Salt cavern gas storage well length open hole section stratum pressure bearing capacity testing method

Abstract

The invention discloses a salt cavern gas storage well length open hole section stratum pressure bearing capacity testing method which sequentially comprises the following steps that S1, according to a stratum pressure bearing capacity value required by target layer design, the annular liquid column pressure equivalent density borne by a casing shoe of a surface casing is calculated; checking the ground breaking pressure equivalent density of the casing shoe according to the well ground breaking pressure test numerical value; s2, judging that the sleeve shoe has a leakage risk; s3, a drifting drilling tool is tripped into a target layer; s4, calculating the density of the high-density drilling fluid; s5, preparing the high-density drilling fluid meeting the requirements; s6, high-density drilling fluid is injected and upwards returned to a safe position point; s7, pulling out the hole to the position above the casing shoe, and closing the semi-closed ram blowout preventer of the corresponding size of the wellhead; and S8, small-displacement pressurization is conducted, the well mouth can be pressurized to the maximum allowable well shut-in pressure of the well mouth, the pressure is stabilized for a period of time, and if the pressure drop does not exceed the set value, it is judged that the well bottom pressure bearing capacity meets the well cementation requirement. The method can accurately obtain the pressure bearing capacity of the well bottom or the target layer.

Description

Technical Field

[0001] The invention relates to a salt cavern gas storage well, in particular to a method for testing the formation pressure bearing capacity of a long open hole section of a salt cavern gas storage well, and belongs to the technical field of salt cavern gas storage. Background Art

[0002] Salt cavern gas storage uses open hole completion in the early stage, because it needs to complete wellbore gas sealing test, cavity making, gas storage and other functions in the later stage. The maximum wellhead casing pressure of some salt cavern gas storages needs to reach about 25MPa. In addition, due to the long operation cycle of gas storages, some are required to operate for more than 50 years. Under the condition of large flow injection and production for a long time, the injection and production wellbore of the gas storage will be subjected to large pressure difference alternating load, which can easily lead to the rupture of cement ring and natural gas leakage. The cementing quality of production casing is required to be high, and the strength, toughness, density of cement stone, and the bonding quality and long-term sealing of cement ring, casing and well wall are required to be high. At the same time, cement slurry is required to return to the ground during cementing.

[0003] The cementing quality of the production casing of the salt cavern gas storage is higher than that of the cementing quality of the oil and gas wells. Due to the current cost saving and simplified wellbore structure, the wells of the salt cavern gas storage are generally not deep, and the wellbore structure is designed as a two-opening system. The surface casing is generally shallow. For example, in a salt cavern gas storage well, the surface casing is about 400m deep. Although it is shallow, in order to ensure the quality of the project, when doing the project design, the surface casing shoes are generally required to be lowered to the stable formation, and the pressure bearing capacity can meet the cementing requirements. Even if some surface casings are shallow and the surface formation is loosely bonded, the formation pressure bearing capacity is low. After drilling through the surface casing shoes, the formation pressure bearing capacity is tested by conventional methods. If it does not meet the requirements, pressure plugging work is immediately carried out to improve the formation pressure bearing capacity and meet the cementing requirements. Therefore, after the second opening is completed, production casing cementing is required. At this time, the open hole section is long and there may be weak links. The cement slurry density of the production casing cementing of the salt cavern gas storage is generally as high as 1.85g / cm 3 As mentioned above, the annular cement slurry column pressure is high, and cement slurry leakage is very likely to occur in weak formations during the cementing construction process, which seriously affects the cementing quality and makes it difficult for the cement slurry to return to the ground, causing the cementing quality to fail to meet the design requirements and having a certain impact on the subsequent well formation and gas storage of the gas storage facility.

[0004] For oil and gas wells, generally after drilling, the entire wellbore pressure test is not performed. Even if leakage occurs during cementing, as long as the oil layer section is sealed, low cement return will not affect the normal development of the oil and gas well.

