A method for determining the shutdown of oil wells in the late development of a multilayer heterogeneous sandstone reservoir
By developing a method for determining well shutdown in the later stages of multi-layered heterogeneous sandstone reservoir development, the unscientific problem of shutting down high water-cut wells has been solved, resulting in reduced oilfield production costs and improved economic benefits.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DAQING OILFIELD CO LTD
- Filing Date
- 2025-01-10
- Publication Date
- 2026-07-10
AI Technical Summary
Current technologies rely on experience or single indicators to make decisions on shutting down high water-cut wells, lacking systematic evaluation methods, which affects the overall production and economic benefits of oil fields.
This paper provides a method for determining well shutdown in the later stages of development of multi-layered heterogeneous sandstone reservoirs. Through a multi-step screening process, including identifying the implementation block, classifying wells, assessing casing damage risk, and determining the well shutdown sequence, the method ensures the scientific and rational nature of well shutdown.
By using scientific methods for determining oil well shutdown, we can reduce production costs, improve resource utilization efficiency, reduce ineffective investment, enhance the economic benefits of oil fields, and avoid environmental risks.
Smart Images
Figure CN122365183A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of petroleum exploration and development technology, and in particular to a method for determining the shutdown of oil wells in the later stages of development of multi-layered heterogeneous sandstone reservoirs. Background Technology
[0002] As oilfield development continues to deepen, water cut continues to rise, and the proportion of high water-cut wells is rapidly increasing. According to statistics, the geological reserves and production scale of sandstone oilfields in my country that have entered the high and ultra-high water-cut stage both account for more than 80%. Taking the Daqing Lasa Xing oilfield as an example, the average annual water cut in 2022 was as high as 96%. Among them, the production volume, oil production and number of wells with water drive water cut greater than 98% of the Lasa Xing wells exceeded 58 million tons, 800,000 tons and 3,600 wells respectively. How to effectively deal with this part of high water-cut wells has become an urgent problem to be solved in oilfield development.
[0003] Shutting down high water-cut wells is an important water control measure in the later stages of water-drive oilfield development. However, while shutting down high water-cut wells can effectively control water production, it can also affect the overall production scale of the oilfield. If left unchecked, it will seriously affect the economic benefits of the oilfield.
[0004] From a technical perspective, shutting down high water-cut wells can alter the fixed flow lines of underground oil and water wells, prompting a redistribution of the reservoir flow field. This reduces inefficient and ineffective fluid production. This redistribution not only helps improve the oil displacement effect of adjacent poorly performing wells but also improves the overall reservoir development effect. Shutting down high water-cut wells can also reduce the burden on the surface gathering and transportation system, lower wastewater treatment costs, and further enhance the economic benefits of oilfield development.
[0005] From a management perspective, shutting down high water-cut wells can save a significant amount of operating costs, such as electricity and maintenance, indirectly improving the economic efficiency of oil fields. This approach is particularly important given the current global oil market's low cost and low oil prices. By rationally shutting down high water-cut wells, oil fields can maintain production while reducing costs and increasing efficiency. Summary of the Invention
[0006] (a) Technical problems to be solved
[0007] This invention provides a method for determining well shutdown in the later stages of development of multi-layered heterogeneous sandstone reservoirs, overcoming the problem that existing technologies often rely on experience or lack a systematic evaluation method for traditional well shutdown decisions.
[0008] (II) Technical Solution
[0009] To achieve the above objectives, the present invention provides a method for determining the shutdown of oil wells in the later stages of development of multi-layered heterogeneous sandstone reservoirs, comprising the following steps:
[0010] Step S1: Determine the implementation block and initially select potential shut-in oil wells based on the water-cut technical limit and economic water-cut limit;
[0011] Step S2: Based on the impact on production target achievement, a second screening of shut-in potential oil wells is conducted;
[0012] Step S3: The shut-in potential oil wells selected in Step S2 are classified into low water-cut, medium water-cut, and high water-cut oil wells according to the average water cut of the implementation block, and into low-pressure, medium-pressure, and high-pressure oil wells according to the average formation pressure of the implementation block. Based on the comprehensive oil well classification results, the implementation block is divided into 9 zones. A three-level water cut and three-level pressure graded control chart is established, and the shut-in potential oil wells selected in Step S2 are screened for the third time according to the three-level water cut and three-level pressure graded control chart.
