CN114112828B - Micro-proppant placement concentration selection method - Google Patents
Micro-proppant placement concentration selection method Download PDFInfo
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- CN114112828B CN114112828B CN202010878804.7A CN202010878804A CN114112828B CN 114112828 B CN114112828 B CN 114112828B CN 202010878804 A CN202010878804 A CN 202010878804A CN 114112828 B CN114112828 B CN 114112828B
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Abstract
The invention discloses a microcrack flow conductivity testing method, and belongs to the field of oil and gas field development, test and research. The method comprises the following steps: obtaining a target rock sample with microcracks based on a Brazilian splitting method by using a core splitting instrument; displacing the sand mixing liquid into the microcracks of the target rock sample for a plurality of times to carry out micro proppant paving, and measuring the flow conductivity of the microcracks after each paving; and selecting the practical micro-proppant laying concentration according to the corresponding micro-proppant laying concentration with the highest diversion capacity after laying. The method can integrate the proppant migration and laying in the simulated real fracture with the diversion capability under the condition of testing different micro proppant laying concentrations, is time-saving and labor-saving, accords with the continuity of actual operation, and enables the experimental result to be closer to the actual condition, so that the micro proppant laying concentration more suitable for the actual requirement can be obtained, and the method provided by the invention can be used for testing the diversion capability of the micro fracture under the condition of testing the micro proppant particle size.
Description
Technical Field
The invention relates to the field of development, test and research of oil and gas fields, in particular to a method for selecting the laying concentration of a micro-propping agent.
Background
Hydraulic fracturing is an effective measure for increasing oil and gas production, and is characterized by that it is formed into cracks in stratum, then sand-filled in the cracks. The sand filling function is to keep the fracture in an open state, so that the fluid in the stratum flows to the bottom of the well from the top end of the fracture through the supporting band with high flow conductivity. The spreading condition of the propping agent in the cracks influences the flow conductivity of the cracks, the flow conductivity of the cracks represents the quality of the hydraulic fracturing effect, and the yield and the recovery ratio of oil gas are influenced. Therefore, the laying condition of the propping agent in the crack is simulated more truly, the flow conductivity of the crack is tested on the basis, and the method is very important for revealing the influence rule of the particle size, the concentration and the like of the propping agent on the flow conductivity of the crack.
In the prior art, the device for researching the dynamic migration and laying of proppants adopts a plurality of visual glass plates. During the test, the gap between glass plates is used for simulating the crack with the fixed seam width of hydraulic fracturing, the gap between glass plates is filled with fracturing fluid with certain viscosity, sand-carrying fluid is injected from one end of the crack simulation experiment device with certain displacement, and finally the migration and sedimentation rule of propping agent and the form of sand dike are observed through the visual glass plates. The experimental study of proppant placement concentration optimization is carried out according to SY-T6302-2009 'short-term flow conductivity evaluation recommendation method of fracturing proppant filling layers', and the relation between the flow conductivity of the supporting crack and the closing stress under different sand placement concentration conditions is evaluated by using an API flow guide chamber pre-sanding method and a rock plate with a smooth surface.
The inventor finds that the prior art has at least the following technical problems:
first, in the prior art, evaluation and research on the dynamic migration and laying of propping agent and the diversion capability of propping fracture are separately carried out, and the failure to simulate the continuity in practice may lead to inaccurate experimental results. Secondly, the visual glass plate and the smooth rock surface are utilized to simulate the crack, so that the influence of the uneven surface of the crack on the laying of the propping agent is ignored, particularly the influence of the uneven property of the surface of the micron-sized crack on the laying of the propping agent, and the laying condition of the propping agent in the real crack can not be well simulated. Thirdly, the proppant flow conductivity evaluation method in the prior art is only suitable for revealing the influence rule of the particle size, the concentration and the like of the millimeter-sized proppant on the flow conductivity of the fracture, and is not suitable for testing the flow conductivity of the microcrack under the condition of micron-sized scale.
Disclosure of Invention
In order to solve the above problems, the embodiment of the invention provides a method for selecting a micro-proppant placement concentration, so as to achieve a micro-proppant placement concentration more suitable for practical needs, which comprises the following specific steps:
a method of selecting a micro-proppant placement concentration, the method comprising:
obtaining a target rock sample with microcracks based on a Brazilian splitting method by using a core splitting instrument;
displacing the sand mixing liquid into the microcracks of the target rock sample for a plurality of times to carry out micro-proppant paving, and measuring the diversion capacity of the microcracks after each paving;
obtaining the spreading concentration of the corresponding micro-propping agent with the highest flow guiding capacity after spreading;
and selecting the practical micro-proppant laying concentration according to the micro-proppant laying concentration after the corresponding secondary laying.
