Crack diagnosis method for multi-type tracer collaborative inversion of proppant laying condition

Abstract

The invention discloses a crack diagnosis method for multi-type tracer collaborative inversion of a propping agent laying condition, and belongs to the technical field of oil and gas field exploitation, and the method comprises the following steps: during fracturing construction, adding trace element tracers into each fracturing section of a horizontal well on the ground to prepare a fracturing fluid with a constant tracer concentration; in the sand-carrying fluid stage, a tracer film-coated propping agent is pumped into the crack of each fracturing section, so that the crack has a preset opening degree; flowback is carried out after fracturing and pump stopping, sampling is carried out at a wellhead of the horizontal well, and the concentration of the microelement tracer agent and the concentration of the carbon quantum dot tracer agent of each fracturing section are detected; according to the detection results of the trace element tracer and the carbon quantum dot tracer in each fracturing section, drawing charts of two curves of the trace element tracer and the carbon quantum dot tracer in the same fracturing section, wherein the concentrations of the trace element tracer and the carbon quantum dot tracer change along with time; analyzing according to the characteristics of the two curves in the drawn chart, and determining the propping agent laying condition and the crack closing condition of each fracturing section.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field exploitation, and in particular to a fracture diagnosis method for cooperative inversion of proppant laying conditions using multiple types of tracers. Background Art

[0002] Hydraulic fracturing technology is the key technology for the development of unconventional oil and gas fields at home and abroad. During the fracturing process, proppant needs to be pumped into the cracks to make the cracks have a certain opening, so as to form complex cracks with high conductivity for oil and gas flow. Therefore, establishing effective support cracks as long as possible is of great significance to improving the development effect of oil and gas reservoirs. The laying of proppant is the key to determining the length of effective support cracks. The laying of proppant varies greatly under different geological and engineering factors. Optimizing the sand adding parameters can significantly increase the effective length of the support cracks. Knowing the laying form of proppant can better optimize the sand adding parameters. Therefore, a safe, efficient and low-cost proppant laying crack diagnosis method is of great significance for the adjustment of subsequent fracturing plans.

[0003] Fracturing tracer technology has shown good application prospects in post-fracturing evaluation due to its advantages such as small tracer dosage, low cost, easy detection, recyclable and accurate results. Fracturing tracer technology includes quantum tracer technology, fracturing fluid tracer technology and radioactive tracer technology. At present, the inversion of proppant laying is mainly achieved through radioactive tracer technology. Its technical principle is to attach radioactive elements to proppant, track proppant in hydraulic fracturing by tracing method, and then process data through spectrum logging to obtain the distribution of proppant in fracture. Radioactive tracer technology has high process maturity and relatively accurate results, but due to the serious harm of radioactive elements to the health of operators, the on-site application of radioactive tracer technology is limited. Quantum tracing technology and fracturing fluid tracing technology are safe and harmless means of fracture monitoring. Their similarities are that they both monitor the fracturing transformation effect by analyzing the tracer concentration curve. The difference is that the principle of quantum tracing technology is to coat carbon quantum dots on the proppant. With the production of oil and gas wells, the carbon quantum dots on the proppant dissolve in the formation fluid and are produced. The fracturing fluid tracing technology is to dissolve the tracer in the fracturing fluid during the fracturing stage and pump it into the formation and produce it with the return fluid.

[0004] Compared with radioactive tracer technology, quantum tracer technology and fracturing fluid tracer technology have higher safety in post-fracturing evaluation. However, there is still no accurate fracture diagnosis method for proppant placement conditions, and it is impossible to effectively provide reliable guidance for the optimization of on-site sand adding parameters. Therefore, establishing a method for collaborative inversion of proppant placement conditions using multiple types of tracers is of great significance for the inversion of proppant placement conditions after fracturing and the optimization of on-site sand adding parameters.

[0005] The above contents are only used to assist in understanding the technical solution of the present invention and do not constitute an admission that the above contents are prior art. Summary of the invention

[0006] The main purpose of the present invention is to provide a fracture diagnosis method for collaborative inversion of proppant placement conditions using multiple types of tracers, aiming to solve or partially solve the above-mentioned problems.

