1. The method for evaluating the residual gas development potential of the developed well of the microgravity monitoring gas reservoir is characterized by comprising the following steps of:

step 1, correcting the actually measured microgravity data by various items to obtain the grid gravity anomaly of a microgravity monitoring target area;

step 2, on the basis of the acquired Booth gravity anomaly, utilizing a chromatography gravity anomaly separation principle to extract residual gravity anomaly of a target layer to acquire residual gravity anomaly in a depth range corresponding to the depth range of the target layer of the monitored gas reservoir, wherein the extracted residual gravity anomaly of the target layer is superposition anomaly of all residual densities in the gas reservoir in the microgravity monitoring range to generate gravity anomaly;

step 3, dividing the acquired microgravity monitoring target area gas reservoir residual gravity anomaly into an anomaly unit which is a positive anomaly unit, a negative anomaly unit and a positive and negative anomaly step band area unit according to the characteristics of the gas-bearing stratum on the residual gravity anomaly section;

step 4, reading the abnormal extreme value of each residual gravity abnormal unit according to the division of the residual gravity abnormal units;

step 5, reading the residual gravity abnormal value delta g of the position of the drilled well in each residual gravity abnormal unit_{Well location}；

Step 6, establishing a residual gas development potential evaluation and development well position evaluation mathematical model based on the microgravity monitoring result for the divided residual gravity abnormal units by utilizing a normalization processing technology according to the divided residual gravity abnormal units;

step 7, according to the established evaluation mathematical model, calculating evaluation factors in the residual abnormal units by using the read residual gravity abnormal extreme values in the residual gravity abnormal units and the residual gravity abnormal values at the drilled well positions in the residual gravity abnormal units;

and 8, evaluating the drilled and developed wells in the residual gravity abnormal units according to the calculated evaluation factors to evaluate the residual gas development potential.

2. The method of claim 1, wherein: correcting various items in the step 1 comprises correcting influences related to time factors and influences caused by space position change factors; wherein the time influence factor correction comprises instrument grid value correction, solid tide correction and zero drift correction; the correction of the influence factors of the spatial position change comprises the correction of an intermediate layer, the correction of height, the correction of terrain and the correction of latitude.

3. The method of claim 1, wherein: the principle of the separation of the analytical gravity anomaly in the step 2 can be expressed as follows: Δ g_l[(x,y)；Δs_h(i+1)]＝Δg_r[(x,y)；Δs_h(i)]-Δg_r[(x,y)；Δs_h(i+1)]Wherein, Δ g_l[(x,y)；Δs_h(i+1)]Denotes the residual gravity anomaly, Δ g, extracted at a depth of h (i +1)_r[(x,y)；Δs_h(i)]Representing the regional gravity anomaly field value extracted at the h (i) depth; Δ g_r[(x,y)；Δs_h(i+1)]The depth h (i) is a functional relationship between the spatial sampling interval Δ d and i, and may be expressed as h (i) ═ C × i × Δ d, i ═ 0,1,2, …, and when i ═ 0, Δ g is used to represent the local gravity abnormal field value extracted at the depth h (i +1), and the depth h (i) is a functional relationship between the spatial sampling interval Δ d and i_r[(x,y)；Δs_h(0)]The specific implementation process of obtaining the Bragg gravity anomaly in the step 1 and obtaining the residual gravity anomaly of the target layer gas reservoir through chromatography gravity anomaly separation can be represented as follows: for a to-be-processed Bragg gravity abnormal field delta g_r[(x,y)；Δs_h(0)]Calculating to obtain the area gravity abnormal field value delta g of h (1) depth by using a second-order surface fitting method_r[(x,y)；Δs_h(1)]Then using the Bragg gravity abnormal field value delta g_r[(x,y)；Δs_h(0)]Subtracting the area gravity abnormal field value delta g extracted at the depth of h (1)_r[(x,y)；Δs_h(1)]Obtaining the residual gravity abnormal field value delta g at the depth h (1)_l[(x,y)；Δs_h(1)](ii) a When the residual gravity abnormal field value at the depth h (2) needs to be obtained, the regional gravity abnormal field value extracted at the depth h (1)Δg_r[(x,y)；Δs_h(1)]On the basis, a second-order surface fitting method is also utilized to extract the area gravity abnormal field value delta g at the depth h (2)_r[(x,y)；Δs_h(2)]Using the value of the regional gravity abnormal field Δ g extracted at the depth h (1)_r[(x,y)；Δs_h(1)]Subtracting the regional gravity anomaly field value Δ g extracted at the depth h (2)_r[(x,y)；Δs_h(2)]Obtaining the residual gravity abnormal value delta g at the depth h (2)_l[(x,y)；Δs_h(2)](ii) a If the remaining gravity anomaly field value at the depth h (i) is obtained, the rest of the gravity anomaly field value Δ g at the depth h (i) can be obtained by analogy_l[(x,y)；Δs_h(i)]。

