CN114370267A - A real-time calculation method of thermal storage temperature encountered during drilling of high temperature geothermal field - Google Patents

Abstract

The invention belongs to the field of geothermal resource exploration, and specifically discloses a real-time calculation method for the temperature of thermal storage encountered during drilling of a high-temperature geothermal field. Step 3, establish a calculation formula for the bottom hole thermal storage temperature; Step 4, calculate the bottom hole thermal storage temperature; Step 5, verify the accuracy of the calculation result. The method of the invention requires less data, and can calculate the temperature of the thermal storage encountered during the drilling process of the high-temperature geothermal field in real time. , density measurement, so that the on-site construction personnel can quickly and timely understand the temperature of the thermal reservoir encountered during drilling, prevent the high-temperature thermal storage encountered during drilling in advance, and ensure the safety of drilling construction; at the same time, it also deploys follow-up drilling work for geological technicians and adjusts at any time. Provide the basis for the drilling design scheme.

Description

A real-time calculation method of thermal storage temperature encountered during drilling of high temperature geothermal field

technical field

The invention belongs to the field of geothermal resource exploration, and in particular relates to a real-time calculation method for the temperature of thermal storage encountered during drilling of a high-temperature geothermal field.

Background technique

Thermal storage temperature is the most important index parameter for evaluating geothermal resources. In the process of geothermal drilling, how to determine the temperature of the thermal storage encountered by drilling is an important task in judging the process of geothermal exploration. Especially for high-temperature geothermal fields, it is of great significance not only for understanding the thermal storage characteristics of geothermal fields, but also for the safety of drilling construction and the deployment of subsequent drilling work.

In the prior art, the thermal storage temperature is mainly judged by geophysical logging (temperature measurement) and geochemical geothermal temperature scale.

Geophysical logging (temperature measurement) is mainly to measure the temperature in the wellbore by placing the temperature measurement equipment near the bottom of the well. According to the geothermal exploration specification, the drilling stop time before temperature measurement is not less than 24 hours, and the drilling stop time for temperature measurement in the seriously lost well section should be appropriately extended. This method usually needs to stop drilling, lift the drill pipe, and then stop the drilling for 24 hours to measure the temperature, which takes a long time and consumes a lot of manpower, material and financial resources.

The geochemical temperature scale is a method of calculating the temperature of underground thermal storage using the chemical composition or concentration ratio of underground hot water. The basis of its establishment is that the geothermal fluid and minerals reach a chemical equilibrium at a certain temperature, and this equilibrium is maintained when the temperature of the geothermal fluid decreases subsequently. Commonly used geochemical temperature scales include silica geothermal temperature scale, potassium-magnesium geothermal temperature scale and potassium-sodium geothermal temperature scale. This method mainly obtains the content of different elements or ions in the geothermal fluid by collecting the geothermal fluid and using chemical analysis, and then inverts the thermal storage temperature. In this way, the collected samples need to be sent to the laboratory for analysis, and the cycle is generally more than one month. And due to the limitation of the sample collection site, the analysis results often have a certain gap with the actual thermal storage temperature.

In addition, predecessors established a semi-dynamic heat transfer model of the temperature in the wellbore. Other scholars have also carried out research on the dynamic mathematical model and numerical solution method of the wellbore annulus. However, the solution process of these methods is complicated, especially when the parameters of the mud (drilling fluid) change, the calculation of the temperature distribution in the wellbore is cumbersome, and it is difficult to use in the construction site.

Therefore, in the prior art, it takes a long time to judge the temperature of the thermal storage encountered by the drilling process in the drilling process, and consumes a lot of manpower, material resources and financial resources, and it is difficult to achieve real-time analysis of the temperature of the thermal storage encountered by the drilling, so as to ensure construction safety and subsequent work deployment. Either the required data parameters are too many, it is difficult to obtain in real time, and the calculation process is complicated, and the field technology and construction personnel are difficult to grasp; neither can real-time judgment of the temperature of the thermal storage encountered during the drilling process.

