JP2718081B2 - How to detect inland oil fields - Google Patents

Description

The present invention relates to a method for detecting an inland oil field.

[Conventional technology]

Conventional oil exploration methods include geological exploration methods and physical exploration methods.Geological exploration methods clarify the state of formation of strata from both stratigraphic and geological history, This is a method of estimating petroleum storage rocks and source rocks by investigating the sedimentary environment. The physical exploration method is a method of predicting the underground structure and lithology from the distribution of reflected and refracted waves and natural gravity and magnetism due to artificial earthquakes, and estimating the presence or absence of reservoir rock.

[Problems to be solved by the invention]

However, with these conventional methods, it is not certain whether or not the reservoir rock actually contains petroleum until actual drilling and physical testing are performed. That is, the conventional petroleum exploration method is, as it were, to conduct an exploration in accordance with a geological or physical signature that predicts the existence of a reservoir rock or an oil reservoir, and the accuracy of success has not been so high. Exploration was time consuming and costly, which made oil exploration difficult.

In this specification, an oil field in a narrow sense including only oil, a field including both oil and gas, and a gas field including only gas are collectively referred to as an oil field.

Therefore, an object of the present invention is to present a novel detection method capable of detecting an inland oil field with high accuracy.

[Means for solving the problem]

The method for detecting an inland oil field according to the present invention measures a radiation dose with respect to gamma rays of a plurality of components including at least radon, thoron, and potassium, and calculates an underground temperature increase rate ΔT using a radiation measurement value of a predetermined component. The depth range in which an oil field can exist is limited based on the underground temperature increase rate ΔT and predetermined oil production temperature conditions.

The method for detecting an inland oil field according to the present invention also measures a radiation dose for gamma rays of a plurality of components including at least radon, thoron and potassium, and calculates an underground temperature increase rate ΔT using a radiation measurement value of a predetermined component, Estimate the trap structure of the oil field based on the change in measured values, estimate the presence or absence of faults and open cracks based on the ratio of the measured values of radiation between specific components,
From the calculated underground temperature increase rate ΔT and the predetermined oil production temperature condition, the depth range where the oil field can exist is limited, and the presence of the oil field is estimated from the estimated trap structure.
The feature is to estimate the absence of oil fields based on the estimated faults and open cracks.

[Action]

By calculating the measured values of radon, thoron, and potassium according to a predetermined formula, the underground temperature increase rate, that is, the underground temperature, can be estimated, and it can be known whether or not the oil production temperature condition is met. In addition, the stratum structure can be estimated from the distribution of thoron, and therefore, it can be estimated whether or not there is a petroleum deposit existing in the stratum, and even if there is an oil deposit, groundwater has entered and destroyed due to open cracks. . These estimates allow for more accurate drilling of oil fields.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

I. Theoretical background (1) Oil production conditions Before describing the examples, the theoretical background will be described. Petroleum is the alteration of organic matter in the remains of animals and plants deposited on the sea floor and lake bottom. The alteration stage is divided into three stages: diagenesis, catagenesis, and metagenesis.
In Diagenesis, the burial depth is shallow and the ground temperature is low.
Organic matter becomes kerogen through microbial decomposition, hydrolysis, and resynthesis. Then, at the stage of catagenesis, the burial depth of the formation becomes deep and the ground temperature rises. Kerogen undergoes thermal cracking, initially producing large quantities of petroleum, and gases containing light hydrocarbons, such as propane, butane and gasoline, with some delay. As the temperature rises to the metagenesis stage, no oil is produced from kerogen, only methane is released, and the previously formed oil is also converted to methane.

It is clear that soil temperature has played an important role in this history of oil production. Thus, the rate of underground temperature increase may be one key in oil exploration.

By the way, if the formation has a gap large enough to allow gas molecules to pass through even if water molecules cannot pass through, gas elements generated by the natural decay of radioactive minerals such as radon and thoron pass through this gap. Come up. By measuring such radon and thoron, underground temperature information can be obtained. The higher the rate of temperature increase with depth in the ground,
This is because a lot of gas (radon and thoron) is supplied to the ground. The gaseous radioactive elements such as radon and thoron have a short half-life and are substituted for bismuth 214 and thallium 208.
These elements have extremely short half-lives, each emitting a unique gamma ray and decaying to the next element. Therefore, by measuring the intensity of this specific gamma ray, the movement of radon and thoron can be understood, and the temperature situation under the ground can be analyzed.