Further, before the displacing the sand mixing fluid into the micro-fractures of the target rock sample for micro-proppant placement, further comprises:
displacing clean water through microcracks of the target rock sample.
Further, measuring the conductivity of the microcracks after each lay, comprising:
displacing clean water through micro-cracks of the target rock sample, and collecting flow;
calculating the flow conductivity of the microcracks according to the acquired flow,
wherein the conductivity of the microcracks measured after each application is measured at different closure stresses.
Further, the flow conductivity of the microcracks is calculated according to the following formula:
wherein Kw is the micro-crack flow conductivity, Q is the flow, mu is the liquid viscosity, L is the crack length, D is the rock sample diameter, and DeltaP is the pressure difference.
Further, the displacement volume of the sand mixing fluid used for each laying is equal to the microcrack volume of the target rock sample.
Further, after measuring the conductivity of the microcracks after each of the deployments, the method further comprises:
drawing a relation curve of the closing stress and the microcrack flow conductivity;
and comparing the relationship curve of the closure stress and the microcrack flow conductivity obtained for multiple times, and when the microcrack flow conductivity of this time is compared with that of the previous time, not paving any more, and considering the previous paving as the corresponding paving with the highest flow conductivity after the paving.
Further, the sand mixing liquid used for each micro-proppant placement is the sand mixing liquid with the same concentration and made of the same mass proppant; the method further comprises the steps of:
collecting the micro propping agent remained outside the micro cracks of the target rock sample after each laying;
measuring the total mass of all the residual micro proppants collected after the corresponding secondary paving with the highest flow conductivity after the paving and before the secondary paving;
and calculating the spreading concentration of the propping agent with the highest flow conductivity after spreading corresponding times according to the spreading times, the propping agent concentration of the sand mixing liquid, the mass of all the residual propping agent and the micro-crack area of the target rock sample.
Further, the method further comprises: calculating the particle size of a micro-propping agent, and selecting the micro-propping agent to prepare the sand mixing liquid according to the calculated particle size, wherein the calculation formula of the particle size of the micro-propping agent is as follows:
d＝(1/3+1/7)×D/2
wherein D is the particle size of the micro proppant and D is the micro crack width.
Further, the material of the micro-propping agent is manganous oxide, titanium dioxide, silicon dioxide or calcium carbonate.
Further, the method is implemented with a micro proppant placement device comprising: a advection pump, an intermediate container, a core holder, a surrounding pressure pump, a micro flowmeter, a solid-liquid separation meter and a computer,
the middle container, the core holder and the solid-liquid separation meter are sequentially communicated through a pipeline;
the output end of the advection pump is communicated with the intermediate container through a pipeline;
the output end of the advection pump is communicated with the core holder through a pipeline;
the confining pressure pump is used for changing confining pressure of the core holder;
the micro flowmeter is arranged on the outer wall of the solid-liquid separation meter, is close to a fluid inlet of the solid-liquid separation meter, and is in signal connection with the computer;
the middle container with set up second pressure sensor between the rock core holder, confining pressure pump with set up third pressure sensor between the rock core holder, rock core holder with set up first pressure sensor on the pipeline between the solid-liquid separation counter, second pressure sensor third pressure sensor with first pressure sensor respectively with computer signal connection.
The technical scheme provided by the embodiment of the invention has the beneficial effects that at least:
the core splitting instrument is utilized, and the target rock sample with micro cracks is prepared based on the Brazilian splitting method, so that the concave-convex state of the surface of a real crack can be better simulated, and the laying state of the propping agent in the crack is closer to the real condition; on the basis of being closer to a real spreading propping agent, after each spreading agent, setting a closing stress, displacing clean water to pass through micro cracks of a target rock sample, collecting flow, calculating the flow measurement capability of the micro cracks under different closing stresses, selecting the most suitable micro-supporting spreading concentration according to the flow measurement capability, integrating the proppant migration spreading in a simulated real crack and the flow measurement capability under different micro-proppant spreading concentrations, saving time and labor, conforming to the continuity of actual operation, enabling an experimental result to be closer to the actual condition, and further obtaining the micro-propping agent spreading concentration more suitable for actual needs; the method provided by the invention can be used for testing the flow conductivity of the microcracks under the condition of the particle size of the micron-sized propping agent.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for selecting a micro-proppant placement concentration according to an embodiment of the present invention;
FIG. 2 is a flow chart of another method for selecting a micro-proppant placement concentration provided by an embodiment of the present invention;
FIG. 3 is a schematic diagram of a micro-proppant placement device that can implement the method of selecting the concentration of micro-proppant placement shown in FIG. 2, according to an embodiment of the present invention;
FIG. 4 is a graph showing the relationship between the closure stress and the microcrack conductivity provided by the embodiment of the present invention;
FIG. 5 is a graph of the micro proppant placement concentration versus the microcrack conductivity provided by an embodiment of the present invention.
