CN114165203A - Stepless viscosity-changing non-matching slickwater field hydraulic fracturing method - Google Patents
Stepless viscosity-changing non-matching slickwater field hydraulic fracturing method Download PDFInfo
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Abstract
本发明提供一种无级变粘免配滑溜水现场水力压裂方法，包括根据压裂施工现场的限制条件进行压裂各阶段施工设计；根据地层水矿化度‑减阻剂浓度‑减阻率关系图版及压裂改造层段的地层水质，确定减阻剂浓度范围；根据流速‑减阻剂浓度‑减阻率关系图版分别确定井口压力一定条件下的前置液施工阶段和顶替液施工阶段的排量；根据流速‑减阻剂浓度‑减阻率关系图版、减阻剂浓度‑粘度‑粘弹性关系图版及施工排量‑粘弹性‑砂比关系图版确定井口压力一定条件下的携砂液施工阶段的排量、砂比及所用压裂液的粘度和/或减阻剂浓度；根据所确定的结果向各压裂层段交替注入前置液和携砂液若干次，以及向压裂层段注入顶替液以将井筒中的携砂液压入裂缝中。
The invention provides an on-site hydraulic fracturing method for stepless variable viscosity and no-distribution of slick water. According to the relationship chart of rate relationship and formation water quality of fracturing stimulation interval, determine the concentration range of drag reducing agent; according to the relationship chart of flow rate-drag reducing agent concentration-drag reduction rate, respectively determine the pre-fluid construction stage and displacement fluid construction under certain wellhead pressure conditions According to the relationship chart of flow rate-drag reducing agent concentration-drag reduction rate, drag reducing agent concentration-viscosity-viscoelasticity relationship chart and construction displacement-viscoelasticity-sand ratio relationship chart, determine the carrying capacity under certain conditions of wellhead pressure The displacement, sand ratio and the viscosity of the fracturing fluid used and/or the concentration of drag reducing agent in the sand liquid construction stage; according to the determined results, alternately inject pre-fluid and sand-carrying liquid into each fracturing interval Displacement fluid is injected into the fractured interval to push the sand-carrying fluid in the wellbore into the fracture.
Description
Technical Field
The invention relates to a stepless viscosity-changing and blending-free slickwater field hydraulic fracturing method, in particular to a method for performing fracturing transformation on a reservoir by adopting stepless viscosity-changing and blending-free slickwater, and belongs to the technical field of oil and gas field exploration and development.
Background
The hydraulic fracturing technology plays an important role in the unconventional oil and gas reservoir transformation process. According to the geological characteristics of unconventional oil and gas reservoirs in China, most fracturing fluids used in fracturing sites at present are slickwater systems, and the percentage of the fracturing fluids is 70-80%. The slickwater generally comprises additives such as water, sand, drag reducer, bactericide, clay stabilizer, cleanup additive and the like, can reduce the friction pressure by 70-80 percent compared with clear water, has stronger anti-swelling performance, and has lower viscosity which is generally below 10mPa & s. Compared with the traditional guar gum fracturing fluid system, the slickwater fracturing fluid has the characteristics of high efficiency and low cost: particularly, the addition amount of the drag reducer is small, the damage of the fracturing fluid to a reservoir matrix and a crack can be reduced, the system is ensured to have a good drag reduction effect, and the construction pressure can be reduced while the construction discharge capacity is improved.
Chinese patent CN 111335862 a discloses a method for variable viscosity sand fracturing, which adopts different types of fracturing fluids, including linear glue or weakly cross-linked fracturing fluid and slickwater fracturing fluids of different viscosities, at different stages of fracturing to realize controllable adjustment of viscosity, so as to realize expected fracturing effect. Although the method for adding the sand with the variable viscosity is innovatively provided, the problems of complex process, complex liquid preparation, need of replacing a fracturing liquid system at any time and the like exist in the field practical application process, and the method has no good practicability. Chinese patent CN 110805419A discloses a slickwater volume fracturing method with large liquid amount, large discharge capacity and large pad fluid and low sand ratio, which adopts slickwater fracturing fluid with lower viscosity to realize the purposes of multistage crack formation and volume fracturing by changing parameters such as discharge capacity, sand ratio and the like of different construction stages. Although the method can realize the purposes of multistage seam making and volume fracturing, the influence of the viscoelastic property of the slickwater on the sand carrying performance is not considered, a single-viscosity slickwater system is adopted in the whole process, the sand ratio of the slickwater sand carrying fluid is improved only by increasing the construction fluid volume and the discharge volume, and the consideration is not carried out on the aspect of stepless adjustment of the viscoelastic property of the slickwater, so that the method has no practical significance. Although the prior art can solve the problem of suspended sand, firstly, both the prior art and the prior art cannot ensure the sand laying form in the crack (sand blockage is easy to form), and secondly, the fracture site may not ensure higher discharge capacity and liquid quantity, and particularly, the application range is limited due to offshore construction.
At present, the problems of complex process, long construction time, low economic benefit and the like exist in on-site slickwater fracturing operation, the stepless adjustment of viscosity cannot be realized in the existing slickwater system, and a high-viscosity guar gum fracturing fluid system is usually required to be replaced to achieve the expected fracturing effect in a sand carrying fluid stage. Therefore, how to simplify the slickwater on-site fracturing construction process, realize the automatic control and the stepless regulation of viscosity, meet the construction requirements of different fracturing stages, have ideal sand carrying performance and sand laying effect simultaneously, and are the key problems faced when fracturing is carried out by adopting slickwater at present.
Therefore, the technical problem to be solved in the field is to provide a novel stepless viscosity-changing and non-matching slickwater field hydraulic fracturing method.
Disclosure of Invention
In order to solve the defects and shortcomings, the invention aims to provide a stepless viscosity-changing and slickwater-free field hydraulic fracturing method. The method provided by the invention can optimize the site fracturing construction parameters based on reservoir characteristic analysis and comprehensive consideration of site construction equipment limitation and economic indexes, and reasonably optimizes the construction parameters such as the concentration of the drag reducer, the construction discharge capacity, the sand ratio and the like used in site fracturing by utilizing four complementary plates in specific implementation.
