Drilling and cementing methods for directional and vertical wells

Abstract

This invention discloses a drilling and cementing method for directional and vertically inclined wells, comprising: obtaining reservoir properties based on logging data; pre-setting a drilling plan based on the reservoir properties; drilling a deviated wellbore according to the drilling plan; and cementing to obtain a directional and vertically inclined well. This invention addresses the differences between the drilling process for vertically inclined wells and vertical wells by linking reservoir properties with the drilling plan. It formulates a drilling plan suitable for the reservoir before drilling, resulting in a highly adaptable and effective plan that reduces problems such as excessive inclination angle deviation and significant discrepancies between actual and predicted drilling conditions during the drilling process.

Description

Technical Field

[0001] This invention belongs to the field of drilling technology, specifically relating to a drilling and cementing method for directional and vertical wells. Background Technology

[0002] Drilling is an engineering process that uses mechanical equipment to drill cylindrical holes of a certain depth into the formation. It is one of the almost essential procedures in the current development of oil and gas reservoirs. In the current development of oil and gas reservoirs, the boreholes used for applications such as oil wells and gas wells are usually drilled vertically. Even for horizontal wells, the vertical section is usually drilled first, and then the horizontal section is gradually transitioned through a build-up section to form a horizontal well.

[0003] However, with the continuous development of directional and driven wells, inclined and vertical well drilling technology emerged abroad in the early 1980s and has been increasingly adopted by some foreign oil fields, while its use is rare in China. In the process of oil and gas reservoir development, it is sometimes necessary to drill inclined wells. For example, if the oil-bearing formation is located below a building area or a natural barrier such as a river, or above the corresponding well location in the ocean, it is not feasible or suitable to build a drilling platform independently. As oil and gas reservoirs are developed, the demand for and importance of vertical and inclined well drilling technology is increasing.

[0004] Similar to vertical drilling, the drilling process for vertically inclined wells typically uses rotary drilling to reach the target reservoir. Rotary drilling is accomplished by rotating a drill string with drill pipe and drill bit at its lower end. Weight is applied to the drill string during rotation to create a borehole in the formation. The drill string is hollow, and drill pipe is added to increase its length as the borehole deepens. However, compared to traditional vertical drilling, the borehole inclination results in significant differences in stress on both sides of the drill string, especially the drill bit, and the influence of buoyancy within the wellbore. This leads to a substantial difference in actual drilling pressure compared to vertical drilling, resulting in potentially large discrepancies between the inclination angle and the down-the-hole angle in vertically inclined wells. Furthermore, due to the inclined drilling, the actual thickness of the rock formation reached also differs significantly from that in vertical drilling. Therefore, empirical parameters from vertical drilling are often difficult to apply to drilling vertically inclined wells within the same reservoir. Summary of the Invention

[0005] The purpose of this invention is to provide a drilling and cementing method for directional vertical wells, which solves the technical problems of high drilling difficulty and poor wellbore inclination angle control in the prior art.

[0006] The technical solution adopted in this invention is: a drilling and cementing method for directional and vertical wells, comprising the following steps:

[0007] Step 1: Obtain reservoir properties based on well logging data;

[0008] Step 2: Pre-determine the drilling plan based on reservoir properties;

[0009] Step 3: Drill the deviated wellbore according to the drilling plan;

[0010] Step 4: Cementing to obtain a directional vertical well.

[0011] The invention is further characterized in that,

[0012] The reservoir properties in step 1 include reservoir stratification, lithology of each stratum, and drilling thickness of each stratum; wherein, the lithology of each stratum includes hardness; the drilling thickness of each stratum is determined by the reservoir thickness of the stratum, the inclination angle α of the reservoir, and the preset inclination angle β of the wellbore, and is calculated as follows: drilling thickness of each stratum = reservoir thickness of the stratum / cosα / cosβ.

[0013] Step 2, the drilling plan includes the drill string structure, drill string parameters, and drilling parameter adjustment plan. The drilling parameters include drilling time and stop time. The drilling time for each layer is preset according to the drilling thickness, and the stop time between adjacent layers is preset according to the reservoir layer. The drill string parameters include drilling pressure and drilling speed. The drilling pressure and drilling speed for each layer are preset according to the hardness of the layer.

[0014] The preset drilling pressure and drilling speed for each layer based on the hardness of the layer include: first, preset the base value of drilling pressure and the base value of drilling speed based on the hardness of the layer; then, calculate the preset value of drilling pressure and the preset value of drilling speed based on the base value of drilling pressure and the base value of drilling speed.