4. The method of claim 1, wherein: dividing the residual gravity abnormal unit in the step 3, wherein the residual gravity abnormal characteristics of the positive abnormal unit are as follows: maximum value Δ g of residual gravity anomaly_{l _ positive}[(x,y)；Δs_h(i)]_maxWith a minimum value Δ g_{l _ positive}[(x,y)；Δs_h(i)]_minAll located in the area with abnormal value greater than 0; the residual gravity anomaly characteristics of the negative anomaly unit are as follows: maximum value Δ g of residual gravity anomaly_{l _ negative}[(x,y)；Δs_h(i)]_maxWith a minimum value Δ g_{l _ negative}[(x,y)；Δs_h(i)]_minAll located in the area with abnormal value less than 0; the residual gravity anomaly characteristics of the positive and negative anomaly step belt area units are as follows: maximum value Δ g of residual gravity anomaly_{l _ step band}[(x,y)；Δs_h(i)]_maxIn the region with abnormal value greater than 0, the minimum value Δ g of the remaining abnormal_{l _ step band}[(x,y)；Δs_h(i)]_minIn the region where the anomaly is less than 0.

5. The method of claim 1, wherein: in the step 4, the abnormal extreme value of each residual gravity abnormal unit is read, and in the residual gravity abnormal positive abnormal unit, the abnormal minimum value area represents an area with relatively high residual gas abundance, so that the abnormal minimum value delta g is read_{l _ positive}[(x,y)；Δs_h(i)]_min(ii) a Remainder ofIn the gravity anomaly negative anomaly unit, the anomaly maximum value area represents an area with relatively high residual gas abundance, so the anomaly maximum value deltag is read_{l _ negative}[(x,y)；Δs_h(i)]_max(ii) a In the residual gravity anomaly positive and negative anomaly step belt area unit, the anomaly minimum value area represents an area with relatively high gas abundance, but because the residual gravity anomaly is partially distributed in the positive anomaly area and partially distributed in the negative anomaly area, the abnormal maximum value delta g needs to be read respectively_{l _ step band}[(x,y)；Δs_h(i)]_maxWith a minimum value Δ g_{l _ step band}[(x,y)；Δs_h(i)]_min。

6. The method of claim 1, wherein: and 6, a mathematical model for evaluating the residual gas development potential of the drilled well established based on the residual gravity abnormal units divided based on the microgravity monitoring result is different in each residual gravity abnormal unit, wherein the mathematical model for evaluating can be expressed as gamma-delta g in the positive abnormal unit_{l _ positive}[(x,y)；Δs_h(i)]_min/Δg_{Well location}(ii) a Negative abnormal unit, the evaluation mathematical model can be expressed as γ ═ Δ g_{Well location}/Δg_{l _ negative}[(x,y)；Δs_h(i)]_max(ii) a The step band area unit, the evaluation mathematical model can be expressed as:

γ＝(Δg_{l _ step band}[(x,y)；Δs_h(i)]_max-Δg_{Well location})/(Δg_{l _ step band}[(x,y)；Δs_h(i)]_max-Δg_{l _ step band}[(x,y)；Δs_h(i)]_min)。

7. The method of claim 1, wherein: the method for evaluating the residual gas development potential of the drilled well according to the calculated evaluation factor gamma in the step 8 comprises the following steps: the evaluation factor gamma is in a value range of gamma belonging to [0,1], and in each divided residual gravity abnormal unit, the peak value area of the residual gravity abnormality is an area with relatively high residual gas abundance, so that when the evaluation factor gamma tends to 1, the residual gravity abnormal value at the drilled well position is closer to the abnormal peak value of the residual gravity abnormal unit at the drilled well position, which indicates that the development potential of the drilled and developed well on the residual gas is larger; conversely, when the evaluation factor gamma tends to 0, the farther the residual gravity abnormal value at the drilled position is from the abnormal peak value of the residual gravity abnormal unit at the drilled position, which indicates that the development potential of the drilled well for the residual gas is smaller.

Background

According to statistics, the number of unconventional gas fields which are explored and developed at home and abroad at present is increased year by year, and the natural gas yield is larger and larger in the global natural gas accumulated yield. The number of unconventional natural gas fields accounts for 75% of the largest total number of natural gas fields in the united states, wherein the production of six major unconventional gas fields, including the san hu an gas field, has been improved to about 20% of the total production of natural gas in the united states since the nineties of the twentieth century; in China, the total geological reserve of the conventional gas field accounts for about 80 percent of the total geological reserve of the gas field. Along with the continuous deepening of development, the initial decline rate of new wells put into production in different years is continuously increased, the number of low-yield low-efficiency gas wells in a block is increased year by year, the water production condition of the gas wells is gradually complicated, and part of the gas wells cannot reach the scheme index. The method is influenced by factors such as thin monolayer thickness of a main reservoir layer, quick transverse phase change, poor integral physical property, strong heterogeneity and the like, and has narrow control range and low control dynamic reserve of a single production well. Therefore, maintaining efficient development of a gas field is critical to ensure long-term high yield and stable production and stable gas supply of the field. In order to improve the recovery ratio of the residual gas of the low-yield and low-efficiency well and perform excavation potential on the residual gas between well patterns, the distribution rule of the residual gas in the area near the production well position and between the production well patterns needs to be researched, and the development potential of the developed well position and the residual gas needs to be evaluated. A new technical means is sought to directly describe the global residual gas distribution condition, and the residual gas distribution is effectively defined to become an important support for the next step gas well excavation and potential transformation and block encrypted well deployment by combining the current description means.