Wherein reference numerals denote:
1-a advection pump; 2-a solid-liquid separation meter; 3-core holder; 4-a pressure surrounding pump; 5-a first valve; 6-a second valve; 7-a third valve; 8-a fourth valve; 9-target rock sample; 10-a first pressure sensor; 11-a second pressure sensor; 12-a third pressure sensor; 13-a stirring device; 14-a lower chamber; 15-a piston; 16-an upper chamber; 17-an intermediate container; 18-a computer; 19-a screen; 20-micro flow meter.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Fig. 1 is a flowchart of a method for selecting a micro-proppant placement concentration according to an embodiment of the present invention, where the method is shown in fig. 1, and the method for selecting a micro-proppant placement concentration may include:
step 101, obtaining a target rock sample with microcracks based on a Brazilian splitting method by using a core splitting instrument;
the microcrack width is typically between 0.146mm and 0.417mm, and the average fracture width is 0.261mm, which is determined by the hydraulic fracture microcrack propagation characteristics.
The slit width of the microcrack of the target rock sample can be determined according to the specific slit width of the target reservoir, and other dimensions of the target rock sample are not limited and can be selected according to experimental conditions.
Illustratively, a cylindrical rock sample having a diameter of 25mm and a length of 50mm was split in an axial direction of the rock sample using a core splitter based on the brazilian split method to produce a target rock sample having a crack width of 0.261 mm.
102, displacing the sand mixing liquid into the microcracks of the target rock sample for multiple times to carry out micro-proppant paving, and measuring the flow conductivity of the microcracks after each paving;
when the particle size of the particles is larger than 1/3 of the width of the crack, the particles are easy to accumulate on a crack bridge of the crack to form a plugging band; when the particle size of the particles is smaller than 1/3 of the width of the crack and larger than 1/7 of the width of the crack, the particles can move in the crack but are influenced by the roughness of the crack surface; when the particle diameter of the particles is less than 1/7 of the width of the crack, the particles can flow in the crack at will without forming bridging. Therefore, in order to maximize the opening degree of the micro-propping agent supporting micro-cracks, the relatively high seepage capability of the supporting layer is ensured, meanwhile, the migration capability of the micro-propping agent in the micro-cracks is considered, and the particle size of the micro-propping agent can be the average value of the matching relation between the particle size and the slit width when particles bridge and flow at random.
For example, the appropriate particle size of the micro-proppant may be calculated using the following first equation, and the micro-proppant is selected based thereon:
d＝(1/3+1/7)×D/2
wherein D is the particle size of the micro proppant, and D is the slit width of the micro fracture of the target rock sample.
Illustratively, the material of the micro-proppant is manganous oxide, titanium dioxide, silicon dioxide, or calcium carbonate, but is not limited to the several listed above.
Step 103, obtaining the spreading concentration of the corresponding micro-propping agent with the highest flow conductivity after spreading;
and 104, selecting the practical micro-proppant laying concentration according to the micro-proppant laying concentration after the corresponding laying with the highest diversion capacity.
In summary, in the method for selecting the spreading concentration of the micro-propping agent provided by the embodiment of the invention, the core splitter is used for preparing the target rock sample with the micro-cracks based on the Brazilian splitting method, so that the concave-convex state of the surface of the real crack is better simulated, and the spreading state of the micro-propping agent in the micro-crack is closer to the real situation. On the basis of spreading the micro propping agent closer to the actual situation, testing the flow conductivity of the micro cracks under different propping agent spreading concentrations, selecting the most suitable micro propping spreading concentration according to the flow conductivity of the micro cracks, integrating the proppant migration spreading in the simulated actual cracks and the flow conductivity under different micro propping agent spreading concentrations, saving time and labor, conforming to the continuity of actual operation, and enabling the experimental result to be closer to the actual situation, thereby obtaining the micro propping agent spreading concentration more suitable for the actual need; the method provided by the invention can be used for testing the flow conductivity of the microcracks under the condition of the particle size of the micron-sized propping agent.
Fig. 2 is a flow chart of another method for selecting a concentration of a micro-proppant placement according to an embodiment of the present invention, and fig. 3 is a micro-proppant placement device that can be used to implement the method.
As shown in fig. 3, the micro proppant placement device includes: a advection pump 1, an intermediate container 17, a core holder 3, a confining pressure pump 4, a micro flow meter 20, a solid-liquid separation meter 2, a computer 18, a first pressure sensor 10, a second pressure sensor 11 and a third pressure sensor 12.