[0015] The baseline values ​​for drilling pressure and drilling speed are the drilling pressure and drilling speed data used in vertical well drilling for strata with intermediate hardness in the reservoir.

[0016] The preset value of drilling pressure is calculated using the following formula:

[0017] Preset value of drilling pressure = Base value of drilling pressure / (tanβ)2 × F / (F buoyancy × cosβ)

[0018] Where F is the weight of the drill bit, and F_buoyancy is the buoyancy force acting on the drill bit during the drilling process;

[0019] The preset drilling rate is calculated using the following formula:

[0020] The preset value of drilling speed = (base value of drilling pressure / preset value of drilling pressure)1 / 2 × base value of drilling speed.

[0021] Step 3 specifically involves injecting drilling fluid between the drill pipe and the wellbore wall. The drilling fluid circulates downward along the drill pipe and upward along the annulus between the drill pipe and the wellbore wall. Specifically, the drilling fluid is injected into the wellbore along the lower inclined side of the drill pipe near the wellbore.

[0022] The viscosity of the drilling fluid shall not exceed 100 mPa·s; the sand-carrying velocity in clean water shall not be less than 1.0 m / s.

[0023] Step 4 specifically involves: withdrawing the drill string and inserting the casing; providing cement slurry containing blast furnace slag and alkali; circulating the cement slurry downwards along the casing and upwards into the annulus formed between the casing and the wellbore wall; wherein the cement slurry is injected into the wellbore along the lower inclined side of the drill pipe away from the wellbore.

[0024] The cement slurry contains clay, and the clay content, by mass fraction, is not less than 6% and not more than 12%.

[0025] The beneficial effects of this invention are as follows: The drilling and cementing method for directional and vertical wells of this invention addresses the differences between the drilling process for vertical and vertical wells and that for straight wells. It links reservoir properties with the drilling plan, formulating a drilling plan suitable for the reservoir before drilling. This results in a highly adaptable and effective plan, reducing problems such as excessive inclination angle deviation and significant discrepancies between actual and predicted drilling results during drilling. Furthermore, this invention links reservoir properties with the drilling plan, especially the stratified lithology and drilling plan itself, adjusting the plan to achieve higher effectiveness and applicability. This reduces the degree and frequency of drilling parameter adjustments during the drilling process, thereby improving drilling efficiency and effectiveness. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the drilling and cementing method for directional vertical wells according to the present invention. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0028] Example 1

[0029] This invention provides a drilling and cementing method for directional and vertically inclined wells, such as... Figure 1 As shown, it includes the following steps:

[0030] Step 1: Obtain reservoir properties based on well logging data, including reservoir stratification, lithology of each stratum, and drilling thickness of each stratum. The lithology of each stratum includes hardness. The drilling thickness of each stratum is determined by the reservoir thickness of the stratum, the inclination angle α of the reservoir, and the preset inclination angle β of the wellbore. The calculation method is: drilling thickness of each stratum = reservoir thickness of the stratum / cosα / cosβ.

[0031] Step 2: Pre-determine the drilling plan based on reservoir properties, including drill string structure, drill string parameters, and adjustment plans for drilling parameters. Drilling parameters include drilling time and downtime. The drilling time for each layer is pre-determined based on the drilling thickness, and the downtime between adjacent layers is pre-determined based on the reservoir layers. Drill string parameters include pressure on drill (PBD) and rate of drill (RWD). The PBD and RWD for each layer are pre-determined based on the hardness of the layers. Specifically: First, base values ​​for PBD and RWD are pre-determined based on the hardness of the layers. These base values ​​are the PBD and RWD data used in vertical well drilling for layers with intermediate hardness in the reservoir. Then, the pre-determined values ​​for PBD and RWD are calculated based on these base values. PBD is directly proportional to the hardness of the layer, and RWD is inversely proportional to the hardness of the layer. The pre-determined PBD value is calculated using the following formula:

[0032] Preset value of drilling pressure = Base value of drilling pressure / (tanβ)2 × F / (F buoyancy × cosβ)

[0033] Where F is the weight of the drill bit, and F_buoyancy is the buoyancy force acting on the drill bit during the drilling process;

[0034] The preset drilling rate is calculated using the following formula:

[0035] The preset value of drilling speed = (base value of drilling pressure / preset value of drilling pressure)1 / 2 × base value of drilling speed.

