CN109958429B - Method for judging shale gas adsorption gas output - Google Patents
Method for judging shale gas adsorption gas output Download PDFInfo
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- CN109958429B CN109958429B CN201711391306.4A CN201711391306A CN109958429B CN 109958429 B CN109958429 B CN 109958429B CN 201711391306 A CN201711391306 A CN 201711391306A CN 109958429 B CN109958429 B CN 109958429B
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- E21—EARTH DRILLING; MINING
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Abstract
The invention provides a method for judging shale gas adsorption gas output, and belongs to the field of shale gas exploration and development. According to the method, whether the adsorbed gas is produced in the production process, the produced time period and the produced times are judged by analyzing the form of the shale gas well pressure recovery log curve or the form of the shale gas well production data log curve. The method can be used for more accurately judging whether the adsorbed gas is produced and the production time interval by applying the shut-in pressure recovery test curve in the production process, judging whether the adsorbed gas is produced or not by applying the production data log-log curve under the condition of lacking of well testing test data, and visually observing whether the adsorbed gas is produced, the production time interval, the production frequency and the like by using the well testing curve.
Description
Technical Field
The invention belongs to the field of shale gas exploration and development, and particularly relates to a method for judging shale gas adsorption gas output.
Background
From the perspective of global energy development strategies, the development of unconventional gas reserves is changing the world's energy landscape and is the focus of global development. The total amount of shale gas resources worldwide is predicted to be about 456 x 1012m3Accounting for about 50% of the total resource of unconventional natural gas (coal bed gas, tight sandstone gas, shale gas). The shale gas exists underground mainly in a free state or an adsorption state, and the free gas is mainly distributed in crack pores and matrix pores; the adsorbed gas is distributed mainly on the inner surface of the micropores of the matrix system. Due to the simultaneous presence of free gas and adsorbed gas, flow in shale reservoirs has a variety of flow characteristics: macroscopically, the artificial fractures created by hydraulic fracturing, as well as the microfractures present in the shale formation, are free gas flow channels in the shale formation and darcy flow still exists in these large scale fractures. Microscopically, the porosity of the shale is generally small and is mostly in the order of nanometers, so that the Darcy flow has low possibility, and the gas flows in the specific surface diffusion, molecular diffusion and Knudsen diffusion modes; after the shale gas reservoir completes drilling construction, the pressure of the stratum is reduced, the original adsorption balance is damaged, and the desorption phenomenon is generated. Therefore, the shale gas has unique desorptionAnd adsorption characteristics, particularly multi-stage and multi-scale seepage characteristics which are obviously different from conventional gases in seepage, and adsorption gases produced by micro-flow such as desorption and diffusion occupy important parts in shale gas yield, and are also indispensable conditions for accurately predicting shale gas capacity. Since the adsorbed gas is adsorbed on the surface of the substrate and only desorbed gas is produced, an effective method for determining when the adsorbed gas is desorbed, i.e., when the adsorbed gas is produced, needs to be established.
The method is widely researched and searched aiming at the existing shale gas adsorbed gas measuring technology, the technology for predicting the adsorbed gas output in the well production process, the shale gas well productivity calculating method and the like, wherein 12 related patents are searched. Some of the currently published patents are based on experimental means and use instruments to measure shale cores so as to determine the content of adsorbed gas in shale formations and determine shale adsorption curves, such as a system (application number: CN201420587194.5) for analyzing the content of adsorbed gas in shale gas, a simple experimental device for shale gas adsorption and desorption (application number: CN201520847718.4) and the like, but they cannot determine whether adsorbed gas is generated and the generation time period of the adsorbed gas for the shale gas wells under production. Some methods are to establish various shale gas yield prediction models, yield decrement methods and the like, perform yield prediction, evaluate single well productivity, such as a method for predicting the recoverable reserves of shale gas wells based on early yield data (CN710436233.X), a shale gas reservoir single well productivity calculation method (CN201610559081.8), an oil and gas well yield decrement analysis method and system (CN201410638125.7), a shale gas horizontal well initial productivity prediction method (CN201510124601.8), a productivity well testing method (CN201410784754.0) and a shale gas horizontal well single well productivity logging prediction method (CN 201710137973.3). None of these six patents consider the production of adsorbed gas from the