The intermediate container 17, the core holder 3 and the solid-liquid separation meter 2 are sequentially communicated through pipelines.
The intermediate container 17 is used for preparing the sand mixture and storing the prepared sand mixture.
Further, the intermediate container 17 is divided by the piston 15 into an upper chamber 16 and a lower chamber 14, the lower chamber 14 is provided with a stirring device 13, and the upper chamber 16 is connected with the output end of the advection pump 1.
The core holder 3 is used for holding a target rock sample 9, so that the target rock sample 9 is horizontally fixed on the core holder 3.
Further, the core holder 3 is a heusler type core holder, and when the rock sample is loaded and unloaded, the core holder 3 does not need to be completely disassembled. And the side wall of the rock sample is sealed by applying radial pressure on the cylindrical surface of the rock sample, and fluid enters from the end face and is discharged from the other end face during testing.
The solid-liquid separation meter 2 is used for carrying out solid-liquid separation on the sand-mixed liquid flowing out from the pipeline port.
Further, the solid-liquid separation meter 2 is a graduated flask, and a screen 19 is provided on the flask for solid-liquid separation.
The output end of the advection pump 1 is communicated with the intermediate container 17 through a pipeline and is used for displacing clean water, so that a piston of the intermediate container moves downwards and the sand mixing liquid is displaced into a microcrack of a target rock sample.
The output end of the advection pump 1 is also communicated with the core holder 3 through a pipeline to provide pressure displacement of clean water through micro-cracks of a target rock sample.
The confining pressure pump 4 is used for controlling confining pressure of the core holder 3 and simulating changes of effective stress applied to a fracture surface in the fracturing and production process of the gas well.
Further, a confining pressure pump 4 is provided above the core holder 3.
The micro flow meter 20 is disposed on the outer wall of the solid-liquid separation meter 2, is located near the fluid inlet of the solid-liquid separation meter 2, and is in signal connection with the computer 18.
The micro flow meter 20 is used to collect the flow rate and the flow velocity of the fluid inlet of the solid-liquid separation meter 2 in real time and send the collected data to the computer 18.
A second pressure sensor 11 is arranged between the intermediate container 17 and the core holder 3, a third pressure sensor 12 is arranged between the confining pressure pump 4 and the core holder 3, a first pressure sensor 10 is arranged on a pipeline between the core holder 3 and the solid-liquid separation meter 2, and the second pressure sensor 11, the third pressure sensor 12 and the first pressure sensor 19 are respectively in signal connection with a computer 18.
The first pressure sensor 10 is used for acquiring the confining pressure of the core holder 3 and sending the acquired data to the computer 18.
The second pressure sensor 11 is used to collect the pressure upstream of the core holder 3 and send the collected data to the computer 18.
The third pressure sensor 12 is used to collect the pressure downstream of the core holder 3 and send the collected data to the computer 18.
As shown in fig. 2, the micro-proppant placement concentration selection method may include:
step 201, obtaining a target rock sample 9 with microcracks based on a Brazilian splitting method by using a core splitter;
wherein the prepared target rock sample 9 with microcracks is placed on the core holder 3.
The microcrack width is typically between 0.146mm and 0.417mm, and the average fracture width is 0.261mm, which is determined by the hydraulic fracture microcrack propagation characteristics.
The slit width of the micro-cracks of the target rock sample 9 may be determined according to the specific slit width of the target reservoir, and other dimensions of the target rock sample 9 are not limited and may be selected according to experimental conditions.
Illustratively, a cylindrical rock sample having a diameter of 25mm and a length of 50mm was split in an axial direction based on a brazil splitting method using a core splitter to produce a target rock sample having a crack width of 0.261 mm.
Step 202, displacing clean water through micro-cracks of the target rock sample 9.
Before the clean water is displaced, confining pressure is firstly applied to a target rock sample 9 in the core holder 3 by using the confining pressure pump 4, closing pressure of cracks is simulated, the first valve 5 and the third valve 7 are closed, the second valve 6 and the fourth valve 8 are opened, and then the clean water is displaced through the target rock sample 9 by using the advection pump 1.
Further, the displacement of the clean water through the microcracks of the target rock sample 9 further comprises: and collecting flow, and calculating the flow conductivity of the microcracks under the unsupported condition according to the collected flow. For example, a minute flow meter 20 provided at the fluid inlet of the solid-liquid separator 2 can collect the flow rate and the flow velocity at the fluid inlet of the solid-liquid separator 2 in real time and transmit the collected data to the computer 18.