At present, aiming at unconventional gas reservoir development at home and abroad, the most direct method for researching and evaluating the distribution rule of the residual gas among wells is to encrypt a developed well pattern and then research and evaluate the development potential of the distribution rule of the residual gas by methods such as a single-well dynamic analysis method, a block geological statistical method and the like. In the indoor research field, scholars at home and abroad research quantitative and qualitative analysis methods of residual gas distribution. The quantitative description method can describe the reserve distribution of the residual gas at a single well point by utilizing a formation pressure variation analysis method, an unstable analysis method of the available residual gas collecting quantity and corrected modern yield decrement analysis method, a dynamic analysis method, numerical simulation and other methods, so that the overall reserve distribution of the residual gas of the gas reservoir is predicted; the method for qualitatively describing the distribution of the residual gas mainly comprises a numerical simulation method based on a static geological model, a position balance method, a volume method and a residual gas distribution description technology based on the combination of three new technologies (seismic fine calibration and multi-well constraint seismic stratum inversion technology, three-dimensional seismic amplitude attribute data body geological modeling technology and gas-water three-dimensional two-phase numerical simulation technology), and qualitative analysis can describe the sweet spot area of the residual gas distributed in the low-permeability sandstone gas reservoir.

The methods are all residual gas description methods based on single well point data and geological model building. The single well point data based description method has no integrity and cannot accurately predict the residual gas distribution among well patterns, and the geological model based description method has integrity, but the description precision depends on the precision of the established geological model, and the artificial interference factor is large. The microgravity monitoring technology is developed in recent years, and is a dynamic oil and gas monitoring technology which converts an overlapping field into a difference field to obtain relatively real change field information, has a monitoring result unrelated to a single well point, is an objective description of the overall density and change of an oil and gas reservoir, is an overall monitoring of the oil and gas reservoir, creates conditions for overcoming multiple interpretations, and has a monitoring result closer to true reality. The technology is mainly applied to development morphology description and production dynamic description of a steam cavity of heavy oil thermal recovery at present. In the aspect of microgravity monitoring of gas reservoirs at home and abroad, the microgravity technology is mainly applied to water flooding front edge monitoring, gas-water boundary monitoring and density dynamic change monitoring generated in the migration process of substances in a reservoir.

As can be seen from the research of the above documents, the microgravity monitoring technology at home and abroad is not applied to the residual gas distribution monitoring, the development well position evaluation and the residual gas development potential evaluation at present.

Aiming at the problems, the method extracts the residual gravity anomaly in the depth range of the gas reservoir target layer for the first time according to the chromatographic microgravity residual gravity anomaly separation technology, and divides the gravity anomaly of the development well location area into three areas according to the residual gravity anomaly distribution characteristics: a positive abnormal area with an abnormal minimum value larger than 0, a negative abnormal area with an abnormal maximum value smaller than 0, and an abnormal transition area with an abnormal maximum value larger than 0 and an abnormal minimum value smaller than 0; then, a mathematical model for evaluating the development potential of the development well on the residual gas based on the microgravity monitoring result is established by utilizing a normalization processing technology according to the subareas, and an evaluation factor is calculated by utilizing the microgravity monitoring gravity abnormal value; and finally, evaluating the potential of the drilled well for residual gas development by utilizing evaluation factors calculated by an evaluation mathematical model. By utilizing the mathematical model for evaluating the residual gas development potential of the development well based on the microgravity monitoring result, the development potential of the residual gas in the current stage development well position and the area near the development well position can be evaluated, the well position of a newly drilled development well can be guided to be deployed, the potential excavation measure scheme can be comprehensively adjusted, and the gas reservoir recovery ratio can be effectively improved.

