CN117371822B - Methods to establish cementing control and evaluation indicators to ensure the stability of hydrate encountered in deepwater drilling - Google Patents

Abstract

The invention belongs to the field of oil-gas well cementation, and particularly relates to a well cementation regulation and control and evaluation index establishment method for guaranteeing stability of a deep water drill when meeting hydrate. According to the invention, a heat conductivity coefficient regulation and control plate can be established according to the well structure and production operation parameters, the produced fluid parameters, the annular fluid parameters, the physical parameters of the well cementation target layer and the physical parameters of the corresponding production layer. The plate can reasonably coordinate the thickness of the cement sheath and the heat conductivity coefficient of the cement sheath, and can clearly guarantee the stable cement sheath heat conductivity coefficient evaluation index of the deep water drilling type hydrate layer under the determined thickness condition of the cement sheath. The thermal insulation performance of the well cementation cement can be regulated and controlled according to the thermal conductivity index during on-site operation, and the effective blocking of heat energy is realized through the cement loop with low thermal conductivity, so that the stability of the stratum of the well Zhou Shuige in the actual production process is ensured, accidents caused by the problem of well cementation quality are effectively avoided, and important guarantee is provided for safe and efficient exploitation of deep-water oil and gas resources.

Description

Methods to establish cementing control and evaluation indicators to ensure the stability of hydrate encountered in deepwater drilling

Technical field

The invention belongs to the field of oil and gas well cementing, and specifically relates to a cementing control method and an evaluation index establishment method to ensure the stability of deepwater drilling when encountering hydrate.

Background technique

Hydrates are widely distributed in shallow layers in the deep water areas of the South China Sea. This makes it easy to encounter hydrate layers in shallow layers during deepwater oil and gas development. If the hydrates become unstable and decompose, it will cause great damage to drilling and production projects. Security risks. Currently, cementing the hydrate layer is a safer and more effective way to seal the hydrate layer than releasing it under reduced pressure. However, during subsequent oil well construction and oil and gas production and development, when the deep thermal fluid returns from the bottom of the well to the shallow hydrate layer, if the heat transferred to the formation through the cement sheath is too large, the stability of the natural gas hydrate will be destroyed. , causing the decomposition of hydrates, causing gas to escape from the wellhead, seriously endangering production safety. At present, scholars mainly solve the problem of wellbore heat loss through pipe string insulation and annulus insulation (for example: CN 201010590928 Continuous nitrogen injection auxiliary insulation method in offshore thermal recovery annulus; CN2005100448019 metal vacuum insulation casing). However, because the cost of pipe string insulation is too high and the heat loss at the coupling cannot be ignored, and annular insulation has problems such as the annular protection liquid accelerating corrosion of the pipe string, it is not widely used.

During oil and gas production, oil and gas move upward along the tubing of the production well. According to the principle of thermodynamic heat transfer, the heat carried by the hot fluid in the oil pipe will be radially transferred to the formation through the oil pipe, each layer of casing and the annulus cement sheath (or annulus liquid). In order to ensure the long-term stability of the hydrate layer, it is necessary to minimize the heat transfer from the hot fluid in the tubing to the formation. According to the structural characteristics of the wellbore, the annulus cement sheath is the main thing that can effectively block heat transfer. Scholars in the field of geothermal well cementing improve heat utilization efficiency by reducing the thermal conductivity of cement, proving the potential of low thermal conductivity cement in hindering heat transfer and ensuring hydrate stability. However, the current research on thermal insulation cementing cement is still in its infancy, and there are no unified, standardized, and appropriate control methods and standards.

Therefore, it is necessary to establish a cementing control method and evaluation index establishment method to ensure the stability of hydrate encountered in deepwater drilling based on the actual cementing conditions and deepwater environment in the South my country Sea, which will provide a basis for the subsequent development of thermal insulation materials and thermal insulation cement systems. Provide theoretical basis for construction research.

