A sand adding method for multi-layer sandstone bottom water gas reservoir and its application

Abstract

The invention discloses a sand adding method for a multi-layer sandstone bottom water gas reservoir and an application thereof. The method combines processes such as fracture control high-pressure fracturing, bottom plugging and proppant combination, and adopts a novel temperature-sensitive fracturing fluid, which can not only fully open each reservoir but also control the fracture to extend downward, and can optimize the fracture profile, so that the fracture height profile of the fracture near the wellbore position and the fracture front end is almost the same, thereby expanding the fracture leakage area; on the basis of adopting different density proppant combinations and different viscosity fracturing fluid combinations to achieve effective plugging of the fracture bottom, the effective laying of the proppant is improved, the fracture conductivity is improved, and the purpose of controlling water and increasing production of the multi-layer sandstone bottom water gas reservoir is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of fracturing transformation of tight sandstone bottom water gas reservoirs, and more specifically to a new method for adding sand to a multi-layer bottom water gas reservoir suitable for tight sandstones. Background Art

[0002] At present, multi-layer sandstone bottom water gas reservoirs are widely distributed in China, such as the Hangjinqi gas reservoir in the Ordos Basin. The main difficulties in fracturing such gas reservoirs are:

[0003] (1) For multi-layer sandstone, it is difficult to effectively open multiple layers at one time in the vertical direction. Even if they are opened, the stress of the mudstone interlayer is relatively large and the clay expands, making the interlayer fracture width narrow. Most of the proppant is distributed in the small layer where the horizontal wellbore passes, and it is difficult to effectively move and lay it in other small layers that the horizontal wellbore does not pass through, especially in the reservoir above the small layer where the horizontal wellbore passes through. Due to the gravity retardation effect of the proppant, it is more difficult to move and lay the proppant in the effective reservoir;

[0004] (2) For the bottom water layer, even if the entire fracture does not communicate with the bottom water layer in the vertical direction, the flow pressure near the wellbore is the smallest, that is, the flow pressure difference is the largest. Due to the seepage effect, the water ridge phenomenon is most likely to occur in the fracture near the wellbore. Once the water ridge phenomenon near the wellbore is formed, a serious water lock effect is generated, which inhibits the effective production of gas in the entire fracture area.

[0005] (3) During the fracturing process, when the near-wellbore cracks start to crack and extend, the size of the cracks is still relatively small, and the pressure in the cracks builds up quickly, which can cause the initial crack height to extend rapidly. With the injection of a large amount of fracturing fluid, the geometric size of the cracks becomes larger and larger. At this time, with the same displacement and fracturing fluid viscosity, the extension of the crack height becomes smaller and smaller. In particular, due to the filtration effect of the fracturing fluid, the height of the far-wellbore cracks becomes smaller and smaller, and the height of the cracks at the end of the cracks may be more limited. The final fracture height profile is wedge-shaped, and the closer to the wellbore crack, the greater the height. It can be said that if the bottom water layer is connected, the possibility of the near-wellbore cracks connecting is the greatest. In this way, superimposed on the seepage mechanism formed by the rising water ridge, the water production after normal pressure increases significantly, resulting in a significant shortening of the gas production and stable production cycle.

[0006] At present, the targeted fracturing measures adopted in literature and patents are mainly to control the scale and displacement of fracturing fluid, use oil-soluble temporary plugging agents to plug the bottom of the cracks, etc., but the water control effect is not ideal. Therefore, it is necessary to study and propose a new fracturing method to solve the above limitations.

[0007] Chinese patent CN101476452A discloses a method for increasing production by water-controlled fracturing of oil and gas wells, which uses a frozen gel system that automatically reduces viscosity when encountering bottom water as a fracturing fluid, and a water-controlled fracturing process with wax-coated sand as part of the proppant. During the fracturing construction, the coated proppant mixed with paraffin wax and quartz sand is carried by a thickener and a cross-linking agent to be chemically degraded, coated and blocked underground to form a plugging layer, which effectively solves the problem that the existing artificial barrier layer cannot effectively prevent oil well flooding and the problem that the fracturing fluid carrying a diverting agent or a temporary plugging agent does not reduce viscosity and has a slow sedimentation rate when encountering a water base. This patent mainly solves the problem of timely settling paraffin wax and quartz sand at the bottom of the crack to achieve the purpose of water control. It does not involve the problem of how to optimize the crack profile and improve the effective support of the proppant and improve the conductivity.

[0008] Chinese patent CN105443100A discloses a fracturing method for controlling fracture height by fixed-surface perforation, which provides a method for controlling fracture height by fixed-surface perforation, wherein the perforating gun is used to perform concentrated perforation in the target layer section, and the perforation thickness is 0.5m, forming two perforation surfaces, the two surfaces are 0.3m apart, and the number of perforations on each perforation surface is three. Among them, the position of each perforation plane is pre-set, and each perforation plane is perpendicular to the longitudinal axis direction of the vertical wellbore arranged at the target layer section. For reservoirs with developed bottom water and reservoirs with poor shielding conditions and easily out-of-control fracture height, it can ensure that the fractures extend in the effective reservoir to avoid communicating with bottom water or invalid formations. This patent only provides a perforation method. As for what kind of fracturing fluid to use, how to effectively increase the transformation volume of multi-layer sandstone gas reservoirs, and effectively communicate all reservoirs, it does not involve how to effectively lay proppants.

