A method for determining a lost circulation location and calculating lost circulation parameters of a drilling fluid

Abstract

The application discloses a method for determining the position of drilling fluid leakage and calculating leakage parameters, which is used for finding the position of well leakage during drilling, calculating the leakage speed and leakage amount of drilling fluid, and estimating the leakage scale. The application describes the principle that the photoelectric absorption cross section Pe value of barite contained in the drilling fluid is abnormally high compared with other rocks, minerals and fluids, and the leakage position is accurately positioned by the characteristics of the high value of the Pe curve measured by the lithology density logging in the leakage well section, and the leakage speed is predicted by the correlation between the Pe logging value and the instantaneous leakage speed, and the leakage amount is calculated by combining the method of multi-mineral analysis with the actual content of barite in the drilling fluid. The method is simple and easy to operate, and the accuracy is reliable. Compared with the data provided by the field, the error of the leakage speed and the leakage amount calculated by the method is small, and the effect is good.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil and gas exploration, and particularly relates to a method for determining a drilling fluid leakage position and calculating leakage parameters. BACKGROUND

[0002] At present, well leakage occurs in most domestic and foreign oilfields, which leads to increased operation cost and delayed construction period. In addition, the plugging fluid used after leakage occurs can pollute the reservoir, so that the logging curve cannot reflect the real information of the formation, which brings great difficulty to the identification of formation fluid in the later period.

[0003] The causes of well leakage are different. Some are caused by the permeation of strata with good third system properties, some are caused by cracks and karst caves in buried hill strata, some are caused by volcanic channels, and some are caused by drilling through fault fracture zones. When the leakage position is determined, the leakage depth point is easy to determine when the drill bit is drilling through the stratum, but there is a certain depth error in the leakage point provided by drilling. In some cases, the upper weak stratum is pressed by the drill bit due to the increase of drilling fluid specific gravity or displacement, so there may be several leakage points, and the leakage depth of each leakage point is difficult to determine, and the leakage amount of each leakage point is unknown.

[0004] For a long time, domestic and foreign scholars have studied the leakage mechanism of fractured strata more, but few people have studied the third system sandstone and mudstone strata. The reason is that it is difficult to determine the leakage position after well leakage. Without accurate leakage interval, further research work cannot be carried out for the leakage interval.

[0005] Imaging logging data can be used to evaluate the leakage interval and leakage channel, but due to the third system sandstone and mudstone strata, the well section is relatively long, and the high logging cost makes such logging projects rare in this stratum. It is particularly important to locate the leakage interval by using conventional logging curves. The leakage mechanism of the easy leakage interval is studied, and the lithology, physical properties, mineral composition and content, rock mechanics properties, and ground stress of the stratum are studied, which can provide reliable basis for the subsequent well trajectory design and optimization of drilling construction scheme. SUMMARY

[0006] The problem to be solved by the present application is to provide a method for determining the drilling fluid leakage position and calculating the leakage parameters. In particular, the photoelectric absorption cross-section curve measured by post-drilling logging is used to reflect the characteristics of the abnormally high value of barite in the drilling fluid, find the leakage point position, predict the leakage rate, and combine the concentration of barite in the drilling fluid to predict the leakage amount of each leakage point by using multi-mineral analysis technology, evaluate the leakage scale of each leakage point in the wellbore, and the error is small and the precision is high.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for calculating drilling fluid leakage parameters, comprising the following steps,

[0008] S1: Calculate the drilling fluid leakage rate. When the drilling fluid in the completed well enters the lost circulation zone, the logging curve Pe shows an abnormally high value due to the influence of the barite. The baseline Pe value is the Pe curve value of the section without lost circulation, and the abnormal Pe curve value is the Pe curve value of the lost circulation zone. The drilling fluid leakage rate V is predicted using the ratio Peˊ of the abnormal Pe curve value to the baseline Pe value. L The formula is:

[0009] V L =20.914×Peˊ-22.435

[0010] R 2 =0.8148;

[0011] S2: Calculate drilling fluid loss, including the following steps.

[0012] S21: Obtain the relative volume content V of barite in the formation. ba ;

[0013] S22: Obtain the mass M of barite in the formation ba， The calculation formula is:

[0014] M ba =σ·V lost ·ρ c

[0015] In the formula: σ is the concentration of barite in the drilling fluid, in v / v;

[0016] V lost Drilling fluid loss, unit: m³ 3 ;

[0017] ρ c The density of the drilling fluid at the leak point, in g / cm³. 3 ;

[0018] S23: Obtain the total volume of barite in the formation.