production of a gas well and are not part of this disclosure. In addition, 4 patents disclose a shale gas well productivity prediction method, wherein the shale gas well productivity evaluation prediction method (CN201410536314.3) determines a shale gas horizontal well staged fracturing yield formula through fitting production data, and simultaneously considers desorption and diffusion characteristics to establish the shale gas productivity evaluation method; a shale gas well productivity determination method (CN201410112840.7) establishes a double-area composite shale gas reservoir material balance equation considering adsorbed gas, and establishes a rapid and accurate shale gas well productivity calculation method; a shale gas reservoir horizontal well multi-section fracturing productivity prediction method and device (CN201510454838.2) utilize original parameters of a shale gas reservoir after fracturing transformation to establish a flow control equation in a matrix and fracture system to obtain fracture pressure distribution, and utilize an productivity equation to obtain shale gas productivity. The method for calculating the adsorption gas amount in the 3 prior patents is to apply a langmuir adsorption formula to predict the adsorption gas yield, and whether the adsorption gas is generated is not judged according to an actual production curve. A shale gas yield decrement analysis method (CN2014108-52718.3) utilizes a diffusion coefficient to calculate the mass of free gas flowing out of a fracture, utilizes gas pressure and shale gas density to determine the mass of desorbed gas, determines a gas well yield decrement rule according to formation parameters, determines the final wellhead yield of a gas well, can only calculate the content of adsorbed gas in a shale formation, and cannot judge when the adsorbed gas is generated in the production process in real time according to an actual production curve. Therefore, the prior patent art does not have the inventive content set forth in the invention.
In the non-patent literature, 7 relevant literatures have been searched. The method comprises the steps of calculating the shale adsorption gas amount of multiple factors and analyzing the effect of influence factors, and establishing an adsorption gas amount calculation model considering three factors of total organic carbon content, kerogen maturity and depth based on the isothermal adsorption experiment result. The new shale adsorbed gas content calculation method based on the isothermal adsorption experiment calculates the change rule of the pressure change on the shale adsorption without considering the influence of the temperature. The new shale adsorbed gas content calculation model considering the formation temperature and the pressure is based on the Langmuir model, and the new shale adsorbed gas content calculation model considering 4 factors of the formation temperature, the pressure, the organic carbon content and the maturity is established according to the relation between the temperature, the pressure, the TOC value, the RO value and the adsorbed gas content. The method for representing the free gas amount and the adsorbed gas amount in the shale by sound wave attenuation is provided. The initial exploration system for the shale isothermal adsorption gas content negative adsorption phenomenon analyzes the reason of the shale isothermal adsorption curve negative adsorption phenomenon, provides a correction suggestion, and provides a basis for accurate determination of shale adsorption gas content and objective evaluation of shale gas resource quantity. The shale gas adsorption comprehensive model and the application thereof carry out a series of calculations on the shale isothermal adsorption curves at different temperatures to obtain the shale gas adsorption comprehensive model, and the isothermal adsorption curves under different temperature and pressure conditions are calculated. The method for correctly evaluating the content of the shale adsorption gas by using the isothermal adsorption method researches the influence of the comprehensive effect of temperature and pressure on the shale adsorption characteristic. The non-patent literature is based on a shale isothermal adsorption experiment or an isothermal adsorption formula, and the content of adsorbed gas in a shale stratum is calculated, so that whether the shale gas well produces the adsorbed gas in the production process or not and the time period of the adsorbed gas production cannot be judged.
Disclosure of Invention
The invention aims to solve the problems in the prior art, and provides a method for judging shale gas adsorbed gas output, which can be used for judging whether adsorbed gas is generated in the production process by using a well shut-in pressure recovery test curve, judging whether adsorbed gas is generated by using a production data log-log curve under the condition of lacking of well testing test data, and visually observing whether adsorbed gas is generated, the time period of output, the output frequency and the like by using a well testing curve.
The invention is realized by the following technical scheme:
a method for judging shale gas adsorbed gas output judges whether adsorbed gas is output in a production process, and the output time interval and the output times of the adsorbed gas are output by analyzing the form of a shale gas well pressure recovery log curve or the form of a shale gas well production data log curve.