[0013] Step S4: Determine the casing damage risk of oil wells based on the underground conditions of the implementation block, and conduct a fourth screening of the oil wells with shut-in potential selected in Step S3, selecting oil wells with relatively low casing damage risk.
[0014] Step S5 involves screening potential wells for shut-in four times and determining the sequence and timing of shutting in potential wells based on the actual difficulty of implementation at the mine.
[0015] Preferably, the water cut technical limit value is 98%, and when the water cut of an oil well reaches 98%, it can be regarded as a potential shut-in oil well;
[0016] When the water cut of all oil wells in the implementation block reaches the water cut technical limit, the potential shut-in oil wells are determined by the economic water cut limit.
[0017] Preferably, the formula for calculating the economic water content limit is:
[0018]
[0019] Where Cc is the annual operating cost of a single well, QL is the daily fluid production of a single well, α is the commodity rate, τ is the well opening rate, P is the crude oil price, and R is the unit tax.
[0020] Preferably, the impact on the production target includes two situations: a tight production target and a relaxed production target.
[0021] When achieving production targets is challenging, wells are ranked and screened from low to high produced fluid volume. When achieving production targets is less challenging, wells are ranked and screened from high to low produced fluid volume.
[0022] Preferably, the third screening involves selecting low-pressure and medium-pressure oil wells from high-water-cut oil wells based on a graded control chart of three levels of water cut and three levels of pressure.
[0023] Preferably, the medium water-cut oil well is an oil well with a water cut 1%-3% different from the average water cut of the block, the low water-cut oil well is an oil well with a water cut lower than that of the medium water-cut oil well, and the high water-cut oil well is an oil well with a water cut higher than that of the medium water-cut oil well.
[0024] Preferably, the medium-pressure oil well is an oil well with a formation pressure 0.5 MPa to 2 MPa different from the average formation pressure of the block, the low-pressure oil well is an oil well with a formation pressure lower than that of the medium-pressure oil well, and the high-pressure oil well is an oil well with a formation pressure higher than that of the medium-pressure oil well.
[0025] Preferably, the determination of casing damage risk of oil wells based on the underground conditions of the implementation block includes:
[0026] Step S41: Construct the oil reservoir connectivity diagram of the implementation block;
[0027] Step S42: Identify the fault locations within the implementation block based on the reservoir connectivity diagram, and mark the oil wells at the fault edges;
[0028] Step S43: Oil wells located at the edge of the fault are not considered as potential shut-in wells due to the risk of casing damage caused by their proximity to the fault.
[0029] (III) Beneficial Effects
[0030] This invention provides a method for determining the shutdown of oil wells in the later stages of development of multi-layered heterogeneous sandstone reservoirs. Based on the development characteristics of high water-cut oilfields, it fully utilizes existing facilities, avoiding the abandonment costs associated with complete decommissioning, thereby reducing production costs. Through a multi-step screening process, including considerations of water-cut technical limits, economic water-cut limits, the impact on production targets, water-cut and pressure tiered control, and comprehensive consideration of underground conditions, it ensures that the oil wells ultimately decided for shutdown are the result of scientific analysis and evaluation, reducing the risks associated with subjective judgment. By meticulously screening and evaluating oil wells, limited human, material, and financial resources can be concentrated on wells with greater potential, improving resource utilization efficiency, avoiding ineffective investment, and ultimately achieving the goal of improving economic benefits and reducing environmental risks. Attached Figure Description
[0031] Figure 1 The flowchart illustrates the process of a method for determining well shutdown in the later stages of development of multi-layered heterogeneous sandstone reservoirs according to the present invention. Detailed Implementation
[0032] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0033] In the description of this invention, it is necessary to understand that the orientations or positional relationships indicated by terms such as "upper," "lower," "left," "right," "inner," "outer," "top," and "bottom" are based on the orientations or positional relationships shown in the accompanying drawings. They are intended only to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the components referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.