Estimating what kind of burial process the petroleum host rock has undergone in the past geological era from surface geological surveys and examining the temperature history of the host rock from radon and thoron analysis as described above, the oil production process You can know. The temperature of catagenesis, the most important stage for oil production, is 50-60 ° C
When this reaches a high temperature of 200 ° C., it enters the stage of metagenesis. The temperature at which large quantities of oil are produced
About 60-150 ° C.

(2) Presence or absence of petroleum deposits Even if the existence of petroleum is estimated from geology and temperature, it is important that petroleum deposits remain underground. Oil is trapped in a unique geological structure. There are structural traps with an anticline structure and a fault as traps, and stratigraphic traps formed by stratigraphic elements. The trap is composed of a combination of reservoir rock and cap rock, and the stratum where the reservoir rock develops is the reservoir, which accumulates gas, oil, and water (brine) in order from the top. Since the gas pressure of the upper gas is higher than the hydrostatic pressure, when drilling, it becomes the driving force to pump oil to the ground.

Focusing on the gaseous elements generated by the spontaneous decay of radioactive minerals such as radon and thoron in the ground, the area where cracks develop deep into the ground will increase the aerial gamma dose above the area. Thus, in areas with high aerial gamma doses, oil deposits, if at all, may be due to infiltration groundwater from developing cracks and gas and oil loss through cracks.
It is considered destroyed.

(3) Gas collection Oil and gas are at the top of the reservoir and have high pressure. This pressure causes gas convection in the formation above the oil reservoir. Therefore, above the reservoir having an oil reservoir, the underground radon and thoron are significantly repelled to the ground, and the aerial gamma dose above the area is increased.
It has a pseudo-concentric distribution that is higher at the center and lower as the distance from the center.

(4) Surface geology Geology of several meters above the ground can be investigated using the gamma dose of potassium 40. Soil and rock always contain potassium as a constituent element, and potassium 40 emits gamma rays and is converted to argon element. Since the gamma dose at that time has a deep correlation with the amount of potassium 39 (normal stable element),
By measuring this gamma dose, the potassium content of soil and rock can be known, and an index of rock classification can be obtained. If the general geology is known, a detailed geological map can be drawn.

II. Petroleum exploration and its equipment (1) Equipment configuration FIG. 1 is a block diagram showing the configuration of an apparatus for carrying out the method of the present invention. Numeral 10 is a multi-channel type gamma ray detector comprising a plurality of NaI scintillators and a gamma ray analyzer for dividing a detection value by the scintillator into an energy band to be described later. 5 types of gamma rays are detected. 13 is a barometric altimeter, 14 is a ground altimeter, 15 is a speedometer, 16 is a positioning device that constantly measures the flight position and outputs a position signal, 18 is a radiation thermometer for measuring the surface temperature of the measurement target area, 20 is a vertical gyro, 22 is a digital gyro that records the output of the devices 10, 13, 14, 15, 16, 18, and 20.
It is a data recorder. 24 is a video camera for photographing the area to be measured, and 26 is a video tape recorder (VTR) for recording the video taken by the video camera 24.
Numeral 28 is a synchronizing signal generator for generating a synchronizing signal for synchronizing various measurements and state detection and recording operations of the digital data recorder 22 and the VTR 26.

Although the positioning device 16 is used to know the flight position, for example, the speedometer 15 may be used. Also, the gamma ray detector 10
It is necessary to convert the detected value of each gamma ray according to the above to a ground value or a value at a fixed altitude using the ground altitude measured by the ground altimeter 14. The data measured by the altimeter 14 is simultaneously recorded in the data recorder 18 for that purpose.

Each of the above devices is mounted on a helicopter. That is, although the details will be described later, a helicopter equipped with these devices is flown over a planned course above the survey destination at an altitude of about 80 to 120 m above the ground, and the above five types of gamma ray data and the like are collected by the gamma ray detector 10. And record it in the data recorder 22.

Reference numeral 30 denotes a personal computer that processes data reproduced from the data recorder 22, 32 is an XY plotter for displaying the processing result in the form of, for example, a terrain sectional view, and 34 is a VTR 28. It is a TV device for displaying a reproduced video. In addition to the XY plotter 32, a printer,
A graphic display device or the like can be used. Of course, it is preferable to use them together according to the display purpose.

