CN109209332B - Acid slickwater composite fracturing method for shale gas horizontal well - Google Patents
Acid slickwater composite fracturing method for shale gas horizontal well Download PDFInfo
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- 230000002378 acidificating effect Effects 0.000 claims abstract description 18
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
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Abstract
The invention discloses an acidic slickwater composite fracturing method for a shale gas horizontal well. The method comprises the following steps: (1) evaluating a reservoir before fracturing; (2) optimizing a perforation scheme; (3) injecting acidic slick water; (4) adding 70-140 mesh proppant; (5) injecting normal slick water with equal viscosity; (6) injecting high-viscosity conventional glue solution; (7) injecting 40-70 mesh and 30-50 mesh proppant. The method of the invention improves the complexity of deep normal pressure shale gas fracturing cracks and the filling rate of crack systems with different scales, further improves the effective reconstruction volume of deep normal pressure shale gas, and improves the yield increasing and stabilizing effects after pressing.
Description
Technical Field
The invention relates to the field of oil and gas exploitation, in particular to an acidic slickwater composite fracturing method for a shale gas horizontal well.
Background
At present, the staged fracturing technology of the horizontal well has been successfully practiced and has a good effect on the sea-phase high-pressure Longmaxi shale gas stratum. However, with the advance of the exploration and development process of the shale gas, the shale gas gradually advances towards the deep layer and the normal pressure. At present, no breakthrough with demonstration significance is obtained in the fracturing reformation of deep shale gas or normal-pressure shale gas. The main reasons are the complex degree of cracks formed by fracturing deep shale gas and normal pressure shale gas and the insufficient effective reconstruction volume.
In general, the existing shale gas horizontal well staged fracturing technology has poor adaptability to deep shale gas and normal pressure shale gas, and the main problems are as follows:
(1) the deep shale gas increases along with the increase of the buried depth, the horizontal stress difference increases, the rock plasticity characteristic becomes strong, the induced stress action is weakened, the micro-fracture size is smaller, and the factors are all unfavorable for improving the fracture modification volume and the fracture complexity degree;
(2) the reduction in atmospheric pressure shale gas pressure coefficient may be the result of the escape of the original shale gas, also resulting in internal microfractures and a reduction in bedding/texture dimensions. Thus, the effective support volume for fracture modification is reduced;
(3) for many current deep shale gases, the deep shale gases often have the characteristics of normal pressure shale gases at the same time, so that the 2 difficulties are combined together, and the fracturing difficulty is increased continuously;
(4) the conventional fracturing mode adopts a method of injecting slickwater, glue solution, 100-mesh proppant, 40/70-mesh proppant and 30/50-mesh proppant, which has better applicability to high-pressure medium-shallow shale gas, but is not necessarily suitable for fracturing deep and normal-pressure shale gas, and particularly, on the premise that the dimensions of micro-fractures and horizontal bedding/textures are generally reduced, the particle size selection and the corresponding addition amount design of small-particle-size proppant may not be suitable, so that the resulting result may be that the 100-mesh proppant is not effectively filled and supported in small-scale fractures, but is possibly mixed with large-particle-size proppant in large-scale fractures to block the large-scale fractures, thereby reducing the fracture conductivity.
Therefore, for deep normal pressure shale gas, a new fracturing technology needs to be developed to solve the above limitations.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides an acidic slickwater composite fracturing method for a shale gas horizontal well. By adopting a liquid system of acid slickwater, slickwater and active glue solution, small-scale micro cracks, bedding/texture cracks and the like are communicated and corroded, the complexity of fracturing cracks is improved, the effective reconstruction volume is increased, the flow conductivity of a multi-scale crack net is improved, and the yield increase and commercial exploitation of deep normal-pressure shale gas are realized.
The invention aims to provide an acid slickwater composite fracturing method for a shale gas horizontal well.
