A fracturing method based on fluid heterogeneity conditions

Abstract

The present application belongs to the technical field of petroleum geology development, and discloses a fracturing method based on fluid heterogeneity, which comprises the following steps: preflush gel fracture creation + gel sand-carrying fracture propping + viscosity reducer rapid filtration loss to expand swept volume + fracture propping fracture mouth and near wellbore zone + post-located viscosity reducer + well killing, according to different conditions of repeated fracturing wells, new well perforation fracturing, old well new perforation interval, and unfractured well in thermal production, appropriate adjustment is made, and the fracturing method is used for field test of 20 wells, and the average single well daily liquid increase is increased from 4.0t of the conventional method to 6.2t, and the daily oil increase is increased from 0.3t to 0.5t.

Description

Technical Field

[0001] The present invention belongs to the technical field of petroleum geological development, and relates to a technical method for increasing energy and production due to deterioration of fluid properties, and specifically to a fracturing method based on fluid heterogeneity conditions. Background Art

[0002] First, for oilfields undergoing long-term waterflooding development, those damaged by water cooling and some wells and formations experiencing ineffective water injection, statistical patterns show an increasing trend in crude oil viscosity due to factors such as the recovery of light components, decreased formation pressure, and water cooling damage. This is particularly true for mature oilfields in the development phase with extremely high water content. As water saturation rises, oil permeability decreases significantly, severely impacting the ability of wells to increase production through fracturing. The question is how to improve oil permeability and crude oil fluidity through fracturing, thereby overcoming the negative impact of this factor on post-fracturing production increases.

[0003] Secondly, for those wells that have no water or have stopped injecting water into the well layers due to ground factors for a long time, and have been in a state of deficit production for a long time, the viscosity of crude oil has increased due to crude oil degassing. Conventional fracturing technology cannot improve the low production caused by factors such as low formation pressure and high crude oil viscosity.

[0004] Third, in view of the problem that conventional fracturing does not increase production significantly or increases production very little in heavy oil blocks due to multiple rounds of thermal recovery without fracturing, it is urgent to invent a method to address the problem of low or no production increase caused by conventional fracturing due to the above three factors. Summary of the Invention

[0005] In oil reservoirs where fluid properties have changed, after long-term waterflooding, multiple rounds of thermal recovery, and long-term development of heavy oil blocks, the content of paraffin, colloid, and asphaltene is on the rise. These three components are the main factors affecting crude oil viscosity. The formation of a stable three-dimensional structure through multiple microscopic interactions between macromolecules is the main mechanism of high crude oil viscosity. Based on the principle of improving quality, efficiency, and effective production, fracturing technologies and methods are adopted under different fluid properties and reservoir characteristics.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A fracturing method and process for perforation fracturing of new wells, new perforation intervals of old wells, and unfractured wells put into production after thermal recovery under heterogeneous fluid conditions has been invented.

[0008] A fracturing method based on fluid heterogeneity conditions, comprising the following steps:

[0009] Pre-fluid gel to create fractures + gel to carry sand to support fractures + viscosity reducer to quickly filter out and expand the affected volume + fracture support fracture mouth and near-wellbore area + post-placement viscosity reducer + wellbore blocking.

[0010] The fluid heterogeneity condition is the fluid heterogeneity condition of the repeatedly fractured well, and the fracturing method includes the following steps:

[0011] Step 1: Select wells and layers based on comprehensive assessment of remaining oil in the block and well formation, fluid changes, formation pressure maintenance, production performance analysis, and conductivity.

[0012] Step 2: Conduct an indoor test on the fluid viscosity of the newly selected well layer. At the same time, it is necessary to check the changes in the fluid properties of the well and the block since they were put into production. Under the same conditions, conduct a comprehensive analysis and comparison. If the viscosity has increased, proceed to step 3. If the fluid properties in the block or the well have not changed, conventional fracturing technology will still be used for the block and the well, and the following steps do not need to be performed.