In order to achieve the above object, the present invention provides a stepless viscosity-changing non-matching slickwater field hydraulic fracturing method, wherein the method comprises the following steps:
(1) carrying out construction design of each fracturing stage according to the limiting conditions of the fracturing construction site;
(2) determining a drag reducer concentration range suitable for a target interval according to a stratum water mineralization degree-drag reducer concentration-drag reducer rate relation chart and the stratum water quality of a fracturing modification interval;
(3) respectively determining the discharge capacities of a pre-liquid construction stage and a displacement fluid construction stage under a certain wellhead pressure condition according to the flow rate-drag reducer concentration-drag reducer relation chart; determining the discharge capacity and sand ratio of the sand-carrying fluid in the construction stage under a certain wellhead pressure condition and the viscosity and/or drag reducer concentration of the used fracturing fluid according to the flow rate-drag reducer concentration-drag reducer rate relation chart, the drag reducer concentration-viscosity-viscoelasticity relation chart and the construction discharge capacity-viscoelasticity-sand ratio relation chart;
(4) according to the results determined in the steps (1) to (3), alternately injecting the pad fluid and the sand carrying fluid into each fracturing interval for a plurality of times to realize multi-stage fracturing crack formation and sand filling, optimizing the laying form of the propping agent in each stage of cracks, forming a multi-stage crack system with high flow conductivity, and improving the fracturing modification effect of the reservoir;
(5) and (4) injecting a displacement fluid into the fracturing interval according to the determined results in the steps (1) to (3) so as to press the sand-carrying fluid in the well bore into the fracture.
As a specific embodiment of the above method of the present invention, in step (1), the limitation condition of the fracturing job site includes a maximum injection pressure that can be reached by the fracturing equipment.
As a specific embodiment of the above method of the present invention, in the step (1), the construction design of each fracturing stage mainly includes the construction design of stages such as a fracturing fluid pad stage, a sand carrying fluid stage and a displacing fluid stage.
As a specific embodiment of the above method of the present invention, in step (2), the salinity of the formation water in the formation water-drag reducer concentration-drag reducer relation chart is calculated by the total concentration of divalent metal cations in the formation water.
The difference of the water salinity of the oil well stratum in different regions is large, the ion species and the ion content are different, but the main cation composition approximately comprises K+、Na+、Ca2+、Mg2+、Fe2+/Fe3+And the like. Previous studies show that monovalent ions have little influence on the drag reduction rate, viscoelasticity and the like of linear guanidine gum or salt-resistant polymers, such as salt-resistant monomer modified polyacrylamide and the like, and high-valence metal ions have great influence on the linear guanidine gum or salt-resistant polymers. Although, at present, the total salinity of oil wells in most regions is distributed in the range of thousands to tens of thousands of milligrams per liter, the amount of divalent salt ions contained in the water is usually in the range of hundreds to thousands, and divalent metal cations have a negative effect on the drag reduction rate, viscoelasticity, etc. of the drag reducer system, the present application regards the total concentration of divalent metal cations in the formation water of the fractured reservoir as the formation water salinity in the formation water-drag reducer concentration-drag reduction rate relationship chart. Correspondingly, before fracturing, the formation water quality of a fractured reservoir needs to be analyzed, and specific respective indexes include: total salinity value, formation water type, ion species and content, such as: k+、Na+、Ca2+、Mg2+、Fe2+/Fe3+、Cl-、HCO- 3、CO2 3 -、SO2 4 -And the like.
As a specific embodiment of the method described above, in step (2), according to the formation water salinity-drag reducer concentration-drag reducer rate relation chart and the formation water quality of the fracture-modified interval, the drag reducer concentration range applicable to the interval of interest is determined under the condition that the drag reducer rate is greater than 60%.
As a specific embodiment of the above method of the present invention, the pad fluid, the sand-carrying fluid and the displacing fluid are slickwater fracturing fluids containing anti-salt drag reducer;
preferably, the salt-resistant drag reducer comprises linear guar gum or salt-resistant monomer modified polyacrylamide;
more preferably, the salt-resistant monomer includes, but is not limited to, sulfonic acid group, N-Dimethylacrylamide (DMAM), 3-acrylamido-propyldimethylammonium chloride (apadc), dimethyldiallylammonium chloride (DMDAAC), and 2-acrylamido-2-methylpropanesulfonic Acid (AMPS), and the like;
further preferably, the salt-resistant monomer modified polyacrylamide copolymer is 2-acrylamido-2-methylpropanesulfonic acid modified polyacrylamide.
The salt-resistant monomer modified polyacrylamide is characterized in that a salt-resistant monomer is grafted on a side chain of polyacrylamide through a chemical reaction, so that the overall salt resistance of the polyacrylamide is improved. In addition, the salt-resistant monomers used in the present invention are conventional materials, and can be obtained commercially or prepared.
The linear guar gum or the salt-resistant monomer modified polyacrylamide used in the invention are all salt-resistant drag reducer systems with good viscosity-changing effect.
In one embodiment of the method of the present invention, the viscosity of the slickwater fracturing fluid containing the salt-resistant drag reducer is 1.5-100mPa · s, and the elastic modulus of the slickwater fracturing fluid is greater than the viscous modulus and the elastic sand-carrying capacity is strong when the concentration of the drag reducer is 0.1-1 wt%. Wherein the drag reducer concentration in the present invention is calculated based on the total weight of the slickwater fracturing fluid containing the salt-resistant drag reducer as 100%.
The salt-resistant drag reducer used in the invention is an emulsion type, and compared with the conventional powdery thickening agent in the field, the salt-resistant drag reducer has the greatest advantage that the viscosity of slickwater fracturing fluid can be linearly adjusted by controlling the addition amount, and the viscosity of a fracturing fluid system formed by the conventional powdery thickening agent in the field cannot be continuously adjusted, so that the stepped characteristic is basically presented.
As a specific embodiment of the above method of the present invention, wherein the step (3) further comprises: and respectively determining the viscosity and/or the drag reducer concentration of the fracturing fluid used in the pre-liquid construction stage and the displacing liquid construction stage under a certain wellhead pressure condition according to the drag reducer concentration-viscosity-viscoelasticity relation chart.
In the pre-fluid construction stage, high-discharge and high-viscosity slickwater fracturing fluid is preferably selected to hydraulically open the main crack, and the early crack expanding process is completed. Therefore, as a specific embodiment of the above method of the present invention, in step (3), on the premise that the concentration of the drag reducer is already optimized based on the relationship chart of the salinity of the formation water, the concentration of the drag reducer and the drag reducer, and the water quality of the formation in the fracturing modification interval, and in combination with the drag reducer required on site, the higher the concentration of the drag reducer is, the higher the viscosity of the slickwater fracturing fluid is, according to the knowledge of the relationship chart of the concentration of the drag reducer, the upper limit value of the numerical range of the concentration of the drag reducer which is selected as the target concentration of the drag reducer, the numerical range of the viscosity of the fracturing fluid which is used is determined according to the relationship chart of the concentration of the drag reducer, the viscosity and the viscoelasticity, and finally the flow rate data is obtained according to the relationship chart of the flow rate, the concentration of the drag reducer and the drag reducer which is combined with the target concentration of the drag reducer and the drag reducer required on site, and converting the flow speed data to obtain construction displacement data.