The method comprises the following steps:
(1) reservoir evaluation before fracturing
(2) Perforation plan optimization
The deep shale gas fracturing adopts multi-section few-cluster perforation;
the normal pressure shale gas fracturing adopts a plurality of sections of multi-cluster perforation;
the cluster number of deep normal pressure shale gas perforation is between the deep shale gas and the normal pressure shale gas;
the perforation mode adopts circumferential perforation formed by hydraulic jet;
(3) acidic slickwater injection
The slickwater has strong acidity, viscosity value of 2-3mPa · s, low injection discharge capacity of 3-5m3/min；
Injecting high-viscosity acid jelly with the volume 1-2 times of that of the vertical well casing after 1/3 of the total injection amount of the acid slickwater; entering high-viscosity acid jelly in the near-well crack for half of the volume of a straight well barrel, and then injecting subsequent acid slick water;
(4) addition of 70-140 mesh proppant
In order to match the injection of the acid slickwater in the step (3), 70-140 meshes of propping agent is added in a slug mode at different stages;
(5) injection of iso-viscosity conventional slickwater
Adopting conventional slickwater with the same viscosity as the acidic slickwater, wherein the using amount of the conventional slickwater is 2-3 times of the total volume of a vertical shaft and a horizontal shaft;
(6) injection of high viscosity conventional glue
Injecting a conventional high-viscosity glue solution system on the basis of the conventional slickwater in the step (5);
among them, preferred are:
in the step (2),
the deep shale gas fracturing adopts multi-section few-cluster perforation; the number of single-segment perforation clusters is 3-5 clusters;
the normal pressure shale gas fracturing adopts a plurality of sections of multi-cluster perforation; the number of single-segment perforation clusters is 2-3 clusters;
the number of clusters of deep normal-pressure shale gas perforation is between that of deep shale gas and normal-pressure shale gas, and the number of clusters of single-stage perforation is between 2 and 4 clusters.
In the step (2), 3-6 holes are circumferentially and internally perforated.
In the step (3), the viscosity ratio of the high-viscosity acid jelly to the acid slickwater is more than 10.
In the step (4), the small-particle size proppant of 70/140 meshes is mixed according to the proportion of 5-15%.
In the step (6), the viscosity of the high-viscosity glue solution system is 40-50 mPas.
In the step (7), if the closing stress exceeds 90MPa, only 40/70-mesh proppant is selected.
The invention recommends mixing the small-particle size proppant of 70/140 meshes according to the proportion of 5-15% in the early stage of injection, and meanwhile, the viscosity of the high-viscosity conventional glue solution can achieve 30-40% of the highest viscosity.
The specific process and steps are as follows:
(1) pre-stress reservoir evaluation with compressibility evaluation as main line
Evaluation of compressibility based on geological desserts and engineered desserts, whether deep-bed shale gas or atmospheric shale gas, or deep-bed atmospheric shale gas, is essential. And conventional methods such as well logging, core testing and the like are adopted to perform conventional evaluations such as lithology, physical properties, rock mechanics, three-dimensional ground stress, geological indexes and the like. In addition, for deep shale gas, as the burial depth increases, the temperature and the ground stress increase, and the rock plasticity characteristics are enhanced, a core test research under the conditions of high temperature and high pressure needs to be simulated.
(2) Perforation plan optimization
The number of perforation clusters is mainly determined by the brittleness of the rock, the better the brittleness, the larger the number of perforation clusters, and vice versa. Deep shale gas fracturing generally adopts a multi-section and cluster-less mode; for the atmospheric pressure shale gas, a plurality of sections and a plurality of clusters of perforation are suitable (the number of perforation clusters of the current foreign atmospheric pressure shale gas is generally 5-10 clusters); for deep atmospheric shale gas, the number of clusters of perforation is recommended to be between that of the deep shale gas and that of the atmospheric shale gas, so that the number of clusters of perforation in a single section is preferably between 2 and 4 clusters.
As for the perforation mode, the circumferential perforation formed by hydraulic jet is preferably adopted, so that a plurality of perforation holes can be conveniently cracked and extended in the same crack, and the conventional spiral perforation mode is easy to generate a plurality of cracks in a cluster and is not particularly suitable for deep shale gas.
The perforation density is according to the requirement of circumferential hole distribution, considering the influence of casing intensity, generally 3-6 holes are perforated in the circumference, the aperture can adopt the conventional 8-12 mm.
In order to increase the induced stress effect of the simultaneous fracturing of multiple fractures, a hydraulic jet series connection method can be considered, the jet speed of each nozzle after series connection is calculated, and if the wellhead pressure is limited and cannot meet the critical speed requirement of jet perforation (generally, the requirement is more than 131 m/s), the parameters such as the number of nozzles and the aperture of each cluster of perforation are adjusted until the minimum requirement of the jet speed is met.
And (3) simulating the pressure and the discharge capacity of the wellhead based on the parameters of the ground stress, the rock mechanics and the like obtained in the step (1), and performing simulation calculation by applying mature shale gas fracture propagation simulation software MEYER.
(3) Acidic slickwater injection
Since the slickwater has strong acidity, acid pretreatment before injection of the conventional slickwater can be omitted. In order to increase the communication and penetration capacity of the acid liquid into small-scale fractures, the acid slickwater with low viscosity is specially designed, the viscosity value is 2-3mPa & s, meanwhile, the injection with lower injection displacement is designed, and the displacement can be 3-5m3Min, so that the acid slickwater is slowly penetrated by the machine and the acid karst etching reaction is carried out. If the discharge capacity is too high, acidic slick water can be quickly pushed into deep parts of cracks, and small-scale microcracks are difficult to effectively erode and communicate at different main crack penetration positions.