[0013] Step 3: Add viscosity reducer, and analyze the viscosity reduction rate according to the concentration between 0.5% and 2%. The viscosity reduction rate is limited to more than 90%. Combined with the analysis of the relationship between increased production and benefits, the optimal ratio is determined. The concentration during construction is 1-2 times the optimal ratio.

[0014] Step 4: Determine the fracturing technology plan and construction process. If the decrease in conductivity is small, but the water content of the well increases rapidly, then fracture by pumping a large displacement of viscosity reducer without adding sand. If the decrease in conductivity is large, first use the pre-fluid gel to create fractures. The design parameters are generally 1.5 times the displacement of the most recent fracturing. Use the gel to carry sand. The displacement is the same as the fracture creation stage. The amount of sand added is 1 times the original. Increase the displacement to pump in the viscosity reducer. The pumping amount is 1.5-2 times the sand-carrying fluid + pre-fluid volume. The gel carries sand, and the sand adding intensity is 0.5 times that of the first stage. Post-vacuum viscosity reducer to increase the fracture conductivity and oil phase permeability of the near-wellbore zone. The well is sealed for 2-3 days and then the well is opened.

[0015] Furthermore, the method of pumping the viscosity reducer at a large displacement without adding sand in step 4 is as follows: the displacement is designed to be 2-4 times the displacement during the most recent fracturing, the total injection volume is designed to be 30-50 cubic meters per meter, and a viscosity reducer with a concentration of 0.5-2% is added. After the construction is completed, the well is sealed, and the viscosity reducer loss is fully integrated with the fluid in the formation and reacts. According to the indoor evaluation, the well is sealed for 2-3 days before the operation is started.

[0016] The fluid heterogeneity condition is the heterogeneity condition of a new well perforation fracturing or a new perforation layer of an old well or a thermal recovery well that has not been fractured. The fracturing method includes the following steps:

[0017] Step 1: Pump in hot water at a low rate, configure low-concentration viscosity reducer for energy storage, and pump in a total liquid volume that is 40-50 cubic meters per meter of the fracturing layer;

[0018] Step 2: Increase the displacement, which is designed to be 2-3 times that of conventional fracturing in this area, and design an appropriate amount of pre-fluid, with a fracture penetration ratio of 50-60%;

[0019] Step 3: The gel carries sand. The displacement is the same as that of the pre-fluid stage. The amount of sand added is determined by calculating the designed crack length * height * width. This stage is designed to be 2 / 3 of the total sand addition amount.

[0020] Step 4: Use hot water to prepare viscosity reducer, and the displacement is designed to be 1.2-1.5 times that of the sand adding stage;

[0021] Step 5: Use the gel to carry sand, the displacement is the same as before, and the amount of sand added is 1 / 3 of the remaining;

[0022] Step 6: Inject hot water to prepare viscosity reducer, reduce the displacement, and the injection volume is based on one wellbore + 10-15 cubic meters of excess displacement;

[0023] Step 7: The well is blocked and the pump is put into production.

[0024] Furthermore, the viscosity reducer is XY-115.

[0025] Furthermore, the low displacement in step one is 2.5 cubic meters per minute.

[0026] Furthermore, the displacement is reduced to 60-80% of the original displacement in step six.

[0027] Furthermore, the time for the well blocking reaction in step seven is 2-3 days.

[0028] The beneficial effects of the present invention compared with the prior art are:

[0029] In the field test of 20 wells, the average daily fluid injection per well increased from the conventional 4.0t to 6.2t, and the daily oil injection increased from 0.3t to 0.5t. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the curve of conductivity change of fractured well;

[0031] Figure 2 It is the curve of skin coefficient change of fractured well;

[0032] Figure 3 It is a comparative production curve of fractured wells;

[0033] Figure 4 It is a fracturing method and flow chart for repeated fracturing wells with heterogeneous fluid;