In the construction stage of the sand carrying fluid, the low-viscosity slickwater fracturing fluid is selected for filling the third-stage cracks of the far well zone, the medium-viscosity and medium-discharge sand carrying fluid is used for filling the second-stage cracks, and the high-viscosity and high-discharge sand carrying fluid is used for filling the main cracks. Therefore, as a specific embodiment of the method described above, in step (3), a low-viscosity slickwater fracturing fluid is selected for filling the tertiary fractures of the far wellbore zone, on the premise that the viscosity range of the low-viscosity slickwater fracturing fluid is specified, the concentration range of the drag reducer in the fracturing fluid is determined according to the drag reducer concentration-viscosity-viscoelasticity relation chart, and then on the premise that the initial sand ratio is specified, the construction displacement range is determined according to the construction displacement-viscoelasticity-sand ratio relation chart and by combining the drag reducer concentration range in the fracturing fluid;
adopting medium-viscosity and medium-discharge capacity sand-carrying fluid for filling a secondary fracture, determining the concentration range of the drag reducer in the fracturing fluid (sand-carrying fluid) according to a drag reducer concentration-viscosity-viscoelasticity relation chart on the premise of specifying the viscosity range of the medium-viscosity and medium-discharge capacity sand-carrying fluid, and then determining the sand ratio range according to the construction discharge capacity-viscoelasticity-sand ratio relation chart and combining the concentration range of the drag reducer in the fracturing fluid on the premise of specifying construction discharge capacity;
the method comprises the steps of adopting high-viscosity and high-discharge sand carrying fluid for filling a main crack, determining the concentration range of the drag reducing agent in the fracturing fluid (sand carrying fluid) according to a drag reducing agent concentration-viscosity-viscoelasticity relation chart on the premise of specifying the viscosity range of the high-viscosity and high-discharge sand carrying fluid, and then determining the sand ratio range according to the construction discharge capacity-viscoelasticity-sand ratio relation chart and combining the concentration range of the drag reducing agent in the fracturing fluid on the premise of specifying the construction discharge capacity.
And in the construction stage of the displacing fluid, preferentially injecting the slickwater fracturing fluid with medium viscosity into the target reservoir. Therefore, as an embodiment of the method described above, in step (3), on the premise of specifying the concentration of the drag reducer in the slickwater fracturing fluid with medium viscosity, the viscosity distribution range of the slickwater fracturing fluid is determined according to the drag reducer concentration-viscosity-viscoelasticity relation chart, and then the flow rate data is obtained according to the flow rate-drag reducer concentration-drag reducer relation chart and by combining the drag reducer concentration in the slickwater fracturing fluid with medium viscosity and the drag reducer data required on site, and then the construction displacement data is obtained by converting the flow rate data.
As a specific embodiment of the method described above, in the pad fluid construction stage, a high-viscosity and high-displacement slickwater fracturing fluid is selected for fracturing construction to form a main fracture in a near wellbore zone, and after the main fracture is pressed open, a low-viscosity slickwater fracturing fluid is used for construction to communicate with an extended fracture system to form a relatively complex fracture network in a far wellbore zone;
preferably, the concentration of the drag reducer in the high-viscosity high-displacement slickwater fracturing fluid is 0.1-0.6 wt%, the viscosity is controlled to be 50-60 mPa & s, and the displacement in site construction is more than 14m3Min; more preferably, the drag reducer concentration in the high viscosity, high displacement slickwater fracturing fluid is 0.6%;
also preferably, the low viscosity is slipperyThe concentration of the drag reducer in the water fracturing fluid is 0.1-0.6 wt%, the viscosity of the drag reducer is controlled to be 2-5 mPa.s, and the initial site construction discharge capacity is 5-7 m3Min, increasing the discharge capacity to 10-12 m with the increase of the injection liquid amount3Min; still more preferably, the low viscosity slickwater fracturing fluid has a drag reducer concentration of 0.1 wt%.
As a specific embodiment of the method, in the sand carrying fluid construction stage, a small-particle-size long slug or continuous sand adding operation mode is adopted, a low-viscosity slickwater fracturing fluid with the drag reducer concentration of 0.1-0.2 wt% and the viscosity of 3-10 mPa & s is selected to carry 70/140-mesh quartz sand proppant for carrying out sand carrying operation, the highest sand ratio is not more than 10%, and the construction discharge capacity is controlled to be 3-5 m3Min to fully fill the tertiary fractures in the far zone;
carrying 40/70-mesh quartz sand propping agent by using a medium-viscosity slick-water fracturing fluid with a drag reducer concentration of 0.3-0.5 wt%, preferably 0.4 wt% and a viscosity of 25-40 mPa & s, wherein the construction discharge capacity is controlled to be 8-10 m3The sand ratio is controlled to be 7 to 15 percent, preferably 10 to 15 percent, so as to fill the secondary cracks;
finally, carrying 70/140-mesh quartz sand propping agent by using high-viscosity slickwater fracturing fluid with the drag reducer concentration of 0.55-0.65 wt%, preferably 0.6 wt% and the viscosity of 50-60 mPa & s, wherein the construction discharge capacity is controlled to be 10-16 m3Min, sand ratio increased from 16% to 22% to fill the vertical main fractures; then carrying out sand carrying operation by using 40/70-mesh quartz sand proppant carried by high-viscosity slickwater fracturing fluid, wherein the sand ratio is increased from 18% to 24% so as to ensure that main cracks are uniformly filled.
In a specific embodiment of the above method of the present invention, in the construction stage of the displacement fluid, a medium-viscosity slickwater fracturing fluid with a drag reducer concentration of 0.3-0.5 wt%, preferably 0.4 wt%, and a viscosity of 20-40 mPa · s is injected into the target reservoir, and the construction displacement is controlled to be 6-8 m3Min; finally, the distance between the rear part of the shaft and the ground is 20-24 m3And (5) injecting clear water into the displacement volume of/min for replacing construction.
As a specific embodiment of the above method of the present invention, the displacement and viscosity of slickwater fracturing fluid used in each injection stage are monitored in real time by an injection allocation system at the wellhead on the ground;
the injection allocation system comprises a viscosity and discharge monitoring device and an automatic control device of a drag reducer storage tank, a fresh water storage tank and a proppant storage tank, wherein the viscosity and discharge monitoring device is used for monitoring the discharge capacity and the viscosity of slickwater fracturing fluid used in each injection stage in real time, and the automatic control device is used for automatically controlling the adding amount of the drag reducer and the injection amount of the slickwater fracturing fluid according to a set program so as to realize that slickwater fracturing fluids with different drag reducer concentrations are prepared according to construction requirements of different stages and meet the construction requirements of different stages.