Disclosure of Invention

In order to realize one purpose of the invention, the invention provides the following technical scheme: the method for evaluating the residual gas development potential of the developed gas reservoir well based on microgravity monitoring comprises the following steps:

step 1, correcting the actually measured microgravity data by various items to obtain the grid gravity anomaly of a microgravity monitoring target area;

step 2, on the basis of the acquired Booth gravity anomaly, utilizing a chromatography gravity anomaly separation principle to extract residual gravity anomaly of a target layer to acquire residual gravity anomaly in a depth range corresponding to the depth range of the target layer of the monitored gas reservoir, wherein the extracted residual gravity anomaly of the target layer is superposition anomaly of all residual densities in the gas reservoir in the microgravity monitoring range to generate gravity anomaly;

step 3, dividing the acquired microgravity monitoring target area gas reservoir residual gravity anomaly into an anomaly unit which is a positive anomaly unit, a negative anomaly unit and a positive and negative anomaly step band area unit according to the characteristics of the gas-bearing stratum on the residual gravity anomaly section;

step 4, reading the abnormal extreme value of each residual gravity abnormal unit according to the division of the residual gravity abnormal units;

step 5, reading the residual gravity abnormal value delta g of the position of the drilled well in each residual gravity abnormal unit_{Well location}；

Step 6, establishing a residual gas development potential evaluation and development well position evaluation mathematical model based on the microgravity monitoring result for the divided residual gravity abnormal units by utilizing a normalization processing technology according to the divided residual gravity abnormal units;

step 7, according to the established evaluation mathematical model, calculating evaluation factors in the residual abnormal units by using the read residual gravity abnormal extreme values in the residual gravity abnormal units and the residual gravity abnormal values at the drilled well positions in the residual gravity abnormal units;

and 8, evaluating the drilled and developed wells in the residual gravity abnormal units according to the calculated evaluation factors to evaluate the residual gas development potential.

Further, the correction in step 1 includes correcting the influence related to the time factor and the influence caused by the spatial position change factor; wherein the time influence factor correction comprises instrument grid value correction, solid tide correction and zero drift correction; the correction of the influence factors of the spatial position change comprises the correction of an intermediate layer, the correction of height, the correction of terrain and the correction of latitude.

Further, the principle of analyzing gravity anomaly separation in step 2 can be expressed as: Δ g_l[(x，y)；Δs_h(i+1)]＝Δg_r[(x，y)；Δs_h(i)]-Δg_r[(x，y)；Δs_h(i+1)]Wherein, Δ g_l[(x，y)；Δs_h(i+1)]Denotes the residual gravity anomaly, Δ g, extracted at a depth of h (i +1)_r[(x，y)；Δs_h(i)]Representing the regional gravity anomaly field value extracted at the h (i) depth; Δ g_r[(x，y)；Δs_h(i+1)]The depth h (i) is a functional relationship between the spatial sampling interval Δ d and i, and may be expressed as h (i) ═ C × i × Δ d, i ═ 0,1,2, …, and when i ═ 0, Δ g is used to represent the local gravity abnormal field value extracted at the depth h (i +1), and the depth h (i) is a functional relationship between the spatial sampling interval Δ d and i_r[(x，y)；Δs_h(0)]The specific implementation process of obtaining the Bragg gravity anomaly in the step 1 and obtaining the residual gravity anomaly of the target layer gas reservoir through chromatography gravity anomaly separation can be represented as follows: for a to-be-processed Bragg gravity abnormal field delta g_r[(x，y)；Δs_h(0)]Calculating to obtain the area gravity abnormal field value delta g of h (1) depth by using a second-order surface fitting method_r[(x，y)；Δs_h(1)]Then using a gridGravity abnormal field value Δ g_r[(x，y)；Δs_h(0)]Subtracting the area gravity abnormal field value delta g extracted at the depth of h (1)_r[(x，y)；Δs_h(1)]Obtaining the residual gravity abnormal field value delta g at the depth h (1)_l[(x，y)；Δs_h(1)](ii) a When the residual gravity abnormal field value at the depth h (2) needs to be obtained, the regional gravity abnormal field value delta g extracted at the depth h (1)_r[(x，y)；Δs_h(1)]On the basis, a second-order surface fitting method is also utilized to extract the area gravity abnormal field value delta g at the depth h (2)_r[(x，y)；Δs_h(2)]Using the value of the regional gravity abnormal field Δ g extracted at the depth h (1)_r[(x，y)；Δs_h(1)]Subtracting the regional gravity anomaly field value Δ g extracted at the depth h (2)_r[(x，y)；Δs_h(2)]Obtaining the residual gravity abnormal value delta g at the depth h (2)_l[(x，y)；Δs_h(2)](ii) a If the remaining gravity anomaly field value at the depth h (i) is obtained, the rest of the gravity anomaly field value Δ g at the depth h (i) can be obtained by analogy_l[(x，y)；Δs_h(i)]。

Further, the remaining gravity anomaly unit in step 3 is divided, and the remaining gravity anomaly characteristics of the positive anomaly unit are as follows: maximum value Δ g of residual gravity anomaly_{l _ positive}[(x，y)；Δs_h(i)]_maxWith a minimum value Δ g_{l _ positive}[(x，y)；Δs_h(i)]_minAll located in the area with abnormal value greater than 0; the residual gravity anomaly characteristics of the negative anomaly unit are as follows: maximum value Δ g of residual gravity anomaly_{l _ negative}[(x，y)；Δs_h(i)]_maxWith a minimum value Δ g_{l _ negative}[(x，y)；Δs_h(i)]_minAll located in the area with abnormal value less than 0; the residual gravity anomaly characteristics of the positive and negative anomaly step belt area units are as follows: maximum value Δ g of residual gravity anomaly_{l _ step band}[(x，y)；Δs_h(i)]_maxIn the region with abnormal value greater than 0, the minimum value Δ g of the remaining abnormal_{l _ step band}[(x，y)；Δs_h(i)]_minIn the region where the anomaly is less than 0.