[0036] Step 3: Drill the deviated wellbore according to the drilling plan. Specifically, drilling fluid is injected between the drill pipe and the wellbore wall. The drilling fluid circulates downwards along the drill pipe and upwards along the annulus between the drill pipe and the wellbore wall. The drilling fluid is injected into the wellbore along the lower slope side of the drill pipe closest to the wellbore, thereby reducing the viscosity on this side and decreasing the filter cake, thus reducing the pressure on the drill pipe on the lower slope. The viscosity of the drilling fluid should not exceed 100 mPa·s; its sand-carrying velocity in clean water should not be less than 1.0 m / s.

[0037] Step 4, cementing, to obtain a directional vertical well, specifically: the drill string is removed and the casing is inserted; a cement slurry containing blast furnace slag and alkali is provided; the cement slurry is circulated downwards along the casing and upwards into the annulus formed between the casing and the wellbore wall; wherein, the cement slurry is injected into the wellbore along the lower inclined side of the drill pipe away from the wellbore, allowing the active components in the cement slurry to first solidify on the upper inclined side. The cement slurry contains clay, and the clay content, by mass fraction, is not less than 6% and not more than 12%.

[0038] Example 2

[0039] In Example 1, step 1 requires clarification. Reservoir stratification is based on the type of rock forming the strata, such as shale, clay, chlorite, and mica schist. Lithology refers to the type, hardness, porosity, filling material, and fracture characteristics of the rocks forming the strata. Since porosity, filling material, and fracture base are directly related to the hardness of the strata, this invention uses hardness directly to represent the lithology of the strata. When acquiring well logging data, this data is obtained by measuring the original rock sample.

[0040] The preset inclination angle β of the wellbore refers to the angle between the wellbore and the vertical wellbore, and is always less than 45°. This is because vertical wells with inclination angles higher than 45° are extremely prone to collapse and blockage during drilling and are rarely used. Therefore, this invention targets vertical wells with inclination angles β all below 45°. Furthermore, to further reduce the difference between the lateral displacement of the drilled wellbore and the actual desired lateral displacement, the preset inclination angle β can be slightly lower than the actual desired inclination angle, such as 2-3° lower.

[0041] Example 3

[0042] In step 2 of Example 1, it should be noted that since the drilling speed of the drill string is usually fixed, the time required for drilling each layer can be estimated based on the drilling thickness, i.e., the preset layer drilling time. Then, the drilling parameters of each layer are adjusted according to the preset layer drilling time.

[0043] At the interface between adjacent strata, the reservoir properties change drastically due to differences in lithology. This inevitably involves adjusting drill string parameters, releasing stress, and assessing drilling conditions. Therefore, when the drill bit moves from one stratum to the interface between the next, an appropriate dwell time is necessary to facilitate parameter adjustment, stress release, and well condition assessment. This dwell time can be adjusted based on the degree of lithological difference between strata, such as the difference in rock hardness. A greater hardness difference requires a longer dwell time; moving from a high-hardness stratum to a low-hardness stratum also requires a longer dwell time. For example, when the hardness of the upper stratum is 6 and the hardness of the lower stratum is 3, the dwell time can be 5–8 minutes; while when the hardness of the lower stratum is 5 and the hardness of the upper stratum is 4, the dwell time can be 2–3 minutes.

[0044] The buoyancy force experienced by the drill bit during drilling is an estimated value, calculated based on the density of the fluid formed during drilling, as well as the volume and density of the drill bit. The calculation method is the same as that used for calculating the buoyancy force experienced by a conventional solid in a fluid.

[0045] The structure of the drilling tools can adopt existing drilling tool structures suitable for inclined and vertical wells. For example, the drill bit can be a PDC drill bit, a roller cone drill bit, or a full-hole drill bit. Multiple drilling tools can also be used in combination. For example, a stabilizing drilling tool with a roller cone drill bit can be used in surface or shallow formations, a stabilizing drilling tool with a PDC drill bit can be used in deep formations with low rock hardness, and a stabilizing drilling tool with a full-hole drill bit can be used in deep formations with high rock density. The diameter of the drill bit, the diameter of the stabilizer, and the diameter of the drill collar can be adjusted according to the diameter of the wellbore to be opened.