Therefore, the method monitors the discharge capacity and viscosity of the slickwater fracturing fluid used in each injection stage in real time through the injection allocation system at the ground wellhead, can realize automatic control and stepless regulation of the viscosity without manual operation, and can meet the construction requirements of each fracturing stage.
Compared with the prior art, the stepless viscosity-changing non-matching slickwater field hydraulic fracturing method provided by the invention has the following beneficial technical effects:
the method provided by the invention has simple process flow, can realize automatic control and stepless regulation of the viscosity of the slickwater fracturing fluid, can overcome the defect that the viscosity regulation control needs to be realized by continuously replacing a fracturing fluid system in the field of the oil field at the current stage, can meet the construction requirements of different fracturing stages, and is convenient to prepare the fracturing fluid and easy to operate; the automatic diagnosis can be carried out according to the change of the construction parameters in the fracturing construction process, and the automatic diagnosis is fed back to the automatic control device in real time, so that intelligent fracturing is realized. The stepless adjustment of the viscosity means that the viscosity of the slickwater fracturing fluid can be adjusted at will, namely, a certain corresponding relation exists between the concentration and the viscosity of the slickwater fracturing fluid.
The slickwater fracturing fluid system used in the invention has strong sand carrying capacity, can realize higher sand adding strength, can optimize the laying form of the propping agent in the fracture, and constructs a multi-stage high-flow conductivity fracture.
The four plates provided by the invention have complementary relationship, can be suitable for fracturing modification projects under different reservoir conditions, and can optimize optimal construction parameters under certain ground fracturing equipment limiting conditions. The various plates provided by the invention are suitable for most of reservoir beds which adopt slickwater fracturing fluid for fracturing transformation at the present stage, and have certain reference and reference significance.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a graphical representation of the formation water salinity-drag reducer concentration-drag reducer relationship provided by an embodiment of the present invention.
Fig. 2 is a graphical representation of a flow rate-drag reducer concentration-drag reduction ratio relationship provided by an embodiment of the present invention.
Fig. 3 is a chart of drag reducer concentration-viscosity-viscoelasticity relationship provided in accordance with an embodiment of the present invention.
Fig. 4 is a chart of the relationship between construction displacement and viscoelastic-sand ratio provided by the embodiment of the invention.
FIG. 5 is a schematic diagram of a network of multiple clusters of fractures formed during slickwater fracturing in an example of the present invention.
Detailed Description
The "ranges" disclosed herein are given as lower and upper limits. There may be one or more lower limits, and one or more upper limits, respectively. The given range is defined by the selection of a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges defined in this manner are combinable, i.e., any lower limit can be combined with any upper limit to form a range. For example, ranges of 60-120 and 80-110 are listed for particular parameters, with the understanding that ranges of 60-110 and 80-120 are also contemplated. Further, if the minimum range values listed are 1 and 2 and the maximum range values listed are 3, 4, and 5, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.
In the present invention, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is only a shorthand representation of the combination of these numbers.
In the present invention, all embodiments and preferred embodiments mentioned herein may be combined with each other to form a new technical solution, if not specifically stated.
In the present invention, all the technical features mentioned herein and preferred features may be combined with each other to form a new technical solution, if not specifically stated.
In the present invention, the term "comprising" as used herein means either an open type or a closed type unless otherwise specified. For example, the term "comprising" may mean that other materials and/or elements not listed may also be included, or that only the listed materials and/or elements may be included.
In order to clearly understand the technical features, objects and advantages of the present invention, the following detailed description of the technical solutions of the present invention will be made with reference to the following specific examples, which should not be construed as limiting the implementable scope of the present invention.
The embodiment of the invention provides a stepless viscosity-changing and slickwater-free on-site hydraulic fracturing method, wherein slickwater fracturing fluid is adopted in the whole fracturing process, the viscosity of the slickwater fracturing fluid can be automatically controlled through a fluid-dispensing pump, stepless regulation and control are realized, and the construction requirements of different fracturing stages can be met. And drawing a relation chart among different parameters according to a large amount of field fracturing data and/or indoor experimental data, so that the relation chart can be used as a reference basis for a fracturing construction process.
In an exemplary embodiment of the invention, the specific process flow of the hydraulic fracturing operation in situ using stepless viscosity change and no-matched slickwater is as follows:
before fracturing construction, basic geological parameters of a reservoir to be modified are obtained, wherein the basic geological parameters comprise rock mechanical parameters, three-dimensional ground stress, lithology, mineral composition, natural fracture characteristics and the like, so that the compressibility of the reservoir is evaluated. And further analyzing the physicochemical properties of the reservoir and formation fluid parameters including porosity, permeability, saturation, formation water mineralization and the like aiming at the compressible reservoir. Wherein, the quality of the stratum water in the fracturing and reconstruction layer section is a key focused index in the invention.
By formation water is meant water in the pores or fractures of the rock, and usually there are always dissolved considerable amounts of metal salts, such as sodium, potassium, calcium, magnesium salts, etc. The salinity of the formation water is usually expressed by the salinity, and the unit is mg/L, and the salinity of the formation water in different reservoirs is very different from thousands of mg/L to tens of thousands of mg/L or even as high as hundreds of thousands of mg/L.
Because the total salinity distribution of the formation water is wide and the difference of different blocks is large, the invention focuses on the concentration of divalent metal cations, namely Ca, in the formation water2+、Mg2+、Fe2+Etc. almost all of the reservoir formation water contains Ca2+、Mg2+While iron ions mainly appear in formations with rich pyrite content, generally volcanic rock sedimentary reservoirs, and the oxidative decomposition of minerals can cause trace iron ions in formation water. The concentration distribution of divalent metal cations in formation water is generally between hundreds of mg/L and thousands of mg/L, and the variation range is relatively small; in addition, the type and amount of divalent metal cations adversely affect the viscosity and drag reduction ratio of drag reducers in slick water, and thus the present invention uses this as a reference to plot the formation water salinity-drag reducer concentration-drag reduction ratio relationship as shown in fig. 1.
The results of both indoor experiments and field experiments show that the drag reduction performance of the slickwater fracturing fluid has a direct relation with the test flow rate or construction discharge capacity, the drag reduction rate of the slickwater fracturing fluid containing the drag reducer with the same concentration is relatively low under the condition of low flow rate, and the drag reduction rate gradually increases and tends to be stable along with the increase of the flow rate, so that the optimal drag reduction effect is achieved. Based on this, the invention combines the data of the indoor experimental test to draw and obtain the chart of the relationship between the drag reduction rate and the flow rate of the variable-viscosity slickwater fracturing fluid under the conditions of different concentration adding amounts, as shown in fig. 2, the chart mainly considers the relationship between the drag reduction rate and the flow rate of the slickwater fracturing fluid, and the flow rate data in the chart can be mutually converted with the site construction discharge capacity.