[0007] To achieve the above object, the present invention provides a fracture diagnosis method for collaborative inversion of proppant placement conditions using multiple types of tracers, comprising: During fracturing construction, a trace element tracer is added to each fracturing section of the horizontal well on the ground to form a fracturing fluid with a constant tracer concentration; in the sand-carrying fluid stage, a tracer-coated proppant is pumped into the cracks of each fracturing section so that the cracks have a preset opening, wherein the tracer-coated proppant is a proppant coated with a carbon quantum dot tracer, the carbon quantum dot tracers in different fracturing sections are different, the trace element tracers in different fracturing sections are different, and the volumes of the carbon quantum dot tracer and the trace element tracer in each fracturing section are the same; After the pump is stopped during fracturing, flowback is performed and samples are taken at the wellhead of the horizontal well to detect the concentrations of trace element tracers and carbon quantum dot tracers in each fracturing section. According to the detection results of trace element tracers and carbon quantum dot tracers in each fracturing stage, two curves of the concentration change of trace element tracers and carbon quantum dot tracers in the same fracturing stage over time are drawn; According to the characteristics of the two curves in the drawn plate, the proppant placement and crack closure conditions of each fracturing stage are determined.

[0008] Preferably, in the fracture diagnosis method of the multi-type tracer collaborative inversion proppant placement condition, the analysis based on the characteristics of the two curves in the drawn plate to determine the proppant placement condition and the fracture closure condition of each fracturing stage includes: According to the half width of the trace element tracer curve, the cracks with poor proppant laying effect and the cracks with good proppant laying effect, as well as the crack closure status, are determined; According to the half width of the carbon quantum dot tracer curve, the cracks with poor proppant laying effect and the cracks with good proppant laying effect, as well as the crack closure status, are determined.

[0009] Preferably, in the fracture diagnosis method of the multi-type tracer collaborative inversion proppant laying condition, the determination of the fractures with poor proppant laying effect and the fractures with good proppant laying effect, as well as the fracture closure condition according to the half width of the trace element tracer curve includes: In the trace element tracer curve, the half width of the crack with poor proppant laying effect is smaller than the half width of the crack with good proppant laying effect; The cracks with poor proppant placement closed faster, while the cracks with good proppant placement closed slower; The fracturing fluid flowback rate in the fractures with poor proppant laying effect is greater than that in the fractures with good proppant laying effect.

[0010] Preferably, in the fracture diagnosis method of the multi-type tracer collaborative inversion proppant laying condition, the determination of the fractures with poor proppant laying effect and the fractures with good proppant laying effect, as well as the fracture closure condition according to the half width of the carbon quantum dot tracer curve includes: In the carbon quantum dot tracer curve, the half width of the crack with poor proppant laying effect is greater than the half width of the crack with good proppant laying effect, and the peak difference of the crack with poor proppant laying effect is greater than the peak difference of the crack with good proppant laying effect; The carbon quantum dot tracer curve will rise at the beginning of flowback. When the carbon quantum dot tracer curve reaches its peak, it indicates that the fracture is completely closed on the carbon quantum dot coated proppant and a fluid migration channel with flow conductivity is formed. After the fracture is closed, the residual fracturing fluid and formation fluid are produced through the proppant filling layer. Since the proppant laying height in the fracture with poor proppant laying effect is higher, it can be seen from the continuity equation that under the condition of a certain flow rate, the larger the cross-section, the smaller the flow rate through the cross-section.

[0011] Preferably, in the fracture diagnosis method of cooperative inversion of proppant placement conditions using multiple types of tracers, the carbon quantum dot tracers in different fracturing stages are different, which is reflected in different sizes of carbon quantum dots.

[0012] Preferably, in the fracture diagnosis method of cooperative inversion of proppant placement conditions using multiple types of tracers, the trace element tracers in different fracturing stages are different, which is reflected in different trace elements.