[0046] Example 4

[0047] The drilling fluid used in step 3 of Example 1 can be a commercially available drilling fluid, such as one containing salt, bentonite, a filter loss inhibitor, a stabilizer, carboxymethyl cellulose, barite, etc. The salt can be common water salts such as sodium chloride and magnesium chloride, and the filter loss inhibitor can be a common filter loss inhibitor such as carboxymethyl starch; the stabilizer can be a common stabilizer such as polyacrylamide. In practical applications, the drilling fluid may also include additives such as lignin sulfonate diluents. The drilling fluid used in this invention can be purchased commercially or prepared by purchasing the above-mentioned components to meet the required viscosity and sand-carrying rate of the drilling fluid.

[0048] Example 5

[0049] The blast furnace slag used in step 4 of Example 1 is a high-glass content slag, typically a hydrogelatinous, glassy granular material formed by the rapid cooling of high-temperature slag melt at 1400℃-1600℃ through direct contact with a large amount of water. Its main chemical components are: silicon dioxide, aluminum oxide, iron oxide, calcium oxide, magnesium oxide, sodium oxide, potassium oxide, and sulfur, which are some of the chemical components found in slag. Preferably, the specific surface area is 2000 cm². 2 / g-15000cm 2 Between / g, especially at 4000cm 2 / g-8500cm 2 High-temperature slag with a density between / g and . The alkali used is usually sodium carbonate, calcium carbonate, sodium hydroxide, or sodium bicarbonate, with sodium carbonate being preferred.

Claims

1. A drilling and cementing method for directional and vertically inclined wells, characterized in that, Includes the following steps: Step 1: Obtain reservoir properties based on well logging data. Reservoir properties include reservoir stratification, lithology of each stratum, and drilling thickness of each stratum. The lithology of each stratum includes hardness. The drilling thickness of each stratum is determined by the reservoir thickness of the stratum, the inclination angle α of the reservoir, and the preset inclination angle β of the wellbore. The calculation method is: Drilling thickness of each stratum = Reservoir thickness of the stratum / cosα / cosβ. Step 2: Pre-determine the drilling plan based on reservoir properties. The drilling plan includes drill string structure, drill string parameters, and adjustment plans for drilling parameters. Drilling parameters include drilling time and stop-drilling time. The drilling time for each layer is pre-determined based on the drilling thickness, and the stop-drilling time between adjacent layers is pre-determined based on the reservoir layers. Drill string parameters include pressure on drill (PBD) and rate of drill (RSD). The PBD and RSD for each layer are pre-determined based on the layer hardness, including: first, pre-determining the baseline values ​​for PBD and RSD based on the layer hardness; then, calculating the pre-determined values ​​for PBD and RSD based on the baseline values ​​for PBD and RSD. The pre-determined value for PBD is calculated using the following formula: The preset value of drilling pressure = {base value of drilling pressure / (tanβ)} 2 }×{F / (F 浮力 ×cosβ)} Where F is the weight of the drill bit, F 浮力 This refers to the buoyancy force experienced by the drill bit during the drilling process; The preset drilling rate is calculated using the following formula: Preset drilling rate = (Base value of drilling pressure / Preset value of drilling pressure) 1 / 2 × Base value for drilling speed; Step 3: Drill the deviated wellbore according to the drilling plan; Step 4: Cementing to obtain a directional vertical well.

2. The drilling and cementing method for directional and vertical wells as described in claim 1, characterized in that, The baseline values ​​for drilling pressure and drilling speed are the drilling pressure and drilling speed data used in vertical well drilling processes for strata with intermediate hardness in the reservoir.

3. The drilling and cementing method for directional and vertical wells as described in claim 1, characterized in that, Step 3 specifically involves injecting drilling fluid between the drill pipe and the wellbore wall. The drilling fluid circulates downward along the drill pipe and upward along the annulus between the drill pipe and the wellbore wall. Specifically, the drilling fluid is injected into the wellbore along the lower inclined side of the drill pipe near the wellbore.

4. The drilling and cementing method for directional and vertical wells as described in claim 3, characterized in that, The viscosity of the drilling fluid is not higher than 100 mPa·s; the sand-carrying velocity in clean water is not less than 1.0 m / s.

5. The drilling and cementing method for directional and vertically inclined wells as described in claim 1, characterized in that, Step 4 specifically involves: extracting the drill string and inserting the casing; providing cement slurry containing blast furnace slag and alkali; circulating the cement slurry downwards along the casing and upwards into the annulus formed between the casing and the wellbore wall; wherein the cement slurry is injected into the wellbore along the lower inclined side of the drill pipe away from the wellbore.

6. The drilling and cementing method for directional and vertical wells as described in claim 5, characterized in that, The cement slurry contains clay, and the clay content, by mass fraction, is not less than 6% and not more than 12%.

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