The collected flow is the flow in unit time after the flow rate of the liquid is stable, for example, the flow rate law in 5 seconds can be observed, if the flow rate is basically maintained at a constant value, the flow rate is stabilized, and therefore the flow conductivity of the microcracks can be calculated according to the flow in unit time after the flow rate is stabilized.
Further, the conductivity of the microcracks was measured at different closure stresses that simulate the change in effective stress experienced by the fracture face of the production process. The confining pressure of the core holder 3 is changed, for example, by using the confining pressure pump 4, and the micro-fracture conductivity of the target rock sample 9 under different closure stresses in the unsupported condition is calculated according to the flow rate of each acquisition.
The magnitude of the closing stress may be set to 1MPa, 5MPa, 10MPa, 15MPa, 20MPa, 25MPa, respectively, for example, although other reasonable values are also possible, without limitation.
Further, the conductivity of the microcracks is calculated by the following second formula,
wherein Kw is the micro-fracture conductivity, Q is the flow, μ is the liquid viscosity, L is the fracture length, D is the rock sample diameter, and ΔP is the differential pressure.
Wherein, the crack length L and the rock sample diameter D are both dependent on the size parameters of the initially manufactured target rock sample 9, Δp is the pressure difference between the upstream and downstream of the target rock sample 9, and in the process of displacing the clean water to the micro-cracks of the target rock sample 9, the second pressure sensor 11 and the first pressure sensor 10 respectively collect the upstream pressure value and the downstream pressure value of the core holder 3 in real time, and the collected data are transmitted to the computer 18, and Δp can be calculated according to the upstream pressure value and the downstream pressure value of the core holder 3 collected by the second pressure sensor 11 and the first pressure sensor 10.
Further, the method further comprises: calculating the particle size of the micro propping agent, and selecting the micro propping agent to prepare the sand mixing liquid according to the calculated particle size. For example, a sand mixture is prepared in the lower chamber 14 of the intermediate container 17 using a micro proppant and clean water, and the prepared sand mixture is stored in the intermediate container 17.
When the particle size of the particles is larger than 1/3 of the width of the crack, the particles are easy to accumulate on a crack bridge of the crack to form a plugging band; when the particle size of the particles is smaller than 1/3 of the width of the crack and larger than 1/7 of the width of the crack, the particles can move in the crack but are influenced by the roughness of the crack surface; when the particle diameter of the particles is less than 1/7 of the width of the crack, the particles can flow in the crack at will without forming bridging. Therefore, in order to maximize the opening degree of the micro-propping agent supporting micro-cracks, the relatively high seepage capability of the supporting layer is ensured, meanwhile, the migration capability of the micro-propping agent in the micro-cracks is considered, and the particle size of the micro-propping agent can be the average value of the matching relation between the particle size and the slit width when particles bridge and flow at random.
For example, the appropriate particle size of the micro-proppant may be calculated using the following first equation, and the micro-proppant is selected based thereon:
d＝(1/3+1/7)×D/2
wherein D is the particle size of the micro proppant, and D is the slit width of the micro fracture of the target rock sample.
Illustratively, the material of the micro-proppant may be selected from the group consisting of trimanganese tetraoxide, titanium dioxide, silicon dioxide, and calcium carbonate, but is not limited to the several listed above.
And 203, displacing the sand mixing liquid into the microcracks of the target rock sample 9 for a plurality of times to perform micro-proppant paving, and after each paving, displacing clean water to pass through the microcracks of the target rock sample 9, collecting flow, and calculating the flow conductivity of the microcracks according to the collected flow.
When the micro propping agent is paved, the second valve 6 is required to be closed, the fourth valve 8 is kept in an open state, the first valve 5 and the third valve 7 are opened, the sand mixing liquid in the middle container 17 is displaced to the target rock sample 9 by using the constant pressure of the advection pump 1, meanwhile, the stirring device 13 in the lower chamber 4 of the middle container 17 is used for stirring the sand mixing liquid, and the fluid carrying sand is simulated to enter a microcrack paving process.
After each proppant is laid, the advection pump 1 is used for displacing clean water through the target rock sample 9 again, and the flow conductivity of the microcracks under different closure stresses is measured, wherein the setting of the closure stresses, the method for collecting the flow and the calculation method of the flow conductivity of the microcracks are the same as those in step 202, and are not repeated here.