However, in order to prevent the collapse of rock skeleton caused by excessive erosion of acid rock in the near-well fracture and influence the flow conductivity of the near-well fracture, it is recommended to inject high-viscosity acid gel (capable of using ground cross-linking acid, and the viscosity ratio of the viscosity to the acid slickwater is kept above 10 times to realize stronger viscous finger-feed effect) with about 1.5 times of the volume of a vertical well barrel after 1/3 of the total injection amount of the acid slickwater is injected. At the moment, the high-viscosity acid gel entering the near well fracture has about half of the volume of the vertical well barrel, and the viscous finger-feed effect of the subsequently re-injected low-viscosity acid slick water enables most of the low-viscosity acid slick water to be rapidly pushed to the deep part of the fracture, so that the rock components of the middle and far wells are corroded. The high-viscosity acid gel has low reaction speed of acid rock near the well casing due to high viscosity, and the temperature reduction effect of early injection makes the near-well crack zone avoid excessive corrosion reaction of the acid rock.
The determination of the later displacement and the total liquid amount can be simulated by the mature MEYER software so as to meet the expected seam length requirement.
(4) Addition of 70-140 mesh proppant
In order to match the injection of the low-viscosity slickwater in the step (3), 70-140 meshes of propping agent is added in a slug mode at different stages so as to fill micro cracks formed in the injection process of the slickwater.
(5) Injection of iso-viscosity conventional slickwater
The conventional slickwater with the same viscosity as the acidic slickwater is adopted, the dosage of the conventional slickwater is 2-3 times of the total volume of a vertical shaft and a horizontal shaft, and the equal viscosity is mainly similar to piston type propulsion generated by the acidic slickwater so as to generate the effect similar to isolation liquid.
Besides the function of the spacer fluid, the slickwater also has the function of continuously extending the small-scale micro-crack, bedding crack/texture crack system communicated with the acidic slickwater in the step (3) to continuously expand the system, so that the saturated filling of the small-particle-size propping agent in the later period is facilitated, and the effective crack reconstruction volume is further improved.
(6) Injection of high viscosity conventional glue
On the basis of the isolating liquid in the step (5), a conventional high-viscosity glue solution system can be injected, and the viscosity can reach about 40-50mPa & s. The proppant is used for further expanding the main fracture and carrying the proppant with large grain diameter to fully fill the main fracture.
(7) Injection of 40-70 mesh and 30-50 mesh proppants
Considering that the closing pressure of the deep well formation is relatively large, construction operation of main fractures can be carried out by taking 40/70-mesh proppant as a main part and 30/50-mesh proppant as an auxiliary part. If the closing stress exceeds 90MPa, only 40/70 mesh proppant is recommended. The experimental results show that even 70-140 mesh proppant has only 10-20% lower conductivity than 30-50 mesh proppant after 90MPa closing pressure, and this is the result under the same proppant placement concentration. In consideration of the fact that the small-particle size proppant can be added more and has higher laying concentration, the expected design effect can be achieved more easily, and therefore, in a practical situation, the fracture conductivity finally obtained by the small-particle size proppant is higher than that of the large-particle size proppant under the condition of high closing pressure. And the proppant with large particle size is easy to generate early sand blocking in the adding process, and has larger influence on the flow conductivity.
Considering that a large amount of acid slickwater has been injected in step (3), micro-cracks and/or lamellar cracks and texture cracks may be communicated and extended in a large proportion, the invention recommends mixing 70/140 mesh small-particle size proppant in a proportion of 5-15% in the early stage of injection, and meanwhile, the viscosity of the early stage glue solution can be 30-40% of the highest viscosity, so as to facilitate the filling of different-particle size proppant to different-size cracks.
(8) And other injection procedures and flowback production-seeking procedures are executed according to a normal flow.
The invention has the following technical characteristics and excellent effects:
the method has the advantages of novel thought, clear system and steps, and feasibility, and provides a novel acidic slickwater composite fracturing technology aiming at the commercial development of deep normal-pressure shale gas, so that the complexity of deep normal-pressure shale gas fracturing cracks and the filling rate of different-scale crack systems are improved, the effective transformation volume of the deep normal-pressure shale gas is further improved, and the yield increasing and stable production effects after the fracturing are improved.
Detailed Description
The present invention will be further described with reference to the following examples.