Further, in step 4, the abnormal extreme value of each remaining gravity abnormal unit is read,in the residual gravity anomaly positive anomaly unit, the anomaly minimum value area represents an area containing relatively high residual gas abundance, so the anomaly minimum value deltag is read_{l _ positive}[(x，y)；Δs_h(i)]_min(ii) a In the residual gravity abnormal negative abnormal cell, the abnormal maximum value area represents the area containing relatively high residual gas abundance, so the abnormal maximum value deltag is read_{l _ negative}[(x，y)；Δs_h(i)]_max(ii) a In the residual gravity anomaly positive and negative anomaly step belt area unit, the anomaly minimum value area represents an area with relatively high gas abundance, but because the residual gravity anomaly is partially distributed in the positive anomaly area and partially distributed in the negative anomaly area, the abnormal maximum value delta g needs to be read respectively_{l _ step band}[(x，y)；Δs_h(i)]_maxWith a minimum value Δ g_{l _ step band}[(x，y)；Δs_h(i)]_min。

Further, the mathematical model for evaluating the residual gas development potential of the drilled well, which is established based on the residual gravity abnormal units divided by the microgravity monitoring result in step 6, is different in each residual gravity abnormal unit, wherein the positive abnormal unit and the evaluation mathematical model can be expressed as gamma-delta g_{l _ positive}[(x，y)；Δs_h(i)]_min/Δg_{Well location}(ii) a Negative abnormal unit, the evaluation mathematical model can be expressed as γ ═ Δ g_{Well location}/Δg_{l _ negative}[(x，y)；Δs_h(i)]_max(ii) a The step band area unit, the evaluation mathematical model can be expressed as:

γ＝(Δg_{l _ step band}[(x，y)；Δs_h(i)]_max-Δg_{Well location})/(Δg_{l _ step band}[(x，y)；Δs_h(i)]_max-Δg_{l _ step band}[(x，y)；Δs_h(i)]_min)。

Further, the method for evaluating the residual gas development potential of the drilled well according to the calculated evaluation factor gamma in the step 8 comprises the following steps: the evaluation factor gamma is in a value range of gamma belonging to [0,1], and in each divided residual gravity abnormal unit, the peak value area of the residual gravity abnormality is an area with relatively high residual gas abundance, so that when the evaluation factor gamma tends to 1, the residual gravity abnormal value at the drilled well position is closer to the abnormal peak value of the residual gravity abnormal unit at the drilled well position, which indicates that the development potential of the drilled and developed well on the residual gas is larger; conversely, when the evaluation factor gamma tends to 0, the farther the residual gravity abnormal value at the drilled position is from the abnormal peak value of the residual gravity abnormal unit at the drilled position, which indicates that the development potential of the drilled well for the residual gas is smaller.

The invention utilizes the advantages of the microgravity monitoring technology in the oil and gas reservoir monitoring (namely, the microgravity monitoring technology converts an overlay field into a difference field to obtain more real change field information, the result of the microgravity monitoring technology is irrelevant to a single well point, the integral density and fluid change of the oil and gas reservoir are objectively described, the integral monitoring of the oil and gas reservoir is carried out, conditions are created for overcoming the multiple solution of explanation, the monitoring result is closer to the true fact), firstly, a mathematical model for evaluating the development potential of the drilled and developed well based on the microgravity monitoring result is established, an evaluation factor is calculated according to the actual microgravity data, then, the development potential of the developed well and the development potential of the developed well area are evaluated according to the evaluation factor, finally, the development potential of the residual gas is comprehensively adjusted and excavated measure is carried out according to the evaluation result, the evaluation result of the development potential of the residual gas in the area near the developed well is classified into the drilling area containing the residual gas, and guiding the deployment of a new well in an undrilled area containing residual gas, thereby improving the recovery ratio of the gas reservoir, and ensuring the long-term high yield and stable production of the gas field and the key of stable gas supply is to maintain the efficient development of the gas field.

The method has the innovation points that the microgravity monitoring technology is applied to the monitoring of the residual gas of the gas reservoir and the evaluation of the development potential, a mathematical evaluation model of the development potential of the residual gas in the development well position and the area near the development well position based on the microgravity monitoring result is established for the first time, the model can guide the comprehensive adjustment of the development potential measures of the residual gas in the drilled well and the area near the drilled well position, the deployment of a new development well in the area containing the residual gas of the un-drilled development well can be guided, and the recovery ratio of the gas reservoir is improved.

