CN114718513A - Method and device for estimating gas production rate of coal bed gas - Google Patents
Method and device for estimating gas production rate of coal bed gas Download PDFInfo
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Abstract
The application discloses a method and a device for estimating gas production rate of coal bed gas, and relates to the technical field of coal bed gas exploitation. According to the method, computer equipment directly determines the average filtration loss of the fracturing fluid according to the total amount of the obtained fracturing fluid, the flow-back amount of the fracturing fluid and the total duration of the fracturing process, and determines the gas production rate of the coal bed gas according to the average filtration loss. The method provided by the application does not need to acquire more coal bed parameters, is simple in calculation process, and is high in efficiency of determining the gas production rate of the coal bed gas.
Description
Technical Field
The application relates to the technical field of coal bed gas exploitation, in particular to a method and a device for estimating gas production rate of coal bed gas.
Background
Coal bed gas refers to hydrocarbon gas stored in coal seams and belongs to unconventional natural gas. The coal bed gas exploitation not only can greatly reduce the gas accident rate of the coal mine and reduce the gas in the mine exhaust greenhouse, but also can be used as clean energy to generate great economic benefit.
In the related art, when coal bed gas in a coal bed gas well is exploited, the coal bed gas well can be fractured so as to improve the gas production rate of the coal bed gas. After the coal bed gas well is fractured, the gas yield of the coal bed gas can be influenced by the coal bed physical property and the geometric parameters of the cracks in the coal bed gas well, so that the coal bed parameters of the coal bed gas well are required to be substituted into the calculation model before the coal bed gas well is fractured so as to calculate the coal bed physical property and the geometric parameters of the cracks in the coal bed gas well, and the gas yield of the coal bed gas is estimated. Wherein, the coal seam parameter includes: the field monitoring parameters of the coal bed gas well, the ground stress in the coal bed gas well, the petrological data and the experimental simulation data.
However, the methods in the related art need to acquire more coal bed parameters, and the calculation process of the calculation model is complex, so that the efficiency of estimating the gas production rate of the coal bed gas is low.
Disclosure of Invention
The application provides a method and a device for estimating the gas production rate of coal bed gas, which can solve the problem of low efficiency of estimating the gas production rate of the coal bed gas in the related technology. The technical scheme is as follows:
on one hand, the method for estimating the gas production rate of the coal bed gas is applied to computer equipment, and comprises the following steps:
acquiring the total amount of fracturing fluid and the return displacement of the fracturing fluid used in the fracturing process;
determining the total fluid loss of the fracturing fluid in the fracturing process based on the total amount of the fracturing fluid and the flow-back amount of the fracturing fluid;
acquiring the total duration of the fracturing process;
determining an average fluid loss of the fracturing fluid based on the total fluid loss of the fracturing fluid and the total duration;
and estimating the gas production rate of the coal bed gas based on the average filtration loss, wherein the gas production rate of the coal bed gas is inversely related to the average filtration loss.
Optionally, the fracturing process includes: a fracture extension stage and a pressure drop stage; the method further comprises the following steps:
obtaining a first time length of the fracture extension stage and a second time length of the pressure drop stage;
acquiring a first slope of a first equation of bottom hole pressure and time of the coal-bed gas well in the fracture extension stage;
acquiring a second slope of a second equation of the bottom hole pressure and the time of the coal-bed gas well in the pressure drop stage;
determining a first fluid loss of the fracture extension stage and a second fluid loss of the pressure drop stage based on the first time period, the second time period, a first slope, the second slope, and the total fluid loss of the fracturing fluid;
and estimating the gas production rate of the coal bed gas based on the first filtration loss and the second filtration loss, wherein the gas production rate of the coal bed gas is in negative correlation with the first filtration loss and the second filtration loss.
Optionally, the obtaining a first slope of a first equation of bottom hole pressure and time of the coal-bed gas well in the fracture extension stage includes:
acquiring the average extension pressure of the fracturing extension stage and the original coal bed pressure of the coal bed gas well;
determining the first slope based on the average extension pressure, the original coal bed pressure, and the first time period, wherein the first slope is positively correlated with the average extension pressure and negatively correlated with the original coal bed pressure and the first time period;
the obtaining a second slope of a second equation of bottom hole pressure and time of the coal-bed gas well in the drawdown phase comprises:
obtaining the pump stopping pressure and the back-flow pressure of the pressure drop stage;
determining the second slope based on the pump deactivation pressure, the return pressure, and the second duration, wherein the second slope is positively correlated with the pump deactivation pressure and negatively correlated with the return pressure and the second duration.
Optionally, the first slope m1 satisfies:
the second slope m2 satisfies:
wherein, PEIs said mean extension pressure, PiΔ T1 is the first time duration, P, for the original coal seam pressuresFor said pump-stop pressure, PhAt 2 is the second duration for the return pressure.
Optionally, the method further includes:
acquiring the well opening pressure of the coal bed gas well;
determining a flowback closure coefficient based on the fracturing fluid flowback volume, the flowback pressure and the well opening pressure, wherein the flowback closure coefficient is positively correlated with the fracturing fluid flowback volume and the well opening pressure and negatively correlated with the flowback pressure;
determining a fracture closure coefficient based on the total amount of fracturing fluid, the average extension pressure, and the original coal bed pressure, wherein the fracture closure coefficient is positively correlated with the total amount of fracturing fluid and the original coal bed pressure and negatively correlated with the average extension pressure;
and estimating the gas production of the coal bed gas based on the flowback close coefficient and the fracturing close coefficient, wherein the gas production of the coal bed gas is in negative correlation with the flowback close coefficient and the fracturing close coefficient.
Optionally, the return closing coefficient n1 satisfies:
the fracture closure coefficient n2 satisfies:
wherein, VAFor the return displacement of the fracturing fluid, PhIs the back pressure, P0For said well opening pressure, VTIs the total amount of the fracturing fluid, PEIs said mean extension pressure, PiIs the original coal seam pressure.
Optionally, the method further includes:
determining the flow back rate of the fracturing fluid based on the total amount of the fracturing fluid and the flow back amount of the fracturing fluid;
and estimating the gas production rate of the coal bed gas based on the flowback rate of the fracturing fluid, wherein the gas production rate of the coal bed gas is inversely related to the flowback rate.