Further, for displacing the sand mixture liquid to the microcracks of the target rock sample 9 a plurality of times, the displacement volume of each time may be set to be equal to the volume of the microcracks of the target rock sample 9, wherein the volume of the microcracks of the target rock sample 9 may be calculated from the length, width and slit width of the microcracks of the target rock sample 9, and of course, if the target rock sample 9 is a cylinder, the width is the diameter of the circular end face. Because the operation of displacing the clean water to the micro-crack to measure the flow conductivity is carried out before the propping agent is paved each time, when the sand-mixing liquid is displaced to the micro-crack each time, when the volume of the clean water displaced by the sand-mixing liquid is equal to the volume of the micro-crack of the target rock sample 9, the sand-mixing liquid is fully filled with the micro-crack of the target rock sample, namely, the displacement volume is equal to the volume of the micro-crack of the target rock sample 9, the displacement volume of each time is set to be equal to the volume of the micro-crack of the target rock sample 9, the variable can be further controlled, and the flow conductivity of the micro-crack measured after each time of paving is more accurate.
And 204, obtaining the spreading concentration of the corresponding micro-propping agent with the highest flow conductivity after spreading.
After measuring the micro-crack conductivity after each laying, the method of the embodiment may further include: and drawing a relation curve of the closed stress and the microcrack flow conductivity, comparing the relation curve of the closed stress and the microcrack flow conductivity obtained for a plurality of times, and when the microcrack flow conductivity after the current paving is compared with the microcrack flow conductivity after the previous paving, not paving any more, namely, after the measured flow conductivity is the highest, not paving a micro-propping agent any more, and terminating the experiment.
By way of example, the relationship curve of the closure stress and the microcrack flow conductivity after each laying is drawn on the same graph, so that the height of the flow conductivity can be intuitively seen, and the corresponding secondary laying with the highest flow conductivity can be found.
After finding the corresponding secondary laying with the highest flow conductivity, the micro-proppant laying concentration corresponding to the corresponding secondary laying with the highest flow conductivity after laying can be calculated, so that the micro-proppant laying concentration after the corresponding secondary laying with the highest flow conductivity after laying is obtained. An exemplary calculation is as follows:
and obtaining the proppant mass in the sand mixing liquid used for each micro proppant laying.
The mass of the propping agent in the sand mixing liquid used for each paving can be directly determined when the sand mixing liquid is prepared, and the mass of the micro propping agent in the sand mixing liquid can be indirectly obtained through the total mass of the prepared sand mixing liquid and the mass of the added clear water.
Illustratively, the sand mixing liquid used for each micro-proppant placement is made of the same mass of micro-proppant, so that the total mass of micro-proppant used until the current time can be conveniently calculated according to the number of times of placement.
The micro proppant remaining outside the micro cracks of the target rock sample 9 after each laying is collected.
Wherein the micro proppant remaining outside the micro-cracks of the target rock sample 9 refers to the total amount of the micro proppant deposited in the intermediate container 17, the solid-liquid separation meter 2, and the pipeline.
Measuring the total mass of all residual micro proppants collected after the corresponding secondary paving with the highest diversion capacity and before the secondary paving after the corresponding secondary paving;
for example, the collected micro proppants remaining outside the micro cracks may be dried at a constant temperature of 80 ℃ by using an oven, but the micro proppants may be dried at other suitable temperature conditions, and the micro proppants may be dried by other drying apparatuses or drying methods, which is not limited herein.
Therefore, the spreading concentration of the micro propping agent with the highest flow conductivity after spreading and corresponding spreading after the spreading can be calculated according to the spreading times, the mass of the micro propping agent in the sand mixing liquid used for each spreading, the total mass of all the micro propping agents remained outside the micro cracks and the micro crack area of the target rock sample 9.
The microcrack area of the target rock sample 9 can be calculated from the length and width of the target rock sample 9, and when the target rock sample 9 is a cylinder, the microcrack area can be calculated from the diameter of the circular end face and the length of the target rock sample 9.
Further, the value is taken in the upper and lower ranges of the spreading concentration value of the micro-propping agent which is preliminarily determined, experiments are conducted again, the spreading of the micro-propping agent is correspondingly conducted according to the value of the spreading concentration, the flow is collected after the fresh water passes through the micro-cracks of the target rock sample 9, the diversion capacity of the micro-cracks under different spreading concentrations is calculated respectively, and the relation curve of the spreading concentration and the diversion capacity of the micro-propping agent is drawn, so that the spreading concentration of the micro-propping agent which is preliminarily determined is optimized, the more suitable spreading concentration of the micro-propping agent is obtained, and the spreading concentration is used as the spreading concentration of the micro-propping agent which is actually used.