Therefore, it is urgent to develop a method for real-time calculation of the thermal storage temperature encountered during the drilling of high-temperature geothermal fields.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a real-time calculation method for the temperature of the thermal storage encountered during the drilling of a high-temperature geothermal field, which requires less data and can calculate the temperature of the thermal storage encountered during the drilling of a high-temperature geothermal field in real time. In the case of geophysical logging (temperature measurement) and its detailed parameters, by measuring the temperature, flow rate and density of the drilling fluid at the wellhead, the on-site construction personnel can quickly and timely understand the temperature of the hot reservoir and prevent the drilling in advance. The high-temperature heat storage ensures the safety of drilling construction; at the same time, it also provides a basis for geological technicians to deploy follow-up drilling work and adjust the drilling design plan at any time.

The technical scheme that realizes the object of the present invention:

A real-time calculation method for the temperature of thermal storage encountered during drilling of a high-temperature geothermal field, the method comprising the following steps:

Step 1. Collect the necessary data during the drilling process;

Step 2, establish the calculation model of the bottom hole temperature;

Step 3, establish the calculation formula of the bottom hole heat storage temperature;

Step 4. Calculate the bottom hole heat storage temperature;

Step 5. Verify the accuracy of the calculation result.

The necessary data in the step 1 includes: Ti, _To , _Th , _Ci , _Co , _Ch , _Vi , _Vo , _ρi , _ρo , _ρh , _Qo , Qi _{, t} , where _Ti , _To , and _Th represent the temperature of the _drilling fluid entering the _wellhead , the temperature of the drilling fluid flowing out of the _wellhead , and the temperature of the thermal reservoir in the hot reservoir; , the specific heat capacity of the drilling fluid flowing out of the wellhead, and the specific heat capacity of the thermal fluid in the hot reservoir; _Vi and V _o represent the drilling fluid flow into the wellhead and the drilling fluid flow out of the wellhead, respectively; ρ _i , ρ _o , and ρ _h represent the The density of the drilling fluid entering the wellhead, the density of the drilling fluid flowing out of the wellhead, and the density of the thermal fluid in the hot reservoir; Q _o and Qi _represent the heat contained in the drilling fluid entering the well head and the amount of drilling fluid flowing out of the well head respectively per unit time. Including heat, t is time.

The calculation model of the bottom hole temperature in the step 2 is as follows: the drilling fluid enters the drill pipe from the wellhead, migrates downward along the drill pipe, and then migrates upward from the peripheral annulus of the drill pipe after reaching the bottom hole.

According to the calculation model of the bottom hole temperature in step 2, the heat contained in the overflowing geothermal fluid when drilling into the thermal reservoir is: The difference ΔQ of the heat.

The step 3 includes:

Step 3.1. Preliminarily establish the calculation formula of bottom hole heat storage temperature;

Step 3.2, establish a simplified calculation formula of bottom hole heat storage temperature.

The calculation formula of the bottom hole heat storage temperature initially established in the step 3.1 is:

_Th ={(T _o ×V _o ×C _o ×ρ _o )−(T _i ×V _i ×C _i ×ρ _i )}/{(V _o −V _i )C _h ×ρ _h }.

The simplified calculation formula of the bottom hole heat storage temperature established in the step 3.2 is:

_Th =(T _o ×V _o )-(T _i ×V _i )}/(V _o -V _i ).

The beneficial technical effect of the present invention is:

1. The real-time calculation method of the thermal storage temperature encountered during the drilling of a high-temperature geothermal field provided by the present invention requires less data. It is effectively avoided that obtaining the thermal storage temperature of the bottom-hole thermal reservoir in the prior art usually requires lowering the temperature measuring equipment to the bottom of the well to measure the temperature in the wellbore; or collecting water samples of the bottom-hole thermal reservoir through the blowout test, Perform geochemical analysis to obtain necessary calculation data; it requires a lot of human, material and financial resources.