The method comprises the following steps:
(1) collecting shale gas well test data;
(2) drawing a shale gas well log curve according to the shale gas well test data;
(3) and analyzing the log curves of the shale gas well, judging whether concave forms appear on the curves, if not, judging that the adsorbed gas is not produced, if so, judging that the adsorbed gas is produced, and obtaining the time period and the times of the produced adsorbed gas according to the positions and the times of the concave forms.
The step (1) is realized by the following steps:
if the shut-in pressure recovery test is carried out in the production process, the collected shale gas well test data is pressure recovery test data;
and if the shut-in pressure recovery test is not carried out in the production process, the collected shale gas well test data is production data.
The stress recovery test data comprises stress and time;
the production data includes wellhead pressure and wellhead production measured daily.
The step (2) is realized by the following steps:
if the shut-in pressure recovery test is carried out in the production process, a shale gas well pressure recovery log-log curve is made on a coordinate graph according to pressure recovery test data, wherein the abscissa of the coordinate graph is time, and the ordinate of the coordinate graph is pressure and a pressure derivative; one of the two curves is a curve of pressure changing along with time, and the other curve is a curve of pressure derivative changing along with time;
if the well shut-in pressure recovery test is not carried out in the production process, drawing a production data log-log curve on a coordinate graph according to production data, wherein the abscissa of the coordinate graph is material balance time, and the ordinate is flow normalized pressure and a flow normalized pressure derivative; one of the two curves is a curve of the flow normalized pressure changing along with the material balance time, and the other curve is a curve of the flow normalized pressure derivative changing along with the material balance time; the material balance time is as follows: cumulative/daily yield, the normalized pressure being: (original formation pressure-wellhead pressure)/daily production.
If the double logarithmic curve of the production data drawn in the step (2) is disordered, drawing the double logarithmic curve by using the material balance time as a horizontal coordinate, the flow normalized pressure integral and the flow normalized pressure integral derivative as a vertical coordinate, wherein one of the two curves is a curve of the flow normalized pressure integral changing along with the material balance time, and the other curve is a curve of the flow normalized pressure integral derivative changing along with the material balance time; if the obtained double-logarithmic curve is still disordered and irregular, the abnormal points are manually removed, and then the double-logarithmic curve is smoothed by the interpretation software.
The step (3) is realized by obtaining the time period of the adsorbed gas production and the times of the adsorbed gas production according to the positions and times of the appearance of the concave shapes:
the time period corresponding to the abscissa of the position where the concave form appears is the time period of the generation of the adsorbed gas;
the frequency of the concave form is the frequency of the adsorbed gas output.
Compared with the prior art, the invention has the beneficial effects that: the invention can not only accurately judge whether the adsorbed gas is produced in the production process and the production time period by applying the shut-in pressure recovery test curve, but also judge whether the adsorbed gas is produced by applying the production data log-log curve under the condition of lacking the well testing test data, and visually observe whether the adsorbed gas is produced, the production time period, the production times and the like by using the well testing curve, so that the application range is greatly increased. The method can be used for directly observing the condition of the adsorbed gas output in the production process by applying the well testing curve, further knowing the multi-scale flow rule of the shale gas reservoir, analyzing the change rule of the production condition of the shale gas well, and playing an important role in evaluating the productivity and economic benefit of the shale gas well. The method can be applied to any production stage in the normal production process of the shale gas well, can be applied to gas wells related to well pressure recovery test data, can also be applied to gas wells without test data, and has wide application prospect.
Drawings
FIG. 1 shale gas formation gas storage mechanism
FIG. 2 is a schematic diagram of a gas molecule migration mechanism of a shale gas formation
FIG. 3 schematic diagram of dual-hole formation flow
FIG. 4 is a schematic view of shale gas flow with adsorption and diffusion considerations
FIG. 5 Dual-hole model log pressure and derivative curves
FIG. 6 well testing curve of adsorption-diffusion model
FIG. 7 pressure and yield curves of production data of example 1
FIG. 8 normalized pressure log-log curve of example 1
FIG. 9 normalized pressure integral log-log curve of example 1
FIG. 10 pressure and yield curves of production data of example 2
FIG. 11 normalized pressure log-log curve of example 2
FIG. 12 normalized pressure integral log-log curve of example 2
FIG. 13 is a block diagram of the steps of the method of the present invention.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
the invention provides a method for judging whether shale gas desorption gas is generated, which is used for deducing a shale micro-flow mechanism, establishing a dual-medium flow model for shale adsorption gas to diffuse into a crack from a nano-pore, analyzing the dual-logarithm curve form through the pressure recovery dual-logarithm curve form of a shale gas well or the dual-logarithm curve form of production data, and judging whether adsorption gas is generated in the production process, the time period of production, the production frequency and the like.