On the other hand, a gas production estimation device of coal bed gas is provided, is applied to computer equipment, the device includes:
the first acquisition module is used for acquiring the total amount of fracturing fluid and the return displacement of the fracturing fluid used in the fracturing process;
the first determination module is used for determining the total fluid loss of the fracturing fluid in the fracturing process based on the total amount of the fracturing fluid and the flow back amount of the fracturing fluid;
the second acquisition module is used for acquiring the total duration of the fracturing process;
a second determination module, configured to determine an average fluid loss of the fracturing fluid based on the total fluid loss of the fracturing fluid and the total duration;
and the third determination module is used for estimating the gas production rate of the coal bed gas based on the average filter loss, wherein the gas production rate of the coal bed gas is inversely related to the average filter loss.
In yet another aspect, a computer device is provided, the computer device comprising: a processor and a memory for storing instructions for execution by the processor, the processor being configured to execute the instructions stored in the memory to implement the method of the above aspect.
In another aspect, a system for estimating gas production of coal bed gas is provided, where the system for estimating gas production includes: one or more acquisition devices, and a computer device as described in the above aspects;
the one or more acquisition devices are used for acquiring parameter information required by the computer device and sending the parameter information to the computer device.
In yet another aspect, a computer-readable storage medium having instructions stored therein is provided, the instructions being loaded and executed by a processor to implement a method as described in the above aspect.
The beneficial effect that technical scheme that this application provided brought includes at least:
the application provides a method and a device for estimating the gas production of coal bed gas. The method provided by the application does not need to acquire more coal bed parameters, is simple in calculation process, and is high in efficiency of determining the gas production rate of the coal bed gas.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a computer device according to an embodiment of the present disclosure;
FIG. 2 is a flowchart of a method for estimating gas production of coal bed methane according to an embodiment of the present disclosure;
FIG. 3 is a graph of pressure versus time provided by an embodiment of the present application;
FIG. 4 is a schematic illustration of a fracture in a hydraulic fracture of a coal bed gas well as provided by an embodiment of the present application;
FIG. 5 is a graph illustrating the relationship between the average extension pressure and the fluid loss wave and radius of a fluid loss zone of a fracturing fluid during an extension stage of fracturing, according to an embodiment of the present disclosure;
fig. 6 is a schematic diagram illustrating a relationship between a flowback pressure and a fluid loss wave and a radius of a fracturing fluid loss area in a pressure drop stage according to an embodiment of the present disclosure;
FIG. 7 is a schematic diagram of the relationship between the pressure during open-hole flowback and the fluid loss wave and radius of a fracturing fluid loss zone during a drawdown phase according to an embodiment of the present disclosure;
FIG. 8 is a flowchart of another method for estimating gas production of coal bed methane according to an embodiment of the present application;
FIG. 9 is a flow chart for determining a first slope according to an embodiment of the present disclosure;
FIG. 10 is a graph illustrating a relationship between a flow-back pressure and a dimensionless time according to an embodiment of the present disclosure;
FIG. 11 is a flow chart for determining a second slope according to an embodiment of the present disclosure;
fig. 12 is a schematic structural diagram of a gas production estimation device for coal bed methane according to an embodiment of the present application;
FIG. 13 is a schematic structural diagram of another coalbed methane gas production estimation device provided in the embodiment of the present application;
fig. 14 is a schematic structural diagram of another computer device provided in the embodiment of the present application.
Detailed Description
To make the objects, technical solutions and advantages of the present application more clear, embodiments of the present application will be described in further detail below with reference to the accompanying drawings.
Coal rock in the coal-bed gas well has the characteristics of small Young modulus, large Poisson ratio, more natural cracks, strong anisotropy and complex seam forming. Hydraulic fracturing is currently the most prevalent means of producing coal seam gas. In addition, hydraulic fracturing is also one of the key means for implementing large-scale efficient development of coal bed gas and improving the gas production rate of the coal bed gas. In the process of fracturing a coal bed gas well, the problems of over-high injection pressure, complex cracks, sand blockage, coal dust blockage and the like easily occur. After hydraulic fracturing is carried out on the coal-bed gas well, the gas production rate of the coal-bed gas in the coal-bed gas well can be estimated, so that the productivity of the coal-bed gas well in the later period is ensured.
In the related technology, the geometrical parameters of the coal bed physical property and the cracks in the coal bed gas well are main factors influencing the gas production rate of the coal bed gas, and are also the basis for calculating the gas production rate of the coal bed gas after hydraulic fracturing and evaluating the economy of the coal bed gas well. At present, fracture calculation models used in mines mainly include two-dimensional models, three-dimensional simulation models, three-dimensional models and the like. Wherein, the two-dimensional model can be PKN (perkins-kernel), or KGD (khrtisaninovich-greensmia-de klerk), and the three-dimensional model can be P3D. Besides on-site fracturing data, the crack calculation models also need corresponding ground stress, petrology data, experimental simulation data and other coal bed parameters in the coal bed gas well, and the model calculation process is complex, so that the efficiency of estimating the gas yield of the coal bed gas is low.
Fig. 1 is a schematic structural diagram of a computer device according to an embodiment of the present application. Referring to fig. 1, the computer device 01 may be a server, a server cluster composed of several servers, or a cloud computing service center. Still alternatively, the computer device 01 may be a computer, a tablet computer, a multimedia player, a laptop portable computer, a desktop computer, or the like.
The method for estimating the gas production rate of the coal bed gas can solve the problem that the efficiency of estimating the gas production rate of the coal bed gas in the related technology is low. The method for estimating gas production of coal bed methane can be applied to the computer device 01 shown in fig. 1, and as can be seen with reference to fig. 2, the method can include:
In an embodiment of the present application, a process of hydraulic fracturing comprises: testing pressure, crack formation, crack extension, filling of fracturing fluid, pump stopping and pressure reduction (crack closure) and flowback (crack further closure). In the process of performing hydraulic fracturing on the coal-bed gas well, one or more acquisition devices can be adopted to acquire various fractured data and send the various data to computer equipment. Wherein the one or more acquisition devices can establish a communication connection with the computer device through wires or wirelessly.