[0005] In order to effectively ensure the cementing quality of the salt cavern gas storage, to ensure that no leakage occurs during cementing construction, and to ensure that the cement slurry returns to the ground, the full wellbore pressure test is required before the production casing cementing of the salt cavern gas storage. The main purpose is to ensure that the full wellbore meets the cementing requirements when testing the pressure bearing capacity of the target formation. If it meets the requirements, cementing will be carried out. If not, pressure plugging work will be carried out to improve the pressure bearing capacity of the formation until the cementing requirements are met.

[0006] Generally, in oil drilling, the conventional method for testing the pressure bearing capacity of the formation is to close the semi-closed gate or the annular blowout preventer after shutting in the well based on the density of the drilling fluid in the original well, and then slowly pressurize the annulus to determine whether the pressure of the target layer section reaches the required value for cementing construction.

[0007] Before the production casing is fixed, the conventional or existing technology is to test the pressure bearing capacity of the whole wellbore: based on the density of the drilling fluid in the original well, shut in the well and slowly build up pressure. When the pressure at the surface casing shoe reaches the formation fracture pressure at the surface casing shoe, if the annulus is pressurized again, the surface casing shoe will break, so stop pressurizing. If the equivalent drilling fluid density of the surface casing shoe meets 1.85g / cm 3 The above means that even if the bearing capacity of the entire wellbore meets the requirements, cementing can be carried out. If the pressure is not stopped and pressure is continued, the equivalent pressure that the formation at the surface casing shoe has to bear has reached the fracture pressure, the formation fractures and leakage occurs, and the wellhead pressure cannot reach the wellhead pressure value required for the equivalent drilling fluid density of the bottom well target layer to meet the cementing requirements, and the formation is artificially opened, resulting in the stagnation of subsequent construction and a high risk of leakage in subsequent cementing construction.

[0008] For example, the HKP1 well of Huai'an salt cavern gas storage was drilled to 1580m in the second opening with a diameter of 311.1mm and a vertical depth of 1531.41m. The drilling was completed in the middle. The upper casing was 470.77m deep, and the equivalent density of the drilling fluid at the casing shoe was 2.40g / cm 3 The actual drilling fluid density before cementing in the second drilling was 1.35g / cm 3 According to cementing requirements, the cement slurry density is designed to be 1.92g / cm 3 Considering the circulating pressure loss, the equivalent drilling fluid density that the bottom of the well should be able to withstand is at least 1.92g / cm 3 .

[0009] According to static calculation, before the second cementing, the original drilling fluid density in the well is used to test the bearing capacity of the downhole formation. After the well is shut in, the wellhead pressure must reach 8.56MPa. Under this wellhead pressure, the well section pressure at the casing shoe = 8.56 + 0.00981 * 470.77 * 1.35 = 14.79MPa, which is equivalent to an equivalent drilling fluid density of 3.20g / cm 3, much larger than the equivalent drilling fluid density of 2.40g / cm at the casing shoe 3 That is, when the wellhead has not reached 8.56MPa, the casing shoe has already lost ground, resulting in the cessation of the pressure test, and it is impossible to determine whether the bottom of the well can withstand 1.92g / cm 3 If the equivalent drilling fluid density is only 2.40g / cm at the casing shoe, 3 When the drilling fluid stops, the wellhead pressure is 4.84 MPa, and the equivalent drilling fluid density at the bottom of the well is 1.67 g / cm 3 , less than 1.92g / cm 3 , it is impossible to determine whether the bottom hole pressure bearing capacity meets the cementing requirements.

[0010] The cement slurry density range during the cementing process of this well is about 1.85-1.92g / cm 3 , which is much lower than the equivalent drilling fluid density of the casing shoe. During the normal cementing process, the casing shoe is in a safe state in the weakest section of the open hole. In this shallow well structure, the original drilling fluid density is used as the formation pressure bearing capacity test method. In order to ensure that the bottom hole pressure bearing capacity meets the cementing requirements, the equivalent drilling fluid density at the casing shoe is much greater than the equivalent drilling fluid density at the casing shoe, resulting in the failure of the pressure test.