[0013] Preferably, in the fracture diagnosis method of the multi-type tracer collaborative inversion of proppant laying conditions, the trace element of the trace element tracer is one of the rare earth elements of praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

[0014] Preferably, in the fracture diagnosis method for the cooperative inversion of proppant laying conditions by multiple types of tracers, in the step of adding trace element tracers to each fracturing stage of the horizontal well on the ground during the fracturing construction to prepare a fracturing fluid with a constant tracer concentration; in the step of pumping tracer-coated proppant into the fractures of each fracturing stage in the sand-carrying fluid stage so that the fractures have a preset opening, the amount of trace element tracer is calculated by the following formula: ; (1) Wherein, FBR is the fracturing fluid flowback rate, in %; V d Designed fracturing construction liquid scale, m 3 ; MDC wj is the minimum detectable concentration of the tracer under the test conditions, in ppt; e wj is the safety factor for the use of aqueous solution, dimensionless; Q lw The maximum water production of a single well or a single section in the neighboring wells of the target well, in m 3 / day; Day is the number of days required for tracer testing of the target well, in day; When Q lw When the water production of the target well is the highest among the wells adjacent to the target well, the safety factor of the water agent is 0 to 10; When Q lw When the water production of a single section of the target well and the adjacent wells is the highest, the safety factor for the use of water agent is 10 to 20.

[0015] Preferably, in the fracture diagnosis method of the multi-type tracer collaborative inversion of proppant laying conditions, in the step of performing flowback after stopping the fracturing pump, sampling at the wellhead of the horizontal well, and respectively detecting the concentrations of trace element tracers and carbon quantum dot tracers in each fracturing section, the trace element tracers are detected by a high-performance mass spectrometer; The carbon quantum dot tracers were detected by UV-visible spectrophotometer.

[0016] Preferably, in the fracture diagnosis method for cooperative inversion of proppant laying conditions by using multiple types of tracers, in the step of drawing two curves of the concentration variation of trace element tracers and carbon quantum dot tracers in the same fracturing stage over time according to the detection results of trace element tracers and carbon quantum dot tracers in each fracturing stage, the horizontal coordinate of the tracer concentration-time variation curve in the drawn plate is time, and the vertical coordinate is the dimensionless concentration of the tracer; The dimensionless concentration is the ratio of the tracer concentration at a certain moment to the peak concentration during the flowback process.

[0017] The present invention has at least the following beneficial effects: The present invention adds trace element tracers to each fracturing section of a horizontal well on the ground during fracturing construction to configure a fracturing fluid with a constant tracer concentration; in the sand-carrying fluid stage, a tracer-coated proppant is pumped into the cracks of each fracturing section so that the cracks have a preset opening, wherein the tracer-coated proppant is a proppant coated with a carbon quantum dot tracer, the carbon quantum dot tracers in different fracturing sections are different, the trace element tracers in different fracturing sections are different, and the volumes of the carbon quantum dot tracers and the trace element tracers in each fracturing section are respectively the same; after the fracturing pump is stopped, the pump is returned to the original position; the tracer-coated proppant is pumped into the cracks of each fracturing section to make the cracks have a preset opening ... Sampling is carried out at the wellhead of the horizontal well to detect the concentrations of trace element tracers and carbon quantum dot tracers in each fracturing section respectively; according to the detection results of trace element tracers and carbon quantum dot tracers in each fracturing section, two curves of the concentration changes of trace element tracers and carbon quantum dot tracers in the same fracturing section over time are drawn; according to the characteristics of the two curves in the drawn plate, the proppant laying situation and crack closure situation of each fracturing section are determined, so that the proppant laying situation can be accurately inverted, which can effectively provide reliable guidance for the optimization of on-site sand adding parameters.

[0018] Furthermore, by using trace element tracers and carbon quantum dot tracers in combination, a concentration-time variation curve of the two tracers is plotted, and the peak value, peak arrival time, peak value difference, half-width, etc. of the two curves in the chart are analyzed to obtain the laying situation of the proppant in the fracture, thus solving the problems mentioned in the background technology.

[0019] Furthermore, according to the proppant placement conditions in each fracturing stage and the initial fracturing design, the fracturing construction parameters that can achieve the optimal proppant placement effect under certain reservoir conditions can be obtained, and the fracturing transformation effect can be improved by increasing the proppant migration distance in the subsequent fracturing process.