[0009] Chinese patent CN105464639A discloses a bottom water reservoir fracturing method using a water-deformable proppant to control water channeling. It provides a proppant that does not change in the oil-based fracturing fluid, but softens, deforms and solidifies when it encounters water. A high-strength, non-permeable barrier layer is formed to prevent bottom water from channeling upward. The fracturing fluid required by this patent is an oil-based fracturing fluid, which is expensive and not very practical, and does not mention the optimization of the fracture profile and the effective laying of the proppant.

[0010] Chinese patent CN104712299A provides a design method for water-controlling and gas-increasing fracturing in gas wells. It is designed for gas wells containing bottom water layers or upper water layers. It mainly uses computer software to simulate and calculate the height of the fracturing cracks to obtain the sand-adding scale and sand ratio suitable for fracturing construction. At the same time, it combines the preferred low-viscosity fracturing fluid to control the net pressure of the fracturing cracks, thereby controlling the extension of the crack height and achieving the purpose of water-controlling and gas-increasing fracturing in gas wells. This patent controls the crack height by optimizing the fracturing construction parameters, and does not involve what kind of fracturing fluid to use and how to optimize the fracture profile, nor does it mention what proppant combination and fracturing fluid combination to use. Summary of the invention

[0011] Multi-layer sandstone bottom water gas reservoirs need to fully transform each reservoir layer through layer fracturing, and also control the fracture height to prevent the fractures from extending downward to press the water layer, causing water ridge phenomenon or even flooding. In order to overcome the problems existing in the prior art, the present invention provides a sand adding method for multi-layer sandstone bottom water gas reservoirs, which combines the fracture control high-pressure fracturing process and adopts a new type of temperature-sensitive fracturing fluid, which can not only fully press open each reservoir layer but also control the fracture to extend downward, and at the same time optimize the fracture profile, so that the fracture height profile near the wellbore position and the fracture front end are almost the same, expanding the fracture leakage area; on the basis of using different density proppant combinations and different viscosity fracturing fluid combinations to achieve effective plugging of the fracture bottom, the effective laying of proppant is improved, the fracture conductivity is improved, and the purpose of controlling water and increasing production of multi-layer sandstone bottom water gas reservoirs is achieved.

[0012] One of the purposes of the present invention is to provide a sand adding method for a multi-layer sandstone bottom water gas reservoir, comprising:

[0013] (I) Using temperature-sensitive fracturing fluid for fracture construction;

[0014] (II) Bottom plugging construction with low-viscosity fracturing fluid carrying high-density proppant;

[0015] (III) Construction using variable viscosity fracturing fluid carrying high-density proppant;

[0016] (IV) Construction using variable viscosity fracturing fluid carrying low density proppant.

[0017] In a preferred embodiment, in step (I), the viscosity of the temperature-sensitive fracturing fluid is 48 mPa.s to 200 mPa.s, and its viscosity gradually increases with increasing temperature.

[0018] In a further preferred embodiment, the viscosity of the temperature-sensitive fracturing fluid at room temperature is 40-60 mPa.s, and the viscosity at 90°C is maintained above 150 mPa.s.

[0019] In the present invention:

[0020] (1) During the pre-fluid fracturing stage, a temperature-sensitive fracturing fluid is used (the fracturing fluid is sensitive to temperature, with viscosity increasing at high temperatures and decreasing at low temperatures) to improve the fracture profile, reduce the fracture height near the wellbore, increase the fracture height at the end, and make the fracture expand and extend evenly in the vertical direction, thereby reducing the risk of water ridges.

[0021] (2) In the pre-fluid fracture formation stage, a temperature-sensitive fracturing fluid is used. Since the front edge of the fracturing fluid contacts the reservoir with the highest temperature during the fracture formation stage, the viscosity of the fracturing fluid is the highest, which can overcome the adverse effects of large initial filtration loss and large wall filtration loss caused by the reduced viscosity of conventional fracturing fluids. In this way, the filtration loss of the fracturing fluid is greatly reduced, and the loss of the displacement transferred to the end of the fracture is greatly reduced. In addition, the advantage of high viscosity can greatly promote the extension of the fracture height at the end of the fracture. At the same time, since the temperature of the fracturing fluid near the wellbore is greatly reduced, the above-mentioned new temperature-sensitive fracturing fluid exhibits low viscosity characteristics at low temperatures, which can further inhibit the continued rapid extension effect of the fracture height near the wellbore, and can also flow quickly to the end of the fracture due to its low viscosity.

[0022] (3) In addition, in the later stage of fracturing with the pre-fluid, due to the wall-building effect of the early fracturing fluid and the barrier effect of the filtration zone, the filtration loss of the fracturing fluid near the wellbore is relatively low, which also promotes the rapid migration of the pre-fluid to the end of the fracture in the later stage of fracturing. After using the above-mentioned temperature-sensitive fracturing fluid, the height profile of the fracture is nearly uniformly distributed along the length of the fracture, which is also conducive to avoiding the bottom water intrusion and water ridge effect caused by excessive fracture height near the wellbore.

[0023] (4) In addition, in the initial stage of fracturing the pre-fluid, the viscosity of the fracturing fluid increases rapidly due to the rapid approach to the highest temperature of the reservoir, which is also conducive to more rapid increase of the net pressure in the fracture and simultaneous opening of multiple layers. And due to the high viscosity, the width of the fracture is relatively large, including the width of the interlayer between multiple reservoirs, which can ensure that the proppant is not blocked by the blocking effect caused by the reduction of the interlayer width and can be smoothly moved and distributed in each reservoir.