[0011] It is extremely difficult to improve the bearing capacity of the formation at the overshoe and finally reach the design bearing capacity. It takes a lot of manpower and material resources to complete the cycle of plugging, testing and plugging again, which greatly affects the progress of drilling and completion construction and is not feasible to a certain extent. Relatively speaking, increasing the density of drilling fluid in the wellbore is an economical and effective method.

[0012] The Chinese invention patent with publication number CN 103015945B discloses a process for improving the pressure bearing capacity of the formation, comprising the following steps: a. According to the data of the formation pore size obtained by coring the exploration well in the block, the formation pore size data of the well is obtained, and the plugging slurry is prepared with gel and plugging particles of corresponding sizes according to the formation pore size; b. The prepared plugging slurry is pumped into the wellbore, and after the wellbore is filled, the well plugger is closed; c. The plugging slurry is continuously pumped into the wellbore to squeeze the plugging slurry in the wellbore into the formation; d. The rigid plugging particles build bridges at the formation pores to establish a skeleton, and the flexible plugging particles fill and plug between the rigid plugging particles, filling the formation pores near the wellbore, so that the casing pressure value of the well plugger is continuously increased, thereby improving the pressure bearing capacity of the formation. The defects of this technical solution are: 1. This process still uses a targeted plugging method to plug the leaky layer. After the plugging is successful, the formation pressure bearing capacity is tested. This method still has the problems of long time consumption, cumbersome operation and high plugging cost for repeated plugging. 2. When plugging the leaky layer according to the coring data, due to the differences between different wells and formations, the previously leaky layer corresponding to the well may not necessarily leak and may not need to be plugged, which leads to doubts about the rationality and necessity of this patented process.

[0013] The Chinese invention patent with publication number CN 106150489B discloses a dynamic test method for formation pressure bearing capacity and a cementing method, which belongs to the field of drilling and cementing technology. The present invention first collects the wellhead pressure when the performance of the drilling fluid outlet and inlet is consistent; then calculates the circulating dynamic friction generated by the drilling fluid in each well section of the annulus according to the collected wellhead pressure, as well as the annulus and casing size parameters; finally, calculates the dynamic fluid column pressure acting on the layer according to the annulus wellbore size and the calculated circulating dynamic friction, and obtains the formation pressure bearing capacity. The present invention uses the circulating dynamic friction generated by the drilling fluid in the circulation channel composed of the casing and the annulus, and acts on the formation together with the static liquid column pressure of the drilling fluid, and changes the size of the circulating dynamic friction by adjusting the circulation displacement, so as to test the pressure bearing capacity of different layers. The defects of this technical solution are: it can only calculate the circulating pressure loss and dynamic bearing capacity under the condition of dynamic circulation of the original drilling fluid density, and it is impossible to detect the bearing capacity of the formation by pressurizing the annulus after shutting in the well when the drilling fluid is static, and it is impossible to detect the bearing capacity of the formation by using different drilling fluid densities in sections. Summary of the invention

[0014] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract of the specification of this application and the title of the invention, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0015] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0016] The purpose of the present invention is to provide a method for testing the pressure bearing capacity of the formation in the long open hole section of a salt cavern gas storage well, in view of the above-mentioned problems existing in the existing method for testing the pressure bearing capacity of the entire wellbore of a salt cavern gas storage well, which can solve the problem that the pressure bearing capacity of the target layer cannot be accurately obtained when the original method is used to test the pressure bearing capacity of the entire wellbore.