According to the research of the shale microscopic seepage mechanism, the adsorbed gas exists in the nano-scale micro pores, and the gas enters large microcracks or other flow channels in the forms of desorption, diffusion and the like and then flows into a well, so that after the adsorbed gas participates in flowing, two different pore media exist in a stratum, two different flowing modes exist, the flowing characteristics similar to those of a dual pore medium are displayed on a pressure recovery log-log curve, and whether the adsorbed gas is produced or not can be judged. The invention judges whether the produced gas has the adsorbed gas or not by the true reaction of the log-log curve drawn by the formation pressure data of the shut-in test, so the judgment result is more true and reliable, and the time when the adsorbed gas is produced in the production process can be judged. The method is not reported in related technologies at home and abroad at present.
The detailed process of the invention is as follows:
shale gas formation gas flow mechanism and characterization
The flow of the shale gas reservoir is generally coupled by two migration mechanisms, namely macroscopic migration mechanism and microscopic migration mechanism, such as pore medium seepage, desorption-diffusion and the like.
The shale gas formation is distributed with tiny pores (natural fractures may exist), and the gas is distributed in the pore (including natural fracture) space in the form of free gas, so that the pore (natural fracture space) pressure is formed; in addition, kerogen in the form of a non-mature released free gas molecule is distributed in the pore space, and gas molecules are adsorbed on the surface of the kerogen by virtue of an adsorption mechanism, and the gas is adsorbed gas. FIG. 1 is a representation of the presence of gas in a shale gas formation.
Free gas is stored in the pore space and gas molecules fill the pore space, causing the existence of pore pressure. When a certain pore is communicated with the pore of the surrounding space and a pressure gradient exists, free gas can perform pore medium seepage under the action of the pressure gradient. Its seepage characteristics generally follow the basic form of darcy's law, but the seepage in shale formations is slightly different due to the smaller pore size.
The adsorption gas is adsorbed on the surface of the kerogen mainly by means of pore pressure. Diffusion is also an important mechanism for gas migration in shale gas formations. In the shale pore spaces, there are kerogen that has not matured. In these kerogen, gas molecules dissolved therein are stored. The concentration of gas molecules in kerogen is greater than the concentration of free gas molecules in the pore space and greater than the concentration of adsorbed gas molecules on the surface of kerogen. The gas molecules inside the kerogen diffuse to the surface where the concentration of gas molecules is low.
FIG. 2 is a schematic illustration of shale gas flow coupled by two flow mechanisms that are ideal. The middle pore space is a main channel for the migration of gas molecules in the shale gas formation and is also a medium for storing free gas; the upper and lower parts represent kerogen contained in the unit shale pore volume, and the interface of the two parts is a medium for adsorbing gas storage. Pressure fluctuation of the pore space and the adjacent pore space in the gas production process forms a pressure gradient, gas molecules flow into the adjacent space at the far well end and flow out of the pore space at the near well end. The flow of free gas causes the change of the number of gas molecules in the pore space, thereby causing the change of the pressure in the pore space, and at the moment, the adsorbed gas on the surface of the kerogen follows the Langmol isothermal adsorption rule to carry out the adsorption or desorption process due to the change of the pressure; the change of the concentration of the gas adsorbed on the surface of the kerogen can cause the change of the gas concentration difference between the interior and the surface of the kerogen, so that the gas molecules in the kerogen can diffuse to the surface of the kerogen to form new adsorbed gas distribution. Thus, it can be said that the pore space is both a storage space and a channel for the migration of gas molecules, whereas kerogen, either surface or internal, is a storage space for gas molecules, i.e. gas molecules do not migrate to other adjacent pore spaces through the kerogen itself.