[0024] In a preferred embodiment, in step (II), the change of the construction pressure curve is first used to determine whether the fracture height is out of control, wherein when the bottom hole pressure drop rate is less than 1 MPa / min, the fracture height continues to extend, and when the bottom hole pressure drop rate reaches more than 1 MPa / min, the fracture height is out of control.

[0025] Among them, first determine whether the fracture height is out of control, and determine whether the fracture height is out of control by the change trend of the bottom hole construction pressure (converted from the wellhead pressure to the bottom hole pressure in real time) curve. If the bottom hole construction pressure continues to drop, it means that the fracture height continues to extend. If the bottom hole pressure drops at a rate of 1MPa / min or more, it is judged that the fracture height is out of control. Combined with the pressure dynamic curve fitting of the fracture simulation software, the fracture height and whether it connects the bottom water layer can be preliminarily determined.

[0026] In a further preferred embodiment, in step (II), if it is determined that the fracture height is out of control and enters the bottom water layer, the fracture width profile and changes in the fracture height direction are calculated in real time, and the fracture simulation software simulates the dynamic fracture width when the large-size proppant in a specific size range is expected to reach the bottom of the bottommost layer in the reservoir, ensuring that the proppant is blocked just at the bottom of the reservoir. Specifically, adding a combination of proppants of different sizes can better achieve bottom blocking.

[0027] In a preferred embodiment, a low-viscosity fracturing fluid carrying a high-density proppant is used for bottom plugging, wherein the viscosity of the low-viscosity fracturing fluid is 2-5 mPa.s, and the apparent density of the high-density proppant is 3.4 g / cm 3 Above; preferably, the high-density proppant is selected from a combination of proppant with a particle size of 40 to 70 meshes and proppant with a particle size of 70 to 100 meshes.

[0028] In a further preferred embodiment, whether effective plugging is achieved is determined by the dynamic change of bottom hole pressure, that is, if the bottom hole pressure gradually changes from decreasing to increasing, and the faster the increasing speed, the better the plugging effect, but the increasing speed should be controlled within 0.5 MPa / min.

[0029] In order to increase the rapid plugging effect, low-viscosity slick water with a viscosity of 2mPa.s to 5mPa.s is used to carry the proppants with different particle size distributions. The apparent density of the proppant is selected to be 3.4g / cm 3 To further enhance the bottom plugging effect, the pump may be stopped for 1 to 2 minutes after the proppants of different particle sizes are added in a certain proportion and in descending order.

[0030] In a preferred embodiment, in step (III), a variable viscosity fracturing fluid of 30 to 50 mPa.s is used to carry a high-density proppant, and the apparent density of the high-density proppant is 3.4 g / cm 3 Above, the particle size is 20 to 40 mesh.

[0031] In a further preferred embodiment, the viscosity of the variable viscosity fracturing fluid of 30 to 50 mPa.s changes from low viscosity to high viscosity.

[0032] In a preferred embodiment, in step (IV), a variable viscosity fracturing fluid of 10 to 20 mPa.s is used to carry a low-density proppant, and the apparent density of the high-density proppant is 1.25 g / cm 3 Below, the particle size is 40 to 70 mesh.

[0033] In a further preferred embodiment, the viscosity of the variable viscosity fracturing fluid of 10 to 20 mPa.s changes from low viscosity to high viscosity.

[0034] Among them, the sand-carrying fluid stage improves the proppant support efficiency and increases the fracture conductivity.

[0035] On the basis of optimizing the fracture profile and effectively plugging the bottom water layer, in order to increase the effective migration and laying efficiency of the reservoir proppant in the upper part of the horizontal wellbore, two densities of proppant are used in the sand adding process. First, high-density proppant (apparent density of 3.4g / cm 3 The proppant is placed in the lower reservoir of the horizontal wellbore, and then a low-density proppant (with an apparent density of 1.25 g / cm 3 As the high-density proppant has been laid at the height of the fracture in the lower part of the horizontal wellbore, the low-density proppant will mainly migrate and distribute to the reservoir in the upper part of the horizontal wellbore during the addition process, so that the proppant can be effectively laid at the upper, middle and lower parts of the fracture.

[0036] In order to increase the diversion effect of the above-mentioned proppants with different densities, a relatively low viscosity fracturing fluid system is used in the sand addition stage, and when injecting high-density proppants, a variable viscosity fracturing fluid is used, which is first relatively low in viscosity to increase the sedimentation effect of high-density proppants. Then, a fracturing fluid system with gradually increasing viscosity is used to prevent the sand plugging effect caused by excessive sedimentation of high-density proppants, and it is also convenient to carry high-density proppants near the wellbore fractures to the far-well fracture zone, so that high-density proppants settle and plug the bottom in the entire wellbore; and in the low-density proppant addition stage, variable viscosity fracturing fluid is also used, and the specific mode and viscosity parameters are the same as those of the above-mentioned high-density proppants. Or the viscosity of the fracturing fluid can be appropriately reduced simultaneously. For the same reason, gradually increasing the viscosity of the fracturing fluid in the later stage can also facilitate the migration and laying of low-density proppants in the top reservoir above the horizontal wellbore.