The method of the invention is based on:

1) the gravity monitoring technology has the advantages of being suitable for complex surface terrain conditions, fast and convenient in construction, low in cost, free of damage, free of influence on production and the like, the monitoring result is that an overlay field is converted into a difference field to obtain real change field information, the achievement is irrelevant to a single well point, objective description on the whole density and fluid change of the gas reservoir is achieved, the integral monitoring of the gas reservoir is achieved, conditions are created for overcoming the explained multi-solution, and the monitoring result is closer to the true reality.

2) The precision of the CG6 type gravimeter is improved from milli-gamma level to micro-gamma level, the variation of 0.1 micro-gamma can be monitored by the gravimeter, gas reservoir development is a water inlet and outlet process, the density difference of a gas-containing rock stratum in the gas reservoir and a water-containing rock stratum is large, and the effective density difference of the gas-containing rock stratum is-0.1 g/cm under the general condition³To-0.25 g/cm³And the generated gravity anomaly can reach dozens of micro-Gals and can be monitored by a gravimeter.

3) Aiming at lithologic trap tight sandstone gas reservoirs, the high part of the trap is the main place for gathering natural gas according to the oil gas gathering rule. In the non-gas-containing trap position, gravity is displayed in a positive direction, namely the high gravity is reflected by a part with high trap density. However, at the gas-containing trap position, gravity is displayed in a negative direction or in a mirror image mode, namely, local gravity low abnormity appears on the gravity high background abnormity, the low-value part of the local gravity low corresponds to the distribution range of residual gas, the extreme value part of the local gravity low is the position with high gas-containing abundance, and the turning part of the gravity abnormity from high to low or from low to high is the gas-water boundary of the gas field.

4) According to the established mathematical model for evaluating the development potential of the residual gas at the drilled well position of the gas reservoir based on the microgravity monitoring technology, the comprehensive adjustment of the development potential measures of the residual gas in the drilled well and the area near the drilled well position can be guided, the deployment of a new development well in the residual gas-containing area of an undrilled development well can be guided, and the development rate and the recovery rate of the gas reservoir are improved.

The invention has the following advantages:

1) the acquired bump gravity anomaly is a superposition result of gravity anomalies generated by all residual density bodies underground, the residual gravity anomaly generated by the residual density bodies outside the depth range of the monitored target is removed through a chromatography gravity anomaly separation technology, a more real residual gravity anomaly result generated by the residual density bodies within the depth range of the monitored target layer is acquired, and conditions are created for overcoming multiple solutions;

2) the microgravity monitoring result is quantified through the established mathematical model for evaluating the residual gas development potential of the developed well, so that the quantitative analysis of the 'static' result of microgravity monitoring is realized, and in the same residual gravity abnormal unit, the evaluation factor is calculated through the mathematical model, so that the influence factors which change linearly or approximately linearly can be eliminated, and the reliability of the developed well for evaluating the residual gas development potential is improved;

3) the established mathematical model for evaluating the development potential of the residual gas at the drilled well position of the gas reservoir based on the microgravity monitoring technology can guide the comprehensive adjustment of the development potential measures of the residual gas in the drilled well and the area near the drilled well position, and improve the development rate of the gas reservoir.

Drawings

FIG. 1 is a flow chart of an evaluation method implementation;

FIG. 2 is a characteristic schematic view of a gas-bearing formation at a residual gravity anomaly profile;

FIG. 3 is a schematic diagram of an evaluation model of a residual gravity anomaly positive anomaly unit;

FIG. 4 is a schematic diagram of an evaluation model of a residual gravity anomaly negative anomaly unit;

FIG. 5 is a schematic diagram of an evaluation model of a residual gravity abnormal positive and negative abnormal step band region;

FIG. 6 is a distribution diagram of abnormal grid gravity in a microgravity monitoring area of a gas reservoir S block;

FIG. 7 is a diagram of residual gravity anomaly and anomaly partition for a target layer of a gas reservoir S block;

FIG. 8 is a bar graph comparing the microgravity evaluation results of the normal abnormal regions corresponding to Table 1 with the production dynamic results;

FIG. 9 is a bar graph comparing microgravity evaluation results and production dynamics results for negative abnormal regions corresponding to Table 2;

figure 10 is a bar graph comparing microgravity evaluation results with production dynamics results for the step band zones corresponding to table 3.

The specific implementation mode is as follows:

the invention relates to a method for evaluating the exploitation well position and the exploitation potential of residual gas of a gas reservoir based on a microgravity monitoring technology, which is characterized in that after actual measured microgravity data is corrected, a multi-scale curved surface method is utilized to extract the residual gravity anomaly of a microgravity monitoring target layer, then according to the characteristics of the gas-containing stratum on the microgravity monitoring residual gravity abnormal section, the residual gas near the well position and between wells is circled to obtain the distribution result of the residual gas near the well position and between wells, then dividing the whole monitoring area into a positive abnormal area, a negative abnormal area and an abnormal transition zone according to the residual gravity abnormal distribution characteristics and the residual gravity abnormal characteristics near the well site, and counting the residual gravity abnormal extreme value and the abnormal value at the well position in the residual gas distribution range circled near the well position in each abnormal area, and then, calculating an evaluation factor according to the established mathematical evaluation model, and finally evaluating the residual gas development potential of the drilled and developed well according to the evaluation factor.