Optionally, the one or more acquisition devices may include: and (4) flow collection equipment. In the process of performing hydraulic fracturing on the coal-bed gas well, flow acquisition equipment can be adopted to acquire the total amount of fracturing fluid and the return displacement of the fracturing fluid, and the total amount of the fracturing fluid and the return displacement of the fracturing fluid are sent to computer equipment. Therefore, the computer equipment can obtain the total amount of the fracturing fluid and the return displacement of the fracturing fluid used in the fracturing process.
And 102, determining the total fluid loss of the fracturing fluid in the fracturing process based on the total amount of the fracturing fluid and the flow-back amount of the fracturing fluid.
In this embodiment, the computer device may determine the total fluid loss of the fracturing fluid in the fracturing process based on the total amount of the fracturing fluid and the flow-back amount of the fracturing fluid. Optionally, the total fluid loss of the fracturing fluid may be equal to the difference between the total amount of the fracturing fluid and the flow back of the fracturing fluid.
And 103, acquiring the total duration of the fracturing process.
In an embodiment of the present application, the one or more acquisition devices may further include: duration collection equipment. In the process of performing hydraulic fracturing on the coal-bed gas well, the total duration of the hydraulic fracturing process can be acquired by adopting the duration acquisition equipment, and the total duration is sent to the computer equipment. Therefore, the computer equipment can acquire the total duration of the fracturing process.
And 104, determining the average fluid loss of the fracturing fluid based on the total fluid loss and the total time length of the fracturing fluid.
In this embodiment, the computer device may determine the average fluid loss of the fracturing fluid based on the total fluid loss of the fracturing fluid obtained in step 101 and the total duration obtained in step 103.
Alternatively, the average fluid loss of the fracturing fluid may be positively correlated to the total fluid loss of the fracturing fluid and negatively correlated to the total duration. For example, the average fluid loss of the fracturing fluid may be equal to the total fluid loss of the fracturing fluid divided by the total length of time.
And 105, estimating the gas production rate of the coal bed gas based on the average filtration loss.
In the embodiments of the present application, the gas production rate of the coal bed gas is generally related to the original coal bed pressure of the coal bed gas well and the development of fractures in the coal bed gas well. For example, the greater the original coal bed pressure of a coal bed gas well, the greater the difficulty of creating fractures during hydraulic fracturing, which may result in a lower number of fractures in the coal bed gas well and a greater gas production rate of the coal bed gas. The lower the original coal bed pressure of the coal bed gas well, the less difficult the fracture formation in the hydraulic fracturing process, and the more fractures in the coal bed gas well may be caused, and the lower the gas production rate of the coal bed gas.
And the original coal bed pressure of the coal bed gas well and the development condition of the crack are related to the average filtration loss. For example, the larger the average fluid loss, the lower the original coal bed pressure of the coal bed gas well, and the greater the number of fractures in the coal bed gas well. The smaller the average filtration loss is, the larger the original coal bed fracturing of the coal bed gas well is, and the smaller the number of cracks in the coal bed gas well is.
Therefore, the computer equipment can estimate the gas production rate of the coal bed gas based on the average filtration loss of the fracturing fluid, and the gas production rate of the coal bed gas is inversely related to the average filtration loss. That is, the larger the average filtration loss is, the smaller the gas yield of the coal bed gas is; the smaller the average fluid loss, the greater the gas production of the coal bed gas.
In the embodiment of the application, after the gas production rate of the coal bed gas is estimated based on the average filtration loss, the fracturing effect on the hydraulic fracturing of the coal bed gas well can be determined based on the estimated gas production rate. If the estimated gas production rate is larger, the fracturing effect of the hydraulic fracturing of the coal-bed gas well can be determined to be better, and under the condition, the coal-bed gas well can be subjected to well opening production. If the estimated gas production rate is smaller, the fracturing effect of the hydraulic fracturing of the coal-bed gas well can be determined to be poorer, and under the condition, the hydraulic fracturing can be performed on the coal-bed gas well again.
In summary, the embodiment of the present application provides a method for estimating gas production of coal bed gas, in which a computer device determines an average fluid loss of a fracturing fluid directly according to an obtained total amount of the fracturing fluid, a flow back amount of the fracturing fluid and a total duration of a fracturing process, and determines the gas production of the coal bed gas according to the average fluid loss. The method provided by the embodiment of the application does not need to acquire more coal bed parameters, is simple in calculation process, and is high in efficiency of determining the gas production rate of the coal bed gas.
In the embodiment of the application, the relationship between each pressure and the time t in the process of hydraulic fracturing of the coal-bed gas well is shown in fig. 3. FIG. 4 is a schematic illustration of a fracture in a coal bed gas well being hydraulically fractured according to an embodiment of the present application. Referring to fig. 3 and 4, before hydraulic fracturing is performed on the coal-bed gas well, the bottom hole pressure of the coal-bed gas well is the original coal-bed pressure Pi。
Referring to fig. 3, in the process of hydraulic fracturing of the coal-bed gas well, a fracturing fluid may be injected into the coal-bed gas well first, so that the pressure in the coal-bed gas well is increased continuously. Bottom hole pressure in coal bed gas well reaches coal bed fracture pressure PFThen, the coal seam in the coal seam gas well is cracked. Then, the fracturing fluid can continuously extend in the fracture, in the fracture extending stage, the volume of the fracture can be larger, and the bottom hole pressure in the coal-bed gas well can be larger and kept constant and is the average extending pressure PE. After the pump is stopped, the bottom hole pressure in the coal-bed gas well can be the pump-stopping pressure PsAnd elastic closure of the crack occurs. Then, as the fracturing fluid can be partially filtered from the fracture, the formation linear flow is generated, and the bottom hole pressure in the coal-bed gas well can be gradually reduced to be the flowback pressure Ph. After that, when the well is opened and flowback is carried out, the fracturing fluid can be partially discharged through the shaft, the crack can be further elastically closed, the fracturing fluid in the crack flows linearly, the filtration effect of the coal bed is weakened, and the bottom hole pressure in the coal bed gas well is the well opening pressure P0。
Referring to fig. 4, it can be seen that the fluid loss wave and radius of the fluid loss zone of the fracturing fluid is smaller, R, during the pressure drop extension phasee1. After the pump is stopped, the fluid loss wave and the radius of the fluid loss area of the fracturing fluid are larger and are Re2。
FIG. 5 shows the fluid loss wave and radius R of a fluid loss zone of a fracturing fluid during an extended stage of a fracture and an extended stage of a mean extension pressure according to an embodiment of the present applicatione1Schematic diagram of the relationship of (1). Referring to FIG. 5, in the fracture extension stage, the average extension pressure PECan be matched with the filtration loss wave and the radius Re1A negative correlation. Fig. 6 shows a fluid loss wave and a radius R of a fracturing fluid loss area in a flow-back pressure and pressure drop stage according to an embodiment of the present disclosuree2Schematic diagram of the relationship of (1). Referring to fig. 6, during the pressure drop phase, the flow-back pressure PhCan be matched with the filtration loss wave and the radius Re2A negative correlation. FIG. 7 shows the fluid loss wave and radius R of a fracturing fluid loss zone during the pressure and pressure drop phases of a well-opening flowback according to an embodiment of the present disclosuree2Schematic diagram of the relationship of (1). Referring to FIG. 7, the well opening pressure P0Can be matched with the filtration loss wave and the radius Re2A negative correlation. In fig. 5 to 7, the abscissa represents the fluid loss and the radius R, and the ordinate represents the pressure P.