Contents of the invention

The present invention proposes a cementing control method and evaluation index establishment method to ensure the stability of deepwater drilling when encountering hydrate. This method can be based on the well structure and production operation parameters, production fluid parameters, annulus fluid parameters, solidification parameters designed on site. The formation parameters of the well target layer and the formation parameters of the corresponding production layer are used to establish a thermal conductivity control chart. This chart can be used to reasonably coordinate the cement sheath thickness and the thermal conductivity of the cement sheath, and clearly define the cement sheath thermal conductivity evaluation index that ensures the stability of the deepwater drilling-type hydrate layer under the condition of determining the cement sheath thickness. During on-site operations, the thermal insulation performance of the cement can be controlled based on the thermal conductivity index, and the low thermal conductivity cement sheath can be used to effectively block thermal energy, thus ensuring the stability of the hydrate formation around the well during the actual production process and effectively avoiding the problems caused by cementing. Accidents caused by quality problems provide important guarantees for the safe and efficient exploitation of deep water oil and gas resources.

The present invention provides a long-term and stable cementing control method for deepwater drilling-type hydrate layers, which includes the following steps:

(1-1) Collect formation samples from the through-type hydrate layer and test their physical property parameters as the physical property parameters of the cementing target layer.

(1-2) Collect stratigraphic samples from the deep oil and gas reservoir production layers at corresponding locations, and test their physical property parameters as the physical property parameters of the production layer.

(1-3) Based on the designed well structure, establish the temperature calculation formula at the two cementing interfaces under the condition of stable heat transfer in the cementing target layer.

(1-4) Based on the designed production operation parameters, produced fluid parameters, annular fluid parameters, physical property parameters of the cementing target layer, and physical property parameters of the corresponding production layer, substituted into the temperature calculation formula, the hydration under different cement sheath thicknesses was obtained The thermal conductivity curve when the material layer is at the upper limit temperature of non-decomposition and the thermal conductivity curve when the hydrate layer is in a completely stable state, with the thickness of the cement ring as the X-axis and the thermal conductivity of the cement ring as the Y-axis, establish a thermal conductivity control chart (such as As shown in Figure 1);

Furthermore, the thermal conductivity curve when the hydrate layer is at the upper limit temperature of non-decomposition is represented by a dotted line, and the thermal conductivity curve when the hydrate layer is in a completely stable state (formation temperature) is represented by a solid line. The two lines divide the thermal conductivity control diagram into the hydrate decomposition zone, the hydrate metastable zone and the hydrate stability zone.

(1-5) Based on the designed cement slurry system formula, after measuring the thermal conductivity of the cement sheath after the cement slurry solidifies in the laboratory, determine the location of the cement sheath thermal conductivity in the drawing based on the designed cement sheath thickness;

If the thermal conductivity of the cement sheath is in the hydrate decomposition zone, it means that the thermal insulation performance of the cement sheath cannot meet the requirements. The thermal conductivity or thickness of the cement sheath needs to be adjusted so that the thermal conductivity of the cement sheath is in the hydrate medium stable zone or hydrate stable zone. Area, proceed to steps (1-6);

If the thermal conductivity of the cement sheath is in the hydrate medium stability zone, it means that the cement sheath has certain thermal insulation properties, which can ensure that the hydrate around the well will not become unstable to a certain extent and can be used. Go to steps (1-6). But not in an optimal state;

If the thermal conductivity of the cement sheath is in the hydrate stable zone, it means that the cement sheath has excellent temperature performance and can completely block heat in the wellbore during the production process to ensure the stability of the formation temperature. Continue to step (1-6).

(1-6) Estimate the amount of cement slurry required for the target section. According to the on-site operation conditions and corresponding construction parameters, inject the insulation cement slurry that meets the test requirements into the formation in the form of a replacement liquid until the cement slurry reaches the predetermined solidification range. .

Further, the physical parameters of the cementing target layer are temperature, pressure, hydrate saturation, hydrate decomposition temperature, and layer depth.

Further, the physical parameters corresponding to the production layer are oil and gas reservoir temperature, pressure, and layer depth.