[0037] In the present invention, the sand adding method combines the processes of fracture control high-pressure fracturing, bottom plugging and proppant combination, and adopts a new type of temperature-sensitive fracturing fluid, which can not only fully open each reservoir but also control the downward extension of the fracture, and at the same time optimize the fracture profile, so that the fracture height profile near the wellbore position and the fracture front end are almost the same, thereby expanding the fracture leakage area; on the basis of using different density proppant combinations and different viscosity fracturing fluid combinations to achieve effective plugging of the fracture bottom, the effective laying of the proppant is improved, the fracture conductivity is improved, and the purpose of controlling water and increasing production of multi-layer sandstone bottom water gas reservoirs is achieved.

[0038] The second object of the present invention is to provide an application of the sand adding method described in the first object of the present invention in the fracturing construction of a multi-layer bottom water gas reservoir.

[0039] The third object of the present invention is to provide a fracturing construction method for a multi-layer bottom water gas reservoir, comprising the following steps:

[0040] 1) Evaluation of key reservoir parameters;

[0041] 2) Determine the completion method and the location of the segmentation and clustering;

[0042] 3) Crack parameter optimization;

[0043] 4) Optimization of fracturing construction parameters;

[0044] 5) Selection of rheological parameters of new temperature-sensitive fracturing fluid before fracturing;

[0045] 6) Determination of rheological parameters of variable viscosity fracturing fluid before fracturing;

[0046] 7) Pre-set pipe string or bridge plug and perforation combined operation;

[0047] 8) Acid pretreatment operations;

[0048] 9) using the sand adding method described in one of the purposes of the present invention to perform sand adding operation;

[0049] 10) Replacement work;

[0050] 11) For the fracturing construction of other sections, if it is casing completion, repeat steps 7) to 10), if it is open hole completion, repeat steps 8) to 13), until all sections are constructed.

[0051] 12) After the well is completed, drilling plugs, flowback, testing and production are performed. For open hole completion, drilling plugs are not required and the conventional processes and parameters are followed, which will not be repeated here.

[0052] In a preferred embodiment, in step 1), the key reservoir parameters include the lithology, physical properties, whole rock mineralogy and sensitivity, rock mechanics and the minimum horizontal principal stress profile of each reservoir and barrier layer, as well as the bottom water layer, and the high-angle natural fracture conditions.

[0053] It can be determined by well logging (FMI imaging logging), mud logging, and test analysis in the core chamber of the pilot well under simulated formation temperature and pressure.

[0054] The distribution of various parameters in the horizontal well section is mainly determined by analogy with logging parameters, and a certain correspondence is established between the logging parameters of the pilot well and the core test results, thereby determining the distribution of the above parameters in the horizontal well section.

[0055] In a preferred embodiment, in step 2), casing completion is generally adopted, and the corresponding perforation cluster can be closed once water flooding occurs.

[0056] In a preferred embodiment, in step 2), if the well is completed by open hole, the segment position, i.e., the sealing position of the open hole packer, is mainly determined. If the well is completed by casing, the sealing position of the bridge plug and the cluster hole position are determined.

[0057] Among them, conventional methods are generally used to determine the geological sweet spots and engineering sweet spots respectively, and then the final comprehensive sweet spot index is determined based on the equal weight method. Whether it is casing completion or open hole completion, the section length is generally 70m to 100m. For casing completion, the selection of cluster perforation positions is generally based on the fact that the comprehensive sweet spot indexes of each cluster in the section are equivalent or the highest and lowest differences are within 20%, and the section spacing is preferably 20m to 30m (not the same concept as the section length). It is determined by comprehensive weighing, combined with the casing cementing quality, short casing and coupling position, etc.

[0058] In a preferred embodiment, in step 3), based on step 1), combined with the data of adjacent wells, a refined Petrel model is established, and the result is imported into the Eclipse model used for the prediction of the production of fractured wells. According to the equivalent conductivity method (in order to reduce the simulation workload, the fracture width is magnified by a certain multiple, and the permeability of the proppant in the fracture is proportionally reduced so that their product, i.e., the conductivity of the fracture, remains unchanged), a hydraulically propped fracture is set. Then, according to the orthogonal design method, the post-fracture production dynamics under different fracture parameter conditions (support half-fracture length, conductivity, fracture spacing, etc.) are simulated, and the fracture parameter system corresponding to the highest relative post-fracture production or the maximum economic net present value is the optimal fracture parameter.

[0059] In a preferred embodiment, in step 4), commonly used commercial software for fracture extension simulation, such as FracProPT, Stimplan, Gohfer, Meyer, etc., is used to simulate fracture geometry and conductivity under different fracturing construction parameter conditions (construction displacement, fracturing fluid viscosity, liquid volume and proportion of different viscosities, proppant dosage and proportion of proppant with different particle sizes, sand-liquid ratio and specific injection procedure, etc.) by orthogonal design method, and the fracturing construction parameters under the fracture parameters that can optimize the fracture parameters in step 3) are preferably obtained, which are the best fracturing construction parameters.

[0060] In a preferred embodiment, in step 5), before fracturing, according to the actual temperature of the reservoir and the fracturing fluid viscosity test standard, at room temperature, the viscosity of the new temperature-sensitive fracturing fluid is 40-60 mPa.s, and at the reservoir temperature, the viscosity of the temperature-sensitive fracturing fluid should be maintained above 150 mPa.s to ensure that the viscosity of the new fracturing fluid increases with the increase in temperature until it reaches the viscosity at the reservoir temperature and has good compatibility with the core in step 1).