[0017] In order to solve the above technical problems, the method for testing the formation pressure bearing capacity of the open hole section of the salt cavern gas storage well of the present invention comprises the following steps in sequence:

[0018] Step S1: Calculate the equivalent density of the annular liquid column pressure ρ borne by the casing shoe of the surface casing according to the formation pressure bearing capacity value required by the target layer design. b当量 According to the well burst pressure test value, the equivalent density of the casing shoe burst pressure ρ is obtained. b ;

[0019] Step S2: Determine ρ b当量 and ρ b The size of b当量 >ρ b , it is determined that the casing shoe will leak when the target layer reaches the formation pressure bearing capacity required by the design, and the process goes to step S3;

[0020] Step S3, lowering the well drilling tool to the target layer;

[0021] Step S4, determining that the well section below the casing shoe needs to be replaced with high-density drilling fluid, simulating the high-density drilling fluid to return from the annulus to a safe distance below the casing shoe, the top position of the high-density drilling fluid is defined as the "safe position point", and the density of the high-density drilling fluid is calculated;

[0022] Step S5, preparing high-density drilling fluid that meets the requirements;

[0023] Step S6, start the pump to inject high-density drilling fluid from the water hole at the bottom of the well drilling tool, and return to the "safe position point" set in step S4;

[0024] Step S7, pulling the drill bit to the top of the casing shoe, and closing the semi-closed gate blowout preventer of corresponding size at the wellhead;

[0025] Step S8, after the semi-closed gate blowout preventer at the wellhead is closed, the pressure is slowly increased at a small displacement to gradually increase the wellhead shut-in pressure; if the wellhead can be pressurized to the maximum allowable wellhead shut-in pressure, the pressure is stabilized for a period of time, and the pressure drop does not exceed the set value, then the pressure bearing capacity meets the design requirements, and it is determined that the bottom hole pressure bearing capacity meets the cementing requirements.

[0026] Furthermore, in step S1, the annular liquid column pressure equivalent density ρ b当量 The calculation formula is as follows:

[0027] P0 =0.00981*H d *(ρ c -ρ m ⑴

[0028] ρ b当量 =P 0 / 0.00981 / H b +ρ m ⑵

[0029] Where: P 0 -Wellhead shut-in pressure, MPa;

[0030] H d -Vertical depth of well bottom, m;

[0031] H b - casing shoe vertical depth, m;

[0032] ρ c - Cementing design requirements for cement slurry density, g / cm 3 ;

[0033] ρ m -Actual drilling fluid density in the well, g / cm 3 ;

[0034] ρ b当量 -Equivalent drilling fluid density at casing shoe, g / cm 3 .

[0035] Furthermore, when there is a weak formation, the casing shoe is vertically lowered to a depth of H b Replaced by the vertical depth of weak formations.

[0036] Furthermore, if b当量 <ρ b , it is determined that there is no risk of casing shoe leakage when the target layer reaches the formation pressure bearing capacity required by the design, then the process goes to step S7;

[0037] Furthermore, the safety distance in step S4 is 30 meters.

[0038] Furthermore, in step S4

[0039] The density of high-density drilling fluid is calculated by reverse calculation using the following formulas:

[0040] P 0max =(ρ b -ρ m )*g*H b ⑶

[0041] P d =ρ c *g*H c +P0max +ρ 高密度 *g*(H d -H c ) (⑷)

[0042] Where: P 0max - Maximum allowable shut-in pressure at the wellhead that does not cause formation rupture at the casing shoe, MPa;

[0043] ρ 高密度 -Density of high-density drilling fluid, g / cm 3 ;

[0044] H c - Vertical depth of top of high-density drilling fluid, m;

[0045] P d - Design required stratum pressure bearing capacity, MPa; the calculation formula is as follows: P d =ρ c *g*H d .

[0046] Furthermore, in step S8, the pressure is slowly increased at a displacement of 2-4 L / s. If the wellhead can be pressurized to the maximum allowable shut-in pressure at the wellhead, the pressure is stabilized for 10 minutes, and the pressure drop is no more than 0.05 MPa, it is determined that the bottom hole pressure bearing capacity meets the cementing requirements.