2. The real-time calculation method of the thermal storage temperature encountered during drilling of a high-temperature geothermal field provided by the present invention has real-time performance for judging the location of the thermal reservoir, and has greater guiding significance for drilling construction safety and subsequent work deployment. The method effectively avoids the defects in the prior art that it takes a long time to obtain data when measuring the temperature in the well and using the geochemical temperature scale to calculate the temperature of the thermal storage, and neither has the capability of real-time observation.

Description of drawings

FIG. 1 is a schematic diagram of a model of water influx after the geothermal drilling encounters a thermal reservoir in the real-time calculation method for the temperature of the thermal storage during drilling in a high-temperature geothermal field provided by the present invention.

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

The present invention provides a real-time calculation method for the temperature of thermal storage during drilling of a high-temperature geothermal field, which specifically includes the following steps:

Step 1. Gather the necessary data during the drilling process

During the drilling process, it is necessary to obtain the necessary data during the drilling process. These data mainly include T _i , To , _Th , _{Ci , Co , Ch , Vi , Vo , ρ i , ρ o , ρ h ,} Q _o , Qi _{, t} and the like.

_Ti , _To , _Th represent the temperature of the _drilling fluid entering the _wellhead , the temperature of the drilling fluid flowing out of the _wellhead , and the temperature of the thermal reservoir in the hot reservoir; The specific heat capacity of the outflowing drilling fluid and the thermal fluid in the hot reservoir; _Vi and V _o respectively represent the drilling fluid flow into the wellhead and the drilling fluid flow out of the wellhead; ρ _i , ρ _o , and ρ _h respectively represent the drilling fluid entering the wellhead The density of the drilling fluid, the density of the drilling fluid flowing out of the wellhead, and the density of the thermal fluid in the hot reservoir; Q _o and Qi _represent the heat content of the drilling fluid entering the wellhead and the heat content of the drilling fluid flowing out of the wellhead respectively per unit time. , t is time.

Step 2. Establish the calculation model of bottom hole temperature

The law of conservation of energy is the theoretical basis for the calculation of bottom hole temperature. Under the law of energy conservation, how to simplify the calculation model of bottom hole temperature is the key to the calculation of bottom hole temperature.

Figure 1 is a model of drilling fluid circulation and thermal reservoir water influx when drilling into thermal storage during drilling. The drilling fluid enters the drill pipe from the wellhead, migrates down the drill pipe, and after reaching the bottom of the well, it migrates upward from the peripheral annulus of the drill pipe. During this process, if the hot reservoir is drilled, the high-temperature geothermal fluid in the hot reservoir will also enter the annulus, mix with the drilling fluid, rise together, and flow out from the wellhead. In this process, on the one hand, the drilling fluid contacts the surrounding formations in the annulus, resulting in temperature transfer and energy exchange; The increase in fluid temperature will also lead to an increase in drilling fluid flow at the wellhead outlet.

In the process of establishing the model, for the convenience of calculation, the heat exchange with the surrounding formation during the circulation of drilling fluid is not considered. Although it will affect the final calculation results, according to the actual situation of a high-temperature geothermal field in Tibet, this effect can be ignored. The reasons are as follows: First, due to the small annular space in the well, the drilling fluid can quickly pass through the annulus when the flow rate is large, the contact time between the formation and the drilling fluid is short, and the exchanged heat is small; Since the temperature difference between the drilling fluid and the geothermal fluid mixed with the formation temperature is not large after drilling into the thermal reservoir, the heat exchange is limited; thirdly, due to the high-temperature bedrock fractured thermal reservoir, the deep fracture system is complex, and it is difficult to establish accurate mathematics model to describe the formation temperature.

Therefore, when using the above calculation model, only the heat contained in the drilling fluid flowing out of the wellhead in a unit time and the heat contained in the drilling fluid entering the wellhead in a unit time are considered. The heat contained in the escaping geothermal fluid during the layer.