In the gamma ray detector 10, CH1 covers the gamma ray energy of 0.50 to 0.80 MeV, CH2 is the gamma ray spectrum of potassium 40 ( ⁴⁰ K) 1.30 to 1.60 MeV, and CH3 is the bismuth
1.60 ~ 2.00Me which is the gamma ray spectrum of 214 ( ²¹⁴ Bi)
V and CH4 cover the gamma ray spectrum of thallium 208 ( ²⁰⁸ Tl), 2.40 to 2.80 MeV, and CH5 covers 0.15 to 3.00 MeV. Bismuth 214 is a radon daughter element, thallium 2
Since 08 is a thoron daughter element, in this specification, bismuth
The radioactivity of the gamma ray spectrum of 214 is treated as radon, and the radioactivity of the gamma ray spectrum of thallium 208 is treated as tron. In addition, the radioactivity of the gamma ray spectrum of potassium 40 is treated as potassium, the gamma ray spectrum of 0.50 to 0.80 MeV is treated as scattered gamma rays, and 0.15 to 3.00
Treat the MeV gamma ray spectrum as environmental gamma rays.

As the altitude increases in the atmosphere, cosmic rays become mixed, but observations at various places indicate that gamma radiation of each of the above components decreases exponentially with increasing altitude below 200 m above ground, It is known that it is not affected by cosmic rays. The attenuation coefficient μ (m ⁻¹ ) varies depending on the region, but the average value is shown in Table 1. For example, Bismuth 214 (Radon) originating in the ground floats in the air, and at 100m above ground, it accounts for 16% of radiation from the ground and at 200m, 35% of radiation from the ground.

(2) Data collection Next, a method for collecting basic data on gamma dose will be described. The above devices 10 to 26 are mounted on a helicopter and fly over the sky at a predetermined altitude so as to scan the detection target area. The standard helicopter flight speed is 72 km / h, the gamma ray detector 10 measures the airborne gamma dose at 0.5 second intervals, and data recorder 22 along with other data.
To record. In the case of the standard flight speed, the data acquisition distance interval is 10 m. Parallel survey lines 250 m apart in the horizontal direction are sequentially set, measurement is performed along the survey lines, and finally, planar measurement data is obtained for the detection target area. Simultaneously with the measurement and recording of airborne gamma rays, data such as the altitude and ground altitude of the observation point, the coordinate position of the measurement, etc. are also recorded.
The tape recorder 26 synchronously records the ground scenery. In order to obtain a wake map, a sign is set on the ground line terminal and observation flight is performed when not using the needle of the video image.

(3) Track map and gamma ray spectrum distribution data The data collected and recorded in this way is reproduced and input to the personal computer 30, and the output and analysis operations described below are performed. First, a wake map is created. In radio surveying, data recorder 22 records coordinate positions at 0.5-second intervals.
And after the observation, the personal computer 30 outputs a flight track map on a map. In the case of a video image needle, the main passage points are manually entered, and the other observation points are interpolated into the recording of the flight speed at 0.5-second intervals. The output of the observation point is shown at the observation position (horizontal distance 100m) every 5 seconds in a 1: 25,000 topographic map.

The gamma ray measurement value on the observation course (the value after the correction to the ground altitude) is shown in parallel with the terrain sectional view. For the topographical cross section, the standard of the horizontal scale is set to 1 / 25,000, and the vertical scale is adjusted according to the specific height difference of the survey area. Gamma dose is displayed on a logarithmic scale. The surface temperature is also displayed in parallel with the topographic profile. Since the data is displayed on a logarithmic scale, the ratio between the components can be directly viewed without calculating the ratio. This figure is suitable for analog and intuitive evaluation. Separately from this, the flight altitude, terrain cross section, and ground surface temperature every 5 seconds, and a total value of 5 seconds of various gamma doses and their ratios are output as a list.

III. Evaluation and analysis of oil deposits Next, evaluation and analysis of oil deposits are performed. In order to show the effectiveness of the present invention, a case will be described as an example in which measurement is performed on an existing oil field in Akita Prefecture. As in the case of normal geological surveys, the measurement is made roughly first, and if signs of the oil field are obtained by the following evaluation and analysis, the location will be measured more finely.

(1) Evaluation of oil production temperature First, the rate of increase in underground temperature is determined from the observed values of aerial gamma rays. The underground temperature increase rate ΔT can be obtained from the measured values of radon Rn, thoron Tn, and potassium K by the following equation.

ΔT = A (Rn−Tn) / K (1) where A is a constant, and in this case, A = 24 from the temperature measured by another method. 200 ° C maximum oil production temperature
Table 2 shows the maximum depth that can be used as an oil basalt, which is the source rock of petroleum. The presence of oil gangs deeper than this does not contribute to oil production.