[0047] Furthermore, in step S8, if the wellhead pressurization cannot be increased to the maximum allowable shut-in pressure at the wellhead, the bottom hole pressure bearing capacity cannot meet the cementing requirements. After entering the pressure-bearing plugging operation to improve the bottom hole pressure bearing capacity, return to step S1 for re-verification until the bottom hole pressure bearing capacity meets the cementing requirements.

[0048] Compared with the prior art, the present invention has achieved the following beneficial effects: the present invention utilizes the specific value of the pressure bearing capacity of the casing shoe or the leaky layer, and the specific value is based on whether there is leakage during the actual drilling process. If there is no leakage, it only needs to be calculated based on the formation fracture pressure data at the casing shoe; by using precise calculation, the drilling fluid of the well section below the leaky layer is replaced with the density required for calculation, thereby reducing the value of wellhead pressurization, avoiding the casing shoe or the leaky layer from bearing pressure exceeding the pressure bearing capacity of the formation, resulting in the inability to accurately obtain the formation pressure bearing capacity value of the entire wellbore. Compared with the conventional formation pressure bearing capacity test method used in the past, the present invention improves the success rate of the formation pressure bearing capacity test, saves a lot of time for the formation pressure bearing capacity test of long open hole sections such as salt cavern gas storage, and improves construction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor. The accompanying drawings are only provided for reference and explanation, and are not used to limit the present invention.

[0050] in:

[0051] Figure 1 This is a flow chart of the method for testing the formation pressure bearing capacity of the long open hole section of the salt cavern gas storage well. DETAILED DESCRIPTION

[0052] In the following description of the present invention, the terms "upper", "lower" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not mean that the device must have a specific position. For a horizontal well section, the position close to the wellhead is "upper" and the position close to the well bottom is "lower".

[0053] In order to make the technical means, creative features, objectives and effects of the present invention easier to understand, the present invention is further described below in conjunction with specific diagrams. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0055] The method for testing the formation pressure bearing capacity of the open hole section of the salt cavern gas storage well of the present invention comprises the following steps in sequence:

[0056] Step S1: Calculate the equivalent density of the annular liquid column pressure ρ borne by the casing shoe of the surface casing according to the formation pressure bearing capacity value required by the target layer design. b当量 According to the well burst pressure test value, the equivalent density of the casing shoe burst pressure ρ b .

[0057] The calculation formula of equivalent drilling fluid density at casing shoe is as follows:

[0058] P 0 =0.00981*H d *(ρ c -ρ m ⑴

[0059] ρ b当量 =P 0 / 0.00981 / H b +ρ m ⑵

[0060] Where: P 0 -Wellhead shut-in pressure, MPa;

[0061] H d -Vertical depth of well bottom, m;

[0062] H b - casing shoe vertical depth, m;

[0063] ρ c - Cementing design requirements for cement slurry density, g / cm 3 ;

[0064] ρ m -Actual drilling fluid density in the well, g / cm 3 ;

[0065] ρ b当量 -Equivalent drilling fluid density at casing shoe, g / cm 3 .

[0066] When there are weak strata, H b Replaced by the vertical depth of weak formations.

[0067] Step S2: Determine ρ b当量 and ρ b The size of b当量 <ρ b , it is determined that there is no risk of casing shoe leakage when the target layer reaches the formation pressure bearing capacity required by the design, then the process goes to step S7;

[0068] As b当量 >ρ b , it is determined that the casing shoe will leak when the target layer reaches the formation pressure bearing capacity required by the design. In order to make the formation pressure bearing capacity test reach a qualified level, it is necessary to enter step S3;

[0069] Step S3, lowering the well drilling tool to the target layer, i.e., the well bottom;