The salt-resistant drag reducer with better viscosity-changing effect, which is referred by the invention, is a common drag reducer system familiar to the technical personnel in the field, such as linear guar gum, AMPS monomer modified polyacrylamide and the like, the dosage of the salt-resistant drag reducer is usually not more than 1 wt%, and the salt-resistant drag reducer has the advantages of reducing friction resistance, increasing viscosity and having strong salt resistance, and is an important component of the variable-viscosity slickwater fracturing fluid.
After the quality of reservoir formation water is definitely fractured, the concentration interval of the drag reducer in the formation with specific mineralization is preferably selected according to the relation chart of the mineralization of the formation water, the concentration of the drag reducer and the drag reducer rate and the mineralization of the formation water. For example, when the concentration of divalent metal cations is 2000mg/L, the drag reduction rate variation range of slickwater fracturing fluids with different drag reducer concentrations is about 57-71%, and if the drag reduction rate is required to be more than 60% on site, the drag reducer concentration is in the range of less than 0.6 wt% and meets the requirement; meanwhile, the optimal value of the drag reducer concentration at different flow rates (or discharge volumes) is determined by combining the flow rate-drag reducer concentration-drag reduction ratio relation chart shown in fig. 2 and is applied to the subsequent construction process.
The viscoelastic characteristics of the slickwater fracturing fluid are key parameters influencing the sand carrying effect of the slickwater fracturing fluid. The viscoelastic characteristics refer to viscous modulus and elastic modulus in rheological parameters of the fracturing fluid, and the mainstream view at present is that the slickwater fracturing fluid mainly carries sand in elasticity, namely, the sand carrying and transporting capacity is better in a range that the elastic modulus is larger than the viscous modulus. The viscosity change and the viscoelasticity characteristics of the salt-resistant drag reduction system at different concentrations are measured on the basis of a large number of indoor rheological experiments, so that a drag reducer concentration-viscosity-viscoelasticity relation chart shown in figure 3 is drawn. As can be seen from the curve in FIG. 3, the viscosity of the slickwater system gradually increases with the increase of the concentration of the drag reducer, and the viscosity distribution range is 1.5-100 mPas; the curves of change of the elastic modulus and the viscous modulus also show a rising trend with increasing drag reducer concentration, the two curves intersect near 1 wt% drag reducer concentration, and then the viscous modulus is larger than the elastic modulus; and in the range that the concentration of the drag reducer is less than 1 wt%, the elastic modulus is always greater than the viscous modulus, and the elastic sand-carrying effect is relatively good.
At present, fracture construction parameter design is mostly realized through commercial software for fracture simulation, the commercial software for fracture simulation can be Fracpro PT, MEYER, STIMPLAN or GOFHER and the like, and the software can simulate the dynamic expansion condition of fractures under different fracture construction parameters, and optimize the fracture parameters such as discharge capacity, injection quantity, viscosity of each stage of slickwater fracturing fluid, proppant type and mesh number, construction sand ratio and the like. The discharge capacity, sand ratio and the viscoelasticity of slickwater are key parameters of fracturing construction design, and the construction sand ratio usually has a direct relation with the discharge capacity and the viscoelasticity of slickwater: under a certain discharge capacity, the sand ratio under different viscoelastic conditions is different; similarly, increasing the displacement also increases the sand ratio under the same viscoelastic conditions. Based on the rule, on the basis of summarizing a large amount of on-site fracturing construction data (including parameters such as construction liquid amount and discharge amount, pad fluid of each fracturing layer section, sand carrying fluid and injection amount of displacement fluid, viscosity of variable-viscosity slickwater fracturing fluid of each fracturing stage, proppant mesh number, sand ratio and the like), a slickwater construction discharge amount-viscoelasticity-sand ratio relation chart shown in figure 4 is creatively drawn, the change conditions of sand ratios under different drag reducer concentrations and construction discharge amounts are determined, and certain reference value is provided for the design of subsequent slickwater fracturing parameters.
In the invention, the slickwater construction displacement-viscoelasticity-sand ratio relation chart as shown in fig. 4 is mainly used for preferably obtaining the construction displacement or sand ratio parameter of the sand carrying fluid construction stage on the basis of the preferred concentration range. Specifically, the sand ratio may be preferred under a specified displacement condition, or the construction displacement may be preferably obtained by using the sand ratio as the specified condition; the invention does not make specific requirements for determining the specified conditions, and technicians in the field can reasonably set the specified conditions according to the actual operation needs on site, thereby reasonably determining other process parameters according to the specified conditions. In addition, the mesh number of the propping agent used in the construction stage of the sand-carrying fluid is not limited, and the mesh number of the propping agent can be reasonably selected by a person skilled in the art according to the actual operation requirement on site as long as the aim of the invention can be realized.
The following will describe in detail how to use four types of charts of formation water mineralization-drag reducer concentration-drag reducer rate relation chart, flow rate-drag reducer concentration-drag reducer rate relation chart, drag reducer concentration-viscosity-viscoelasticity relation chart and construction displacement-viscoelasticity-sand ratio relation chart to guide the on-site hydraulic fracturing production process, with reference to an exemplary embodiment, wherein the stepless viscosity change and no-matching slickwater on-site hydraulic fracturing method comprises the following specific steps:
determining the mineralization degree of stratum water of a reconstructed layer before fracturing construction, particularly determining divalent metal cations (Ca) in the stratum water2+、Mg2+、Fe2+Etc.) and then determining an appropriate drag reducer concentration boost in conjunction with a chart of the formation water salinity-drag reducer concentration-drag reduction ratio relationship as shown in fig. 1. For example, the total mineralization of divalent metal cations in the formation water is 2000mg/L, and the drag reduction rates corresponding to different concentrations of drag reducer at the mineralization of 2000mg/L can be seen in conjunction with FIG. 1. For field construction, the drag reduction rate is mainly related to the magnitude of the friction drag differential in the injection string, and the magnitude of the friction drag differential is directly related to the pressure of the fracturing fluid reaching the bottom of the well (bottom pressure ═ wellhead pressure + liquid column pressure-pipeline friction drag pressure). Therefore, under the limited condition of ground construction equipment, the effective bottom hole pressure can be achieved only by reducing the friction pressure of the pipeline as much as possible. In addition, since the larger the drag reduction rate is, the smaller the pipe friction pressure difference is, the drag reduction rate is usually required to be at least more than a certain value according to the restriction of the ground equipment in the field construction. In this embodiment, taking 60% as an example, that is: the drag reduction ratio is more than 60%, and the concentration of the drag reduction agent is preferably 0.1-0.6 wt% from the graph 1, and the drag reduction agent concentration can meet the field construction requirement within the numerical range.