In summary, the process of flowing shale gas from the formation into the wellbore is as follows: as the formation pressure drops, the adsorbed gas that is adsorbed in the kerogen is desorbed and diffuses into the pore space where the gas reaches the wellbore by percolation. Thus the whole flow process is composed of two flows of micro-flow (adsorption, diffusion) and seepage, which are equivalent to the flow in two pore media, if the adsorbed gas is also produced, the micro-flow is also involved in the flow of the gas, and the flow characteristics of the dual pore media should be shown on the well test curve.
(II) shale gas well adsorption and diffusion considered mathematical model establishment
When the adsorbed gas and the free gas are produced simultaneously in the shale gas well production process, the flow in the formation is similar to the flow characteristics of a dual medium formation, namely desorption and diffusion flow of the adsorbed gas from kerogen to a pore space and seepage flow of the free gas from the pore space to a wellbore, which are equivalent to flow of a matrix to a crack and flow of the crack to a wellbore in a dual-hole model, and the flow characteristics of the dual-hole formation and the flow characteristics of the shale gas after adsorption and diffusion are considered are compared and schematically shown in fig. 3 and 4. From fig. 3 and 4, it can be seen that the flow of adsorption and diffusion and the seepage of pore space are similar to the two flows of matrix and crack in the double holes, and the flow characteristics of the double hole model are shown on the test curve of the shale gas well. Therefore, the storage-capacity ratio omega and the channeling coefficient lambda can be defined, and a mathematical model for considering the adsorption and diffusion of the shale gas is established.
The gas in the shale gas is a mixed gas mainly containing methane, and the equation after considering seepage and diffusion is as follows:
wherein V is the concentration of the mixed gas in the shale; p is the pressure of the gas in the formation; t is the temperature of the gas in the formation; μ is the gas viscosity; z is a gas deviation factor in a real gas state equation; k is the formation permeability; t is the production time and the index sc indicates the physical quantity in the standard state. The gas concentration in shale may be given by the following relationship:
wherein D is the gas diffusion coefficient in the shale; r is the outer radius of gas diffusion in the shale; vEThe gas concentration is in an equilibrium state; vicThe gas concentration when t is 0. After considering the pressure-sensitive and the gas PVT, the standard pressure is defined:
defining a dimensionless variable standard pressure:
dimensionless time:
elastic storage capacity ratio:
the channeling coefficient:
dimensionless distance:
wherein the subscript i represents a physical quantity in an initial state,. phi.is porosity, and q.scIs the flow rate in the standard state, BgIs the gas volume coefficient, CgAnd tau is the adsorption time in the shale gas:
alpha is the comprehensive storage capacity coefficient:
l is the sum of the half-length of the crack:
after dimensionless, the equation becomes:
in laplace space, the expression of the equation is:
where s is the laplace variable.
If the shale gas adsorption equation is written as follows according to the Langmuir equation under standard pressure conditions:
wherein m isLIs Langmuir adsorption standard pressure, VLIs Langmuir adsorption standard pressure, micLangmuir adsorption pressure at t ═ 0. The following equation is assumed to be constant:
equation (16) can be written as:
VED＝-αmD (18)
then, equation (15) can be expressed as:
wherein:
substituting the above equation into equation (12) yields:
wherein the coefficient function is:
(III) difference between adsorption-diffusion model and two-hole model
However, the adsorption diffusion model is not identical to the double-hole model, and has essential difference in flow law, which also causes the well testing curve characteristics caused by adsorbed gas output to be different from the well testing curve form of the double-hole model.
1. Different definitions of elastic storage capacity ratio and channeling coefficient
In the double-hole model, a matrix is used as a reservoir space, a crack is used as a flow channel, the elastic reservoir volume ratio in the double-hole model is defined as the ratio of the change of the crack volume to the change of the total volume in a unit volume of rock, and the expression is as follows:
the blow-by coefficient λ is expressed as:
omega and lambda in the two-hole model are related to the porosity, compressibility, permeability, shape factor of the matrix and fracture, and describe the flow process of gas in the matrix flowing into the fracture and then flowing from the fracture into the wellbore, and the ability of gas in the matrix to flow into the fracture is evaluated.
While ω and λ in the adsorption-diffusion model defined above are related to adsorption time, desorption amount, etc. of the adsorbed gas, it describes that the flow is the process of desorbing the adsorbed gas from the matrix, diffusing into the microcracks, and flowing into the wellbore, and the whole flow mechanism is different from that of the two-hole model.