[0034] Figure 5 It is a fracturing method and flow chart for perforation fracturing of new wells / new perforation intervals of old wells / unfractured wells put into production by thermal recovery under fluid heterogeneity;

[0035] Figure 6 It is a diagram of the specific sand delivery sequence and the effects achieved during fracturing under fluid heterogeneity. DETAILED DESCRIPTION

[0036] The present invention is described in detail below by specific examples, but the scope of protection of the present invention is not limited. Unless otherwise specified, the experimental methods adopted in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0037] The present invention is mainly aimed at the fracturing technology methods and processes for repeated fracturing wells, newly drilled oil wells fracturing after perforation, old wells perforating new layers fracturing, old wells thermal recovery and unfracturing well layers, and old wells where the fluid heterogeneity has changed greatly after the fluid properties have changed.

[0038] Refracturing refers to old wells that were previously perforated and fractured. Re-fracturing of old wells involves perforating and fracturing new layers within the old wells, which have not yet been utilized. Newly perforated and fractured wells refer to wells that were perforated and fractured in newly drilled oil wells during the year. Thermal recovery huff-and-puff wells involve steam injection after perforation, without previously being fractured.

[0039] The present invention develops a fracturing technology method and process design for the above-mentioned well layers. In order to solve the problem of low production increase due to changes in fluid properties in the above four types of well layers, conventional fracturing technology has been developed. The invention also provides a fracturing technology method and process for refracturing wells, as well as a fracturing technology method and process for new well fracturing, re-pressurizing new layers in old wells, and thermal recovery and huff-and-puff fracturing of unfractured well layers. The difference between refracturing wells and the other three types is that refracturing wells have artificial fractures, and some proppants in the reservoir still have flow conductivity, while the other three types have not been fracturing-modified. Therefore, these three types of wells need to be fractured first in the development of fracturing technology methods, and then the fractures are created and propped up before viscosity reduction.

[0040] Example 1 Fracturing method for repeated fracturing wells with heterogeneous fluid

[0041] Re-fracturing refers to a second or more re-fracturing reformation of a perforated well. Based on the reservoir characteristics, fluid characteristics, formation pressure, and current conductivity, a comprehensive analysis is conducted to determine the appropriate fracturing technology and process. Figure 4 The specific steps are:

[0042] Step 1: Geological planners select wells and layers based on comprehensive judgment of the remaining oil in the block and well layer, fluid changes, formation pressure maintenance, production dynamic analysis, and conductivity.

[0043] Step 2: Conduct indoor testing of fluid viscosity and other parameters in the newly selected well layer. Simultaneously, review changes in fluid properties in the well and block since production began, conducting a comprehensive analysis and comparison under the same conditions. If viscosity increases, proceed to Step 3. If fluid properties in the block or well remain unchanged, conventional fracturing techniques are still used for the block and well, eliminating the need for the following steps and disposing of the invention.

[0044] Step 3: Viscosity increases. We analyze the viscosity reduction rate of our independently developed viscosity reducer, XY-115, at different concentrations ranging from 0.5% to 2%. The viscosity reduction rate is set at greater than 90%. The optimal ratio is determined by analyzing the relationship between increased production and profitability. Due to the high volume of reservoir fluid during construction, the laboratory evaluation concentration under formation conditions does not meet the viscosity standard under laboratory mixing conditions. Therefore, it is recommended to increase the concentration by 1-2 times during construction.

[0045] Step 4: Determine the fracturing technology plan and construction process. First, determine the conductivity of the selected well layer, and then analyze the fracturing well production curve analysis method, injection-production relationship analysis method, and pressure test analysis method (see attached). Figure 1-4 ). If the decrease in conductivity is small (fracturing process is carried out as follows), but the water content of the well increases rapidly, it is generally believed that this is due to the poor fluidity of crude oil and a significant decrease in oil phase permeability. The conductivity of the proppant in the crack has not been weakened. At this time, the fracturing will be carried out by pumping a viscosity reducer in a large displacement without adding sand. The displacement is designed to be 2-4 times the displacement of the most recent fracturing, and the total injection volume is designed to be 30-50 cubic meters per meter. 0.5-2% viscosity reducer is added. After the construction is completed, the well is sealed until the viscosity reducer is fully integrated with the fluid in the formation and reacts. Generally, the well is sealed for 2-3 days according to the indoor evaluation before the operation is started. If the decrease in conductivity is large, it means that the well and the layer have been under closed stress conditions for a long time due to the long time since the most recent fracturing. The conductivity has dropped significantly. At this time, the following fracturing technology plan is followed.

