermittent pumping to obtain intermittent pumping operation schemes and the total operation time of the corresponding operation schemes under different pressure recovery ratios, different invasion depths and different continuous invasion speeds; Step 5: Determine the optimal pressure recovery ratio; Step 6: Obtain the intermittent pumping operation plan and the total operation time of the operation plan under the continuous intrusion rate of the mud filtrate and the optimal pressure recovery ratio.

2. The intermittent pump sampling method for low permeability reservoirs according to claim 1, characterized in that: In step 1, calculating the lower limit of formation mobility for continuous pump sampling includes the following steps: S1. Determine the initial pump hydraulic pressure: Determine the initial pump hydraulic pressure according to the reservoir characteristics of the target area; S2. Determine the pumping fluid flow rate: Obtaining a pump displacement according to an initial pump hydraulic pressure, and obtaining a pumped fluid flow rate according to the pump displacement; S3. Calculate the flow pressure according to the flow rate of the pumped fluid; S4. Calculate the pressure after the pump according to the flow pressure and pump hydraulic pressure; S5. Calculate the lower limit of the formation fluidity of the continuous pumping of the pump module and probe module instrument combination and determine the pumping method.

3. The intermittent pump sampling method for low permeability reservoirs according to claim 2, characterized in that: In S2, the calculation formula of the pump displacement is: y=-1.2524·10 -17 ·x 5 +1.1166·10 -13 x 4 -3.0068·10 -10 ·x 3 +1.2524 ·10 -17 ·x 2 -1.2525·10 -17 ·x+1.0218 Where y is the pump displacement; x is the pump hydraulic pressure; The formula for calculating the pumping fluid flow rate is: Where POFR is the pumping fluid flow rate; s is the motor speed; D u is the substitution coefficient.

4. The intermittent pump sampling method for low permeability reservoirs according to claim 2, characterized in that: In S3, the pressure difference between the formation pressure and the flow pressure is calculated according to the flow rate of the pumped fluid, and the flow pressure is calculated according to the pressure difference between the formation pressure and the flow pressure and the formation pressure. The calculation formula for the pressure difference between the formation pressure and the flow pressure is: Wherein, ΔP is the pressure difference between formation pressure and flow pressure; is the formation fluidity; c s is the probe shape factor.

5. The intermittent pump sampling method for low permeability reservoirs according to claim 2, characterized in that: In S4, the calculation formula of the pressure after the pump is: P m0 =D u ·P h +P l Among them, P m0 is the pressure after the pump; P l is the flow pressure; P h For pump hydraulics.

6. The intermittent pump sampling method for low permeability reservoirs according to claim 1, characterized in that: In the step 2, the original invasion depth of the drilling fluid is obtained by inversion based on the pumping breakthrough volume and porosity of the conventional well.

7. The intermittent pump sampling method for low permeability reservoirs according to claim 1, characterized in that: In step three, the continuous invasion speed during the pumping process is determined according to the original invasion depth of the mud.

8. The intermittent pump sampling method for low permeability reservoirs according to claim 1, characterized in that: In step four, when simulating the key factors of intermittent pumping, the ultra-large diameter probe is taken as the research object, the basic parameters of the model are input and determined, a numerical simulation grid is established, and a pumping breakthrough volume breakthrough map is established based on the numerical simulation grid to obtain the sampleable pumping volume of the ultra-large probe under different porosity and intrusion depth conditions.

9. The intermittent pump sampling method for low permeability reservoirs according to claim 8, characterized in that: The basic parameters of the model include porosity, horizontal permeability, vertical permeability, invasion depth, formation fluid viscosity, formation fluid density, overbalance pressure, water-based mud filtrate viscosity, and water-based mud filtrate density.

10. The intermittent pump sampling method for low permeability reservoirs according to claim 1, characterized in that: In the step five, the optimal pressure recovery degree is 50% to 70%.

Images