[0019] S24: Obtain the mass M of barite in the formation ba， The calculation formula is:

[0020]

[0021] S25: The mass M of barite obtained using S22 ba The barite mass M obtained from S24 ba Calculate drilling fluid loss V lost .

[0022] Furthermore, the relative volume content V of barite in the stratum ba The calculation formula is:

[0023]

[0024] In the formula: ρ b These are density logging measurements, in g / cm³. 3 ;

[0025] ρ cl This is the density value of the clay skeleton, in g / cm³. 3 ;

[0026] ρ f This is the fluid density value, in g / cm³. 3 ;

[0027] ρ ba This is the density value of barite, in g / cm³. 3 ;

[0028] ρ sd This is the density value of the sandstone framework, in g / cm³. 3 ;

[0029] △t represents the measurement value of sonic transit time logging, in μs / ft;

[0030] △t cl The acoustic transit time value for the clay skeleton is expressed in μs / ft.

[0031] △t f This represents the fluid acoustic wave transit time, in μs / ft.

[0032] △t ba The time difference of the sound wave in barite is expressed in μs / ft.

[0033] △t sd The acoustic transit time value for the sandstone skeleton is expressed in μs / ft.

[0034] Pe is the Pe value measured in well logging, with units of b / e;

[0035] Pe cl Pe value for clay skeleton, in units of b / e;

[0036] Pe f This is the fluid Pe value, in units of b / e;

[0037] Pe ba This is the Pe value of barite, expressed in b / e.

[0038] Pe sdPe is the value of sandstone skeleton, unit is b / e;

[0039] V is the relative volume content of various minerals and fluids, unit is v / v.

[0040] Further, the total volume of the formation barite is The calculation formula is:

[0041]

[0042] In the formula, r max The mud invasion depth, unit is m;

[0043] r w The wellbore radius, unit is m;

[0044] h is the mud invasion formation thickness, unit is m;

[0045] V ba The relative volume content of barite, unit is v / v.

[0046] Further, the calculation formula of the drilling fluid loss amount V lost is:

[0047]

[0048] The drilling fluid loss amount is:

[0049]

[0050] The present application has the advantages and positive effects that:

[0051] The present application describes the principle that the photoelectric absorption cross section Pe value of barite contained in the drilling fluid is abnormally high than any other rock, mineral and fluid, accurately locates the loss position through the characteristics of high value of Pe curve in the loss well section measured by litho-density logging, and predicts the loss rate by using the correlation between Pe logging value and instantaneous loss rate, and uses the method of multi-mineral analysis and the actual content of barite in the drilling fluid to calculate the loss amount. The method is simple and easy to operate, and the accuracy is reliable. The error of the loss rate and the loss amount calculated by the method is small compared with the data provided by the field, and the effect is good. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 The present application is a drilling fluid loss position determination method.

[0053] Figure 2 The present application is a drilling fluid loss parameter calculation method.

[0054] Figure 3is a leak rate-photoelectric absorption cross section Pe cross plot of an embodiment of the present application.

[0055] Figure 4 is a formation volume model plot of an embodiment of the present application.

[0056] Figure 5 is a Pe positioning leak location plot of QHDX-a well in an embodiment of the present application.

[0057] Figure 6 is a calculated leak rate plot of QHDX-a well in an embodiment of the present application.

[0058] Figure 7 is a barite content plot of QHDX-a well in an embodiment of the present application. DETAILED DESCRIPTION

[0059] The technical solutions of the present application will be described clearly and completely below in conjunction with the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0060] The embodiments of the present application will be further described below in conjunction with the drawings:

[0061] As shown in the figure, a drilling fluid leak location determination method comprises the following steps, Figure 1

[0062] S1: litho-density measurement is performed on the well completion to obtain a density curve and a photoelectric absorption cross section Pe curve;

[0063] S2: the drilling fluid leak location is determined using the high abnormal value of the photoelectric absorption cross section Pe curve. Specifically, the Pe value of barite in the well completion is 266.82 b / e, and the Pe values of other rocks, minerals and fluids are between 0.095 and 21.48 b / e. When the drilling fluid in the well completion enters the leak layer section, the well logging curve Pe shows an abnormal high value affected by the barite.