The salt-resistant drag reducer used in this example was 2-acrylamido-2-methylpropanesulfonic acid-modified polyacrylamide.
In this embodiment, the formation water salinity-drag reducer concentration-drag reducer rate relation chart may be drawn based on a large amount of summarized field experimental data or by indoor simulation experimental data, and here, the drawing process is described in detail by taking the drawing by the indoor simulation experimental data as an example:
under laboratory conditions, firstly, anhydrous calcium chloride and magnesium chloride are used for preparing a series of salt solutions with different concentrations according to a ratio of 1:1 (namely, the concentrations of calcium ions and magnesium ions in the formed salt solutions are equal), wherein the total content of divalent metal ions in the solutions is respectively 200mg/L, 400mg/L, 600mg/L, 800mg/L, 1000mg/L, 2000mg/L, 3000mg/L and 4000 mg/L; then under the condition of each mineralization degree, namely the total content of divalent metal ions, sequentially measuring the drag reduction rate when the concentration of the drag reduction agent is from 0.1 wt% to 0.8 wt% and each increment is 0.1 wt% by adopting an indoor loop friction resistance testing system, namely measuring the maximum drag reduction rate of the drag reduction agent with different concentrations in water with different mineralization degrees; and drawing the relation chart of the formation water salinity-drag reducer concentration-drag reducer rate according to 64 groups of measured experimental data.
It should be noted that the maximum drag reduction ratio is measured at the highest flow rate (2000m/min) to determine the best drag reduction effect at different drag reducer loadings.
In the pre-fluid construction stage, high-discharge and high-viscosity slickwater fracturing fluid is preferably selected to hydraulically open the main crack, and the early crack expanding process is completed. Wherein the displacement is preferably primarily referenced to the flow rate-drag reducer concentration-drag reduction ratio relationship chart shown in fig. 2, and the preflush stage displacement is preferably without regard to sand ratio issues. As can be seen in fig. 2, the drag reduction ratio of slickwater fracturing fluids of the same drag reducer concentration increased gradually with increasing test flow rate. It is worth noting that the abscissa in fig. 2 is the flow rate of the pipeline during the indoor friction test, and the magnitude of the flow rate can be converted into the displacement in the actual fracturing process in the field. For example, the displacement in the field is 10m3Min, and a P110 steel grade phi 139.7mm multiplied by 10.54mm high-extrusion casing is adopted on site, the flowing speed of the slickwater fracturing fluid in the pipeline is calculated according to the following formula 1), the calculated result is 904.88m/min, and the conversion is realized in the field application processThe relation is calculated by combining the model of the oil casing pipe which is actually used;
in equation 1), Q is the site discharge capacity in m3/min；
r is the pipe diameter of the sleeve used on site, and the unit is m;
ν is the velocity of the slickwater fracturing fluid flowing in the pipeline, and the unit is m/min.
In this embodiment, the chart of the relationship between flow rate, drag reducer concentration and drag reduction ratio can be drawn based on a large amount of field experimental data or by indoor simulation experimental data, and the drawing process is described in detail by taking the drawing by the indoor simulation experimental data as an example:
through the indoor loop friction resistance test system, measure the drag reduction rate of slick water fracturing fluid of arbitrary drag reducer concentration under different experimental flow rates, the experimental flow rate is set for respectively: 250m/min, 750m/min, 1000m/min, 1250m/min, 1500m/min, 1750m/min and 2000m/min, drag reducer concentration from 0.1 wt% to 0.8 wt%, each increment of 0.1 wt%; and drawing the relation chart of the flow rate, the drag reducer concentration and the drag reduction rate according to the 56 groups of measured experimental data. It can be seen from this plate that the drag reduction is generally lower at low flow rates, with the rate increasing with increasing flow rate.
As shown above, it is preferable that the drag reducer concentration is in the range of 0.1 to 0.6 wt% according to the formation water mineralization and the chart shown in fig. 1, and as shown in the chart of the drag reducer concentration-viscosity-viscoelasticity relationship shown in fig. 3, the higher the drag reducer concentration is, the higher the viscosity of the slickwater fracturing fluid is, at this time, the slickwater fracturing fluid with the drag reducer concentration of 0.6 wt% should be selected, and as can be seen from fig. 3, when the drag reducer concentration in the slickwater fracturing fluid is 0.6 wt%, the viscosity of the slickwater fracturing fluid corresponds to about 58mPa · s, but because errors may exist in the fluid preparation and testing processes, the viscosity of the slickwater fracturing fluid in the embodiment can be controlled to be between 50 to 60mPa · s; as can be seen from FIG. 2, the drag reducer concentration isWhen the flow rate is 0.6 wt%, the drag reduction rate can be more than 60% in the range of the flow rate being more than 1250m/min, and the corresponding displacement range is about 14m3Min (related to oil casing size).
In the embodiment, a high-viscosity high-displacement pad fluid is selected firstly to form a main crack (first-stage crack) in a near wellbore zone, and a low-viscosity slickwater fracturing fluid with lower viscosity is adopted immediately after the main crack is pressed open, at this time, the slickwater fracturing fluid with the drag reducer concentration of 0.1 wt% is selected, as can be seen from fig. 3, when the drag reducer concentration in the slickwater fracturing fluid is 0.1 wt%, the viscosity of the slickwater fracturing fluid corresponds to about 3mPa · s, but errors may exist in the fluid preparation and test processes, so the viscosity of the slickwater fracturing fluid can be controlled to be about 2-5 mPa · s in the embodiment; according to the figure 2, the flow speed is preferably about 875m/min, corresponding to the site discharge capacity of 7-8 m3Min, along with the increase of the injected liquid amount, the subsequent discharge capacity can be increased to 10-12 m3Min, the purpose of which is to communicate with the extended fracture system to form a relatively complex fracture network (secondary, tertiary) in the far zone, as shown in fig. 5.
In this embodiment, the drag reducer concentration-viscosity-viscoelastic relationship chart may be prepared by plotting the drag reducer concentration-viscosity-viscoelastic relationship chart based on a large amount of field experimental data summarized or based on indoor simulation experimental data, and the plotting process is described in detail by taking the plotting through the indoor simulation experimental data as an example:
the drawing process of the plate is mainly carried out based on the indoor rheological experiment result. Specifically, the viscosity and viscoelastic characteristics were measured using an HAAKE MARS rheometer (conventional in the art) at a drag reducer concentration in distilled water of from 0.1 wt% to 0.8 wt% at 0.1 wt% increments, with the shear rate at the time of the test set to 170s-1The experimental conditions are normal temperature and normal pressure. The viscoelasticity characteristic test mainly measures two indexes of elastic modulus G 'and viscous modulus G' under constant shear rate, and the relative size of the numerical value reflects the relative strength of the viscosity and elasticity of the slickwater fracturing fluid; and establishing a chart of the relationship of the drag reducer concentration-viscosity-viscoelasticity according to the obtained test result.