The method of the invention is characterized in that it comprises the following steps:

1) correcting the actually measured microgravity data by various items to obtain the Bragg gravity anomaly of the microgravity monitoring target area;

2) on the basis of the acquired Booth gravity anomaly, performing residual gravity anomaly extraction on a target layer by utilizing a chromatography gravity anomaly separation principle to acquire residual gravity anomaly in a depth range corresponding to the depth range of the target layer of the monitored gas reservoir, wherein the extracted residual gravity anomaly of the target layer is superposition anomaly of gravity anomaly generated by all residual densities in the gas reservoir in a microgravity monitoring range;

3) dividing the acquired microgravity monitoring target region gas reservoir residual gravity anomaly into a positive anomaly unit, a negative anomaly unit and a positive and negative anomaly step belt region unit according to the characteristics of the gas-bearing stratum on the residual gravity anomaly section;

4) reading the abnormal extreme value of each residual gravity abnormal unit according to the division of the residual gravity abnormal units;

5) reading the residual gravity abnormal value delta g at the position of the drilled well in each residual gravity abnormal unit_{Well location}；

6) According to the divided residual gravity abnormal units, a mathematical model for evaluating the development potential of the development well on the residual gas based on the microgravity monitoring result is established for the divided residual gravity abnormal units by utilizing a normalization processing technology;

7) according to the established evaluation mathematical model, calculating evaluation factors in the residual abnormal units by using the read residual gravity abnormal extreme values in the residual gravity abnormal units and the residual gravity abnormal values at the drilled well positions in the residual gravity abnormal units;

8) and evaluating the residual gas development potential of the drilled wells in the residual gravity anomaly units according to the calculated evaluation factors.

1-6, FIG. 1 is a flow chart of an evaluation method implementation, FIG. 2 is a gas reservoir with a anticline structure at the lower part, and the gas reservoir residual gravity abnormal response at the upper part, and it can be seen from the figure that the gas reservoir has obvious gravity low at the upper part, and shows the gas-containing gravity abnormal characteristic that the abnormal contour line of a 'bulging and concave' or slope part is regularly and upwardly twisted, and in the section along the actual microgravity monitoring line, one (or two) 'two high-one low' abnormality occurs at each abnormal part with a low value; gravity anomalies have the typical "crowning and dishing" characteristic;

FIG. 3 is a schematic diagram of a model showing the relative distance between abnormal extreme values in the residual gravity abnormal unit on the abscissa and the magnitude of abnormal value in the residual gravity abnormal unit on the ordinate, wherein all the residual gravity abnormal values in the residual gravity abnormal unit are greater than or equal to 0; FIG. 4 shows that the horizontal and vertical coordinates have the same meanings as those of the horizontal and vertical coordinates in FIG. 3, and it can be seen from the schematic diagram of the model that all the residual gravity abnormal values in the residual gravity abnormal units are less than or equal to 0; the horizontal and vertical coordinates of fig. 5 are the same as those of fig. 3, and it can be seen from the schematic diagram of the model that the abnormal values in the residual gravity abnormal unit have a part greater than 0 and a part less than 0, and the magnitude of the residual gravity abnormal value at the well location in the actual gravity data may be greater than 0 and may be less than 0;

to make a pair of drilled wells remainEvaluating residual gas development potential, calculating evaluation factors of the divided residual gravity abnormal units by adopting a mathematical evaluation model of the invention, wherein the parameters of the mathematical model are as follows: the residual gravity abnormal value delta g of the well position in each residual gravity abnormal unit_{Well location}Residual gravity anomaly minimum value Δ g in residual gravity anomaly positive anomaly unit_{l _ positive}[(x，y)；Δs_h(i)]_minResidual gravity anomaly maximum value Δ g in residual gravity anomaly negative anomaly cell_{l _ negative}[(x，y)；Δs_h(i)]_maxMaximum value delta g of residual gravity anomaly in residual gravity anomaly positive and negative anomaly step belt area units_{l _ step band}[(x，y)；Δs_h(i)]_maxWith a minimum value Δ g_{l _ step band}[(x，y)；Δs_h(i)]_min. Calculating the evaluation factor in each residual gravity abnormal unit through the established mathematical evaluation model, wherein the evaluation factor gamma belongs to [0,1]]When the evaluation factor gamma tends to 1, the more the residual gravity abnormal value at the drilled well position is close to the abnormal peak value of the residual gravity abnormal unit at the drilled well position, and the development potential of the drilled well on the residual gas is larger; conversely, when the evaluation factor gamma tends to 0, the farther the residual gravity abnormal value at the drilled position is from the abnormal peak value of the residual gravity abnormal unit at the drilled position, which indicates that the development potential of the drilled well for the residual gas is smaller.