Further, the wellbore structure includes the size of the tubing, the size of each layer of casing, the size of the wellbore, and the number of cement sheath layers.

Further, the calculation formula for the temperature at the two cementing interfaces under the condition of stable heat transfer is:

(1)

In the formula, T _a is the temperature at the interface, K; T _p is the inner wall temperature of the oil pipe, K; c _d is the specific heat capacity of the fluid in the oil pipe, J·(g·K) ^-1 ; ρ _d is the density of the fluid in the oil pipe, kg· m ^-3 ; A _p is the cross-sectional area of the oil pipe, m ² ; v _p is the flow rate of drilling fluid in the drill string, m·s ^-1 ; r _ti is the inner radius of the oil pipe, m; k _cem is the thermal conductivity of the cement sheath, W·(m·K) ^-1 ; Δ r is the cement sheath thickness, m; r _co is the outer diameter of the casing, m; r _o and r _i are the outer and inner diameters of the annulus, m; k _c is the heat conduction of the annulus fluid Coefficient, W·(m·K) ^-1 .

Further, the production operation parameters are design output and design output temperature.

Further, the parameters of the produced fluid are fluid specific heat capacity and fluid density.

Further, the annular fluid parameters are filling medium and annular fluid thermal conductivity.

Furthermore, the thermal conductivity control chart is a required range of cement sheath thermal conductivity that does not cause the risk of hydrate decomposition in deep oil and gas production based on the temperature calculation formula at the two cementing interfaces under stable heat transfer conditions.

Furthermore, the hydrate decomposition area in the thermal conductivity control chart indicates that the cement sheath in this area cannot ensure the stability of hydrates. At this time, the heat transferred to the formation will make the formation temperature higher than the hydrate decomposition temperature, resulting in Decomposition of hydrates around the well; the hydrate meso-stability zone indicates that the cement sheath in this area can provide heat insulation. Although the formation temperature will rise at this time, it is lower than the decomposition temperature of hydrates and will not cause hydrates to decompose. Instability; the hydrate stable zone means that the cement sheath in this area can well block heat inside the wellbore, allowing most of the heat to continue to migrate upward along the wellbore. At this time, the formation temperature will not be affected, and the hydrate layer will be completely in a stable state.

The present invention also proposes a method for establishing evaluation indicators to ensure the stability of deepwater drilling when encountering hydrate. Based on the above-mentioned cementing control method, it includes the following steps:

(2-1) Establish a thermal conductivity control chart; the establishment process is the same as steps (1-1)-(1-4);

(2-2) According to the designed thickness of the cement sheath, confirm in the drawing the thermal conductivity k ₁ (dashed line) when the hydrate layer is at the upper limit temperature of non-decomposition and the thermal conductivity k ₂ (solid line) when the hydrate layer is in a completely stable state. Wire);

(2-3) Establish a thermal conductivity evaluation index. Based on whether the formed cement ring can effectively hinder heat transfer to the formation, the thermal insulation performance of the cement ring is divided into three levels.

Furthermore, when k ≤ k ₂ , it means that the cement ring can completely block heat, and the environmental temperature performance of cement is rated as excellent; when k ₂ <k ≤ k ₁ , it means that the cement ring can partially block heat, and the environmental temperature performance of cement is rated as Good; when k>k ₁ , it means that the cement ring cannot block heat, and the temperature performance of the cement ring is rated as unqualified;

Among them: k is the thermal conductivity of the designed cement ring, unit W·(m·K) ^-1 ;

k ₁ is the thermal conductivity when the hydrate layer is at the upper limit temperature of non-decomposition, unit W·(m·K) ^-1 ;

k ₂ is the thermal conductivity when the hydrate layer is in a completely stable state, in unit W·(m·K) ^-1 .