The determination of the highest conductivity placement and the corresponding micro-support placement concentration for the highest conductivity placement is further described in connection with one embodiment below:
firstly, under the condition that a propping agent is not paved, the flow conductivity of microcracks when the closure stress is 1MPa, 5MPa, 10MPa, 15MPa, 20MPa and 25MPa is respectively calculated by displacing clean water through microcracks of a target rock sample 9; after the micro propping agent is paved for the 1 st time, calculating the flow conductivity of the micro cracks under different closing stresses by the method, and calculating the paving concentration of the micro propping agent at the current time; and then carrying out the 2 nd, 3 rd and 4 th times of laying of the micro propping agent, testing the diversion capability by the same method, and finally obtaining the corresponding relation among the closing stress, the laying concentration of the micro propping agent and the diversion capability as shown in the table 1:
TABLE 1 microcrack conductivity evaluation results Table
According to the data in table 1, the graph of the relationship between the closing stress and the micro-crack flow conductivity is drawn by dot plot method to obtain fig. 4, and it is known from fig. 4 that when the closing stress is between 15MPa and 25MPa, for the flow conductivity of the micro-proppants measured after the previous 3 times of laying, the flow conductivity of the micro-proppants measured after the next laying is higher than the flow conductivity of the micro-proppants measured after the previous laying, that is, the larger the laying concentration of the micro-proppants is, the higher the flow conductivity of the corresponding micro-cracks is. However, the curve obtained after the 4 th laying is located below the curve obtained after the 3 rd laying, and thus it is known that the concentration of the corresponding micro-proppant after the 4 th laying is not only not improved but also the flow conductivity of the micro-cracks is hindered, and thus the laying of micro-struts is not necessary, the flow conductivity of the corresponding micro-proppant after the 3 rd laying is the highest, and the concentration of the corresponding micro-proppant after the 3 rd laying is 0.0873kg/m 2 。
Further, the preliminary determined spreading concentration of the micro-proppant was further optimized at 0.0873kg/m 2 And (3) taking values in the upper and lower ranges, re-testing, testing the flow conductivity of the micro-cracks under different laying concentrations under the condition of closing stress of 20MPa and 25MPa, and drawing a graph of the relation between the laying concentration and the flow conductivity of the micro-propping agent, wherein the graph is shown in fig. 5. As can be seen from FIG. 5, the paving concentration corresponding to the maximum value of the flow conductivity is 0.078kg/m 2 The spreading concentration is more suitable, so the spreading concentration of the actual micro-proppants is determined to be 0.078kg/m 2 。
And 205, selecting the practical micro-proppant laying concentration according to the micro-proppant laying concentration after the corresponding laying with the highest diversion capacity.
In the operation process of actual oil and gas field exploitation, the corresponding spreading concentration of the micro propping agent with the highest diversion capability obtained in the step 204 is selected for actual spreading of the micro propping agent, so that the function of the propping agent is fully exerted, the diversion capability of the stratum crack is optimized, and the exploitation amount of oil and gas is improved.
In summary, in the method for selecting the spreading concentration of the micro-propping agent provided by the embodiment of the invention, the core splitter is used for preparing the target rock sample with micro-cracks based on the Brazilian splitting method, so that the concave-convex state of the surface of the real crack is better simulated, and the spreading state of the propping agent in the crack is closer to the real condition. On the basis of spreading the micro-propping agent closer to the actual situation, setting the size of the closing stress after spreading the micro-propping agent each time, driving clean water to pass through micro-cracks of the target rock sample, calculating the diversion capacity of the micro-cracks after each time of spreading according to the collected flow, drawing the relation curve of different closing stress and the diversion capacity of the micro-cracks, comparing the relation curve obtained after the next spreading with the relation curve obtained before, determining the corresponding spreading time with the highest diversion capacity, wherein the concentration of the micro-propping agent corresponding to the corresponding spreading time with the highest diversion capacity is the most suitable micro-propping spreading concentration, thereby selecting the spreading concentration of the micro-propping agent in actual use, realizing the integrated implementation of the diversion capacity under the spreading of the propping agent in the simulated actual cracks and testing the spreading concentration of the different micro-propping agents, saving time and effort, and conforming to the continuity of the operation in actual practice, so that the experimental result is closer to the actual situation, and the spreading concentration of the micro-propping agent more suitable for the actual requirement can be obtained; the method provided by the invention can be used for testing the flow conductivity of the microcracks under the condition of the particle size of the micron-sized propping agent.
It should be understood that the sequence of steps in the foregoing embodiments of the present invention can be appropriately adjusted, and the steps can be increased or decreased accordingly according to circumstances, and the method for selecting the concentration of the micro-proppant placement provided by the present invention is not limited to the steps of the method that have been described above and shown in the drawings, and any modification, equivalent replacement, improvement, etc. that are within the spirit and principle of the present invention should be included in the protection scope of the present invention.
It should be noted that, the implementation of the method for selecting the concentration of the micro-proppant placement provided by the present invention is not limited to the above-mentioned micro-proppant placement device, and any other device for implementing the method for selecting the concentration of the micro-proppant placement is also included in the scope of the present invention.