[0070] Step S4, determine that the well section below the casing shoe needs to be replaced with high-density drilling fluid; for safety reasons, after the high-density drilling fluid flows out of the cone water hole, it returns from the annulus to a safe distance below the casing shoe, usually 30 meters. The top position of the high-density drilling fluid is defined as the "safe position point", and the density of the high-density drilling fluid is calculated by reverse calculation using the following formulas (3) and (4):

[0071] P 0max =(ρ b -ρ m )*g*H b ⑶

[0072] P d =ρ c *g*H c +P 0max +ρ 高密度 *g*(H d -H c ) (⑷)

[0073] Where: P 0max - Maximum allowable shut-in pressure at the wellhead that does not cause formation rupture at the casing shoe, MPa;

[0074] ρ 高密度 -Density of high-density drilling fluid, g / cm 3 ;

[0075] H c - Vertical depth of top of high-density drilling fluid, m;

[0076] P d - Design required stratum pressure bearing capacity, MPa; the calculation formula is as follows: P d =ρ c *g*H d .

[0077] Step S5: prepare 高密度 Required high-density drilling fluid;

[0078] Step S6, start the pump to inject high-density drilling fluid from the water hole at the bottom of the well drilling tool, and return to the "safe position point" set in step S4;

[0079] Step S7: For safety reasons, the well is pulled up to the casing shoe, and the through-hole drilling tool is placed in the surface casing before the well is shut down. According to the specific size of the drilling tool used, the semi-closed gate blowout preventer of the corresponding size at the wellhead is closed;

[0080] Step S8, after the semi-closed gate blowout preventer at the wellhead is closed, the pressure is slowly increased at a displacement of 2-4 L / s to gradually increase the wellhead shut-in pressure;

[0081] If the wellhead can be pressurized to the maximum allowable shut-in pressure at the wellhead, the pressure can be stabilized for 10 minutes, and the pressure drop is no more than 0.05MPa, which meets the design pressure bearing capacity, then it is determined that the bottom hole pressure bearing capacity meets the cementing requirements; subsequent operations enter the stage of cementing the lowering of the production casing.

[0082] If the wellhead pressurization cannot be increased to the maximum allowable shut-in pressure at the wellhead, the bottom hole pressure bearing capacity cannot meet the cementing requirements. After entering the pressure-bearing plugging operation to improve the bottom hole pressure bearing capacity, return to step S1 for re-verification until the bottom hole pressure bearing capacity meets the cementing requirements. Subsequent operations enter the production casing cementing stage.

[0083] The following is an explanation of the method for testing the formation pressure bearing capacity of the open hole section of the salt cavern gas storage well of the present invention in conjunction with the construction of a specific well.

[0084] Example: Taking the HKP1 well of Huai'an salt cavern gas storage as an example, the well was drilled to 1580m with a diameter of Φ311.1mm and a vertical depth of H d The depth of the upper casing is 470.77m. According to the ground breaking pressure test value of the well, the ground breaking pressure equivalent density ρ at the casing shoe is obtained. b 2.40g / cm 3 , actual drilling fluid density before cementing in the second drilling m 1.35g / cm 3 According to cementing requirements, cement slurry density ρ is required by cementing design. c 1.92g / cm 3 Considering the circulating pressure loss, the equivalent drilling fluid density that the bottom of the well should be able to withstand is at least 1.92g / cm 3 .

[0085] Step S1: Calculate the wellhead shut-in pressure P according to formula (1): 0 :

[0086] P 0 =0.00981*H d *(ρ c -ρ m )=0.00981*1531.41*(1.92-1.35)=8.56MPa.

[0087] Calculate the equivalent drilling fluid density ρ at the casing shoe according to formula (2) b当量 :

[0088] ρ b当量 =P 0 / 0.00981 / H b +ρ m =8.56 / 0.00981 / 470.77+1.35=3.20g / cm 3 .