Compared with the prior art, the present invention has the following advantages:

(1) Innovatively propose a cementing control method to ensure the stability of deepwater drilling when encountering hydrate. This method can be used to reasonably coordinate the thickness of the cement sheath and the thermal conductivity coefficient of the cement stone according to the specific temperature and production parameters of the oil and gas layer on site, so as to Ensure the stability of formation hydrates around the well during the actual production process, providing an important guarantee for the safe and efficient exploitation of oil and gas resources in deep water hydrate layers;

(2) Based on the cementing control method, a method is proposed to establish an evaluation index to ensure the stability of the hydrate encountered in deep water drilling. This method can be used to determine the cement sheath thermal conductivity evaluation index to ensure the stability of the hydrate layer encountered in deep water drilling under the condition of determining the thickness of the cement sheath. , during on-site operations, the thermal insulation performance of the cement can be controlled based on the thermal conductivity index, and the low thermal conductivity cement sheath can be used to effectively block thermal energy, thereby ensuring the stability of hydrates during the cementing period and subsequent production operations. Effectively avoid accidents caused by cementing quality problems.

Description of drawings

Figure 1 is a schematic diagram of the thermal conductivity control chart of the present invention;

Figure 2 is a schematic structural diagram of a well A in the South China Sea in the embodiment.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further elaborated below in conjunction with the drawings and examples. It should be noted that the following description is only for explaining the present invention and does not limit its content. .

Example 1

The cementing control method to ensure the stability of hydrate encountered in deepwater drilling will be achieved through the following steps:

(1) Collect formation samples from the cross-type hydrate layer in the cementing target layer, use the temperature and pressure sensor on the drill pipe to measure the temperature and pressure of the formation, use logging tools to measure the hydrate saturation, and determine the hydrate decomposition temperature.

(2) Collect formation samples corresponding to the production layers of the oil and gas reservoir, use the temperature and pressure sensor on the drill pipe to measure the temperature and pressure of the formation, and determine the well depth.

(3) Based on the designed well structure (taking Well A in the South China Sea in Figure 2 as an example, the target layer has only one cement sheath), establish the temperature calculation formula at the two cementing interfaces under the condition of stable heat transfer in the cementing target layer:

(2).

(4) It is known that the water depth of the well is 1239 m, the seabed temperature is 3°C, and the reservoir temperature is 99°C. Under the current pressure, the specific heat capacity of the fluid in the oil pipe is c _d =2156 J·(g·K) ^-1 , the fluid density is ρ _d =0.7 kg·m ^-3 , and the thermal conductivity of the annulus fluid is k _c =0.6 W·(m ·K) ^-1 . During the production period, when the oil well started producing at a production rate of 113.3×10 ⁴ m ³ ·d ^-1 , the wellhead temperature (i.e., the design production temperature) finally stabilized at around 78°C; the existence of a hydrate layer was confirmed around the well, and it is known that Its depth below the mud line is about 217 m, the formation temperature is about 15°C, and the decomposition temperature of hydrate at this depth is about 20°C. At the same time, well logging data shows that the fluid temperature in the tubing at the same depth is about 80°C;

The design output (113.3×10 ⁴ m ³ ·d ^-1 =13.3 m ³ ·s ^-1 ), design output temperature, produced fluid specific heat capacity, produced fluid density, annulus fluid thermal conductivity, oil pipe size (inside and outside the oil pipe diameter), the casing size of each layer (the inner and outer diameter of the casing, calculate the annulus thickness), the wellbore size (the outer diameter of the cement sheath, the outer diameter of the cement sheath - the outer diameter of the casing = Δ r ), etc. are substituted into formula (2) to establish Thermal conductivity control chart (shown in Figure 1).