Step 3. Establish the calculation formula of bottom hole heat storage temperature

Step 3.1. Preliminarily establish the calculation formula of bottom hole heat storage temperature

The heat of drilling fluid entering the wellhead per minute Qi = 1 × T _i ×V _i ×C _i ×ρ _i ×t

The heat of drilling fluid flowing out of the wellhead per minute Q _o =1×T _o ×V _o ×C _o ×ρ _o ×t

The heat contained in the geothermal fluid gushing out of the well per minute △Q=Q _o -Q _i

The formula for calculating the temperature of the thermal storage in the borehole is _Th =△Q/{(V _o -V _i )C _h ×ρ _h ×t}

T _h ={(T _o ×V _o ×C _o ×ρ _o ×t)-(T _i ×V _i ×C _i ×ρ _i ×t)}/{(V _o -V _i )C _h

×ρ _h ×t}={(T _o ×V _o ×C _o ×ρ _o )-(T _i ×V _i ×C _i ×ρ _i )}/{(V _o -V _i )C _h ×ρ _h }

Step 3.2. Establish a simplified calculation formula for bottom hole heat storage temperature

Specific heat capacity: When the drilling fluid is water, although the specific heat capacity of water is different at different temperatures, the difference in specific heat capacity of water is only 0.5% from 10°C to 70°C. The results have little impact. Therefore, to simplify the calculation, C _o , C _i and C _h are uniformly replaced by C _i .

Density: Similarly, when the drilling fluid is water, the density of water at different temperatures is also different. However, from 10°C to 70°C, the density of water differs by about 2%. Therefore, to simplify the calculation, the densities ρ _o , ρ _i and ρ _h of the drilling fluid are uniformly replaced by ρ _i .

Thus, the above formula can be simplified as _Th =(T _o ×V _o )-(T _i ×V _i )}/(V _o -V _i ).

Step 4. Calculate the bottom hole heat storage temperature

Take a high-temperature geothermal field in Tibet as an example. During the drilling process, the drilling process is carried out with clear water. When drilling to a certain depth, the wellhead temperature increases significantly, and the wellhead flow rate increases rapidly, indicating that a hot reservoir with higher temperature may be encountered. At this time, the drilling fluid temperature at the wellhead inlet was 34.5°C, and the flow rate was 1.81 cubic meters per minute; the drilling fluid temperature at the wellhead outlet was 65.1°C, and the flow rate was 2.62 cubic meters per minute. Substituting the above data into the calculation formula, it can be obtained that the temperature of the drilled thermal reservoir is 133.5℃.

Step 5. Verify the accuracy of the calculation results

After the above calculation formula is established, the accuracy of the formula needs to be checked according to the situation. After completing the staged drilling, according to the geothermal exploration specification, the temperature of the geothermal drilling was measured 24 hours after the drilling was stopped, and it was obtained that the well temperature at this depth was 139.9°C. The difference between the temperature measurement results and the calculated results is 6.4 °C. It shows that the calculation result is not much different from the actual situation and is within the acceptable range.

It can be seen that this method can estimate the thermal storage temperature encountered during the drilling process with few parameters, and the error is not large, which is within the acceptable range.

The technical principle of the present invention is: the law of energy conservation. Under normal circumstances, during the drilling process, the temperature of the drilling fluid at the wellhead outlet is higher than the inlet temperature of the drilling fluid at the wellhead. Under the premise that the well depth is not large, the temperature difference between them is generally not large. The heat contained in the drilling fluid at the wellhead outlet is higher than that of the inlet drilling fluid, and the difference in heat is mainly obtained from the downhole through heat conduction during the drilling fluid circulation process. For high-temperature geothermal drilling, if high-temperature geothermal fluid is encountered in deep drilling, the geothermal fluid mainly contributes to the increase in the temperature of the drilling fluid at the wellhead. By simply measuring the temperature, density and flow rate of the drilling fluid at the inlet and outlet of the wellhead, the temperature of the deep drilling hot reservoir can be reversed.

The use of the above invention has the following prerequisites:

(1) It is feasible under the condition that the well depth is relatively shallow, the borehole diameter is small, and the drilling fluid flow rate is fast (large pump volume). When the well depth is deep, the diameter of the borehole and the flow rate of the drilling fluid are slow, the residence time of the drilling fluid in the well will be caused, and the heat exchange between the drilling fluid and the formation will occur. If the calculation model does not match, using this formula again will lead to a large error in the calculation result.