[0089] Step S2, determine ρ b当量 and ρ b The size of b当量 >ρ b , it is determined that leakage will occur at the casing shoe when the target layer reaches the formation pressure bearing capacity required by the design. In order to make the formation pressure bearing capacity test reach a qualified level, it is necessary to enter step S3.

[0090] Step S3, lower the well drilling tool to the target layer, i.e., the bottom of the well. The well drilling tool is, from bottom to top, Φ311.1mm cone + Φ203mm spiral drill collar * 3 + Φ178mm spiral drill collar * 6 + Φ127mm heavy drill pipe * 21 + Φ127mm drill pipe.

[0091] Step S4, calculate according to formula (3):

[0092] P 0max =(ρ b -ρ m )*g*H b =(2.4-1.35)*0.00981*470.77=4.85MPa;

[0093] For safety reasons, after high-density drilling fluid flows out of the cone water hole, it returns from the annulus to a safe distance below the casing shoe, that is, the well depth is 500m, calculated according to formula (4):

[0094] P d =ρ m *g*H b +P 0 +ρ 高密度 *g*(H d -H b ) is transformed into:

[0095] ρ 高密度 =(P d -ρ m *g*H b -P 0 ) / g / (H d -H b )

[0096] =(1.92*0.00981*1531.41-1.35*0.00981*500-4.85) / 0.00981 / (1531.41-500)

[0097] =1.71g / cm 3 ;

[0098] The density of high-density drilling fluid is 1.71 g / cm 3 , the 500m-1580m section needs to be replaced with a density of 1.71g / cm 3 High density drilling fluid.

[0099] Step S5, preparing a density of 1.71 g / cm 3 High-density drilling fluid;

[0100] Step S6, start the pump to inject high-density drilling fluid from the drill bit water hole, and return to the "safe position point" set in step S4;

[0101] Step S7, for safety reasons, the drill is pulled up to the casing shoe, the through-hole drilling tool is placed in the surface casing at a well depth of 460m, and then the Φ127mm semi-closed gate blowout preventer is closed;

[0102] Step S8, after the well is closed, slowly increase the pressure at a displacement of 2-4L / s to gradually increase the wellhead shut-in pressure. When the maximum wellhead shut-in pressure of 4.85MPa is reached, the pressure is stabilized for 10 minutes, and the pressure drop is no more than 0.05MPa, which meets the design pressure bearing capacity. At this point, the subsequent production casing cementing operation can be carried out.

[0103] The above is only a preferred embodiment of the present invention, which shows and describes the basic principles, main features and advantages of the present invention, but does not limit the scope of patent protection of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. In addition to the above embodiments, the present invention may have other implementation modes without departing from the spirit and scope of the present invention. The present invention may also have various changes and improvements, and all technical solutions formed by equivalent substitution or equivalent transformation fall within the scope of protection required by the present invention. The scope of protection required by the present invention is defined by the attached claims and their equivalents. The technical features not described in the present invention can be realized by or using existing technologies, which will not be repeated here.

Claims

1. A method for testing the formation pressure bearing capacity of a salt cavern gas storage well length open hole section, characterized in that: The steps are as follows: Step S1: Calculate the equivalent density of the annular liquid column pressure ρ borne by the casing shoe of the surface casing according to the formation pressure bearing capacity value required by the target layer design. b当量 According to the well burst pressure test value, the equivalent density of the casing shoe burst pressure ρ is obtained. b ; Step S2: Determine ρ b当量 and ρ b The size of b当量 >ρ b , it is determined that the casing shoe will leak when the target layer reaches the formation pressure bearing capacity required by the design, and the process goes to step S3; Step S3, lowering the well drilling tool to the target layer; Step S4, determining that the well section below the casing shoe needs to be replaced with high-density drilling fluid, simulating the high-density drilling fluid to return from the annulus to a safe distance below the casing shoe, the top position of the high-density drilling fluid is defined as the "safe position point", and the density of the high-density drilling fluid is calculated; Step S5, preparing high-density drilling fluid that meets the requirements; Step S6, start the pump to inject high-density drilling fluid from the water hole at the bottom of the well drilling tool, and return to the "safe position point" set in step S4; Step S7, pulling the drill bit to the top of the casing shoe, and closing the semi-closed gate blowout preventer of corresponding size at the wellhead; Step S8, after the semi-closed gate blowout preventer at the wellhead is closed, the pressure is slowly increased at a small displacement to gradually increase the wellhead shut-in pressure; if the wellhead can be pressurized to the maximum allowable wellhead shut-in pressure, the pressure is stabilized for a period of time, and the pressure drop does not exceed the set value, then the pressure bearing capacity meets the design requirements, and it is determined that the bottom hole pressure bearing capacity meets the cementing requirements.