(5) Based on the designed cement slurry system formula, after measuring the thermal conductivity of the cement sheath after the cement slurry solidifies in the laboratory, determine the location of its thermal conductivity in the drawing based on the designed thickness of the cement sheath. If it is in the hydrate medium stability zone , it means that the cement sheath has a certain thermal insulation performance, which can ensure that the hydrate around the well will not become unstable to a certain extent and can be used, but it is not in an optimal state; if it is in the hydrate stable zone, it means that the cement sheath has a certain temperature It has excellent performance and can completely block heat in the wellbore during the production process to ensure the stability of the formation temperature; if it is in the hydrate decomposition zone, it means that the thermal insulation performance of the cement sheath cannot meet the requirements;

When the thermal conductivity of the cement sheath is in the hydrate decomposition zone, it indicates that the thermal insulation performance of the cement sheath needs to be improved. If it is difficult to control the thermal conductivity of the cement stone, it is necessary to redesign the thickness of the cement sheath and use the method in step (4) The thermal conductivity chart is used to judge until the thermal conductivity of the cement sheath is in the hydrate medium stable zone or stable zone to achieve effective heat isolation, thereby ensuring that the formation temperature around the well is lower than the temperature of hydrate decomposition during the actual production process, ensuring Hydrate stability.

(6) Estimate the amount of cement slurry required for the target section, and inject the insulation cement slurry that meets the test requirements into the formation in the form of a replacement liquid according to the on-site operation conditions and corresponding construction parameters until the cement slurry reaches the predetermined solidification range.

Example 2

The establishment method of evaluation indicators to ensure the stability of deepwater drilling when encountering hydrate will be achieved through the following steps:

(1) Taking Well A in the South China Sea in Figure 2 as an example, establish a thermal conductivity control chart (Figure 1);

(2) The thickness of the cement sheath in Well A is 80mm. It is confirmed in the drawing that the thermal conductivity k ₁ when the hydrate layer is at the upper limit temperature of non-decomposition (20°C) is 0.283 W·(m·K) ^-1 and the hydrate layer is at The thermal conductivity k ₂ in completely stable state (15°C) is 0.244 W·(m·K) ^-1 ;

(3) Establish thermal conductivity evaluation indicators, as shown in Table 1:

.

It should be understood that the above-described specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, improvements, equivalent substitutions, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Furthermore, it is intended that the appended claims of the present invention cover all changes and modifications that fall within the scope and boundaries of the claims, or equivalents of such scopes and boundaries.

Claims (9)