[0061] In a preferred embodiment, in step 6), the temperature field is simulated at different stages of sand addition, and the experimental conditions are determined by the temperature. According to the test standard, the viscosity of the fracturing fluid in the high-density proppant stage is in the range of 30mPa.s to 50mPa.s, and the viscosity of the fracturing fluid in the low-density proppant stage is in the range of 10mPa.s to 20mPa.s. The fracturing fluid formula is determined in this way, and has good compatibility with the core in step 1).

[0062] In a preferred embodiment, in step 7), if the well is completed in an open hole, a prefabricated string of open hole sliding sleeve packers is installed; if the well is completed in a casing, a string of bridge plugs and cluster perforators is installed, but no bridge plug is installed in the first section, and perforating is first performed by using a tubing to carry a perforating gun, and other sections are pumped to carry bridge plugs and cluster perforators.

[0063] In a preferred embodiment, in step 8), when the carbonate content of the sandstone reservoir is high, acid pretreatment is used. Generally, the acid scale for a single stage is 10m 3 ~15m 3 , the acid injection displacement is 0.5m 3 / min~1.0m 3 / min.

[0064] In a further preferred embodiment, the displacement is higher when replacing acid, 2m 3 / min~3m 3 / min.

[0065] In a further preferred embodiment, after the acid reaches the first cluster of perforations near the heel, the displacement is reduced to the previous acid injection displacement, and then the acid replacement displacement is appropriately increased 1 to 2 times according to the number of clusters to increase the probability of uniform acid injection at multiple cluster perforations.

[0066] In a preferred embodiment, in step 10), the displacement fluid volume is calculated as 1.05 to 1.1 times the volume of the wellbore at that section and the volume of the surface pipeline, and the displacement is the maximum displacement optimized in step 4).

[0067] Among them, the surplus amount of displacement fluid was reduced by a certain proportion because low-density proppant was used in the later stage of sand addition, and the sand settling effect in the wellbore was relatively reduced.

[0068] In a further preferred embodiment, the displacement fluid may be low-viscosity slippery water with a viscosity of 2 mPa.s to 5 mPa.s.

[0069] The endpoints and any values ​​of the scope disclosed in the present invention are not limited to the precise scope or value, and these scopes or values ​​should be understood to include values ​​close to these scopes or values. For numerical ranges, the endpoint values ​​of each scope, the endpoint values ​​of each scope and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article. Hereinafter, in principle, each technical solution can be combined with each other to obtain a new technical solution, which should also be regarded as specifically disclosed in this article.

[0070] Compared with the prior art, the present invention has the following beneficial effects: the fracturing method for multi-layer sandstone bottom water gas reservoirs proposed in the present invention provides a guiding scheme for opening multiple reservoirs to expand the transformation volume while avoiding opening the bottom water layer, and improving the fracture conductivity. According to this method, fracturing construction can expand the oil leakage area in the horizontal direction and increase the transformation volume in the vertical direction, providing a powerful means for achieving water control and production increase in multi-layer sandstone bottom water gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 A schematic flow chart of the fracturing construction method for a multi-layer bottom water gas reservoir according to the present invention is shown. DETAILED DESCRIPTION

[0072] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0073] It should also be noted that the various specific technical features described in the following specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0074] In addition, the various embodiments of the present invention may be arbitrarily combined as long as they do not violate the concept of the present invention. The technical solutions thus formed belong to part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0075] The raw materials used in the examples and comparative examples, unless otherwise specified, are disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0076] The composition of the temperature-sensitive fracturing fluid used is: 0.16% thickener+0.1% cross-linking agent+0.3% anti-swelling agent+0.1% drainage aid+3.4% temperature-sensitive polymer.

[0077] [Example 1]

[0078] Well X is a multi-layer bottom-water sandstone gas well in the Ordos Basin. It is a horizontal well with a horizontal section length of 1000m, a completed well depth of 3720m, and a vertical depth of 2632m. The target layer is the Upper Shihezi Formation H 2 Layer, thickness is 38m. It contains three small layers, namely H 2 1 ,H 2 2 and H 2 3 , the mudstone layers between the small layers are 3.2m and 4.7m thick, and the underlying H 1 is the water layer, H 1 Layer and H 2 There is a 5.4m mudstone interlayer between the layers. The target layer section of the well is 2697.0m~3697.0m; the lithology of the target layer section is mainly gravel-containing coarse-grained and coarse-grained lithic sandstone, with a small amount of lithic quartz sandstone; the target layer is a low-porosity and low-permeability reservoir with developed vertical natural fractures, with an average porosity of 18.6%, an average permeability of 9.5mD, a reservoir pressure coefficient of 0.92, and a reservoir temperature of 89℃.

[0079] The following is the specific implementation process of the embodiment:

[0080] 1) Evaluation of key reservoir parameters

[0081] The lithology, physical properties, whole-rock mineralogy and sensitivity, rock mechanics, minimum horizontal principal stress profiles of each reservoir and barrier layer, as well as the bottom water layer, and high-angle natural fractures.

[0082] 2) Determination of completion method and segmentation and clustering locations

[0083] The well was completed with casing. After the geological sweet spots and engineering sweet spots were determined by conventional methods, the final comprehensive sweet spot index was determined based on the equal weight method. Finally, 8 fracturing stages were determined, with 2 to 3 clusters in each stage.