Example 1
A deep shale gas exploration well a, which is a typical deep atmospheric shale gas well:
(1) key reservoir parameter evaluation
According to conventional methods such as well logging, pilot hole core experiment and the like, parameters such as lithology, physical properties, rock mechanics, three-dimensional ground stress, geological indexes and the like of a target layer are evaluated.
(2) Perforation plan optimization
The well is designed to fracture 19 sections, and the number of single-section perforation clusters is between 2 and 3 clusters. The perforation mode adopts the circumferential perforation formed by hydraulic jet, so that a plurality of perforation holes can be conveniently cracked and extended in the same crack. The circumferential density of the perforation is 4-6 holes, and the aperture is 10 mm.
(3) Acidic slickwater injection
According to the fracturing design, the well adopts acidic slickwater pump injection with the viscosity of 3 mPa.s, and the designed discharge capacity is 3-5m3And/min, injecting high-viscosity acid gel with the volume 1.5 times that of the vertical well casing for isolation after 1/3 pump of the total amount of the acid slickwater.
(4) Addition of 70-140 mesh proppant
The well was staged with 100 mesh powder ceramic proppant to fill micro-fractures formed during slickwater injection.
(5) Injection of iso-viscosity conventional slickwater
The conventional slickwater with the same viscosity (3 mPas) is used, the dosage of the slickwater is 2.5 times of the total volume of a vertical shaft and a horizontal shaft, and the slickwater plays a role of a spacer fluid.
(6) Injection of high viscosity conventional cement and 40/70 mesh proppant
And (3) injecting a conventional high-viscosity (50mPa & s) glue solution system on the basis of the spacer solution in the step (5). The proppant is used for further expanding the main fracture and carrying the proppant with large grain diameter to fully fill the main fracture.
In the high-viscosity glue injection stage, 40/70-mesh proppant is added in a slug mode, 10% of 100-mesh proppant is mixed in the high-viscosity glue, and only 100-mesh proppant and 40/70-mesh proppant are used in the whole well.
(7) And other injection procedures and flowback production-seeking procedures are executed according to a normal flow.
The well adopts a novel acid slickwater composite fracturing technology to complete fracturing operation, construction is smooth, pump pressure is always controlled within a safe pressure range, sand addition is smooth, all engineering designs are completed, the yield of the well after the well is pressurized is 50000 ten thousand square meters, and the yield of other exploration wells in the same region is improved by more than 59 percent.
Example 2
B well of a certain deep normal-pressure shale gas well:
(1) key reservoir parameter evaluation
According to conventional methods such as well logging, pilot hole core experiment and the like, parameters such as lithology, physical properties, rock mechanics, three-dimensional ground stress, geological indexes and the like of a target layer are evaluated.
(2) Perforation plan optimization
The well is designed to fracture 22 sections, and the number of single-section perforation clusters is between 2 and 3 clusters. The method adopts hydraulic jet circumferential perforation, the circumferential density of the perforation is 4-6 holes, and the aperture is 10 mm.
(3) Acidic slickwater injection
According to the fracturing design, the well adopts acidic slickwater pump injection with the viscosity of 3 mPa.s, and the designed discharge capacity is 3-5m3And/min, injecting high-viscosity acid gel with the volume 1.5 times that of the vertical well casing for isolation after 1/3 pump of the total amount of the acid slickwater.
(4) Addition of 70-140 mesh proppant
The well was staged with 100 mesh powder ceramic proppant to fill micro-fractures formed during slickwater injection.
(5) Injection of iso-viscosity conventional slickwater
The conventional slickwater with the same viscosity (3 mPas) is used, the dosage of the slickwater is 2 times of the total volume of a vertical shaft and a horizontal shaft, and the slickwater plays a role of isolating fluid.
(6) Injection of high viscosity conventional cement and 40/70 mesh proppant
And (3) injecting a conventional high-viscosity (45mPa & s) glue solution system on the basis of the spacer solution in the step (5). The proppant is used for further expanding the main fracture and carrying the proppant with large grain diameter to fully fill the main fracture.
In the high-viscosity glue injection stage, 40/70-mesh proppant is added in a slug mode, and 30/50-mesh proppant with large particle size is added in the last construction stage for supporting the main fracture.
(7) And other injection procedures and flowback production-seeking procedures are executed according to a normal flow.
The well adopts a novel acid slickwater composite fracturing technology to complete fracturing operation, construction is smooth, pump pressure is always controlled within a safe pressure range, sand addition is smooth, all engineering designs are completed, and the yield of the well after the well is pressurized is 75000 ten thousand square meters, which is improved by more than 32 percent compared with other exploration wells in the same region.