[0020] Furthermore, the fracture closure status can be obtained by analyzing the tracer concentration-time variation curve. When the carbon quantum dot tracer concentration-time variation curve of a certain fracturing section reaches a peak value, the fracture is basically closed. After confirming that the fracture is closed, the degree of proppant reflux is significantly reduced, and on-site staff can adjust the production system to the greatest extent according to production needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart of a fracture diagnosis method for collaborative inversion of proppant placement conditions using multiple types of tracers according to the present invention; Figure 2 A schematic diagram of cracks after the horizontal well hydraulic fracturing construction of the present invention is completed; Figure 3 for Figure 2 The shape of a crack half with poor proppant placement effect; Figure 4 for Figure 3The tracer concentration-time variation chart in the medium fracture; Figure 5 for Figure 2 The shape of the fracture half where a certain proppant has a better effect; Figure 6 for Figure 5 The tracer concentration-time variation chart in the medium fracture.

[0022] 1-wellbore; 2-fracturing fluid containing the first trace element; 3-fracturing fluid containing the second trace element; 4-fracturing fluid containing the third trace element; 5-first carbon quantum dot coated proppant; 6-second carbon quantum dot coated proppant; 7-third carbon quantum dot coated proppant; 8-crack with poor proppant laying effect; 9-first proppant laying height; 10-fluid flow direction; 11-unsupported first crack; 12-first trace element tracer curve; 13-first peak difference; 14 -the first carbon quantum dot tracer curve; 15-the half width of the first carbon quantum dot tracer curve; 16-the half width of the first trace element tracer curve; 17-the crack with better proppant laying effect; 18-the second proppant laying height; 19-the second unsupported crack; 20-the second trace element tracer curve; 21-the second peak difference; 22-the second carbon quantum dot tracer curve; 23-the half width of the second carbon quantum dot tracer curve; 24-the half width of the second trace element tracer curve.

[0023] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0024] In the embodiments of the present invention, the term "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0025] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0026] In the embodiments of the present invention, the term "plurality" refers to two or more than two, and other quantifiers are similar.

[0027] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. However, it can be understood by those skilled in the art that in the embodiments of the present invention, many technical details are proposed in order to enable the reader to better understand the present invention. However, even without these technical details and various changes and modifications based on the following embodiments, the technical scheme claimed in the present invention can also be implemented. The division of the following embodiments is for the convenience of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined and referenced with each other under the premise of no contradiction.

[0028] The present invention provides a fracture diagnosis method for inverting proppant placement conditions using multiple types of tracers, such as Figure 1 shown.

[0029] In step S100, during fracturing construction, trace element tracers are added to each fracturing section of the horizontal well on the ground to form a fracturing fluid with a constant tracer concentration; in the sand-carrying fluid stage, tracer-coated proppants are pumped into the cracks of each fracturing section so that the cracks have a preset opening, wherein the tracer-coated proppants are proppants coated with carbon quantum dot tracers, the carbon quantum dot tracers in different fracturing sections are different, the trace element tracers in different fracturing sections are different, and the volumes of the carbon quantum dot tracers and the trace element tracers in each fracturing section are the same.

[0030] It should be noted that the volume of proppant added to each fracturing stage must be consistent, and the other sand adding parameters may be different. The horizontal well fracturing process includes the pre-fluid stage, the sand-carrying fluid stage and the displacement fluid stage. The trace element tracer is obtained through screening. The carbon quantum dot tracer is soluble in the formation fluid.

[0031] Specifically, the volumes of the carbon quantum dot tracer and the trace element tracer in each fracturing stage are respectively the same, which means that the volume of the carbon quantum dot tracer in each fracturing stage is the same, and the volume of the trace element tracer in each fracturing stage is the same.

[0032] Horizontal well segmented night hunting is a segmented fracturing of horizontal wells in clusters. Other sand adding parameters include proppant particle size combination, injection sequence, sand ratio, etc.