[0084] 3) Crack parameter optimization

[0085] On the basis of step 1), the Petrel model of Well X was established by combining the data of adjacent wells. The modeling results were imported into the Eclipse model of Well X, and the hydraulic support fracture parameters were set according to the equivalent conductivity method. According to the orthogonal design method, the post-fracture production dynamics under different fracture parameter conditions (support half-fracture length, conductivity, fracture spacing, etc.) were simulated. The fracture parameter system corresponding to the highest post-fracture production or the maximum economic net present value was the optimal fracture parameter. Combined with the optimization results, the optimal fracture parameters were finally obtained as 8 fracturing stages, 2 to 3 clusters per stage, 32m cluster spacing, 152m half-length of each fracture cluster, and 19D.cm conductivity.

[0086] 4) Optimization of fracturing construction parameters

[0087] The crack propagation simulation commercial software Meyer was used to simulate the crack parameters required for step 3) and the construction displacement was 4m 3 / min~8m 3 / min, the viscosity of the new temperature-sensitive fracturing fluid is 48mPa.s~200mPa.s, the viscosity of the fracturing fluid for sand-carrying fluid is 10mPa.s~50mPa.s, and the amount of fluid used in each section is 600~800m 3 The amount of proppant used in each section is 60 to 90 m 3 , a combination of 40-70 mesh proppants, 70-100 mesh proppants and 20-40 mesh proppants was used, with an average sand-to-liquid ratio of 18%.

[0088] 5) Selection of rheological parameters of new temperature-sensitive fracturing fluid before fracturing

[0089] The formula of the new fracturing fluid was optimized at reservoir temperature, and the viscosity of the fracturing fluid was measured to be 48mPa.s at room temperature. At 90°C, the viscosity of the fracturing fluid was measured to be maintained at 185mPa.s.

[0090] 6) Determination of rheological parameters of variable viscosity fracturing fluid before fracturing

[0091] At different stages of sand addition, the temperature field is simulated, and the experimental conditions are determined by the temperature. According to the test standard, the viscosity of the fracturing fluid in the high-density proppant stage is in the range of 30mPa.s to 50mPa.s, and the viscosity of the fracturing fluid in the low-density proppant stage is in the range of 10mPa.s to 20mPa.s. The fracturing fluid formula is determined accordingly, and has good compatibility with the core in step 1).

[0092] 7) Lower the fracturing operation string

[0093] The well was completed with casing and staged fracturing was carried out using cluster perforation + drillable bridge plug. Two cluster perforations were carried out using tubing before fracturing.

[0094] 8) Acid pretreatment

[0095] Acid pretreatment is used before fracturing. The amount of acid used is 15m 3 , the acid injection displacement is 1.0m 3 / min. When replacing acid, the displacement is 3m 3 After the acid reaches the first cluster of perforations near the heel, the displacement is reduced to 1.0m 3 / min, injection 5m 3 Then the displacement was increased to 1.5m 3 / min until all the acid is replaced.

[0096] 9) New temperature-sensitive fracturing fluid fracture construction

[0097] Apply the new temperature-sensitive fracturing fluid formula determined in step 5) and carry out the first stage of fracturing according to the fluid volume and displacement optimized in step 4). The new temperature-sensitive fracturing fluid used in this stage is 160m 3 , displacement is 6m 3 / min.

[0098] 10) Bottom plugging construction with low viscosity fracturing fluid carrying high density proppant

[0099] A low-viscosity fracturing fluid (viscosity 5mPa.s) is used to carry a high-density proppant (density 3.53g / cm 3 ) to seal the bottom, and judge that the fracture height is not out of control by the change of the construction pressure curve (the rate of decline of the bottom hole pressure is less than 1MPa / min). The construction displacement at this stage is 6m 3 / min, liquid volume is 100m 3 , 40-70 mesh high-density proppant dosage is 8m 3 , 70-100 mesh high-density proppant dosage is 4m 3 .

[0100] 11) Construction of variable viscosity fracturing fluid carrying high-density proppant

[0101] The variable viscosity fracturing fluid (viscosity of 30-50 mPa.s) is used to carry high-density proppant (density 3.53 g / cm 3 ) for construction, the construction displacement at this stage is 6m 3 / min, liquid volume is 180m 3 , the dosage of 20-40 mesh high-density proppant is 33m 3 .

[0102] 12) Construction of variable viscosity fracturing fluid carrying low-density proppant

[0103] The variable viscosity fracturing fluid (viscosity of 10-20 mPa.s) is used to carry low-density proppant (density 1.24 g / cm 3 ) for construction, the construction displacement at this stage is 6m3 / min, liquid volume is 150m 3 , 40-70 mesh low-density proppant dosage is 27m 3 .

[0104] 13) Replacement work

[0105] Low viscosity fracturing fluid (viscosity of 10-20 mPa.s) is used for displacement.

[0106] 14) For the fracturing construction of other sections, repeat steps 7) to 13) until all sections are constructed.

[0107] 15) Post-pressure drilling plug, flowback, testing and production.

[0108] Compared with adjacent wells, the water production after fracturing in the above scheme was reduced by 30% and the gas production was increased by 15%.

[0109] [Example 2]

[0110] Well X is a multi-layer bottom-water sandstone gas well in the Ordos Basin. The well is a horizontal well with a horizontal section length of 800m, a completed well depth of 3514m, and a vertical depth of 2527m. The target layer is the Upper Shihezi Formation H 2 Layer, thickness is 33m. It contains three small layers, namely H 2 1 ,H 2 2 and H 2 3 , the mudstone layers between the small layers are 2.5m and 3.4m thick, and the underlying H 1 is the water layer, H 1 Layer and H 2 There is a 6.3m mudstone interlayer between the layers. The target layer section of the well is 2783.0m~3496.0m; the lithology of the target layer section is mainly gravel-containing coarse-grained and coarse-grained lithic sandstone, with a small amount of lithic quartz sandstone; the target layer is a low-porosity and low-permeability reservoir with developed vertical natural fractures, with an average porosity of 16.7%, an average permeability of 8.8mD, a reservoir pressure coefficient of 0.92, and a reservoir temperature of 86℃.