[0046] First, pre-fluid gel is used to create fractures. The design parameters are generally 1.5 times the displacement of the most recent fracturing (the stress shielding effect of the interlayer needs to be considered) to increase the length and height of the fracture.

[0047] Secondly, the method of using frozen gel to carry sand is adopted. The discharge volume is consistent with the joint making stage, and the amount of sand added is 1 times the original amount to improve the crack support capacity.

[0048] Increase the displacement again and pump in the viscosity reducer, with the pumping amount being 1.5-2 times the sand-carrying fluid + pre-fluid volume, to quickly filter out into the reservoir cracks and microcracks to reduce the fluid viscosity; freeze the gel to carry sand again, with the sand addition intensity being 0.5 times that of the first stage, in order to support the near-wellbore area and improve the conductivity of the near-wellbore area.

[0049] Finally, the post-placed viscosity reducer increases the fracture conductivity and oil permeability in the near-wellbore zone, thereby improving the fluidity of crude oil.

[0050] The last step is to seal the well for 2-3 days and then start the well operation.

[0051] Example 2: Fracturing method under fluid heterogeneity in new well perforation fracturing / new perforation interval of old well / unfractured well put into production by thermal recovery

[0052] The fracturing technology methods adopted are as follows Figure 5 As shown, specifically:

[0053] Step 1: Low displacement, generally 2.5 cubic meters per minute, pumps in hot water to prepare low-concentration viscosity reducer for energy storage. The total amount of liquid pumped in is 40-50 cubic meters per meter of the fracturing layer;

[0054] Step 2: Increase the displacement rate. The displacement rate is designed to be 2-3 times that of conventional fracturing of wells in this area. The displacement rate design should take into account the stress difference between the upper and lower layers to improve the degree of vertical and horizontal stimulation. The appropriate amount of pre-fluid is designed, and the fracture penetration ratio is designed to be 50-60% to ensure that the fracture control area of ​​a single well is expanded to the middle zone of the oil well row;

[0055] Step 3: The gel carries sand. The displacement is the same as that of the pre-fluid stage. The amount of sand added is determined by calculating the designed crack length * height * width. This stage is designed to be 2 / 3 of the total sand addition amount.

[0056] Step 4: Use hot water to prepare viscosity reducer. The displacement is designed to be 1.2-1.5 times that of the sand adding stage. This will quickly increase the viscosity reducer and the reformed area formed by the propped cracks. Through dialysis and other effects, the fluidity of the crude oil in the propped area will be reduced.

[0057] Step 5: Use the gel to carry sand, the displacement is the same as before, and the amount of sand added is 1 / 3 of the remaining;

[0058] Step 6: Inject hot water with a viscosity reducer to reduce the displacement rate to 60-80% of the original rate. The injection rate is 10-15 cubic meters per wellbore for overdisplacement. The goal is to push the wellbore proppant into the target formation, improve the conductivity of the near-wellbore zone, and enhance the fluidity of the crude oil in the near-wellbore zone.

[0059] Step 7: The well is blocked and reacts, which usually takes 2-3 days, and the pump is put into production. (Attached Figure 6 )

[0060] Problem 1: Due to deteriorating oil properties after thermal recovery, asphaltene and resin content increases significantly, significantly impacting production capacity after multiple cycles. Because these wells are considered deficit wells, adjacent wells lack energy replenishment, leading to a significant decline in production capacity. Therefore, fracturing must consider not only viscosity reduction but also energy replenishment.