It should be noted that the process of fracturing and fracture-making a coal-bed gas well can be summarized as the problem of unstable seepage of an infinite flow guide vertical fracture. The method provided by the embodiment of the application is adopted to estimate the gas production rate of the coal bed gas, and the following conditions can be met: (1) assuming that a vertical crack is pressed on a homogeneous coal seam, the crack is symmetrical to a shaft, and the length of a half seam is xf. (2) The pressure in the whole crack is the same and is the extension pressure PEAnd the influence of the permeability of the fracture is not considered in the fracturing process. (3) The width of the fracture is small and remains constant during the fracturing process. (4) In the process of making the fracture, the fracturing fluid generates linear flow loss along the fracture. (5) The fracture area remained constant after the pump was stopped and fracture closure was manifested as a decrease in fracture width.
Fig. 8 is a flowchart of another method for estimating gas production of coal bed methane according to an embodiment of the present application. The method may be applied to the computer device 01 shown in fig. 1, and as can be seen with reference to fig. 8, the method may include:
In an embodiment of the present application, a process of hydraulic fracturing comprises: pressure testing, crack formation, crack extension, filling of fracturing fluid, pump stopping and pressure reduction (crack closure) and flowback (crack further closure). In the process of performing hydraulic fracturing on the coal-bed gas well, one or more acquisition devices can be adopted to acquire various fractured data and send the various data to computer equipment. Wherein the one or more acquisition devices can establish a communication connection with the computer device through wires or wirelessly.
Optionally, the one or more acquisition devices may include: and (4) flow collection equipment. In the process of performing hydraulic fracturing on the coal-bed gas well, the total amount of fracturing fluid and the return displacement of the fracturing fluid can be obtained by adopting flow acquisition equipment, and the total amount of the fracturing fluid and the return displacement of the fracturing fluid are sent to computer equipment. Therefore, the computer equipment can obtain the total amount of the fracturing fluid and the return displacement of the fracturing fluid used in the fracturing process.
And 202, determining the total fluid loss of the fracturing fluid in the fracturing process based on the total amount of the fracturing fluid and the flow-back amount of the fracturing fluid.
In this embodiment, the computer device may determine the total fluid loss of the fracturing fluid in the fracturing process based on the total amount of the fracturing fluid and the flow-back amount of the fracturing fluid. Optionally, the total fluid loss V of the fracturing fluidLCan satisfy the following conditions:
VL＝VT-VAformula (1)
In the above formula (1), VTTotal amount of fracturing fluid, VAThe flow rate of the fracturing fluid is returned. That is, the total fluid loss of the fracturing fluid may be equal to the difference between the total amount of fracturing fluid and the flow back of the fracturing fluid.
And step 203, acquiring the total duration of the fracturing process.
In an embodiment of the present application, the one or more acquisition devices may further include: duration collection equipment. In the process of performing hydraulic fracturing on the coal-bed gas well, the total duration of the hydraulic fracturing process can be acquired by adopting the duration acquisition equipment, and the total duration is sent to the computer equipment. Therefore, the computer equipment can obtain the total duration of the fracturing process.
Wherein the fracturing process may include: a fracture extension phase and a pressure drop phase. The total duration of the fracturing process may be equal to the sum of the first duration of the fracture extension stage and the second duration of the pressure drop stage.
And step 204, determining the average fluid loss of the fracturing fluid based on the total fluid loss and the total time length of the fracturing fluid.
In this embodiment, the computer device may determine the average fluid loss of the fracturing fluid based on the total fluid loss of the fracturing fluid obtained in step 201 and the total duration obtained in step 203.
Alternatively, the average fluid loss of the fracturing fluid may be positively correlated to the total fluid loss of the fracturing fluid and negatively correlated to the total duration. Such as the average fluid loss q of the fracturing fluidLCan satisfy the following conditions:
qL＝VLformula/t (2)
In the above formula (2), t is the total duration. That is, the average fluid loss of the fracturing fluid is equal to the total fluid loss of the fracturing fluid divided by the total length of time.
And step 205, estimating the gas production rate of the coal bed gas based on the average filtration loss.
In the embodiments of the present application, the gas production rate of the coal bed gas is generally related to the original coal bed pressure of the coal bed gas well and the development of fractures in the coal bed gas well. For example, the greater the original coal bed pressure of a coal bed gas well, the greater the difficulty of creating fractures during hydraulic fracturing, which may result in a lower number of fractures in the coal bed gas well and a greater gas production rate of the coal bed gas. The smaller the original coal bed pressure of the coal bed gas well is, the smaller the difficulty of making the fracture in the hydraulic fracturing process is, and the more the number of the fractures in the coal bed gas well is, the smaller the gas production rate of the coal bed gas is.
And the original coal bed pressure of the coal bed gas well and the development condition of the crack are related to the average filtration loss. For example, the larger the average fluid loss, the lower the original coal bed pressure of the coal bed gas well, and the greater the number of fractures in the coal bed gas well. The smaller the average filtration loss is, the larger the original coal bed fracturing of the coal bed gas well is, and the smaller the number of fractures in the coal bed gas well is.