[0111] The following is the specific implementation process of the embodiment:

[0112] 1) Evaluation of key reservoir parameters

[0113] The lithology, physical properties, whole-rock mineralogy and sensitivity, rock mechanics, minimum horizontal principal stress profiles of each reservoir and barrier layer, as well as the bottom water layer, and high-angle natural fractures.

[0114] 2) Determination of completion method and segmentation and clustering locations

[0115] The well was completed with casing. After the geological sweet spots and engineering sweet spots were determined by conventional methods, the final comprehensive sweet spot index was determined based on the equal weight method. Finally, 8 fracturing stages were determined, with 2 to 3 clusters in each stage.

[0116] 3) Crack parameter optimization

[0117] On the basis of step 1), the Petrel model of Well X was established by combining the data of adjacent wells. The modeling results were imported into the Eclipse model of Well X, and the hydraulic support fracture parameters were set according to the equivalent conductivity method. According to the orthogonal design method, the post-fracture production dynamics under different fracture parameter conditions (support half-fracture length, conductivity, fracture spacing, etc.) were simulated. The fracture parameter system corresponding to the highest post-fracture production or the maximum economic net present value was the optimal fracture parameter. Combined with the optimization results, the optimal fracture parameters were finally obtained as 8 fracturing stages, 2 to 3 clusters per stage, 35m cluster spacing, 143m half-length of each fracture cluster, and 20D.cm conductivity.

[0118] 4) Optimization of fracturing construction parameters

[0119] The crack propagation simulation commercial software Meyer was used to simulate the crack parameters required for step 3) and the construction displacement was 4m 3 / min~6m 3 / min, the viscosity of the new temperature-sensitive fracturing fluid is 40mPa.s~200mPa.s, the viscosity of the fracturing fluid for sand-carrying fluid is 10mPa.s~50mPa.s, and the amount of fluid used in each section is 600~800m 3 The amount of proppant used in each section is 60 to 90 m 3 , a combination of 40-70 mesh proppants, 70-100 mesh proppants and 20-40 mesh proppants was used, with an average sand-to-liquid ratio of 18%.

[0120] 5) Selection of rheological parameters of new temperature-sensitive fracturing fluid before fracturing

[0121] The formula of the new fracturing fluid was optimized at reservoir temperature, and the viscosity of the fracturing fluid was measured to be 40 mPa.s at room temperature and 155 mPa.s at 85°C.

[0122] 6) Determination of rheological parameters of variable viscosity fracturing fluid before fracturing

[0123] At different stages of sand addition, the temperature field is simulated, and the experimental conditions are determined by the temperature. According to the test standard, the viscosity of the fracturing fluid in the high-density proppant stage is in the range of 30mPa.s to 50mPa.s, and the viscosity of the fracturing fluid in the low-density proppant stage is in the range of 10mPa.s to 20mPa.s. The fracturing fluid formula is determined accordingly, and has good compatibility with the core in step 1).

[0124] 7) Lower the fracturing operation string

[0125] The well was completed with casing and staged fracturing was carried out using cluster perforation + drillable bridge plug. Two cluster perforations were carried out using tubing before fracturing.

[0126] 8) Acid pretreatment

[0127] Acid pretreatment is used before fracturing. The amount of acid used is 15m 3 , the acid injection displacement is 1.0m 3 / min. When replacing acid, the displacement is 3m 3 After the acid reaches the first cluster of perforations near the heel, the displacement is reduced to 1.0m 3 / min, injection 5m 3 Then the displacement was increased to 1.5m 3 / min until all the acid is replaced.

[0128] 9) New temperature-sensitive fracturing fluid fracture construction

[0129] Apply the new temperature-sensitive fracturing fluid formula determined in step 5) and carry out the first stage of fracturing according to the fluid volume and displacement optimized in step 4). The new temperature-sensitive fracturing fluid used in this stage is 120m 3 , displacement is 5m 3 / min.

[0130] 10) Bottom plugging construction with low viscosity fracturing fluid carrying high density proppant

[0131] A low-viscosity fracturing fluid (viscosity 5mPa.s) is used to carry a high-density proppant (density 3.53g / cm 3 ) to seal the bottom, and judge that the fracture height is not out of control by the change of the construction pressure curve (the rate of decline of the bottom hole pressure is less than 1MPa / min). The construction displacement at this stage is 5m 3 / min, liquid volume is 100m 3 , 40-70 mesh high-density proppant dosage is 8m 3 , 70-100 mesh high-density proppant dosage is 4m 3 .

[0132] 11) Construction of variable viscosity fracturing fluid carrying high-density proppant

[0133] The variable viscosity fracturing fluid (viscosity of 30-50 mPa.s) is used to carry high-density proppant (density 3.53 g / cm 3 ) for construction, the construction displacement at this stage is 5m 3 / min, liquid volume is 160m 3 , the dosage of 20-40 mesh high-density proppant is 28m 3 .