It should be noted that: the fracturing system used for obtaining the drag reducer concentration-viscosity-viscoelasticity relation chart is the same as the fracturing system used for obtaining the formation water salinity-drag reducer concentration-drag reducer rate relation chart and the flow rate-drag reducer concentration-drag reducer rate relation chart, but in the practical experiment process, the applicant finds that other additives in the fracturing fluid system do not influence the rheological property of the slickwater fracturing fluid, so that when the drag reducer concentration-viscosity-viscoelasticity relation chart is obtained, a system formed by distilled water and the drag reducer is usually adopted for convenience.
And in the stage of carrying the sand, slickwater sand-carrying fracturing fluid with different viscosities, sand ratios, discharge capacities and proppant meshes is adopted to sequentially fill the third-stage cracks, the second-stage cracks and the first-stage cracks formed by fracturing in the stratum, so that the supporting effect is optimized, and the flow conductivity of a complex crack network is improved. In the sand carrying liquid stage, a small-particle-size long slug or continuous sand adding operation mode is adopted, the sand carrying operation is preferably carried out by using a low-viscosity slick water fracturing liquid with the drag reducer concentration of 0.1-0.2 wt% and the viscosity of 3-10 mPa & s to carry 70/140-mesh quartz sand propping agent, the highest sand ratio is not more than 3%, and the construction discharge capacity is controlled to be 3-6 m3Min to fully fill the tertiary fractures in the far zone. It should be noted that, due to the addition of the proppant, the density of the slickwater sand-carrying fracturing fluid in the shaft is increased, the generated fluid column pressure is increased, and the bottom hole pressure generated by the same ground equipment is increased, so that the requirement on the drag reduction rate of the fracturing fluid can be slightly weakened in the sand-carrying fluid stage; then, a slickwater fracturing fluid with medium viscosity and medium discharge capacity and carrying 40/70-mesh quartz sand is used for filling a second-stage crack, the viscosity of the fracturing fluid is controlled to be 25-40 mPa & s, the concentration of a drag reducer is 0.3-0.5 wt%, the preferred concentration is 0.4 wt%, the sand ratio can be slightly improved in the stage, and the discharge capacity is controlled to be 8-10 m3The sand ratio can reach 7 to 15 percent, preferably 10 to 15 percent; finally, filling the vertical main crack with high viscosity (viscosity is 50-60 mPa.s) and high-displacement sand-carrying fluid, wherein the concentration of the drag reducer is 0.55-0.65 wt%, preferably 0.6 wt%, and the construction displacement is controlled to be 10-16 m3Permin, the main fracture extending end is filled with 70/140 mesh small-particle-size quartz sand proppant, the sand ratio can be increased from 16 percent to 22 percent, and then the mesh is changed to 40/70 meshThe quartz sand proppant fills main cracks of a near-well zone, the sand ratio can be increased from 18 percent to 24 percent, and the main cracks are uniformly filled.
The following will specifically describe how to determine parameters such as the viscosity, the construction displacement, and the sand ratio of the fracturing fluid involved in the sand carrying fluid stage in the present embodiment according to the flow rate-drag reducer concentration-drag reducer rate relation chart shown in fig. 2, the drag reducer concentration-viscosity-viscoelasticity relation chart shown in fig. 3, and the construction displacement-viscoelasticity-sand ratio relation chart shown in fig. 4.
The low-viscosity slickwater fracturing fluid is selected for filling the third-stage fractures of the far well zone, the viscosity range of the given low-viscosity slickwater fracturing fluid in the embodiment is 3-10 mPa · s, and as can be seen from FIG. 3, the concentration range of the drag reducer corresponding to the viscosity range is 0.1-0.2 wt%; the initial sand ratio of the stage is required to be determined according to field experience, and the near-well end crack blockage can be caused by the excessive sand ratio, so the initial sand ratio of the stage can be controlled within 3 percent, and therefore, when the concentration of the drag reducer in the fracturing fluid is 0.1-0.2 wt percent and the sand ratio is 3 percent, the corresponding discharge capacity is about 3-6 m when the concentration of the drag reducer in the fracturing fluid is shown in figure 43/min；
The middle-viscosity and middle-displacement sand-carrying fluid is adopted for filling the second-stage fracture, the parameters used in the stage are preferably similar to those used in the previous stage (namely the stage of filling the third-stage fracture in the far well zone), the viscosity of the middle-viscosity and middle-displacement sand-carrying fluid adopted for filling the second-stage fracture in the embodiment is 25-40 mPa & s, and as can be seen from FIG. 3, the viscosity range corresponds to the concentration range of the drag reducer which is 0.3-0.5 wt%; the sand ratio is optimized through construction discharge capacity at the stage, and for most of on-site fracturing, the construction discharge capacity is 8-10 m3The/min belongs to the middle discharge capacity range, and therefore, the construction discharge capacity is 8-10 m as can be seen by combining the graph of FIG. 43Min, when the concentration range of the drag reducer in the fracturing fluid is 0.3-0.5 wt%, the corresponding sand ratio range is about 7-15%, preferably 10-15%;
in this embodiment, the viscosity of the high-viscosity and high-displacement sand carrier fluid is set to be 50 to 60mPa · s, and as can be seen from fig. 3, the viscosity range corresponds to the concentration range of the drag reducerIs 0.55 to 0.65 wt%; the sand ratio is optimized through construction discharge capacity at the stage, and for most of on-site fracturing, the construction discharge capacity is 10-16 m3The/min belongs to the high discharge range, so that the construction discharge is 10-16 m3Min, when the concentration range of the drag reducer in the fracturing fluid is 0.55-0.65 wt%, the corresponding sand ratio is about 16-24%;
during the actual fracturing process in the field, 70/140 mesh small-particle-size quartz sand proppant is preferably used for filling the extending tail end of the main fracture, and the sand ratio is controlled between 16% and 22%; then, quartz sand proppant with the mesh number of 40/70 is used for filling the main cracks of the near-well zone, and the sand ratio variation range is controlled between 18% and 24% so as to ensure that the main cracks are uniformly filled.
In the sand-carrying fluid stage of this embodiment, after the construction displacement is determined, it may be checked according to the chart of relationship between flow rate and drag reducer concentration and drag reducer as shown in fig. 2 and the conversion relationship between construction displacement and flow rate to determine whether the determined construction displacement is reasonable. In general, when the construction displacement determined in the embodiment is checked to be reasonable according to the flow rate-drag reducer concentration-drag reducer relation chart shown in fig. 2, the field requirement can be met as long as the determined drag reducer data is not particularly low (the high and low conditions of the drag reducer data can be reasonably determined by a person skilled in the art according to the actual operation requirement of the field).