[0061] Problem 2: For newly perforated fracturing zones in older wells and newly commissioned wells, some wells may lack surrounding water wells for energy replenishment, or have weak injection-production relationships. The fracturing technology and process are consistent with the following: If the formation has sufficient energy and a clear injection-production relationship, step 1 of the fracturing process can be omitted and the process can begin with step 2.

[0062] Example 3

[0063] A statistical analysis of eight oil wells that were fractured before 2000 and had pressure measurement data for five consecutive years showed that after fracturing, as production time increased, the reservoir conductivity and fracture half-length decreased significantly, the skin damage coefficient increased, and the oil well production decreased. After about three years of production, it basically stabilized. If production is to be increased, fracturing is needed again.

[0064] As the post-fracturing production time increases, the cracks gradually close and the conductivity decreases. Figure 1 -Attached Figure 3 The flow conductivity is analyzed using the pressure measurement data method and the production curve method respectively.

[0065] The above-described embodiments are only preferred embodiments of the present invention, and are not intended to be all feasible embodiments of the present invention. Any obvious modifications made by a person skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A fracturing method based on fluid heterogeneity conditions, characterized in that: The following steps are involved: Pre-fluid gel to create fractures + gel to carry sand to support fractures + viscosity reducer to quickly filter out and expand the swept volume + fracture support fracture mouth and near-wellbore area + post-placement viscosity reducer + wellbore blocking; The fluid heterogeneity condition is the fluid heterogeneity condition of the repeatedly fractured well, and the fracturing method includes the following steps: Step 1: Select wells and layers based on comprehensive assessment of remaining oil in the block and well formation, fluid changes, formation pressure maintenance, production performance analysis, and conductivity. Step 2: Conduct an indoor test on the fluid viscosity of the newly selected well layer. At the same time, it is necessary to check the changes in the fluid properties of the well and the block since they were put into production. Under the same conditions, conduct a comprehensive analysis and comparison. If the viscosity has increased, proceed to step 3. If the fluid properties in the block or the well have not changed, conventional fracturing technology will still be used for the block and the well, and the following steps do not need to be performed. Step 3: Add viscosity reducer, and analyze the viscosity reduction rate at a concentration between 0.5% and 2%. The viscosity reduction rate is limited to more than 90%. Combined with the analysis of the relationship between increased production and benefits, the optimal ratio is determined. The concentration during construction is 1-2 times the optimal ratio. Step 4: Determine the fracturing technology plan and construction process. If the decrease in conductivity is small, but the water content of the well increases rapidly, then fracture by pumping a large displacement of viscosity reducer without adding sand. If the decrease in conductivity is large, first use the pre-fluid gel to create fractures. The design parameters are generally 1.5 times the displacement of the most recent fracturing. Use the gel to carry sand. The displacement is the same as the fracture creation stage. The amount of sand added is 1 times the original. Increase the displacement to pump in the viscosity reducer. The pumping amount is 1.5-2 times the sand-carrying fluid + pre-fluid volume. The gel carries sand, and the sand adding intensity is 0.5 times that of the first stage. Post-vacuum viscosity reducer to increase the fracture conductivity and oil phase permeability of the near-wellbore zone. The well is sealed for 2-3 days and then the well is opened.

2. A fracturing method based on fluid heterogeneity conditions according to claim 1, characterized in that the steps The fourth method of pumping viscosity reducer at a large displacement without adding sand is as follows: the displacement is designed to be 2-4 times the displacement of the most recent fracturing, the total injection volume is designed to be 30-50 cubic meters per meter, and a viscosity reducer with a concentration of 0.5-2% is added. After the construction is completed, the well is sealed, and the viscosity reducer loss is allowed to fully merge and react with the fluid in the formation. According to the indoor evaluation, the well is sealed for 2-3 days before the operation is started.

Images