1. recoverable amount of geothermal fluid
(1) Constraints of Recyclable Quantity Calculation
According to the Code for Geological Exploration of Geothermal Resources (GB/T11615-2010), and with reference to the Special Research Report on Exploration, Development and Utilization Planning of Geothermal Resources in Tianjin (2008-2010).
The calculation time of Neogene geothermal fluid recoverable amount lasted 100 years;
Figure 5-22 Curve comparison between observed values and simulated values of some long-term observation wells during model inspection.
Table 5-5- 10 hydrogeological parameter values
The maximum allowable buried depth of geothermal fluid exploitation in Neogene thermal reservoir is150m;
Use the land subsidence control index to control the allowable maximum subsidence depth, and judge whether it will cause geological environment problems.
(2) recoverable amount of geothermal fluid
The exploitable resources of geothermal fluid depend on the recharge under the mining conditions, and are also related to the technical and economic conditions of mining and the mining scheme. Under certain constraints, the rationality of production well layout becomes the key to calculate recoverable amount. Based on the existing geothermal wells in the evaluation area, the recoverable amount of thermal fluid in Guantao Formation is calculated by adding a virtual production well in the blank area of geothermal development. The time started from the geothermal fluid flow field in June 2007 at 5438+ 10, and ended in June 2006 at 265438+ 10. In the calculation, the output is adjusted, and the geothermal fluid output with the closest water level of 100 to 150m is taken as the recoverable resource of the thermal reservoir. The results are shown in table 5- 1 1, figure 5-23 and figure 5-24. See table 5- 12 for the ground settlement calculated in this scheme.
Table 5- Conversion and Comparison List of Recoverable Geothermal Fluid in Thermal Reservoir +0 1 ng
Figure 5-23 Ng Distribution Map of Recoverable Calculation Production Wells
It can be seen from Table 5- 1 1 that the total recoverable amount of geothermal fluid in Binhai New Area is 5.78× 108m3, and the average production of this thermal reservoir in recent years is 679× 104m3/a, which has exceeded the recoverable amount. According to the average temperature of geothermal fluid in this layer of 65℃, the heat of * * is12.21×10/6 j, which is equivalent to 338× 108kWh of electric energy; The total recoverable geothermal fluid of Neogene in Binhai New Area is 8.68× 108m3, and the * * heat is15.99×10/6j, which is equivalent to 443× 108kWh electric energy.
Compared with the recoverable heat, the recoverable heat of geothermal fluid in Binhai New Area only accounts for 2.26% of the recoverable heat in this layer. Accounting for 0.63% of static reserves.
Figure 5-24 Isogram of 2 106 Hot Fluid Water Level at the End of Natural Gas Recoverable Calculation
Table 5- 12 calculation of recoverable amount of thermal fluid in thermal reservoir Ng land subsidence table
Land subsidence index is used to control the maximum allowable depth drop. According to 100 year, the maximum allowable buried depth of Neogene groundwater level is 150m, and the ground subsidence value in this area is calculated by model operation, which is substituted into the model calculation according to the recoverable mining scheme. The results show that the maximum cumulative settlement is 86.67mm, and the maximum annual average settlement is 0.82mm/year. ..
According to the above analysis, the recoverable amount of geothermal fluid accounts for 0.63% of its static reserves, indicating that the recoverable amount provided is guaranteed to some extent; The maximum annual average land subsidence caused by minable mining is less than 1mm, which generally does not cause geological and environmental problems. Therefore, it is feasible to calculate the recoverable amount of geothermal fluid by limiting the mining year to 100 year and the maximum allowable depth to 150m.
2. Prediction of mining potential and optimization of development scheme
The mining potential is predicted according to five schemes (the number of mining wells in each scheme does not include 6 abandoned geothermal wells). Through comprehensive comparison of the five schemes, the fifth scheme is the best. Scheme 5 is designed as follows:
(1) production and distribution of production wells
The excavation mode is shown in Figure 5-25. According to the annual recharge amount of each recharge well 10× 104m3/a, the total recharge amount reaches 40% of the total production. See table 5- 13 for the distribution of production. Time is divided into two stress periods every year, namely, heating period (10 to March 25th of the following year10, *** 135 days) and non-heating period (March 26th to165438+/kloc). The time step is 15 days. According to different stress periods, each production well is substituted into the model to participate in the calculation. The recharge wells are recharged according to the heating load, and the remaining irrigation amount is evenly distributed to the non-heating period. The changes of geothermal fluid water level in each layer in 10 and 30 years are predicted respectively, as shown in Figure 5-26 and Figure 5-27.
Figure 5-25 Optimal Production Well Distribution of Guantao Formation
Table 5- 13 Optimal Mining Distribution Table of Guantao Formation
Fig. 5-26 10 isoline map of predicted geothermal fluid water level of Guantao Formation
Figure 5-27 Isogram of Geothermal Fluid Water Level Predicted in Guantao Formation in 30 Years
(2) Summary of potential prediction and optimization scheme.
Because most of the mining wells are concentrated in two concentrated mining areas-Tanggu and Dagang, two main funnel areas have also been formed. Ng thermal reservoir is missing on the west side, which makes the missing area form a water-resisting boundary; There is also an internal missing area in the southern evaluation area, forming an internal water separation area. These water-blocking areas have great influence on the whole thermal storage and are extremely sensitive to the increase of exploitation resources (schemes 2, 3, 4 and 5). The sedimentary environment in the south of the evaluation area is poor, and the increase of mining has a great influence on it (Scheme 3 and Scheme 5). Therefore, the layout of natural gas exploitation should be based on the principle of relieving the exploitation amount in the funnel area. In addition to arranging geothermal wells in the blank area outside the centralized mining area as far as possible, special attention should be paid to the influence of the missing area of this layer on the development of geothermal resources, and the layout of wells should be far away from the missing area. The exploitation of geothermal resources should be strictly controlled in the south of the evaluation area, so as not to increase the exploitation amount of geothermal resources as much as possible, increase the recharge amount of geothermal resources, slow down the exploitation pressure and drop pressure in the central area of the funnel, and ensure the sustainable development and utilization of geothermal resources.
To sum up, geothermal fluid resources are deeply buried, with a single recharge route and limited recharge conditions. In order to develop and utilize geothermal resources reasonably, in addition to fully considering the distribution characteristics of geothermal resources, increasing the recharge of geothermal resources is the most direct and effective method to reduce the mining pressure and head pressure in the central area of geothermal mining funnel.