The method of the present invention is described below with an example of microgravity monitoring of a gas reservoir S block, as shown in fig. 6-7, where fig. 6 is a distribution diagram of microgravity abnormality of microgravity monitoring areas of a gas reservoir S block, and fig. 7 is a diagram of remaining residual gravity abnormality and abnormal subareas of a target layer of a gas reservoir S block; fig. 7 is a bragg gravity anomaly distribution diagram of the microgravity monitoring target area obtained by performing various corrections on the actually measured microgravity data in step 1; fig. 7 shows that, on the basis of the acquired bragg gravity anomaly, residual gravity anomaly extraction is performed on the target layer by using a chromatography gravity anomaly separation principle in step 2 of the method of the present invention, so as to acquire residual gravity anomaly within a depth range corresponding to the depth range of the target layer of the monitored gas reservoir. The partitioning of the exception cells described in step 3 can be performed according to the results of fig. 7: in fig. 7, the warm color system is a positive abnormal unit, the cold color system is a positive abnormal unit, and the transition area between the warm color system and the cold color system is a step belt area unit.

As shown in tables 1,2 and 3 below, other method steps of the present invention are illustrated based on the abnormal cell condition divided in step 3,

TABLE 1 statistical table for each development well in microgravity monitoring area of S block of certain gas reservoir

TABLE 2 statistical table for each development well in microgravity monitoring area negative anomaly unit area of certain gas reservoir S area

TABLE 3 statistical table for each development well in step belt unit area of microgravity monitoring area of certain gas reservoir S block

The Δ g values in tables 1 to 3 above correspond to the abnormal value and abnormal extreme value at the development well site read in steps 4 and 5, respectively, γ values in tables 1,2 and 3 correspond to the evaluation factor described in step 7, and the evaluation factor described in step 7 is calculated by using the mathematical evaluation model established in step 6 and the gravity abnormal value read in step 4 and step 5 (wherein the positive abnormal unit area evaluation factor calculation model is expressed as γ ═ Δ g)_{l _ positive}[(x，y)；Δs_h(i)]_min/Δg_{Well location}The negative abnormal unit area evaluation factor calculation model is expressed as: gamma is Δ g_{Well location}/Δg_{l _ negative}[(x，y)；Δs_h(i)]_maxSection assessment of transition zoneThe price factor calculation model is expressed as: γ ═ Δ g_{l _ step band}[(x，y)；Δs_h(i)]_max-Δg_{Well location})/(Δg_{l _ step band}[(x，y)；Δs_h(i)]_max-Δg_{l _ step band}[(x，y)；Δs_h(i)]_min). ) Then according to the description in step 8: evaluating drilled wells in the residual gravity anomaly units according to the calculated evaluation factors to evaluate the residual gas development potential, wherein the evaluation factors specifically comprise the following steps: when the evaluation factor gamma tends to 1, the more the residual gravity abnormal value at the drilled well position is close to the abnormal peak value of the residual gravity abnormal unit at the drilled well position, which shows that the drilled well has greater development potential on residual gas; conversely, when the evaluation factor gamma tends to 0, the farther the residual gravity abnormal value at the drilled position is from the abnormal peak value of the residual gravity abnormal unit at the drilled position, which indicates that the development potential of the drilled well for the residual gas is smaller. Then, according to the evaluation factors calculated in the table, aiming at the positive abnormal unit area, the development potential of the development well on the residual gas is sequentially from large to small: s5 > S4 > S3 > S1; the potential of the development well of the negative abnormal unit area on the residual gas is sequentially from large to small: s10 > S13 > S7 > S6 > S9; the potential of the development well of the transition zone unit area on the residual gas is sequentially from large to small: s8 > S12 > S2 > S16 > S14 > S11 > S15 > S17. For wells with larger residual gas development potential, the development wells have better production effect and relatively higher corresponding exploitation degree in the early production period (namely, the development wells with larger development potential have larger corresponding exploitation degree). From the mining degree results in the table, the mining degrees of the normal abnormal unit areas are as follows from small to small: s5 is more than S4 is more than S3 is more than S1, and all wells are consistent by comparing microgravity monitoring evaluation results; the mining degree of the negative abnormal unit area is as follows from small to small: s13 is more than S10 is more than S7 is more than S6 is more than S9, and only the S10 well is inconsistent compared with the microgravity monitoring evaluation result; the mining degrees of the unit areas of the step belt are sequentially from small to small; s8 > S12 > S16 > S14 > S11 > S15 > S17 > S2, and only S2 wells do not match. From the statistical result, the coincidence rate of the evaluation result of the residual gas development potential of the developed well of the gas reservoir based on microgravity monitoring and the actual production dynamic result reaches 88.23%, which shows that the evaluation symbol of the residual gas development potential of the developed well of the gas reservoir based on microgravity monitoringAnd the method is objective and practical, so that the accuracy of the evaluation of the residual gas development potential of the developed well of the gas reservoir based on microgravity monitoring is verified.