[0064] As shown in Table 1, the Pe value of barite is much higher than that of other rocks, minerals and fluids, which is several tens of times or even hundreds of times of their values. In the drilling process, in order to prevent the occurrence of blowout, well kick and other accidents, barite is often selected as a drilling fluid weighting agent to increase the specific gravity; before open hole logging, barite is added to the drilling fluid to increase the mud specific gravity, prevent wellbore collapse during logging, and cause resistance or sticking. When the well leakage occurs, the drilling fluid containing barite will seep into the formation, and the Pe curve measured by litho-density logging will show an abnormal high value at the leak layer location. The characteristics of the abnormal high Pe value can be used to accurately determine the leak location.

[0065] ​Preferably, the method is not regional, well site, layer, or lithology-specific, and can be used to identify lost circulation as long as the drilling fluid contains barite.

[0066] Table 1 Pe values of different minerals or rocks and fluids

[0067]

[0068]

[0069] As shown in Figure 2 , the present application also provides a drilling fluid loss parameter calculation method, comprising the following steps.

[0070] S1: Calculate the drilling fluid leakage rate. Specifically, during drilling, different amounts of barite are added according to the different formation pressures, resulting in different concentrations of barite in the drilling fluid of each well, and the measured Pe curve base value is also different. Select the average Pe logging curve value of the wellbore section above 100 m, which is regular and has not occurred leakage, as the base value. Since the photoelectric absorption cross section Pe is nonlinear, the ratio of the Pe value of the lost layer section to the base value is used as a variable to establish a relationship with the instantaneous leakage rate. Specifically, the present embodiment selects 25 leakage point data from 23 exploratory wells in 4 oilfields, which has good correlation. As shown in Figure 3 , the drilling fluid leakage rate is predicted by the ratio of the Pe curve anomaly to the Pe base value Pe' to predict the leakage rate V L The formula is:

[0071] Pe' = Pe / Pe base value

[0072] V L = 20.914*Pe' - 22.435

[0073] R 2 = 0.8148 (Formula 1).

[0074] The actual instantaneous leakage rate of the leaked exploratory well is compared and analyzed with the leakage rate obtained by using the leakage rate formula (1). The absolute error is within 10 m 3 / h, and the relative error is less than 20% except for one well which is greater than 20%. The results are shown in Table 2.

[0075] Table 2 Leakage rate comparison table

[0076]

[0077]

[0078] S2: calculating the drilling fluid loss amount. Specifically, the multi-mineral model analysis is based on the component analysis principle, considers a lithology complex formation as being composed of several locally uniform parts, and uses an optimal interpretation method to process the well logging data of the complex lithology formation, so as to distinguish the mineral categories and the volume content of the formation in the single well profile, thereby the well logging lithology identification and the formation parameter calculation can be performed.

[0079] The optimal well logging interpretation is based on the generalized inversion theory of geophysics, takes the actual well logging value which reflects the formation characteristics more truly after the environmental influence correction as the basis, establishes a target function according to the appropriate mineral model and the well logging equation according to the non-linear weighted least square method principle, continuously adjusts the unknown reservoir parameters by using the optimal technology to make the target function value reach the minimum through the reasonable selection of the initial value of the regional interpretation parameter and the initial value of the reservoir parameter, and calculates the corresponding theoretical well logging value, and compares with the actual well logging value until they are fully approximated, at this time, the unknown quantity used for calculating the theoretical well logging value is the reservoir parameter value which fully reflects the actual value, i.e. the optimal well logging interpretation result.

[0080] Specifically, the Tertiary sandstone and mudstone formation of Bohai oilfield is taken as the target area, and the barite leaked into the formation is regarded as a special mineral in the formation, so the formation can be divided into four parts in the multi-mineral model, as shown in Figure 4 , including the pore, the sandstone skeleton, the argillan and the barite.

[0081] S21: obtaining the relative volume content V ba of the barite in the formation; the response equation of the well logging curve is:

[0082]

[0083] In the formula, ρ b is the density logging measurement value, the unit is g / cm 3 ;

[0084] ρ cl is the argillan skeleton density value, the unit is g / cm 3 ;

[0085] ρ f is the fluid density value, the unit is g / cm 3 ;

[0086] ρ ba is the barite density value, the unit is g / cm 3 ;

[0087] ρ sd is the sandstone skeleton density value, the unit is g / cm 3 ;

[0088] △t is the acoustic time difference logging measurement value, the unit is μs / ft;

[0089] Δt cl is the shale matrix acoustic travel time value, in μs / ft;

[0090] Δt f is the fluid acoustic travel time value, in μs / ft;

[0091] Δt ba is the barite acoustic travel time value, in μs / ft;

[0092] Δt sd is the sand matrix acoustic travel time value, in μs / ft;

[0093] Pe is the Pe value measured by logging, in b / e;

[0094] Pe cl is the shale matrix Pe value, in b / e;

[0095] Pe f is the fluid Pe value, in b / e;

[0096] Pe ba is the barite Pe value, in b / e;

[0097] Pe sd is the sand matrix Pe value, in b / e;

[0098] V is the relative volume content of various minerals and fluids, in v / v.