In this embodiment, the construction displacement-viscoelastic-sand ratio relation chart can be drawn by summarizing a large amount of field experimental data and by indoor simulation experimental data, and the drawing process is described in detail here:
the drawing process of the chart is mainly based on the pump injection procedure of the site fracturing construction and the relevant data of the indoor dynamic sand carrying experiment. The on-site pumping program comprises discharge capacity and injection quantity of each stage of fracturing fluid pad fluid, sand carrying fluid and displacing fluid, and sand ratio parameters mainly reflect in the sand carrying fluid stage. The displacement range in the field fracturing process is usually 3m3/min～16m3Between/min, this is related to the physical parameters of the modified reservoir and the fracturing construction stage: the displacement of compact shale reservoir is often lowIt is desirable to avoid rapid pressurization of the wellhead equipment; the fracturing pad fluid stage generally adopts large-displacement construction, and the sand-carrying fluid stage generally reduces the displacement. The sand ratio is related to the construction discharge capacity and the viscoelasticity of the fracturing fluid, the discharge capacity is large, the sand carrying capacity is strong, and the sand ratio is high. The sand ratio data of the experiment is obtained by combining field data and an indoor dynamic sand carrying experiment. The indoor dynamic sand carrying experiment mainly aims at researching the influence of the viscoelasticity of the slickwater on the sand carrying effect. By integrating the drag reducer concentration-viscosity-viscoelasticity relationship chart (see fig. 3), the viscoelasticity characteristics under different drag reducer concentrations are determined, further, a dynamic sand carrying experiment of slickwater fracturing fluid with the same viscosity under different discharge capacities is carried out, the shape and the settlement migration distance of a sand bank formed by a propping agent in a fracture template are analyzed, and the maximum value of the sand ratio under the conditions of fixed discharge capacity and drag reducer concentration is obtained through testing, so that the maximum value is used as a data point in the chart shown in fig. 4. And by analogy, measuring the maximum value of the sand ratio obtained under each discharge capacity and viscoelastic condition, and drawing to obtain a construction discharge capacity-viscoelastic-sand ratio relation chart.
In addition, the ratio of the elastic modulus to the viscous modulus, which is obtained mainly from the experimental data in fig. 3, is also shown in fig. 4, and the ratio can be used as a bridge to link the three parameters of viscosity, displacement and sand ratio. Furthermore, the slimy slick used in the present invention is actually dominated by elastic sand-carrying, which can also be verified from the G'/G "ratio shown in fig. 4, i.e.: in a reasonable concentration range, the elastic modulus G' is always larger than the viscous modulus G ", the viscous modulus can be generally reflected by the index of viscosity, but at present, the index of elasticity like the elasticity does not exist in the field to reflect the elastic modulus, so the term viscosity is used more in field application, and the sand ratio is also referred to in the invention to be related to the viscosity and the discharge capacity. However, in practice, more and more research has found that elastic sand carrying is more convincing than viscous sand carrying.
Preferentially injecting a medium-viscosity slickwater fracturing fluid into a target reservoir stratum in a displacing fluid stage, wherein the medium-viscosity slickwater fracturing fluid used in the embodiment is a medium-viscosity slickwater fracturing fluid with the drag reducer concentration of 0.3-0.5 wt%, and preferably 0.4 wt%; accordingly, as can be seen from the chart of the relationship between the concentration of the drag reducer and the viscosity and the viscoelasticity shown in fig. 3, when the concentration of the drag reducer in the slickwater fracturing fluid is 0.3 to 0.5 wt%, the viscosity of the slickwater fracturing fluid is distributed in the range of 20 to 40mPa · s, and the slickwater fracturing fluid belongs to the medium viscosity range, so that the requirements of site construction can be met;
and determining the flow rate according to the relation chart of the flow rate-drag reducer concentration-drag reducer as shown in fig. 2, and further determining the construction discharge capacity, specifically, as can be seen from fig. 2, when the concentration of the drag reducer in the slickwater fracturing fluid is 0.3-0.5 wt%, the flow rate is in the range of more than 950m/min, the drag reducer can reach more than 60%, and the site construction discharge capacity corresponding to the flow rate range is about 6-8 m3/min；
Finally, the high discharge capacity (20-24 m) is adopted in the shaft3Min) filling clear water for replacement construction, ensuring that residual sand-carrying liquid in a shaft completely enters a crack system, reducing casing abrasion and ensuring good construction effect, and supposing from a chart of relationship between flow velocity, drag reducer concentration and drag reducer as shown in figure 2, the discharge capacity is large, namely 20-24 m3The drag reduction rate at/min can reach more than 60 percent.
In this embodiment, the pad fluid, the sand carrier fluid and the displacing fluid are slickwater fracturing fluids containing salt-resistant drag-reducing agent, which contains water (water content is usually above 98 wt%) and additives such as drag-reducing agent (content is less than 2 wt%); wherein, other additives besides the drag reducer, such as bactericide, oxygen scavenger, surfactant, etc. can be reasonably selected according to actual needs.
When the stepless viscosity-changing non-matching slickwater provided by the embodiment of the invention is adopted for construction operation, the construction parameters of each stage can be preset and completed on a computer, and the viscosity and discharge monitoring device at the wellhead can monitor the discharge capacity and viscosity of slickwater fracturing fluid injected into a shaft in each injection stage in real time. How to realize automatic mixing mainly depends on automatic control devices arranged on a drag reducer storage tank, a fresh water storage tank and a propping agent storage tank, mixing requirements of all stages can be completed according to preset programs, each raw material can be added into a sand mixing tank in proportion, and then the raw materials are pumped into a shaft through an output pipeline, so that real automatic monitoring and stepless viscosity change are realized, the construction process is simple, and the operation risk is lower.
The above description is only exemplary of the invention and should not be taken as limiting the scope of the invention, so that the invention is intended to cover all modifications and equivalents of the embodiments described herein. In addition, the technical features and the technical inventions of the present invention, the technical features and the technical inventions, and the technical inventions can be freely combined and used.
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| CN117821050A (en) * | 2023-12-22 | 2024-04-05 | 中国石油天然气集团有限公司 | Compact gas reservoir fracturing fluid system and fracturing method |
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| CN115126462A (en) * | 2022-06-16 | 2022-09-30 | 中国石油大学(北京) | Active control method for hydraulic fracture net |
| CN115126462B (en) * | 2022-06-16 | 2024-06-04 | 中国石油大学(北京) | Active control method for hydraulic fracture network |
| CN117821050A (en) * | 2023-12-22 | 2024-04-05 | 中国石油天然气集团有限公司 | Compact gas reservoir fracturing fluid system and fracturing method |
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