Therefore, the computer equipment can estimate the gas production rate of the coal bed gas based on the average filtration loss of the fracturing fluid, and the gas production rate of the coal bed gas is inversely related to the average filtration loss. That is, the larger the average filtration loss is, the smaller the gas yield of the coal bed gas is; the smaller the average fluid loss, the greater the gas production of the coal bed gas.
And step 206, acquiring a first time length of the fracture extension stage and a second time length of the pressure drop stage.
In order to ensure the accuracy of the estimated gas production rate of the coal bed gas, the estimated gas production rate of the coal bed gas can be estimated through other parameters besides the estimation based on the average filtration loss. For example, the computer device may determine a first fluid loss during the fracture extension phase and a second fluid loss during the pressure drop phase, respectively, and estimate a gas production rate of the coal bed gas based on the first and second fluid losses.
In this embodiment, the duration acquiring device may further acquire the first duration of the fracture extension stage and the second duration of the pressure drop stage, respectively, when acquiring the total duration of the fracturing process of the hydraulic fracture. And, the duration collection device can also send the first duration and the second duration to the computer device. Therefore, the computer equipment can obtain the first duration and the second duration.
And step 207, acquiring a first slope of a first equation of bottom hole pressure and time of the coal-bed gas well in a fracture extension stage.
In the embodiment of the application, a first equation of the bottom hole pressure of the coal bed gas well in the fracturing extending stage and the time can be stored in the computer equipment in advance. Thereafter, the computer device may determine a first slope of the first equation based on the first equation.
Optionally, the first equation may satisfy:
in the above formula (3), PEThe average extension pressure is expressed in megapascals (MPa). PiIs the original coal bed pressure in MPa. q. q.sL1Is the first fluid loss in liters per minute (L/min). x is the number offThe length of the half seam of the crack in the coal-bed gas well. μ is viscosity in units of millipascal-seconds (mPa · s). K is reservoir permeability in units of 10-3 square microns (mum)2)。CtIs the coal rock comprehensive compression factor with the unit of MPa-1。
Is porosity. Δ T1 is a first duration.
As can be seen from the above equation (3), the first slope m1 of the first equation satisfies:
in the above equation (4), the first slope m1 has a unit of megapascals per root per minute
In the embodiment of the present application, referring to fig. 9, this step 207 may include:
In an embodiment of the present application, the one or more acquisition devices may further include: and (4) pressure acquisition equipment. Prior to hydraulic fracturing of a coal-bed gas well, pressure acquisition equipment may be employed to acquire the original coal-bed pressure of the coal-bed gas well. And in the process of performing hydraulic fracturing on the coal-bed gas well, the average extension pressure in the fracturing extension stage is acquired by adopting pressure acquisition equipment. The pressure acquisition device may then transmit the acquired average extension pressure and the raw coal seam pressure to the computer device. Therefore, the computer equipment can acquire the average extension pressure and the original coal bed pressure.
Referring to equation (4) above, the first slope may be related to the average extension pressure, the original coal seam pressure, and the first time period. Thus, the computer device may determine the first slope based on the average extension pressure and the original coal seam pressure obtained at step 2071, and the first duration obtained at step 206.
And 208, acquiring a second slope of a second equation of the bottom hole pressure and the time of the coal-bed gas well in the pressure drop stage.
In the embodiment of the application, a second equation of the bottom hole pressure and the time of the coal bed gas well in the pressure drop stage can be stored in the computer device in advance. Thereafter, the computer device may determine a second slope of the second equation based on the second equation.
Optionally, the second equation may satisfy:
in the above formula (5), Ph(T2) is the drainback pressure in MPa as a function of the second duration. PsThe unit is MPa for the pump-off pressure. q. q.sL2Is the second filtrate loss in L/min. At 2 is the second duration.
As can be seen from the above equation (5), the second slope m2 of the second equation satisfies:
in the above formula (6), PhIs the flow back pressure in MPa. As can be seen from the above equation (6), the second slope m2 may be a fixed value during the pressure drop phase. Also, referring to fig. 10, the flowback pressures P of the different coal bed gas wells (first to seventh)hRelative to dimensionless time
The change curve of (2) is substantially a straight line, and the slope of the curve (second slope m2) is substantially a fixed value.
In the embodiment of the present application, referring to fig. 11, this step 207 may include:
and 2081, obtaining the pump stopping pressure and the return pressure in the pressure drop stage.
In the embodiment of the application, in the process of performing hydraulic fracturing on the coal-bed gas well, the pump stopping pressure and the flow-back pressure in the pressure drop stage are acquired by adopting the pressure acquisition equipment. The pressure collection device may then send the collected pump shut-down pressure and the return pressure to the computer device. Therefore, the computer equipment can obtain the pump stopping pressure and the back flow pressure.
Referring to equation (6) above, it can be seen that the second slope can be related to the pump deactivation pressure, the return pressure, and the second duration. Thus, the computer device may determine the second slope based on the pump stop pressure and the return pressure obtained in step 2081, and the second duration obtained in step 206.
In the embodiment of the application, the first fluid loss is the average fluid loss of the fracture extension stage, and the second fluid loss is the average fluid loss of the pressure drop stage. Whereby the total fluid loss V of the fracturing fluidLCan satisfy the following conditions:
VL＝qL1×ΔT1+qL2formula (7) of X.DELTA.T 2
According to the formula (7), the total fluid loss V of the fracturing fluidLMay be equal to the fluid loss q in the fracture extension stageL1X Δ T1 and fluid loss q during pressure dropL2The sum of X.DELTA.T 2.
And, the ratio of the first slope to the second slope may be equal to the ratio of the first fluid loss to the second fluid loss, that is, the following is satisfied:
m1/m2＝qL1/qL2formula (8)
In the above formula (7) and the above formula (8), the total fluid loss V of the fracturing fluidLThe first duration Δ T1, the second duration Δ T2, the first slope m1, and the second slope m2 are known quantities. That is, the above equation (7) and the above equation (8) may constitute with respect to the first fluid loss qL1And a second fluid loss qL2A system of equations of a first order of two, the computer device may calculate the first fluid loss and the second fluid loss in conjunction with equation (7) and equation (8).