[0034] like Figure 1 As shown, this invention provides a method for determining the shutdown of oil wells in the later stages of development of multi-layered heterogeneous sandstone reservoirs, comprising the following steps:
[0035] Step S1: Determine the implementation block and initially select potential shut-in oil wells based on the water-cut technical limit and economic water-cut limit;
[0036] The technical limit for water cut is 98%. When the water cut of an oil well reaches 98%, it can be considered a potential shut-in well. When the water cut of all oil wells in the implementation block reaches 98%, the economic water cut limit is used to screen potential shut-in wells. The formula for calculating the economic water cut limit is as follows:
[0037]
[0038] Where Cc is the annual operating cost of a single well, QL is the daily fluid production of a single well, α is the commodity rate, τ is the well opening rate, P is the crude oil price, and R is the unit tax.
[0039] The economic water cut limit of the implementation block is calculated using the economic water cut limit calculation formula. Oil wells in the implementation block are then screened based on the economic water cut limit value, and oil wells with a water cut limit value higher than the economic water cut limit value are selected.
[0040] Step S2: Based on the impact on production target achievement, a second screening of potential shut-in wells is conducted.
[0041] The impact on achieving production targets includes two scenarios: a tight target and a relaxed target.
[0042] When the overall production of an oilfield is close to or below the annual planned target, the pressure to achieve the production target is greater. In this case, maintaining production should be given priority. Even if the economic benefits of some oil wells are low, they should not be shut down easily. Wells should be sorted and screened in order of produced fluid volume from low to high in order to reduce the impact of reduced oil production on the production target.
[0043] When the overall production of an oilfield is much higher than the annual planned target, the pressure to achieve the production target is relatively small. In this case, priority can be given to improving economic efficiency. Even if some oil wells have high production, if their economic efficiency is low, they can be shut down. Wells can be sorted and screened from high to low produced fluid volume in order to maximize economic efficiency.
[0044] Step S3: The shut-in potential oil wells selected in Step S2 are classified into low water-cut, medium water-cut, and high water-cut oil wells according to the average water cut of the implementation block, and into low-pressure, medium-pressure, and high-pressure oil wells according to the average formation pressure of the implementation block. Based on the comprehensive oil well classification results, the implementation block is divided into 9 zones. A three-level water cut and three-level pressure graded control chart is established, and the shut-in potential oil wells selected in Step S2 are screened for the third time according to the three-level water cut and three-level pressure graded control chart.
[0045] The medium-water-cut oil well is defined as an oil well with a water cut 1%-3% lower than the average water cut of the implementation block; the low-water-cut oil well is defined as an oil well with a water cut lower than that of the medium-water-cut oil well; the high-water-cut oil well is defined as an oil well with a water cut higher than that of the medium-water-cut oil well; the medium-pressure oil well is defined as an oil well with a formation pressure 0.5 MPa-2 MPa lower than the average formation pressure of the implementation block; the low-pressure oil well is defined as an oil well with a formation pressure lower than that of the medium-pressure oil well; and the high-pressure oil well is defined as an oil well with a formation pressure higher than that of the medium-pressure oil well.
[0046] Based on the above classification criteria, the implementation area is divided into 9 zones, each corresponding to a specific combination of water cut and formation pressure. The specific zones are as follows: low water cut low pressure oil wells, low water cut medium pressure oil wells, low water cut high pressure oil wells, medium water cut low pressure oil wells, medium water cut medium pressure oil wells, medium water cut high pressure oil wells, high water cut low pressure oil wells, high water cut medium pressure oil wells, and high water cut high pressure oil wells.