Comparative example
A conventional slickwater and glue solution system is adopted for fracturing construction transformation of a certain deep normal-pressure shale gas well X well, 100-mesh, 40/70-mesh and 30/50-mesh propping agent combinations are adopted, and the condition that construction pressure is obviously increased when a glue solution carries a large-particle-size propping agent to enter a crack occurs. The gas yield is 42000m3 after the well pressure is increased, but the yield is reduced rapidly, and the modification effect is obviously lower than that of a shale gas well modified by the new technology.
Claims (6)
1. An acid slickwater composite fracturing method for a shale gas horizontal well is characterized by comprising the following steps:
(1) reservoir evaluation before fracturing
(2) Perforation plan optimization
The deep shale gas fracturing adopts multi-section few-cluster perforation;
the normal pressure shale gas fracturing adopts a plurality of sections of multi-cluster perforation;
the cluster number of deep normal pressure shale gas perforation is between the deep shale gas and the normal pressure shale gas;
the perforation mode adopts circumferential perforation formed by hydraulic jet;
(3) acidic slickwater injection
The slickwater has strong acidity, viscosity value of 2-3mPa · s, low injection discharge capacity of 3-5m3/min；
Injecting high-viscosity acid jelly with the volume 1-2 times of that of the vertical well casing after 1/3 of the total injection amount of the acid slickwater; entering high-viscosity acid jelly in the near-well crack for half of the volume of a straight well barrel, and then injecting subsequent acid slick water;
the viscosity ratio of the high-viscosity acid jelly to the acid slickwater is more than 10;
(4) addition of 70-140 mesh proppant
In order to match the injection of the acid slickwater in the step (3), 70-140 meshes of propping agent is added in a slug mode at different stages; mixing the proppant with small particle size of 70/140 meshes according to the proportion of 5-15%;
(5) injection of iso-viscosity conventional slickwater
Adopting conventional slickwater with the same viscosity as the acidic slickwater, wherein the using amount of the conventional slickwater is 2-3 times of the total volume of a vertical shaft and a horizontal shaft;
(6) injection of high viscosity conventional glue
Injecting a conventional high-viscosity glue solution system on the basis of the conventional slickwater in the step (5);
(7) injection of 40-70 mesh and 30-50 mesh proppants
The closing pressure of the deep well stratum is relatively large, construction operation of main fractures is carried out by using 40/70-mesh proppant as a main material and 30/50-mesh proppant as an auxiliary material;
if the closing stress exceeds 90MPa, only 40/70-mesh proppant is selected.
2. The acid slickwater complex fracturing method of shale gas horizontal wells of claim 1, characterized in that:
in the step (2),
the deep shale gas fracturing adopts multi-section few-cluster perforation; the number of single-segment perforation clusters is 2-3 clusters.
3. The acid slickwater complex fracturing method of shale gas horizontal wells of claim 1, characterized in that:
the normal pressure shale gas fracturing adopts a plurality of sections of multi-cluster perforation; the number of single-segment perforation clusters is 3-5 clusters.
4. The acid slickwater complex fracturing method of shale gas horizontal wells of claim 1, characterized in that:
the number of clusters of deep normal-pressure shale gas perforation is between that of deep shale gas and normal-pressure shale gas, and the number of clusters of single-stage perforation is between 2 and 4 clusters.
5. The acid slickwater complex fracturing method of shale gas horizontal wells of claim 2, characterized in that:
in the step (2), 3-6 holes are circumferentially and internally perforated.
6. The acid slickwater complex fracturing method of shale gas horizontal wells of claim 1, characterized in that:
in the step (6), the viscosity of the high-viscosity glue solution system is 40-50 mPas.
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| CN111911128B (en) * | 2019-05-08 | 2022-11-29 | 中国石油化工股份有限公司 | High-tectonic stress normal-pressure shale gas-accumulation fracturing method |
| CN112177582B (en) * | 2019-07-01 | 2022-09-27 | 中国石油化工股份有限公司 | Shale gas well staged multi-cluster fracturing method under casing tripping condition |
| CN112443306B (en) * | 2019-09-04 | 2023-02-28 | 中国石油化工股份有限公司 | Pressure-control fracturing method for increasing fracture complexity of deep shale gas well |
| CN113445976B (en) * | 2020-03-25 | 2023-09-26 | 中国石油化工股份有限公司 | Fracturing method and application of high-plasticity stratum |
| CN115126461A (en) * | 2021-03-29 | 2022-09-30 | 中石化石油工程技术服务有限公司 | Composite fracturing method for continental shale oil reservoir |
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