[0033] In addition, the tracer in the present invention is an oilfield indicator that can indicate the fluid injection direction, seepage velocity and carry reservoir information back to the ground. The trace element tracers in different fracturing stages are different, so that the trace element tracers in each fracturing stage are different from each other and do not interfere with each other during analysis and testing. The carbon quantum dot tracers in each fracturing stage are different from each other and do not interfere with each other during analysis and testing. The carbon quantum dot tracers in different fracturing stages are different.

[0034] The trace element of the trace element tracer is generally one of the rare earth elements such as praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. Different trace elements can be selected for the trace element tracers of different fracturing sections. In addition, the screened trace element tracers should have the characteristics of high sensitivity, strong stability, good compatibility, low background concentration, many types, wide sources, and low cost. The formation fluid includes fracturing fluid, oil, gas, water, etc. in the formation. The difference of trace element tracers in each fracturing section is reflected in the difference of elements. Among them, strong stability means that the physical and chemical properties of the tracer do not change under the high temperature and high pressure conditions of the reservoir, good compatibility means that there is no chemical reaction between the tracer and the fracturing fluid and the underground fluid, and low background concentration means that there is no tracer component in the underground fluid or fracturing fluid or the content is extremely low.

[0035] The carbon quantum dot tracer will have special fluorescence under ultraviolet light. The difference in the carbon quantum dot coating on the proppant in each fracturing stage is reflected in the different sizes of the carbon quantum dots, and the carbon quantum dots of different sizes will emit different fluorescence in different regions of the spectrum.

[0036] The dosage of the trace element tracer is calculated by the following formula: ; (1) Wherein, FBR is the fracturing fluid flowback rate, in %; V d Designed fracturing construction liquid scale, m 3 ; MDC wj is the minimum detectable concentration of the tracer under the test conditions, in ppt; e wj is the safety factor for the use of aqueous solution, dimensionless; Q lw The maximum water production of a single well or a single section in the neighboring wells of the target well, in m 3 / day; Day is the number of days required for tracer testing of the target well, in days.

[0037] When Q lw When the water production of the target well is the highest among the wells adjacent to the target well, the safety factor of the water agent is 0 to 10; When Q lw When the water production of a single section of the target well and the adjacent wells is the highest, the safety factor for the use of water agent is 10 to 20.

[0038] The fracturing fluid flowback rate is obtained from the fractured wells with the same or similar fracturing construction scale in the same block.

[0039] At step S200, after the pump is stopped during fracturing, flowback is performed, and samples are taken at the wellhead of the horizontal well to detect the concentrations of trace element tracers and carbon quantum dot tracers in each fracturing section; Specifically, the flowback after the fracturing pump is stopped is a common flowback for all fracturing stages. The trace element tracer is detected by a high-performance mass spectrometer. The carbon quantum dot tracer is detected by an ultraviolet-visible spectrophotometer. The detection results of the trace element tracer and the carbon quantum dot tracer do not interfere with each other. Sampling is performed by a sampling bottle, the capacity of the sampling bottle is not less than 500mL, and the sampling volume during the sampling is not less than 300mL.

[0040] In this embodiment, the accuracy of the high-performance mass spectrometer should be greater than 10 -9 The principle of the UV-Vis spectrophotometer is based on the absorption and scattering characteristics of light. The computer system built into the instrument calculates the absorbance of the sample based on the signal of the photodetector, and further performs quantitative analysis through a standard curve or samples of known concentration.

[0041] It should be noted that before the fracture is closed, the fracturing fluid containing trace element tracers can be backflowed through the channel above the proppant, and the fluid flow resistance of the channel above the proppant is less than the fluid flow resistance of the proppant layer. After the fracture is closed, the channel above the proppant is basically closed, and the backflow of the fracturing fluid containing trace element tracers has basically ended. The fracture closure forms a fluid flow channel with a certain flow conductivity on the proppant layer. During the production process, the formation fluid is produced through the proppant filling layer under the action of pressure difference. During the production process, the carbon quantum dot tracer coated on the proppant is gradually produced under the scouring action of the formation fluid.