[0047] Priority should be given to shutting down oil wells with high water cut and low formation pressure. These wells not only produce less oil due to their high water cut, but also, due to their low formation pressure, continued production may lead to more water entering the oil layer, further reducing the production efficiency of the wells. Shutting down these wells can reduce unnecessary water intrusion, protect the oil layer, and extend the life cycle of the oil field. Therefore, wells in this range can be shut down. The second priority should be given to shutting down oil wells with high water cut and relatively medium formation pressure. Water injection at the water well end in this range needs to be controlled. Appropriate shutdown of these wells can avoid the formation pressure increase caused by excessive water injection. Therefore, wells in this range can be appropriately shut down based on the water injection control situation.
[0048] It should be noted that when the number of oil wells that can be shut down is too small, shutting down medium-water-cut high-pressure oil wells and high-water-cut high-pressure oil wells can be considered. Water injection at the water well end in this range needs to be controlled. Oil wells in this range can be shut down appropriately based on the water injection control situation.
[0049] Step S4: Determine the casing damage risk of oil wells based on the underground conditions of the implementation block, and conduct a fourth screening of the oil wells with shut-in potential selected in Step S3, selecting oil wells with relatively low casing damage risk.
[0050] For oilfields in the later stages of development, with a long development period and unstable underground conditions in some areas, there is a significant risk of casing damage to oil and water wells. Therefore, it is necessary to assess the impact on casing damage before taking shutdown measures, mainly based on the current underground conditions of the well group.
[0051] The assessment of casing damage risk of oil wells based on the underground conditions of the implementation block includes:
[0052] Step S41: Construct the oil reservoir connectivity diagram of the implementation block;
[0053] Collect geological data of all oil wells in the implementation block, including oil layer thickness, permeability and porosity parameters. Collect production data of oil wells, including daily oil production, daily water production and water cut. Using geological data and production data, establish a three-dimensional geological model of the implementation block. Mark the location of each oil well and its corresponding oil layer information in the model. The connectivity diagram shows the connectivity between each oil well, including the connectivity of oil layers and the location of faults.
[0054] Step S42: Identify the fault locations within the implementation block based on the reservoir connectivity diagram, and mark the oil wells at the fault edges;
[0055] Step S43: Oil wells located at the edge of the fault are not considered as potential shut-in wells due to the risk of casing damage caused by their proximity to the fault.
[0056] Step S5: Through four rounds of screening of potential shut-in oil wells, the sequence and timing of shutting in potential oil wells are determined based on the actual difficulty of implementation at the mine.
[0057] Specifically, this includes: assessing the difficulty of shutting down each oil well based on the actual conditions of the wellhead equipment and devices; determining the difficulty level of each oil well by considering factors such as geographical location, equipment condition, and personnel allocation; determining the order of well shut-down implementation based on the assessment results, implementing the less difficult oil wells first, and then gradually advancing to the more difficult oil wells; and rationally arranging the well shut-down time for each oil well according to the implementation order.
[0058] Regular maintenance is also required for shut-in wells to ensure that the equipment is in good condition. This includes inspecting wellhead equipment, lubricating moving parts, and replacing worn parts. Just like normal production wells, regular well inspections should be carried out on shut-in wells, and basic data should be filled out carefully and the results of each inspection should be recorded.
[0059] The following is a detailed description of the practical application of a method for determining well shutdown in the later stages of development of multi-layered heterogeneous sandstone reservoirs.
[0060] This example provides a method for determining the shutdown of oil wells in the later stage of development of multi-layered heterogeneous sandstone reservoirs. Specifically, it takes Gaotaizi in the western part of the central area of the Sazhong Development Zone of Daqing Oilfield as an example.
[0061] After nearly 60 years of development, the overall water cut of the block reached 98.19% in 2022. Due to the poor development benefits of high water cut, a method for determining the shutdown of oil wells in the later stage of development of multi-layer heterogeneous sandstone reservoirs was implemented in this block.