And step 210, estimating the gas production rate of the coal bed gas based on the first filtration loss and the second filtration loss.
In this embodiment, the computer device may estimate the gas production rate of the coal bed gas based on the average fluid loss of the fracturing fluid, the first fluid loss of the fracture extension stage, and the second fluid loss of the pressure drop stage. Therefore, the accuracy of the estimated gas production rate of the coal bed gas can be improved.
Optionally, the gas production rate of the coal bed gas may be inversely related to both the first fluid loss and the second fluid loss.
And step 211, acquiring the well opening pressure of the coal-bed gas well.
In the embodiment of the application, when the fracturing fluid is drained back after the coal-bed gas well is subjected to hydraulic fracturing, the well opening pressure of the coal-bed gas well is collected by adopting fracturing collection equipment. The pressure acquisition device may then transmit the acquired well opening pressure to the computer device. Therefore, the computer equipment can obtain the well opening pressure.
In an embodiment of the present application, the computer device may determine the flowback closure factor based on the flowback volume of the fracturing fluid obtained in step 201, the flowback pressure obtained in step 2081, and the well opening pressure obtained in step 211. Wherein the flow-back closure coefficient is positively correlated with the flow-back volume of the fracturing fluid and the well opening pressure and negatively correlated with the flow-back pressure.
Optionally, the flow-back closing coefficient n1 satisfies:
in the above formula (9), P0Is the well opening pressure.
In the embodiment of the application, the flow-back closing coefficient n1 can be equal to the coal rock comprehensive compression factor CtFracture volume V associated with pressure drop phasef2The product of (a). Wherein the fracture volume V of the pressure drop stagef2Satisfies the following conditions: vf2＝2xfhRe2. h is the thickness of the coal seam. Fracture volume V based on the above equation (9) and pressure drop phasef2The back-discharge pressure V can be obtainedASatisfies the following conditions:
In an embodiment of the present application, the computer device may determine the fracture closure factor based on the total amount of the fracturing fluid obtained in step 201, the average extension pressure obtained in step 2071, and the original coal seam pressure. Wherein the fracture closure coefficient is positively correlated with the total amount of the fracturing fluid and the original coal seam pressure and negatively correlated with the average extension pressure.
Optionally, the fracture closure factor n2 satisfies:
in the embodiment of the application, the fracture closure coefficient n2 can be equal to the coal rock comprehensive compression factor CtFracture volume V associated with pressure drop phasef1The product of (a). Wherein the fracture volume V of the fracture extension stagef1Satisfies the following conditions: vf1＝2xfhRe1. Fracture volume V based on the above equation (10) and fracture extension stagef1The total amount V of the fracturing fluid can be obtainedTSatisfies the following conditions:
and 214, estimating the gas production rate of the coal bed gas based on the flowback closure coefficient and the fracturing closure coefficient.
In the embodiment, the gas production rate of the coal bed gas is also related to the flowback closure coefficient n1 and the fracture closure coefficient n 2. The flowback closure coefficient n1 is the comprehensive effect of the elasticity and the fracturing volume of the coal seam and can reflect the closure capability of the fractured coal seam. The smaller the flowback closure coefficient n1 is, the stronger the flowback capability is, and the larger the gas production rate of the coal bed gas is. The smaller the flowback closure coefficient n2 is, the weaker the flowback capability is, and the lower the gas yield of the coal bed gas is. The fracture closure factor n2 can be used to judge how easily it is to make a fracture. The smaller the fracture closure factor n2, the greater the original coal seam pressure, the more difficult it is to make a seam, and the higher the gas production of the coal seam gas may be. The larger the fracture closure coefficient n2 is, the smaller the original coal seam pressure is, the more easily the seam is formed, and the less gas production of the coal seam gas is possible.
Therefore, the gas yield of the coal bed gas is inversely related to the flowback closure coefficient and the fracturing closure coefficient.
In this embodiment, the computer device may further determine the flowback rate of the fracturing fluid based on the total amount of the fracturing fluid and the flowback amount of the fracturing fluid obtained in step 201. Optionally, the flowback rate of the fracturing fluid may be positively correlated with the flowback amount of the fracturing fluid and negatively correlated with the total amount of the fracturing fluid. For example, the flow back rate of the fracturing fluid may be equal to the ratio of the flow back of the fracturing fluid to the total amount of fracturing fluid.
And step 216, estimating the gas production rate of the coal bed gas based on the flowback rate of the fracturing fluid.
In this application embodiment, the computer device may also estimate the gas production rate of the coal bed gas based on the flowback rate of the fracturing fluid. Wherein the gas production rate of the coal bed gas can be inversely related to the flowback rate. That is, the larger the flowback rate is, the larger the gas production rate of the coal bed gas can be, the smaller the flowback rate is, and the smaller the gas production rate of the coal bed gas can be.
In the embodiment of the application, referring to table 1, the computer device may obtain each acquisition value of a plurality of coal-bed gas wells. And referring to table 2, for each coal bed gas well, the computer device may calculate the relevant parameters based on the acquired data in table 1 to estimate the gas production rate of the coal bed gas.
TABLE 1
TABLE 2
After the computer device acquires the acquired values in the table 1, the calculated values in the table 2 can be determined according to the method provided by the embodiment of the application, and the gas production rate of the coal-bed gas well can be comprehensively estimated according to the calculated values in the table 2, so that the estimation accuracy is ensured.
Also, the computer device may have or be connected to a display screen. After estimating the gas production rate of the coal bed gas, the computer device can display the estimated gas production rate on the display screen.
In the embodiment of the application, after the gas production rate of the coal bed gas is estimated, an operator can determine the fracturing effect on the hydraulic fracturing of the coal bed gas well based on the estimated gas production rate. If the estimated gas production rate is larger, the fracturing effect of the hydraulic fracturing of the coal-bed gas well can be determined to be better, and under the condition, the coal-bed gas well can be subjected to well opening production. If the estimated gas production rate is smaller, the fracturing effect of the hydraulic fracturing of the coal-bed gas well can be determined to be poorer, and under the condition, the hydraulic fracturing can be performed on the coal-bed gas well again.