[0042] In step S300, two curves of the concentration changes of the trace element tracer and the carbon quantum dot tracer over time in the same fracturing stage are drawn according to the detection results of the trace element tracer and the carbon quantum dot tracer in each fracturing stage.

[0043] It should be noted that the horizontal axis of the tracer concentration-time variation curve in the plotted graph is time, and the vertical axis is the dimensionless concentration of the tracer, where the dimensionless concentration is the ratio of the tracer concentration at a certain moment to the peak concentration during the flowback process.

[0044] Specifically, according to the detection results of tracers in each fracturing section, the tracers of different fracturing sections are distinguished. Each fracturing section should contain a trace element tracer and a carbon quantum dot tracer. The concentration-time variation curves of the trace element tracer and the carbon quantum dot tracer of the first fracturing section at the toe end of the horizontal well are placed on the same coordinate axis and drawn as a plate containing the concentration-time variation curves of the two tracers. According to this method, and in the order from the toe end to the heel end of the horizontal well, a plate is drawn for each fracturing section.

[0045] In step S400, the proppant placement and crack closure conditions of each fracturing stage are determined by analyzing the characteristics of the two curves in the drawn chart.

[0046] It should be noted that the proppant placement includes the proppant placement length and height in the fracture. Fracture closure is caused by the combined effect of the minimum horizontal ground stress and the pressure in the fracture during the post-pressure flowback process. The longer the proppant placement length, the better the placement effect.

[0047] Among them, the characteristics of the curve include the peak value, peak arrival time, half width, etc. The peak value of the curve is the peak value of each of the two tracer concentration-time variation curves. The laying length and height of the proppant in the fracture are obtained by analyzing the peak value, peak difference, half width and other information of the two tracer curves. The peak arrival time of the concentration-time variation curve of the trace element tracer is generally earlier than that of the concentration-time variation curve of the carbon quantum dot tracer. The fracture closure situation is mainly obtained by the peak arrival time of the carbon quantum dot tracer.

[0048] According to the proppant laying conditions of each fracturing stage, the fracturing construction parameters used for reservoir conditions can be obtained, thereby improving the proppant laying effect in the cracks during the subsequent fracturing construction process. The proppant laying conditions include the laying length and height of the proppant in the cracks. The crack closure is caused by the combined effect of the minimum horizontal ground stress and the pressure in the cracks during the post-fracturing backflow process. The longer the proppant laying length, the better the laying effect.

[0049] Figure 2 The schematic diagram of the cracks after the horizontal well fracturing construction of the present invention is illustrated. Figure 2 There are 3 middle fracturing stages. The wellbore 1 is connected with the first fracturing stage, the second fracturing stage, and the third fracturing stage. Among them, the first fracturing stage includes a fracturing fluid 2 containing a first trace element and a first carbon quantum dot coated proppant 5. The second fracturing stage includes a fracturing fluid 3 containing a second trace element and a second carbon quantum dot coated proppant 6. The third fracturing stage includes a fracturing fluid 4 containing a third trace element and a third carbon quantum dot coated proppant 7.

[0050] Figure 3 It indicates that Figure 2 The shape of one half of a crack where the proppant placement effect is poor. Figure 4 for Figure 3 The tracer concentration-time variation chart in the medium fracture.

[0051] Figure 5 It indicates that Figure 2 A crack half morphology with better proppant placement effect. Figure 6 for Figure 5 The tracer concentration-time variation chart in the medium fracture.

[0052] Under the premise that the amount of proppant pumped into the fracture is certain (that is, the amount of proppant pumped into each fracturing section is the same), the length of the proppant laid in the fracture determines the effect of the proppant laying. The longer the proppant laying length, the better the proppant laying effect.

[0053] like Figures 3 to 6 As shown, in the first trace element tracer curve 12 and the second trace element tracer curve 20, the fracture 8 with poor proppant laying effect closes faster, while the fracture 17 with good proppant laying effect closes slower, and the fracturing fluid return rate in the fracture 8 with poor proppant laying effect is greater than that in the fracture 17 with good proppant laying effect. Therefore, the half width 16 of the first trace element tracer curve is smaller than the half width 24 of the second trace element tracer curve.