[0062] First, since the overall water cut of the implementation block has exceeded 98%, the economic water cut limit was considered for selection. The economic water cut limit of the implementation block is 98.7%, and a total of 67 oil wells with shut-in potential were selected.
[0063] Secondly, considering the impact on achieving the production target, a second selection was made. Since the production target for this implementation block is relatively lenient, the priority was to improve economic efficiency, followed by achieving the production target. The 67 oil wells with the potential to be shut down were sorted and screened according to the amount of fluid produced from the wells from high to low in order to maximize economic efficiency. Considering that the maximum daily oil production impact is less than 12 tons, 20 oil wells were selected as shut-down targets in the second selection.
[0064] Secondly, a graded control chart for water cut and pressure was established. Since the water cut of this implementation block is relatively high with an average water cut of 98.19%, the average water cut of the block and the economic water cut boundary were taken as the intermediate water cut value. The average formation pressure of this implementation block is 10.13 MPa. Based on the actual situation of the mine, an upward fluctuation of 0.5 MPa was selected as the intermediate pressure value, as shown in Table 1.
[0065] Table 1. Grading and Control Chart of Aquifer and Pressure
[0066]
[0067] Based on the water cut and pressure classification control chart, 12 oil wells with low pressure + high water cut and medium pressure + high water cut were selected.
[0068] Based on the underground conditions of the implementation block, the casing damage risk of 12 oil wells was determined, and an oil layer connectivity map of the implementation block was constructed. Through the oil layer connectivity map, it can be observed that 3 of the 12 oil wells are located at the edge of a fault. Shutting them down may cause pressure buildup and thus generate casing damage risk. After excluding the 3 oil wells, a total of 9 oil wells were selected.
[0069] Based on the actual conditions of the mine and the ease of implementation, a sequence for shutting down the oil wells was determined. The pumping equipment at the wellheads of the nine wells was inspected and ordered according to their completeness and maintenance level. Based on mine experience, the oil wells were gradually shut down by reducing the fluid volume by 1% to 5% per month, avoiding a one-time shutdown of all oil wells.
[0070] Regular maintenance should be performed on the shut-in wells and the nine shut-in wells. Well inspections should be conducted as if they were normal production wells, and basic data should be carefully recorded. Anti-theft measures should be implemented for the control boxes, motors, and surface oil gathering pipelines on the pumping unit wells to ensure the equipment is in good condition. Shut-in wells should be periodically test-started to observe whether they can operate normally. Reasonable resumption plans should be developed for the shut-in wells so that they can be resumed production at any time.
[0071] It is understood that the various embodiments mentioned above in this invention can be combined with each other to form combined embodiments without violating the principle and logic. Due to space limitations, this invention will not elaborate further.
[0072] Those skilled in the art will understand that, in the above-described method of the specific implementation, the order in which each step is written does not imply a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of each step should be determined by its function and possible internal logic.
[0073] This invention provides a method for determining the shutdown of oil wells in the later stages of development of multi-layered heterogeneous sandstone reservoirs. Based on the development characteristics of high water-cut oilfields, it makes full use of existing facilities, avoiding the abandonment costs associated with complete decommissioning, thereby reducing production costs. Through a multi-step screening process, including considerations of water-cut technical limits, economic water-cut limits, the impact on production targets, water-cut and pressure tiered control, and comprehensive consideration of underground conditions, it ensures that the oil wells ultimately decided for shutdown are the result of scientific analysis and evaluation, reducing the risks associated with subjective judgment. By meticulously screening and evaluating oil wells, limited human, material, and financial resources can be concentrated on wells with greater potential, improving resource utilization efficiency, avoiding ineffective investment, and ultimately achieving the goal of improving economic benefits and reducing environmental risks.
[0074] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.