2. The differential equations of the two models are different
The differential equation of the adsorption model is shown in equation (21), and the differential equation of the two-hole model is equation (25).
Adsorption model:
a double-hole model:
m in the double-hole modelfDWhich is the standard pressure in a fracture system, is basically the same in terms of differential equations, but where the coefficient functions f(s) are defined completely differently.
Coefficient function of adsorption model:
coefficient function of the two-hole model:
the coefficients of the two-hole model are only related to omega and lambda, so the model describes the flow process from the matrix to the crack and from the crack to the well bore, while the coefficients of the adsorption model are also related to alpha in addition to omega and lambda, and describe the desorption and diffusion process of the adsorbed gas, so the flow mechanisms described by the two differential equations are different, and the expressed physical meanings are different.
Well testing curve characteristic of shale gas considering adsorption and diffusion model
As described above, the flow of adsorption and diffusion and the seepage of pore space are considered to be similar to the two flows of matrix and fracture in the double pores, so that the well test curve of the shale gas well also shows the characteristic similar to the well test curve form of the double-pore model, namely, the concave curve form similar to the double-pore model can be seen on the well test curve considering the adsorption and diffusion models.
However, the flow mechanism of the adsorption and diffusion model is different from that of the double-hole model, in the flow of the double-hole model, all gas in the matrix flows into the cracks and then flows into the well bore from the cracks, the flow from the matrix to the cracks is continuous and occupies a large proportion in the whole flow process, and the concave part on the test curve of the double-hole model represents the flow of the gas from one pore medium to the other pore medium (as shown in fig. 5), so that the concave part on the curve is large and only has a concave curve characteristic; the flow in the adsorption and diffusion model is that when the desorption condition is met, the adsorbed gas in the matrix is desorbed and diffuses into the crack to form free gas, and then the free gas flows into the shaft from the crack, the desorption and diffusion process is discontinuous, the flow can be generated when the desorption and diffusion condition is met, when the condition is not met, the desorption and diffusion flow is stopped, and the volume of the gas desorbed and diffused each time is small, so that the well test curve shows a concave form (as shown in figure 6), but the concave pattern is small, and the curve shows a plurality of concave forms, which can not appear on the curve of the double-hole model. Therefore, whether the adsorbed gas is produced or not can be judged according to the curve morphological characteristics, and a double-hole stratum model and an adsorbed gas production model can be distinguished
(V) method for judging whether shale gas adsorption gas is produced or not by applying well testing curve
According to the analysis in the step (IV), the shale gas considers the well test curve characteristics of the adsorption and diffusion model, and is different from the well test curve forms of any other models, so that whether adsorption and diffusion flow occurs in the flow rule of the shale gas well can be judged by using the unique well test curve forms of the adsorption and diffusion model, and whether adsorption gas output occurs in the produced gas is judged.
As shown in fig. 13, the determination method of the present invention is as follows:
(1) firstly, shale gas well test data are collected. If the shut-in pressure recovery test is carried out in the production process, the pressure recovery test data (namely the pressure recovery test data) can be used for judgment; if no shut-in test is performed during production, the production data (i.e., pressure and production data at the wellhead) may be used for the determination. The formation testing data before commissioning is not recommended for judgment, because the fracturing modification is not performed at this time, and normal production is not performed, so that the normal production process cannot be represented. The pressure recovery test data is data tested by a pressure gauge which is arranged in the well and is replayed on a computer, wherein the data comprises time, pressure, temperature and the like, the time and pressure data are applied to the pressure recovery test data, and the replay data format is shown in the table 1.
TABLE 1
(2) And drawing a double logarithmic curve of the shale gas well. If the pressure recovery test data is used for judgment, a well testing log curve can be made by using well testing interpretation software, the abscissa of the curve is time, and the ordinate is pressure and the derivative of the pressure. The double logarithmic curve has two curves, the upper curve is a pressure change line along with time, the lower curve is a pressure derivative change line along with time, and the concave characteristic is generally on the pressure derivative curve, so that the change of the lower pressure derivative curve can be seen when judging. Production data are different from well closing pressure recovery data, the production data comprise daily wellhead pressure and wellhead yield measured by a wellhead, if the production data are used for judgment, a flow normalized pressure method is required to be applied to process the production data, during actual use, production data interpretation software (such as Topace software) can be applied to draw a log-log curve, and the abscissa of the log-log curve at the moment is material balance time (namely cumulative yield)Daily production) and the ordinate is the flow normalized pressure and the derivative of the flow normalized pressure. The expression for normalized pressure is: (original formation pressure-wellhead pressure)/daily production, i.e.