[0099] S22: obtaining the barite mass M in the formation ba . Specifically, for each well, according to the information provided by the drilling daily report, the concentration of barite in the drilling fluid before logging is calculated as σ, and the drilling fluid loss amount V lost in the formation is calculated, the drilling fluid density at the leakage point is calculated as p c , and the barite mass leaked into the formation is calculated as:

[0100] M ba = σ · V lost · p c (Equation 3)

[0101] In the equation, σ is the concentration of barite in the drilling fluid, in v / v;

[0102] V lost is the drilling fluid loss amount, in m 3 ;

[0103] p c is the drilling fluid density at the leakage point, in g / cm 3 .

[0104] S23: obtaining the total volume V of the formation barite ba . The formation mud invasion depth r is calculated max , combined with the barite volume fraction V calculated by multi-mineral inversion ba , the total volume of the barite invaded into the formation can be calculated as:

[0105]

[0106] In the formula: r max is the mud invasion depth, with the unit of m;

[0107] r w is the wellbore radius, with the unit of m;

[0108] h is the mud invasion formation thickness, with the unit of m;

[0109] V ba is the relative volume content of barite, with the unit of v / v.

[0110] S24: obtaining the mass M of the barite in the formation ba .

[0111] Since the density of barite is between 4.3-4.5 g / cm 3 , we take the intermediate value 4.4 g / cm 3 , then the mass of the barite in the formation can be calculated according to the reservoir inversion parameters as:

[0112]

[0113] S25: obtaining the drilling fluid loss amount V lost .

[0114] By combining formula (3) and formula (5), we can get:

[0115]

[0116] The drilling fluid loss amount can be obtained by conversion deformation as:

[0117]

[0118] The technical scheme of the present application is further illustrated below by combining with specific examples, taking a well QHDX-a in X oilfield of Qinhuangdao as an example, according to the geological daily report: the fourth opening drilling is carried out to 3061.0 m, the return is suddenly reduced, the circulating pool liquid level is lowered, the drilling tool is immediately lifted off the well bottom, the ground pipeline is checked to be normal, it is determined that the loss occurs in the well, the instantaneous leakage rate is monitored to be 27 m 3 / h. The discharge capacity is reduced to 500 L / min, the circulating leakage rate is measured to be 16 m 3 / h; PF-SEAL, PFSZDL were added into the circulation tank, the leakage rate gradually reduced to 10 m 3 / h, the base reported, decided to drill to replace the simple drilling assembly. This time, the total loss of drilling fluid was 43 m 3 .

[0119] Determine the location of the lost circulation zone.

[0120] The geological daily report of this well describes the location of the leak point at 3061.0 m, where the values of each logging curve are normal, with no well leakage response characteristics, as shown in Figure 5 . The Pe curve anomaly high value method was used to correct and locate the lost circulation zone at 3054.5-3057.8 m. The other parts of the lost circulation section have the following logging curve characteristics: the borehole diameter expansion is serious, the dual lateral and microsphere curve values are significantly reduced in the lost circulation section, and the density curve is distorted due to the influence of borehole diameter expansion and well leakage, with abnormally low values. These curve response characteristics further confirm that this section is a well leakage section.

[0121] Calculate the leakage rate.

[0122] Read the average Pe value of the QHDX-a well borehole regular and non-leaking formation as the base value, which is 3.3b / e. Read the Pe value of the lost circulation well section as 8.4b / e. Substitute Pe' = 8.4 / 3.3 = 2.54b / e into formula (1) to calculate the leakage rate as 31 m 3 / h, the geological daily report of this lost layer records the actual instantaneous leakage rate as 27 m 3 / h, the absolute error is 4.0 m 3 / h, the relative error is 13%. The crossplot position of the leak point in this well is shown in Figure 6 .

[0123] Calculate the loss volume.