Claims
1. A method for determining the shutdown of oil wells in the later stages of development of multi-layered heterogeneous sandstone reservoirs, characterized in that, Includes the following steps: Step S1: Determine the implementation block and initially select potential shut-in oil wells based on the water-cut technical limit and economic water-cut limit; Step S2: Based on the impact on production target achievement, a second screening of shut-in potential oil wells is conducted; Step S3: The shut-in potential oil wells selected in Step S2 are classified into low water-cut, medium water-cut, and high water-cut oil wells according to the average water cut of the implementation block, and into low-pressure, medium-pressure, and high-pressure oil wells according to the average formation pressure of the implementation block. Based on the comprehensive oil well classification results, the implementation block is divided into 9 zones. A three-level water cut and three-level pressure graded control chart is established, and the shut-in potential oil wells selected in Step S2 are screened for the third time according to the three-level water cut and three-level pressure graded control chart. Step S4: Determine the casing damage risk of oil wells based on the underground conditions of the implementation block, and conduct a fourth screening of the oil wells with shut-in potential selected in Step S3, selecting oil wells with relatively low casing damage risk. Step S5 involves screening potential wells for shut-in four times and determining the sequence and timing of shutting in potential wells based on the actual difficulty of implementation at the mine.
2. The method for determining well shutdown in the later stages of development of multi-layered heterogeneous sandstone reservoirs according to claim 1, characterized in that, The water cut technical limit value is 98%. When the water cut of an oil well reaches 98%, it can be regarded as a potential shut-in oil well. When the water cut of all oil wells in the implementation block reaches the water cut technical limit, the potential shut-in oil wells are determined by the economic water cut limit.
3. The method for determining well shutdown in the later stages of development of multi-layered heterogeneous sandstone reservoirs according to claim 2, characterized in that, The formula for calculating the economic water cut limit is as follows: Where Cc is the annual operating cost of a single well, QL is the daily fluid production of a single well, α is the commodity rate, τ is the well opening rate, P is the crude oil price, and R is the unit tax.
4. The method for determining well shutdown in the later stages of development of multi-layered heterogeneous sandstone reservoirs according to claim 3, characterized in that, The impact on production targets includes two scenarios: tight targets and relaxed targets. When achieving production targets is challenging, wells are ranked and screened from low to high produced fluid volume. When achieving production targets is less challenging, wells are ranked and screened from high to low produced fluid volume.
5. The method for determining well shutdown in the later stages of development of multi-layered heterogeneous sandstone reservoirs according to claim 4, characterized in that, The third screening involves selecting low-pressure and medium-pressure oil wells from high-water-cut oil wells based on the graded control chart of three levels of water cut and three levels of pressure.
6. The method for determining well shutdown in the later stages of development of multi-layered heterogeneous sandstone reservoirs according to claim 5, characterized in that, The medium water-cut oil well is an oil well whose water cut differs from the block average by 1%-3%, the low water-cut oil well is an oil well with a water cut lower than that of the medium water-cut oil well, and the high water-cut oil well is an oil well with a water cut higher than that of the medium water-cut oil well.
7. The method for determining well shutdown in the later stages of development of multi-layered heterogeneous sandstone reservoirs according to claim 6, characterized in that, The medium-pressure oil well is an oil well whose formation pressure differs from the average formation pressure of the block by 0.5 MPa to 2 MPa. The low-pressure oil well is an oil well whose formation pressure is lower than that of the medium-pressure oil well. The high-pressure oil well is an oil well whose formation pressure is higher than that of the medium-pressure oil well.
8. The method for determining well shutdown in the later stages of development of multi-layered heterogeneous sandstone reservoirs according to claim 1, characterized in that, The assessment of casing damage risk of oil wells based on the underground conditions of the implementation block includes: Step S41: Construct the oil reservoir connectivity diagram of the implementation block; Step S42: Identify the fault locations within the implementation block based on the reservoir connectivity diagram, and mark the oil wells at the fault edges; Step S43: Oil wells located at the edge of the fault are not considered as potential shut-in wells due to the risk of casing damage caused by their proximity to the fault.