(2) When simplifying the formula, this method is mainly carried out for the case where the drilling fluid is clear water. If the drilling fluid is a high density mud, simplification cannot be made when using this formula. At the same time, the density of inlet mud and outlet mud should be monitored in real time.

The invention requires less data, and can use a small amount of data obtained in the drilling process to calculate the temperature of the thermal reservoir encountered by the drilling in real time, so that the field construction and technical personnel can quickly understand and grasp the temperature of the thermal storage encountered by the drilling. Actively take reasonable countermeasures to ensure construction safety and improve follow-up work efficiency.

The present invention has been described in detail above in conjunction with the accompanying drawings and embodiments, but the present invention is not limited to the above-mentioned embodiments, and within the scope of knowledge possessed by those of ordinary skill in the art, various kind of change. The content that is not described in detail in the present invention can use the prior art.

Claims (7)

1. A real-time calculation method for the heat storage temperature of a drill in the drilling process of a high-temperature geothermal field is characterized by comprising the following steps:

step 1, collecting necessary data in the drilling process;

step 2, establishing a calculation model of the bottom hole temperature;

step 3, establishing a calculation formula of the bottom hole heat storage temperature;

step 4, calculating the bottom heat storage temperature;

and 5, verifying the accuracy of the calculation result.

2. The method as claimed in claim 1, wherein the necessary data in step 1 includes: t is_i、T_o、T_h、C_i、C_o、C_h、V_i、V_o、ρ_i、ρ_o、ρ_h、Q_o、Q_iT, wherein T_i、T_o、T_hRespectively representing the temperature of the drilling fluid entering the wellhead, the temperature of the drilling fluid flowing out of the wellhead and the heat storage temperature of the reservoir subjected to heat drilling; c_i、C_o、C_hSpecific heat capacity of drilling fluid entering wellhead, specific heat capacity of drilling fluid flowing out of wellhead, and drilling reservoir exposed to heatHot fluid specific heat capacity of (1); v_i、V_oRespectively representing the flow of the drilling fluid entering the wellhead and the flow of the drilling fluid flowing out of the wellhead; rho_i、ρ_o、ρ_hRespectively representing the density of drilling fluid entering a wellhead, the density of drilling fluid flowing out of the wellhead and the density of hot fluid in a reservoir exposed to heat; q_o、Q_iRespectively represents the heat contained in the drilling fluid entering the wellhead and the heat contained in the drilling fluid flowing out of the wellhead in unit time, and t is time.

3. The method as claimed in claim 1, wherein the model for calculating the bottom hole temperature in step 2 is: the drilling fluid enters the drill rod from the wellhead, moves downwards along the drill rod, and moves upwards from the peripheral annular space of the drill rod after reaching the bottom of the well.

4. The method as claimed in claim 3, wherein the calculation model of the bottom hole temperature in step 2 is used to calculate the heat of the geothermal fluid overflowing during drilling the hot reservoir as follows: the difference value delta Q between the heat contained in the drilling fluid flowing out of the wellhead in unit time and the heat contained in the drilling fluid entering the wellhead in unit time.

5. The method as claimed in claim 1, wherein the step 3 comprises:

3.1, preliminarily establishing a calculation formula of the bottom hole heat storage temperature;

and 3.2, establishing a simplified calculation formula of the bottom heat storage temperature.

6. The method as claimed in claim 5, wherein the calculation formula of the bottom hole heat storage temperature preliminarily established in step 3.1 is as follows:

T_h＝{(T_o×V_o×C_o×ρ_o)-(T_i×V_i×C_i×ρ_i)}/{(V_o-V_i)C_h×ρ_h}。

7. the method as claimed in claim 6, wherein the simplified calculation formula of the thermal storage temperature at the bottom of the well established in step 3.2 is:

T_h＝(T_o×V_o)-(T_i×V_i)}/(V_o-V_i)。

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