Although the horizontal and vertical coordinates of the curves made by the two types of test data are different, the morphological characteristics of the log-log curves are the same, and whether the adsorbed gas is produced or not can be judged by applying the method.
(3) Analysis of the log-log curve, as shown in fig. 6, shows that if a shale gas well produces adsorbed gas, the curve will exhibit a dip behavior that is different from the dip of the two-hole model characteristics, which is much smaller in scale than the dip of the two-hole curve, and which will exhibit several dip behaviors throughout the curve, which are not possible in the two-hole model. Therefore, the adsorbed gas is produced in the shale gas production process, and the concave phenomenon is caused by the flow of the adsorbed gas which is desorbed and diffused into the cracks.
(4) It should be noted that the quality of data recorded in production data is poor, and the curves are relatively disordered due to the influence of various external or human factors in the daily production process, so that many abnormal points can cover the expression of the production rule. Therefore, when the production data double-logarithmic curve is drawn, if the normalized pressure and the normalized pressure derivative are used for drawing, the curve is relatively disordered and has no regularity, the normalized pressure integral and the normalized pressure integral derivative can be used as the ordinate for drawing, and a more regular double-logarithmic curve can be obtained. If the curve is still messy, the abnormal points are manually removed, and then the dual-logarithm curve is smoothed by the interpretation software, so that the regular dual-logarithm curve can be obtained.
The embodiment of the method of the invention is as follows:
example 1:
the application of the invention is illustrated by taking a multi-section fracturing shale gas horizontal well of a certain foreign oil field as an example. The original formation pressure of the well is 48.26MPa, the horizontal well section length is 1219.2m, and the fracturing series is 24. The well was judged using production data with production time of 7056 hours and daily production and pressure data of 1 point per 24 hours for 295 sets of data. The production data is used to plot the daily production, cumulative production versus time, and pressure versus time for the wellhead as shown in FIG. 7.
Production data log curves are plotted using well testing software, such as normalized pressure and pressure integral log curves in fig. 8 and 9, respectively. From the comparison of the curves, fig. 8 shows that the normalized pressure log-log curve form in this embodiment is clearer, from the well testing curve form, after the early wellbore storage stage, the gas well production is basically in the linear flow stage, and it can be distinguished that the adsorbed gas production is respectively performed at the early stage of the linear flow, approximately when 200 hours and 800 hours of production are performed, and fig. 9 shows that the well testing log-log curve is drawn by applying the normalized pressure integral and integral derivative as vertical coordinates, the curve form is more regular, and similarly, the form indication of the two adsorbed gas production forms can be identified, and the production time has a little error.
Example 2:
the application of the invention is illustrated by taking one-opening multi-section fracturing shale gas horizontal well of the Fuling block as an example. The original formation pressure of the well is 36.9MPa, the length of a horizontal well section is 1007m, and the fracturing grade number is 13. The well was judged using production data with a production time of 18600 hours and daily production and pressure data of 1 point per 24 hours for 776 sets of data. The production data is used to plot the daily production, cumulative production versus time, and pressure versus time for the wellhead as shown in FIG. 10.
Production data log curves were generated using well testing software, such as normalized pressure and pressure integral log curves in FIGS. 11 and 12, respectively. From the comparison of the curves, the application of the log-log curve (fig. 11) with normalized pressure and pressure derivative as ordinate is disordered, cannot identify the flow regularity in production, and therefore cannot be applied. Fig. 12 is a log-log test curve drawn by applying normalized pressure integral and integral derivative, the curve form is relatively clear, from the view of the well test curve form, the early wellbore storage stage cannot be observed, the gas well production is basically in a linear flow stage, and the concave curve form of the adsorbed gas production appears for many times in the production process, as indicated by the reference in fig. 12. It can be roughly recognized that adsorbed gas was produced at 700 hours, 2000 hours, 4000 hours, and 7000 hours of production, respectively.