On the other hand, the temperature at the oil base rock depth is obtained from the already known oil base rock depth using ΔT of Expression (1). Table 3 shows the relationship with oil production. The term of the oil production temperature in Table 3 is a value obtained in this example. In addition,
There is a Hachimori oil field between Noshiro Port and Yachimori Town, and the existing oil field has the above-mentioned oil production temperature range (60 ° C to 150 ° C;
00 ° C). In other words, it can be seen that the measurement amount of gamma rays, specifically, the underground temperature increase rate of Expression (1) is effective for the requirement of the oil production temperature. From the attainment depth of the underground temperature of 200 ° C. in Table 2, it is possible to judge to what depth to try in an area where the existence of an ore deposit is estimated.

(2) Presence or absence of petroleum deposits A large amount of gas released from rocks, such as radon and thoron, escapes from the ground to the ground because a gas passage is formed between the ground and the underground. It is nothing less than. Therefore, even if there is an oil reservoir underground, in areas where radon and thoron are often observed in the air, the pressure of flammable gas in the reservoir decreases, and in addition, the reservoir enters the reservoir of groundwater. Be replaced. This gas passage is specifically a fault, and is an open crack in which groundwater accumulates. From the data measured by the present inventor in various places, it is known that the tron / radon ratio is large at a place where a fault or an open crack develops and exceeds 0.5 (Japanese Patent Application No. 62-311).
From this, it can be seen from the fact that even if there is an oil layer, it remains. Table 4 shows the measurement data for oil fields in Akita Prefecture. The difficulty in escaping gas from the ground to the ground was calculated from the following equation, as the cap rock thickness D0.

D0 = BC (Tn / Rn) (2) where B and C are constants, where B = 770 and C = 1100
And

From Table 4, it can be seen that the oil layer cannot exist unless the radon is 203 or less, the thoron is 92 or less, the thoron / radon is 0.48 or less, and the cap rock thickness is 277 m or more.

By the above analysis, at least a portion where the oil layer does not exist and a portion where the oil layer is broken can be excluded.

(3) Detecting gas signature from oil reservoirs In some cases, gas is gushing from oil reservoirs. The gas signature can be known from the gamma ray spectrum distribution. This is explained using the Hachimori oil field as an example. In the vicinity Hachimori, there are about 50 pieces of producing well over a prolonged 1km, oil and 13 million m ³ of gas 117 thousand kl from a depth of 90~430m is produced in 43 years from 1939 .
Reservoir layer is a oil-containing layer over 330 thousand m ² in tuffaceous sandstone has an effective layer thickness of 37m, anticline and fault is in the trap. Fig. 2 shows the airborne gamma dose measured for the approximately 10km section across the Yamori Oil Field. For reference, the topographic cross section and the ground surface temperature are also shown. In addition, 50, 52, and 53 are open cracks estimated from the distribution of radon and thoron.

a. Detection of fold structure The stratum bends due to crustal movement, forming an anticline structure. Oil and gas accumulate around the anticline of the anticline structure. The distance between the ground and the reservoir of oil and gas increases as the distance from the anticlinal axis increases. As a result, in the aerial gamma ray spectral composition, while the potassium is kept at a constant level, the number of trons increases toward the anticline, showing a dome-shaped distribution corresponding to the fold structure. In the Hachimori oil field, the distance from the anti-incline axis to the syncline axis is 4 km. In FIG. 2, the regions 40 and 42 where the tron distribution in the air becomes domed are shown.
Then, the existence of an oil layer is presumed. In the region 44, the value of tron is high overall and the horn is not bent.
It can be determined that no oil layer exists.

b. Oil reservoir destruction Even in the fold, if a fault cuts the oil reservoir and a short circuit occurs with groundwater, the oil reservoir will be destroyed. Among the open cracks, in the fault short-circuited to the groundwater, the thoron rapidly decreases in the aerial gamma-ray spectrum composition, so that the oil layer destruction can be determined from the thoron distribution. In the region 40 in FIG. 2, the dome-shaped distribution of the tron is rapidly reduced near its top (open crack 50), and it is considered that the oil layer has been destroyed. On the other hand, in the region 42, the tron rapidly decreases at a position slightly off the top of the dome-shaped distribution of the tron, and although the open crack 52 is presumed, the oil layer is maintained near the top.