Claims (7)
1. A method of selecting a micro-proppant placement concentration, the method comprising:
obtaining a target rock sample with microcracks based on a Brazilian splitting method by using a core splitting instrument;
displacing the sand mixing liquid into the microcracks of the target rock sample for a plurality of times to carry out micro-proppant paving, and measuring the diversion capacity of the microcracks after each paving;
obtaining the spreading concentration of the corresponding micro-propping agent with the highest flow guiding capacity after spreading;
selecting the practical micro-proppant laying concentration according to the micro-proppant laying concentration after the corresponding secondary laying;
the method further comprises the steps of: acquiring the mass of the micro propping agent in the sand mixing liquid used for each micro propping agent laying;
collecting the micro propping agent remained outside the micro cracks of the target rock sample after each laying;
measuring the total mass of all the residual micro proppants collected after the corresponding secondary paving with the highest flow conductivity after the paving and before the secondary paving;
according to the number of times of laying, calculating the laying concentration of the propping agent with the highest flow conductivity after the laying and corresponding times of laying according to the mass of the propping agent in each sand mixing liquid, the mass of all the residual propping agent and the micro-crack area of the target rock sample;
the method further comprises the steps of: calculating the particle size of a micro-propping agent, and selecting the micro-propping agent to prepare the sand mixing liquid according to the calculated particle size, wherein the calculation formula of the particle size of the micro-propping agent is as follows:
wherein D is the particle size of the micro propping agent and D is the width of the micro cracks;
the method is implemented with a micro proppant placement device comprising: a advection pump, an intermediate container, a core holder, a surrounding pressure pump, a micro flowmeter, a solid-liquid separation meter and a computer,
the middle container, the core holder and the solid-liquid separation meter are sequentially communicated through a pipeline;
the output end of the advection pump is communicated with the intermediate container through a pipeline;
the output end of the advection pump is communicated with the core holder through a pipeline;
the confining pressure pump is used for controlling confining pressure of the core holder;
the micro flowmeter is arranged on the outer wall of the solid-liquid separation meter, is close to a fluid inlet of the solid-liquid separation meter, and is in signal connection with the computer;
a second pressure sensor is arranged between the middle container and the core holder, a third pressure sensor is arranged between the confining pressure pump and the core holder, a first pressure sensor is arranged on a pipeline between the core holder and the solid-liquid separation meter, and the second pressure sensor, the third pressure sensor and the first pressure sensor are respectively connected with the computer through signals; the third pressure sensor is used for collecting confining pressure of the core holder and sending collected data to the computer; the second pressure sensor is used for collecting the pressure at the upstream of the core holder and sending the collected data to the computer; the first pressure sensor is used for collecting the pressure of the downstream of the core holder and sending collected data to the computer.
2. The method of selecting a micro proppant placement concentration according to claim 1, further comprising, prior to the plurality of displacements of the sand mixture into the microcracks of the target rock sample:
displacing clean water through microcracks of the target rock sample.
3. The method of selecting a concentration of micro-proppant placement according to claim 2, wherein measuring the conductivity of the micro-fracture after each placement comprises:
displacing clean water through micro-cracks of the target rock sample, and collecting flow;
calculating the flow conductivity of the microcracks according to the acquired flow,
wherein the conductivity of the microcracks measured after each application is measured at different closure stresses.
4. The method of claim 3, wherein the conductivity of the microcracks is calculated according to the following formula:
wherein Kw is the micro-crack flow conductivity, Q is the flow, mu is the liquid viscosity, L is the crack length, D is the rock sample diameter, and DeltaP is the pressure difference.
5. The method of selecting a micro proppant placement concentration according to claim 4, wherein the displacement volume of the sand mixture used for each placement is equal to the micro fracture volume of the target rock sample.
6. The method of selecting a micro proppant placement concentration according to claim 5, wherein after measuring the conductivity of the micro fracture after each placement, the method further comprises:
drawing a relation curve of the closing stress and the microcrack flow conductivity;
comparing the relationship curve of the closure stress and the microcrack flow conductivity obtained for multiple times;
when the current micro-crack flow conductivity is compared with the previous micro-crack flow conductivity, the paving is not performed any more, and the previous paving is regarded as the corresponding paving with the highest flow conductivity after the paving.
7. The method of claim 1, wherein the material of the micro-proppant is manganous oxide, titanium dioxide, silicon dioxide, or calcium carbonate.
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| 林启才.低渗气藏压裂中裂缝导流能力的影响因素研究.《油气井测试》.2007,第16卷(第S1期),第22-25页. * |
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