[0054] For the crack 8 with poor proppant laying effect, under the action of closing stress, the fracturing fluid above the first proppant laying height 9 of the crack 8 with poor proppant laying effect flows back from the crack to the wellbore, and the fracturing fluid at the unsupported first crack 11 is discharged through the proppant filling layer under the action of gravity, and the carbon quantum dot tracer attached to the proppant begins to dissolve in the fracturing fluid and is discharged, so the first carbon quantum dot tracer curve 14 will rise at the beginning of the flowback. When the first carbon quantum dot tracer curve 14 reaches the peak value, it indicates that the crack is completely closed on the carbon quantum dot coated proppant and forms a certain conductivity. The fluid migration channel of the force, after the fracture is closed, the residual fracturing fluid and the formation fluid are produced through the proppant filling layer. Since the second proppant laying height 18 in the fracture 8 with poor proppant laying effect is higher, it can be known from the continuity equation that under the condition of a certain flow rate, the larger the cross-section, the smaller the flow rate through the cross-section. Therefore, at this time, the fluid flow rate in the fracture 8 with poor proppant laying effect is smaller than that in the fracture 17 with good proppant laying effect. Since the dissolution rate of the carbon quantum dot tracer is proportional to the fluid flushing rate, the carbon quantum dots on the proppant in the fracture 8 with poor proppant laying effect dissolve slowly. Therefore Figure 4 The first carbon quantum dot tracer curve half width is greater than 15 Figure 6 The half width of the second carbon quantum dot tracer curve is 23 and Figure 4 The first peak difference is greater than 13 Figure 6 The second peak difference is 21.

[0055] Obviously, the embodiments described above are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, ordinary technicians in this field can make other different forms of changes or modifications without creative work, which should fall within the scope of protection of the present invention.

Claims

1. A fracture diagnosis method for collaborative inversion of proppant placement using multiple types of tracers, characterized in that: include: During fracturing construction, trace element tracers are added to each fracturing section of the horizontal well on the ground to prepare a fracturing fluid with a constant tracer concentration; In the sand-carrying fluid stage, a tracer-coated proppant is pumped into the cracks of each fracturing stage so that the cracks have a preset opening, wherein the tracer-coated proppant is a proppant coated with a carbon quantum dot tracer, the carbon quantum dot tracers in different fracturing stages are different, the trace element tracers in different fracturing stages are different, and the volumes of the carbon quantum dot tracers and the trace element tracers in each fracturing stage are the same; After the pump is stopped during fracturing, flowback is performed and samples are taken at the wellhead of the horizontal well to detect the concentrations of trace element tracers and carbon quantum dot tracers in each fracturing section. According to the detection results of trace element tracers and carbon quantum dot tracers in each fracturing stage, two curves of the concentration change of trace element tracers and carbon quantum dot tracers in the same fracturing stage over time are drawn; According to the characteristics of the two curves in the drawn plate, the proppant placement and crack closure conditions of each fracturing stage are determined.

2. The fracture diagnosis method for collaborative inversion of proppant placement conditions using multiple types of tracers as claimed in claim 1, characterized in that: The analysis based on the characteristics of the two curves in the drawn plate to determine the proppant laying conditions and crack closure conditions of each fracturing stage includes: According to the half width of the trace element tracer curve, the cracks with poor proppant laying effect and the cracks with good proppant laying effect, as well as the crack closure status, are determined; According to the half width of the carbon quantum dot tracer curve, the cracks with poor proppant laying effect and the cracks with good proppant laying effect, as well as the crack closure status, are determined.

3. The fracture diagnosis method for cooperative inversion of proppant placement conditions using multiple types of tracers as claimed in claim 2, characterized in that: The method of determining cracks with poor proppant laying effect and cracks with good proppant laying effect, as well as crack closure conditions, based on the half width of the trace element tracer curve includes: In the trace element tracer curve, the half width of the crack with poor proppant laying effect is smaller than the half width of the crack with good proppant laying effect; The cracks with poor proppant placement closed faster, while the cracks with good proppant placement closed slower; The fracturing fluid flowback rate in the fractures with poor proppant laying effect is greater than that in the fractures with good proppant laying effect.