It should be noted that the sequence of the steps of the method for estimating the gas yield of coal bed methane provided by the embodiment of the present application may be appropriately adjusted, and the steps may also be correspondingly increased or decreased according to the situation. For example, step 205, step 210, step 214, and step 216 may be performed synchronously, and steps 206 through 216 may be deleted as the case may be. Any method that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application is covered by the protection scope of the present application, and thus the detailed description thereof is omitted.
In summary, the embodiment of the present application provides a method for estimating gas production of coal bed gas, in which a computer device determines an average fluid loss of a fracturing fluid directly according to an obtained total amount of the fracturing fluid, a flow back amount of the fracturing fluid and a total duration of a fracturing process, and determines the gas production of the coal bed gas according to the average fluid loss. The method provided by the embodiment of the application does not need to acquire more coal bed parameters, is simple in calculation process, and is high in efficiency of determining the gas production rate of the coal bed gas.
Fig. 12 is a schematic structural diagram of a gas production estimation apparatus for coal bed methane according to an embodiment of the present application. The gas production estimation device can be applied to computer equipment. As can be seen with reference to fig. 12, the apparatus may comprise:
the first obtaining module 301 is configured to obtain the total amount of fracturing fluid and the return displacement amount of the fracturing fluid used in the fracturing process.
The first determining module 302 is configured to determine a total fluid loss of the fracturing fluid in the fracturing process based on the total amount of the fracturing fluid and the flow back amount of the fracturing fluid.
And a second obtaining module 303, configured to obtain a total duration of the fracturing process.
A second determination module 304 to determine an average fluid loss of the fracturing fluid based on the total fluid loss of the fracturing fluid and the total duration.
And a third determination module 305 for estimating the gas production of the coal bed methane based on the average fluid loss.
Wherein the gas production of the coal bed gas is inversely related to the average filtration loss.
Optionally, the fracturing process may include: a fracture extension phase and a pressure drop phase. Referring to fig. 13, the apparatus may further include:
a third obtaining module 306 is configured to obtain the first duration of the fracture extension phase and the second duration of the pressure drop phase.
The fourth obtaining module 307 is configured to obtain a first slope of the first equation of bottom hole pressure versus time of the coalbed methane well in the fracture extension stage.
And a fifth obtaining module 308 for obtaining a second slope of a second equation of the bottom hole pressure and the time of the coal-bed gas well in the pressure drop stage.
A fourth determining module 309, configured to determine the first fluid loss of the fracture extension stage and the second fluid loss of the pressure drop stage based on the first time length, the second time length, the first slope, the second slope, and the total fluid loss of the fracture fluid.
And a fifth determining module 310, configured to estimate a gas production rate of the coal bed methane based on the first fluid loss and the second fluid loss.
And the gas yield of the coal bed gas is inversely related to the first filtration loss and the second filtration loss.
Optionally, the fourth obtaining module 307 may be configured to:
acquiring the average extension pressure of a fracturing extension stage and the original coal bed pressure of a coal bed gas well; a first slope is determined based on the average extension pressure, the raw coal seam pressure, and the first time period.
Wherein the first slope is positively correlated with the average extension pressure and negatively correlated with the original coal seam pressure and the first time period.
The fifth obtaining module 308 may be configured to:
obtaining the pump stopping pressure and the return pressure in the pressure drop stage; a second slope is determined based on the pump deactivation pressure, the drainback pressure, and the second duration.
Wherein the second slope is positively correlated with the pump deactivation pressure and negatively correlated with the return pressure and the second duration.
Optionally, the first slope m1 satisfies:
the second slope m2 satisfies:
wherein, PETo average extension pressure, PiΔ T1 is a first duration, P, for the original coal seam pressuresFor stopping the pump pressure, PhAt 2 is the second duration for the return pressure.
Optionally, referring to fig. 13, the apparatus may further include:
and the sixth obtaining module 311 is configured to obtain the well opening pressure of the coal-bed gas well.
A sixth determination module 312 determines a flow back closure factor based on the fracturing fluid flow back volume, the flow back pressure, and the well opening pressure. The flow-back closure coefficient is positively correlated with the flow-back volume of the fracturing fluid and the well opening pressure, and is negatively correlated with the flow-back pressure.
A seventh determination module 313 for determining a fracture closure factor based on the total amount of fracturing fluid, the average extension pressure, and the baseline coal seam pressure. The fracture closure coefficient is positively correlated with the total amount of the fracturing fluid and the original coal seam pressure and negatively correlated with the average extension pressure.
And the eighth determining module 314 is configured to estimate the gas production rate of the coal bed methane based on the flowback closing coefficient and the fracture closing coefficient. And the gas yield of the coal bed gas is inversely related to the flowback closure coefficient and the fracturing closure coefficient.
Optionally, the flow-back closing coefficient n1 satisfies:
the fracture closure coefficient n2 satisfies:
wherein, VAFor the return displacement of the fracturing fluid, PhTo return pressure, P0For well-opening pressure, VTFor total amount of fracturing fluid, PETo average extension pressure, PiIs the original coal seam pressure.
Optionally, referring to fig. 13, the apparatus may further include:
and a ninth determining module 315, configured to determine a flow back rate of the fracturing fluid based on the total amount of the fracturing fluid and the flow back amount of the fracturing fluid.
And a tenth determining module 316, configured to estimate the gas production rate of the coal bed methane based on the flowback rate of the fracturing fluid. Wherein the gas production of the coal bed gas is inversely related to the flowback rate.
To sum up, this application embodiment provides a gas production of coal bed gas estimation device, and the device can be directly according to the fracturing fluid total amount that obtains, fracturing fluid flow back volume and fracturing process total duration, confirms the average filtration loss of fracturing fluid to the gas production of coal bed gas is confirmed according to average filtration loss. The device provided by the embodiment of the application does not need to acquire more coal bed parameters, the calculation process is simpler, and the efficiency of determining the gas production rate of the coal bed gas is higher.
Fig. 14 is a schematic structural diagram of another computer device provided in the embodiment of the present application. As can be seen with reference to fig. 14, the computer apparatus may include: a processor 011 and a memory 012. The memory 012 may be configured to store instructions executed by the processor 011, and the processor 011 is configured to execute the instructions stored in the memory 012 to implement the method for estimating gas production rate of coal bed methane provided in the foregoing embodiments.