[0124] As shown in Figure 7 , in the rock volume analysis track, the black filled part is the relative volume content of barite calculated by the multi-mineral analysis method, which has a good correlation with the well leakage layer identified by the Pe curve on the rightmost track. Using the multi-mineral analysis method, the relative volume content of barite in the leak point formation is calculated as V ba = 0.009, the thickness of the lost layer is read as h = 3.3 m using the Pe curve, and according to the drilling report, the yield value is 11 Pa, the drilling fluid density is p c = 1.40 g / cm 3 , the barite concentration is s = 19.6%, the equivalent circulating density is ECD = 1.43 g / cm 3 , and the differential pressure is calculated as AP = ECD·g·h-Pp = 6.48 MPa, where Pp is calculated from the acoustic curve. The borehole radius r w= 8.5 / 2*0.0254 = 0.108m, the lost circulation of this section is 51m calculated by formula (7) 3 The actual lost circulation of this section is 43m 3 The absolute error is 8m 3 The relative error is 18.6%.

[0125] In summary, the present application describes the principle that the photoelectric absorption cross section Pe value of barite contained in drilling fluid is abnormally high than any other rock, mineral and fluid, the characteristics of high value of Pe curve measured by litho-density logging in the lost circulation section is used to accurately locate the lost circulation position, the correlation between Pe logging value and instantaneous leakage rate is used to predict the leakage rate, and the method of multi-mineral analysis is combined with the actual content of barite in drilling fluid to calculate the lost circulation volume. The method for determining the lost circulation position is simple and easy to operate, and the precision is reliable. The leakage rate and lost circulation volume calculated by the method have small error and good effect compared with the data provided by the field.

[0126] The above describes one embodiment of the present application in detail, but the content described is only the preferred embodiment of the present application, and cannot be considered as limiting the implementation range of the present application. Any equivalent changes and improvements made according to the scope of the present application should still belong to the patent coverage range of the present application.

Claims

1. A method for calculating a drilling fluid loss parameter, the method comprising: The method comprises the following steps of: ​ S1: calculating the drilling fluid leakage rate, when the drilling fluid in the well is entering the lost circulation interval, the logging curve Pe is affected by barite to show an abnormally high value, the Pe base value is the average value of the Pe curve of the well section without loss, and the Pe curve abnormal value is the Pe curve value of the loss interval, and the drilling fluid leakage rate is predicted by the ratio of the Pe curve abnormal value to the Pe base value Pe' to predict the leakage rate V L The formula is: V L = 20.914 x Pe' - 22.435 R 2 ＝0.8148； S2: calculating the drilling fluid leakage, comprising the following steps of: S21: obtaining the relative volume content V of barite in the stratum ba ; S22: Obtain the quantity M of barite in the stratum ba， The calculation formula is: M ba = σ · V lost · ρ c In the formula, σ is the concentration of barite in the drilling fluid, in units of v / v; V lost L is the leakage of the drilling fluid, in m 3 ; ρ c ρ is the density of the drilling fluid at the leak point, in g / cm 3 ; S23: Obtain the total volume of the formation barite S24: Obtain the quantity M of barite in the stratum ba， The calculation formula is: S25: Calculate the barite quality M using the barite quality M obtained in S22 ba and the barite quality M obtained in S24 ba , calculate the drilling fluid loss V lost .

2. The method of claim 1, wherein: The relative volume content V of barite in the formation ba The calculation formula is: wherein: p b is the density log measurement in g / cm 3 ; ρ cl is the shale matrix density value in g / cm 3 ; p f p is the fluid density value in g / cm3 3 ; p ba is the density value of barite in g / cm 3 ; p sd is the sandstone skeleton density value, in g / cm3 3 ; △t is the acoustic travel time logging measured value, in units of μs / ft; Δt cl Δt is the mud-laden frame acoustic traveltime value in μs / ft; Δt f Δt is the fluid acoustic travel time in μs / ft; Δt ba is the barite acoustic traveltime value in μs / ft; Δt sd Δt is the acoustic traveltime difference for the sandstone matrix, in μs / ft; Pe is the logging measured Pe value, in units of b / e; Pe cl Pe is the value of the argillaceous matrix, in b / e; Pe f Pe is the value of the fluid, in b / e; Pe ba The value of barite Pe is in b / e. Pe sd Pe is the value of the sandstone skeleton, in b / e; V is the relative volume content of various minerals and fluids, in units of v / v.

3. The method of calculating a loss parameter of a drilling fluid according to claim 1 or 2, characterized in that: the total volume of the formation barite The formula for calculating this is: where: r max is the mud invasion depth, in meters; r w R is the wellbore radius in meters; h is the mud invasion formation thickness, in units of m; V ba For barite phase relative volume content, unit is v / v.

4. The method of claim 3, wherein: The drilling fluid leakage amount V lost The calculation formula is: The drilling fluid leakage is obtained through conversion deformation:

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