4. The fracture diagnosis method for collaborative inversion of proppant placement conditions using multiple types of tracers as claimed in claim 2, characterized in that: The method of determining cracks with poor proppant laying effect and cracks with good proppant laying effect, as well as crack closure conditions, based on the half width of the carbon quantum dot tracer curve includes: In the carbon quantum dot tracer curve, the half width of the crack with poor proppant laying effect is greater than the half width of the crack with good proppant laying effect, and the peak difference of the crack with poor proppant laying effect is greater than the peak difference of the crack with good proppant laying effect; The carbon quantum dot tracer curve will rise at the beginning of flowback. When the carbon quantum dot tracer curve reaches its peak, it indicates that the fracture is completely closed on the carbon quantum dot coated proppant and a fluid migration channel with flow conductivity is formed. After the fracture is closed, the residual fracturing fluid and formation fluid are produced through the proppant filling layer. Since the proppant laying height in the fracture with poor proppant laying effect is higher, it can be seen from the continuity equation that under the condition of a certain flow rate, the larger the cross-section, the smaller the flow rate through the cross-section.

5. The fracture diagnosis method for collaborative inversion of proppant placement conditions using multiple types of tracers as claimed in claim 1, characterized in that: The carbon quantum dot tracers in different fracturing stages are different, which is reflected in the different sizes of the carbon quantum dots.

6. The fracture diagnosis method for cooperative inversion of proppant placement conditions using multiple types of tracers as claimed in claim 1, characterized in that: The trace element tracers in different fracturing stages are different, which is reflected in the different trace elements.

7. The fracture diagnosis method for cooperative inversion of proppant placement conditions using multiple types of tracers as claimed in claim 6, characterized in that: The trace element of the trace element tracer is one of the rare earth elements of praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

8. The fracture diagnosis method for cooperative inversion of proppant placement conditions using multiple types of tracers as claimed in claim 1, characterized in that: In the step of adding trace element tracers to each fracturing section of the horizontal well on the ground during fracturing construction to prepare a fracturing fluid with a constant tracer concentration; and pumping tracer-coated proppant into the cracks of each fracturing section during the sand-carrying fluid stage so that the cracks have a preset opening, the amount of trace element tracers is calculated by the following formula: ；(1) Wherein, FBR is the fracturing fluid flowback rate, in %; V d Designed fracturing construction liquid scale, m 3 ; MDC wj is the minimum detectable concentration of the tracer under the test conditions, in ppt; e wj is the safety factor for the use of aqueous solution, dimensionless; Q lw The maximum water production of a single well or a single section in the neighboring wells of the target well, in m 3 / day; Day is the number of days required for tracer testing of the target well, in day; When Q lw When the water production of the target well is the highest among the wells adjacent to the target well, the safety factor of the water agent is 0 to 10; When Q lw When the water production of a single section of the target well and the adjacent wells is the highest, the safety factor for the use of water agent is 10 to 20.

9. The fracture diagnosis method for collaborative inversion of proppant placement conditions using multiple types of tracers as claimed in claim 1, characterized in that: In the step of performing flowback after stopping the pump for fracturing, sampling at the wellhead of the horizontal well, and detecting the concentrations of trace element tracers and carbon quantum dot tracers in each fracturing section, the trace element tracers are detected by a high-performance mass spectrometer; The carbon quantum dot tracers were detected by UV-visible spectrophotometer.

10. The fracture diagnosis method for cooperative inversion of proppant placement conditions using multiple types of tracers as claimed in claim 1, characterized in that: In the step of drawing two curves of the trace element tracer and carbon quantum dot tracer concentration changes over time in the same fracturing stage according to the detection results of the trace element tracer and the carbon quantum dot tracer in each fracturing stage, the horizontal axis of the tracer concentration-time change curve in the drawn plate is time, and the vertical axis is the dimensionless concentration of the tracer; The dimensionless concentration is the ratio of the tracer concentration at a certain moment to the peak concentration during the flowback process.

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