1. A cementing control method to ensure the stability of deepwater drilling when encountering hydrate, which is characterized by including the following steps: (1-1) Collect formation samples from the through-type hydrate layer, test their physical properties, and use them as the physical properties of the cementing target layer; (1-2) Collect stratigraphic samples from the production layers of oil and gas reservoirs in the corresponding deep layers, and test their physical parameters as the physical parameters of the production layers; (1-3) Based on the designed well structure, establish the temperature calculation formula at the two cementing interfaces under the condition of stable heat transfer in the cementing target layer; The temperature calculation formula at the two interfaces of cementing under the condition of stable heat transfer is: ; In the formula, T _a is the temperature at the interface, K; T _p is the inner wall temperature of the oil pipe, K; c _d is the specific heat capacity of the fluid in the oil pipe, J·(g·K)-1; ρ _d is the density of the fluid in the oil pipe, kg· m ^-3 ; A _p is the cross-sectional area of the oil pipe, m ² ; v _p is the flow rate of drilling fluid in the drill string, m·s ^-1 ; r _ti is the inner radius of the oil pipe, m; k _cem is the thermal conductivity of the cement sheath, W·(m·K) ^-1 ; Δr is the cement sheath thickness, m; r _co is the outer diameter of the casing, m; r _o and r _i are the outer and inner diameters of the annulus, m; k _c is the heat conduction of the annulus fluid Coefficient, W·(m·K) ^-1 ; (1-4) Based on the designed production operation parameters, produced fluid parameters, annular fluid parameters, physical property parameters of the cementing target layer, and physical property parameters of the corresponding production layer, substituted into the temperature calculation formula, the hydration under different cement sheath thicknesses was obtained The thermal conductivity curve when the material layer is at the upper limit temperature of non-decomposition and the thermal conductivity curve when the hydrate layer is in a completely stable state are used to establish a thermal conductivity control chart; the thermal conductivity control chart is divided into a hydrate decomposition zone and a hydrate metastable zone and hydrate stability zone; (1-5) Based on the designed cement slurry system formula, after measuring the thermal conductivity of the cement sheath after the cement slurry solidifies in the laboratory, determine the area of the thermal conductivity in the drawing based on the designed thickness of the cement sheath; If the thermal conductivity of the cement sheath is in the hydrate decomposition zone, adjust the thermal conductivity or thickness of the cement sheath so that the thermal conductivity of the cement sheath is in the hydrate medium stable zone or the hydrate stable zone, and proceed to steps (1-6); If the thermal conductivity of the cement sheath is in the hydrate medium stable zone or hydrate stable zone, proceed to steps (1-6); (1-6) Estimate the amount of cement slurry required for the target layer, and inject the insulation cement slurry that meets the test requirements into the formation in the form of a replacement liquid according to the on-site operation conditions and corresponding construction parameters until the cement slurry reaches the predetermined solidification range. 2. The cementing control method to ensure the stability of deepwater drilling when encountering hydrate according to claim 1, characterized in that the physical parameters of the cementing target layer are temperature, pressure, hydrate saturation, hydrate decomposition temperature, Layer depth. 3. The cementing control method to ensure the stability of deepwater drilling when encountering hydrate according to claim 1, characterized in that the physical parameters corresponding to the production layer are oil and gas reservoir temperature, pressure, and layer depth. 4. The cementing control method to ensure the stability of deepwater drilling when encountering hydrate according to claim 1, characterized in that the well structure includes the size of the tubing, the size of each layer of casing, the size of the wellbore, and the number of cement sheath layers. 5. The cementing control method to ensure the stability of deepwater drilling when encountering hydrate according to claim 1, characterized in that the production operation parameters are design output and design output temperature; the output fluid parameters are fluid specific heat capacity, Fluid density; the annulus fluid parameters are filling medium and annulus fluid thermal conductivity. 6. The cementing control method to ensure the stability of deepwater drilling when encountering hydrate according to claim 1, characterized in that the X-axis of the thermal conductivity control chart is the thickness of the cement sheath, and the Y-axis is the thermal conductivity of the cement sheath. 7. The cementing control method to ensure the stability of hydrate encountered in deepwater drilling according to claim 1, characterized in that the thermal conductivity control chart is divided into a hydrate decomposition zone, a hydrate metastable zone and a hydrate stabilization zone. 8. A method for establishing evaluation indicators to ensure the stability of deepwater drilling when encountering hydrate based on the cementing control method of claim 1, characterized by: (2-1) Establish a thermal conductivity control chart; (2-2) According to the designed thickness of the cement sheath, confirm in the drawing the thermal conductivity k ₁ when the hydrate layer is at the upper limit temperature of non-decomposition and the thermal conductivity k ₂ when the hydrate layer is in a completely stable state; (2-3) Establish a thermal conductivity evaluation index. Based on whether the formed cement ring can effectively hinder heat transfer to the formation, the thermal insulation performance of the cement ring is divided into three levels. 9. The method of establishing an evaluation index to ensure the stability of deepwater drilling when encountering hydrate according to claim 8, characterized in that the thermal conductivity evaluation index is: when k ≤ k ₂ , it means that the cement ring can completely block heat, The environmental temperature performance of cement is rated as excellent; when k ₂ < k ≤ k ₁ , it means that the cement ring can partially block heat, and the environmental temperature performance of cement is rated as good; when k > k ₁ , it means that the cement ring cannot block heat, and the cement is environmentally friendly. Temperature performance is rated unsatisfactory; Among them: k is the thermal conductivity of the designed cement ring, unit W·(m·K) ^-1 ; k ₁ is the thermal conductivity when the hydrate layer is at the upper limit temperature of non-decomposition, unit W·(m·K) ^-1 ; k ₂ is the thermal conductivity when the hydrate layer is in a completely stable state, in unit W·(m·K) ^-1 .