2. The method for testing the formation pressure bearing capacity of the open hole section of the salt cavern gas storage well according to claim 1 is characterized by: In step S1, the annular liquid column pressure equivalent density ρ b当量 The calculation formula is as follows: P0=0.00981*H d *(r c -r m )⑴ r b当量 =P0 / 0.00981 / H b +r m ⑵ Where: P0-wellhead shut-in pressure, MPa; H d -Vertical depth of well bottom, m; H b - casing shoe vertical depth, m; ρ c - Cementing design requirements for cement slurry density, g / cm 3 ; ρ m -Actual drilling fluid density in the well, g / cm 3 ; ρ b当量 -Equivalent drilling fluid density at casing shoe, g / cm 3 .

3. The method for testing the formation pressure bearing capacity of the open hole section of the salt cavern gas storage well according to claim 2 is characterized by: When there is a weak formation, the casing shoe should be vertically lowered to a depth of H. b Replaced by the vertical depth of weak formations.

4. The method for testing the formation pressure bearing capacity of the open hole section of the salt cavern gas storage well according to claim 1 is characterized by: As b当量 <ρ b , it is determined that there is no risk of casing shoe leakage when the target layer reaches the formation pressure bearing capacity required by the design, then the process goes to step S7.

5. The method for testing the formation pressure bearing capacity of the open hole section of the salt cavern gas storage well according to claim 1 is characterized by: The safety distance in step S4 is 30 meters.

6. The method for testing the formation pressure bearing capacity of the open hole section of the salt cavern gas storage well according to claim 1 is characterized by: In step S4 The density of high-density drilling fluid is calculated by reverse calculation using the following formulas: P 0max =(ρ b -r m )*g*H b ⑶ P d =ρ c *g*H c +P 0max +ρ 高密度 *g*(H d -H c )⑷ Where: P 0max - Maximum allowable shut-in pressure at the wellhead that does not cause formation rupture at the casing shoe, MPa; ρ 高密度 -Density of high-density drilling fluid, g / cm 3 ; H c - Vertical depth of top of high-density drilling fluid, m; P d - Design required formation pressure bearing capacity, MPa; The calculation formula is as follows: d =ρ c *g*H d .

7. The method for testing the formation pressure bearing capacity of the open hole section of the salt cavern gas storage well according to claim 1 is characterized by: In step S8, the pressure is slowly increased at a displacement of 2-4 L / s. If the wellhead can be pressurized to the maximum allowable shut-in pressure at the wellhead, the pressure is stabilized for 10 minutes, and the pressure drop is no more than 0.05 MPa, it is determined that the bottom hole pressure bearing capacity meets the cementing requirements.

8. The method for testing the formation pressure bearing capacity of the open hole section of the salt cavern gas storage well according to claim 1 is characterized by: In step S8, if the wellhead pressurization cannot be increased to the maximum allowable shut-in pressure at the wellhead, the bottom hole pressure bearing capacity cannot meet the cementing requirements. After entering the pressure-bearing plugging operation to improve the bottom hole pressure bearing capacity, return to step S1 for re-verification until the bottom hole pressure bearing capacity meets the cementing requirements.

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