[0134] 12) Construction of variable viscosity fracturing fluid carrying low-density proppant

[0135] The variable viscosity fracturing fluid (viscosity of 10-20 mPa.s) is used to carry low-density proppant (density 1.24 g / cm 3 ) for construction, the construction displacement at this stage is 5m 3 / min, liquid volume is 120m 3 , 40-70 mesh low-density proppant dosage is 25m 3 .

[0136] 13) Replacement work

[0137] Low viscosity fracturing fluid (viscosity of 10-20 mPa.s) is used for displacement.

[0138] 14) For the fracturing construction of other sections, repeat steps 7) to 13) until all sections are constructed.

[0139] 15) Post-pressure drilling plug, flowback, testing and production.

[0140] Compared with adjacent wells, the water production after fracturing in the above scheme decreased by 33% and the gas production increased by 12%.

[0141] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

Claims

1. A sand adding method for a multi-layer sandstone bottom water gas reservoir, comprising: (I) Using temperature-sensitive fracturing fluid for fracture construction; (II) Bottom plugging construction with low-viscosity fracturing fluid carrying high-density proppant, wherein the viscosity of the low-viscosity fracturing fluid is 2-5 mPa.s, and the apparent density of the high-density proppant is 3.4 g / cm 3 above; (III) A variable viscosity fracturing fluid of 30-50 mPa.s is used to carry a high-density proppant, wherein the apparent density of the high-density proppant is 3.4 g / cm 3 above; (IV) A variable viscosity fracturing fluid of 10-20 mPa.s is used to carry a low-density proppant, wherein the apparent density of the low-density proppant is 1.25 g / cm 3 the following.

2. The sand adding method according to claim 1, characterized in that: In step (I), the viscosity of the temperature-sensitive fracturing fluid is 48 mPa.s to 200 mPa.s, and its viscosity gradually increases with increasing temperature.

3. The sand adding method according to claim 1, characterized in that: In step (I), the viscosity of the temperature-sensitive fracturing fluid at room temperature is 40-60 mPa.s, and the viscosity at 90° C. is maintained above 150 mPa.s.

4. The sand adding method according to claim 1, characterized in that: In step (II), the change of the construction pressure curve is used to determine whether the fracture height is out of control. When the bottom hole pressure decreases at a rate less than 1 MPa / min, the fracture height continues to extend. When the bottom hole pressure decreases at a rate greater than 1 MPa / min, the fracture height is out of control.

5. The sand adding method according to claim 4, characterized in that: In step (II), a low-viscosity fracturing fluid carrying a high-density proppant is used for bottom plugging, wherein the high-density proppant is selected from a combination of a proppant with a particle size of 40 to 70 meshes and a proppant with a particle size of 70 to 100 meshes.

6. The sand adding method according to claim 5, characterized in that: Whether effective plugging is achieved is determined by the dynamic change of bottom hole pressure, that is, if the bottom hole pressure gradually changes from decreasing to increasing, and the faster the increasing speed, the better the plugging effect, but the increasing speed should be controlled within 0.5MPa / min.

7. The sand adding method according to any one of claims 1 to 6, characterized in that: In step (III), the particle size of the high-density proppant is 20-40 mesh.

8. The sand adding method according to claim 1, characterized in that: The viscosity of the variable viscosity fracturing fluid of 30-50 mPa.s changes from low viscosity to high viscosity.

9. The sand adding method according to claim 7, characterized in that: In step (IV), the particle size of the low-density proppant is 40-70 mesh.

10. The sand adding method according to claim 1, characterized in that: The viscosity of the variable viscosity fracturing fluid of 10-20 mPa.s changes from low viscosity to high viscosity.

11. Application of the sand adding method according to any one of claims 1 to 10 in fracturing construction of multi-layer bottom water gas reservoirs.

12. A fracturing construction method for a multi-layer bottom water gas reservoir, comprising the following steps: 1) Evaluation of key reservoir parameters; 2) Determine the completion method and the location of the segmented clusters; 3) Optimization of crack parameters; 4) Optimization of fracturing operation parameters; 5) Selection of rheological parameters of new temperature-sensitive fracturing fluid before fracturing; 6) Determination of rheological parameters of variable viscosity fracturing fluid before fracturing; 7) Pre-set pipe string or bridge plug and perforation combined operation; 8) Acid pretreatment operations; 9) Using the sand adding method according to any one of claims 1 to 10 to perform sand adding operation; 10) Replacement work; 11) Fracturing construction of other sections: if it is casing completion, repeat steps 7) to 10); if it is open hole completion, repeat steps 8) to 13) until all sections are completed; 12) Drill plug, flowback, testing and production after pressure drilling. Open hole completion does not require drilling plug.

13. The fracturing construction method according to claim 12, characterized in that: In step 8), acid pretreatment is used, and the single-stage acid scale is 10m 3 ~15m 3 , the acid injection displacement is 0.5m 3 / min~1.0m 3 / min, the acid displacement is 2m 3 / min~3m 3 / min.

14. The fracturing construction method according to claim 13, characterized in that: After the acid reaches the first cluster of perforations near the heel, the displacement is reduced to the acid injection displacement, and then the acid replacement displacement is increased 1 to 2 times.

15. The fracturing construction method according to any one of claims 12 to 14, characterized in that: In step 10), the displacement fluid volume is calculated as 1.05 to 1.1 times the wellbore volume and the surface pipeline volume of the current section, and the displacement volume is the maximum displacement volume optimized in step 4).

16. The fracturing construction method according to claim 15, characterized in that: Use low-viscosity slippery water with a viscosity of 2mPa.s to 5mPa.s for displacement.

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