In other words, in both regions 40 and 42, the fold structure can be inferred from the distribution of trons, and the existence of the reservoir can be predicted.
In 40, it can be determined that the oil layer has been destroyed by the open crack 50. In other words, when the distribution of the tron is dome-shaped and the tron does not decrease rapidly near its apex, it can be estimated that there is an oil layer.

The increase in trons indicates that random microcracks have been remarkably developed so as not to infiltrate groundwater, and no oil layer is formed unless the oil host rock has developed in the lower stratum .

Table 5 shows the aerial gamma ray spectral composition of the Hachimori oil field.

By the above analysis, at least the part where the stratum cannot exist can be surely excluded, and then, in the district where the existence of the reservoir is presumed, more precise measurement is performed by the same method.

In the present embodiment, the collected data is temporarily recorded in the data recorder and analyzed on the ground, but the collected data may be transmitted to the personal computer 30 on the ground by radio. In this case,
Further, the calculation result may be immediately graphed and displayed / printed.

In recent years, since the terrain information of each place has been converted into electronic data, the electronic data is associated with the flight position, and the measured results of the gamma ray components and the analysis results based on the calculated values are displayed as images on a TV monitor device. You may do so. In this way, the presence or absence of an oil field can be determined and evaluated immediately and visually.

In the above description, data collection by helicopter has been taken as an example. However, the present invention may use other air vehicles, or collect necessary data by on-site reconnaissance or taxi vehicles.

〔The invention's effect〕

As can be easily understood from the above description, according to the present invention, since the underground temperature can be estimated from the underground temperature increase rate ΔT, the depth range in which an oil field can exist is limited based on this and the oil production temperature conditions. it can. As a result, for example, boring can be made more efficient.

In addition, the trap structure of the oil field can be estimated by the surface change of the gamma ray measurement value, and the presence or absence of faults and open cracks can be estimated by the ratio of the measurement values between specific components, so the possibility of the oil field existence is quantitatively highly accurate Can be determined.

As a result, the accuracy of oil field exploration can be improved and the analysis time can be shortened, and the cost required for oil field exploration can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an apparatus for implementing the method of the present invention, and FIG. 2 is an example of actual measurement data. 10: Multi-channel gamma ray detector, 13: Barometric altimeter, 14: Ground altimeter, 15: Speedometer, 16: Positioning device, 18: Radiation thermometer, 20: Vertical gyro, 22 …… Digital data recorder, 24 …… Video camera, 26 …… Video tape recorder, 28 ……
Synchronous signal generator, 30 personal computer,
32 XY plotter, 34 TV device

Claims (7)

(57) [Claims] 1. An underground temperature increase rate ΔT is calculated by using a radiation measurement value of a predetermined component to measure a radiation dose with respect to a plurality of gamma rays including at least radon, thoron and potassium. A method for detecting an inland oil field, wherein a depth range where an oil field can exist is limited based on the rate ΔT and predetermined oil production temperature conditions. 2. The measured value of radon is Rn and the measured value of thoron is T.
Assuming that the measured value of n and potassium is K, the underground temperature increase rate ΔT is ΔT = A (Rn−Tn) / K where A is a constant. How to detect oil fields. 3. A radiation dose is measured for gamma rays of a plurality of components including at least radon, thoron, and potassium, and an underground temperature increase rate ΔT is calculated using a radiation measurement value of a predetermined component. Estimate the trap structure of the oil field, estimate the presence or absence of faults and open cracks based on the ratio of radiation measurements between specific components, and determine the presence of the oil field from the calculated underground temperature increase rate ΔT and the specified oil production temperature conditions A method for detecting an inland oil field, comprising: limiting an allowable depth range, estimating the presence of an oil field from the estimated trap structure, and estimating the absence of the oil field based on the estimated fault and open crack. 4. The method for detecting an inland oil field according to claim 3, wherein the underwater fold structure is estimated from the radiation dose distribution of the tron as the trap structure. 5. The method for detecting an inland oil field according to claim 4, wherein the portion where the radiation dose of the tron is rapidly reduced in the dome-shaped distribution is assumed to have entered groundwater. 6. The measured value of radon is Rn and the measured value of thoron is T.
Assuming that the measured value of n and potassium is K, the underground temperature increase rate ΔT is given by ΔT = A (Rn−Tn) / K where A is a constant. Item 14. The method for detecting an inland oil field according to any one of the above items. 7. The measured value of radon is Rn, and the measured value of thoron is Tn.
In this case, when Tn / Rn is equal to or more than a predetermined value, it is estimated that there is a fault or an open crack, and the detection of an inland oil field according to any one of claims (3) to (6). Method.