After the embodiment is implemented, the following effects are achieved: (1) the shale gas well production data is applied to draw a log-log well test curve, and the morphological characteristics of the log-log curve when normalized pressure and normalized pressure integral are taken as vertical coordinates are compared, so that the application range and effect are summarized; (2) and (3) aiming at a well testing log-log curve drawn by production data, identifying flow field characteristics in the production process on the curve, identifying each flow section, and judging whether the shale gas is produced or not and the approximate production time by applying the curve characteristics of the adsorption and diffusion models.
The above-described embodiment is only one embodiment of the present invention, and it will be apparent to those skilled in the art that various modifications and variations can be easily made based on the application and principle of the present invention disclosed in the present application, and the present invention is not limited to the method described in the above-described embodiment of the present invention, so that the above-described embodiment is only preferred, and not restrictive.
Claims (6)
1. A method for judging shale gas adsorption gas output is characterized by comprising the following steps: the method comprises the steps of analyzing the form of a shale gas well pressure recovery log curve or the form of a shale gas well production data log curve, and judging whether adsorbed gas is produced in the production process, the produced time interval and the produced times based on an adsorption diffusion model;
the method comprises the following steps:
(1) collecting shale gas well test data;
(2) drawing a shale gas well log curve according to the shale gas well test data;
(3) and analyzing the log curves of the shale gas well, judging whether concave forms appear on the curves, if not, judging that the adsorbed gas is not produced, if so, judging that the adsorbed gas is produced, and obtaining the time period and the times of the produced adsorbed gas according to the positions and the times of the concave forms.
2. The method of determining shale gas adsorption gas production as claimed in claim 1, wherein: the step (1) is realized by the following steps:
if the shut-in pressure recovery test is carried out in the production process, the collected shale gas well test data is pressure recovery test data;
and if the shut-in pressure recovery test is not carried out in the production process, the collected shale gas well test data is production data.
3. The method of determining shale gas adsorption gas production as claimed in claim 2, wherein: the stress recovery test data comprises stress and time;
the production data includes wellhead pressure and wellhead production measured daily.
4. The method of determining shale gas adsorption gas production as claimed in claim 3, wherein: the step (2) is realized by the following steps:
if the shut-in pressure recovery test is carried out in the production process, a shale gas well pressure recovery log-log curve is made on a coordinate graph according to pressure recovery test data, wherein the abscissa of the coordinate graph is time, and the ordinate of the coordinate graph is pressure and a pressure derivative; one of the two curves is a curve of pressure changing along with time, and the other curve is a curve of pressure derivative changing along with time;
if the well shut-in pressure recovery test is not carried out in the production process, drawing a production data log-log curve on a coordinate graph according to production data, wherein the abscissa of the coordinate graph is material balance time, and the ordinate is flow normalized pressure and a flow normalized pressure derivative; one of the two curves is a curve of the flow normalized pressure changing along with the material balance time, and the other curve is a curve of the flow normalized pressure derivative changing along with the material balance time; the material balance time is as follows: cumulative/daily production, the flow normalized pressure being: (original formation pressure-wellhead pressure)/daily production.
5. The method of determining shale gas adsorption gas production as claimed in claim 4, wherein: if the double logarithmic curve of the production data drawn in the step (2) is disordered, drawing the double logarithmic curve by using the material balance time as a horizontal coordinate, the flow normalized pressure integral and the flow normalized pressure integral derivative as a vertical coordinate, wherein one of the two curves is a curve of the flow normalized pressure integral changing along with the material balance time, and the other curve is a curve of the flow normalized pressure integral derivative changing along with the material balance time; if the obtained double-logarithmic curve is still disordered and irregular, the abnormal points are manually removed, and then the double-logarithmic curve is smoothed by the interpretation software.
6. The method of determining shale gas adsorption gas production as claimed in claim 5, wherein: the step (3) is realized by obtaining the time period of the adsorbed gas production and the times of the adsorbed gas production according to the positions and times of the appearance of the concave shapes:
the time period corresponding to the abscissa of the position where the concave form appears is the time period of the generation of the adsorbed gas;
the frequency of the concave form is the frequency of the adsorbed gas output.
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