The embodiment of the application also provides a computer-readable storage medium, and the computer-readable storage medium stores instructions, which can be loaded and executed by a processor to implement the method for estimating the gas production rate of coal bed methane provided by the above embodiment.
The embodiment of the application also provides a system for estimating the gas production rate of the coal bed gas. The gas production estimation system may include: one or more acquisition devices, and a computer device 01 as provided in the above embodiments. The one or more acquisition devices may establish a communication connection with the computer device 01 via a wired or wireless network. The one or more acquisition devices may be configured to acquire parameter information required by the computer device and send the parameter information to the computer device.
Optionally, the one or more acquisition devices may include: flow acquisition equipment, duration acquisition equipment, and pressure acquisition equipment. For example, the flow rate collecting device may be a flow meter, the duration collecting device may be a timer, and the pressure collecting device may be a pressure sensor.
The above description is only exemplary of the present application and should not be taken as limiting, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims (10)
1. The method for estimating the gas production rate of the coal bed gas is applied to computer equipment and comprises the following steps:
acquiring the total amount of fracturing fluid and the return displacement of the fracturing fluid used in the fracturing process;
determining the total fluid loss of the fracturing fluid in the fracturing process based on the total amount of the fracturing fluid and the flow-back amount of the fracturing fluid;
acquiring the total duration of the fracturing process;
determining an average fluid loss of the fracturing fluid based on the total fluid loss of the fracturing fluid and the total duration;
and estimating the gas production rate of the coal bed gas based on the average filter loss, wherein the gas production rate of the coal bed gas is inversely related to the average filter loss.
2. The method of claim 1, wherein the fracturing process comprises: a fracture extension stage and a pressure drop stage; the method further comprises the following steps:
obtaining a first time length of the fracture extension stage and a second time length of the pressure drop stage;
acquiring a first slope of a first equation of bottom hole pressure and time of the coal-bed gas well in the fracture extension stage;
acquiring a second slope of a second equation of bottom hole pressure and time of the coal-bed gas well in the pressure drop stage;
determining a first fluid loss of the fracture extension stage and a second fluid loss of the pressure drop stage based on the first time period, the second time period, a first slope, the second slope, and the total fluid loss of the fracturing fluid;
and estimating the gas production rate of the coal bed gas based on the first filtration loss and the second filtration loss, wherein the gas production rate of the coal bed gas is in negative correlation with the first filtration loss and the second filtration loss.
3. The method of claim 2, wherein obtaining a first slope of a first equation of bottom hole pressure versus time for the coalbed methane well in the fracture extension phase comprises:
acquiring the average extension pressure of the fracturing extension stage and the original coal bed pressure of the coal bed gas well;
determining the first slope based on the average extension pressure, the original coal bed pressure, and the first time period, wherein the first slope is positively correlated with the average extension pressure and negatively correlated with the original coal bed pressure and the first time period;
the obtaining a second slope of a second equation of bottom hole pressure and time of the coal-bed gas well in the drawdown phase comprises:
obtaining the pump stopping pressure and the flow-back pressure of the pressure drop stage;
determining the second slope based on the pump deactivation pressure, the return pressure, and the second duration, wherein the second slope is positively correlated with the pump deactivation pressure and negatively correlated with the return pressure and the second duration.
4. The method of claim 3,
the first slope m1 satisfies:
the second slope m2 satisfies:
wherein, PEIs said mean extension pressure, PiFor the original coal seamPressure, Δ T1, is the first duration, PsFor said pump-stop pressure, PhAt 2 is the second period of time, at the return pressure.
5. The method of claim 3, further comprising:
acquiring the well opening pressure of the coal bed gas well;
determining a flowback closure coefficient based on the fracturing fluid flowback volume, the flowback pressure and the well opening pressure, wherein the flowback closure coefficient is positively correlated with the fracturing fluid flowback volume and the well opening pressure and negatively correlated with the flowback pressure;
determining a fracture closure coefficient based on the total amount of fracturing fluid, the average extension pressure, and the original coal bed pressure, the fracture closure coefficient being positively correlated with the total amount of fracturing fluid and the original coal bed pressure and negatively correlated with the average extension pressure;
and estimating the gas production of the coal bed gas based on the flowback close coefficient and the fracturing close coefficient, wherein the gas production of the coal bed gas is in negative correlation with the flowback close coefficient and the fracturing close coefficient.
6. The method of claim 5,
the return flow closing coefficient n1 satisfies:
the fracture closure coefficient n2 satisfies:
wherein, VAFor the return discharge of the fracturing fluid, PhIs the back pressure, P0For the well opening pressure, VTIs the total amount of the fracturing fluid, PEIs said mean extension pressure, PiIs the original coal seam pressure.
7. The method of any of claims 1 to 6, further comprising:
determining the flow back rate of the fracturing fluid based on the total amount of the fracturing fluid and the flow back amount of the fracturing fluid;
and estimating the gas production rate of the coal bed gas based on the flowback rate of the fracturing fluid, wherein the gas production rate of the coal bed gas is negatively correlated with the flowback rate.
8. The utility model provides a gas production of coal bed gas predicts device which characterized in that is applied to computer equipment, the device includes:
the first acquisition module is used for acquiring the total amount of fracturing fluid and the return displacement of the fracturing fluid used in the fracturing process;
the first determination module is used for determining the total fluid loss of the fracturing fluid in the fracturing process based on the total amount of the fracturing fluid and the flow back amount of the fracturing fluid;
the second acquisition module is used for acquiring the total duration of the fracturing process;
a second determination module, configured to determine an average fluid loss of the fracturing fluid based on the total fluid loss of the fracturing fluid and the total duration;
and the third determination module is used for estimating the gas production rate of the coal bed gas based on the average filter loss, wherein the gas production rate of the coal bed gas is inversely related to the average filter loss.
9. A computer device, characterized in that the computer device comprises: a processor and a memory, the memory for storing instructions for execution by the processor, the processor for executing instructions stored in the memory to implement the method of any of claims 1 to 7.
10. The utility model provides a gas production volume prediction system of coal bed gas which characterized in that, the gas production volume prediction system includes: one or more acquisition devices, and a computer device as claimed in claim 9;
the one or more acquisition devices are used for acquiring parameter information required by the computer device and sending the parameter information to the computer device.
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