Geophysical Exploration of Karst Hydrogeology in Guizhou Karst Area

1. Introduction to achievements

The working objectives of the project are: to cooperate with the hydrogeological environmental geological survey in key karst areas of Guizhou, select typical sections, and use remote sensing and geophysical techniques to find out the spatial distribution characteristics of karst groundwater occurrence structures; We will carry out research on the application of conventional methods and technologies and experimental research on new technologies and methods, and form a technical system for karst groundwater exploration in different geological units and types, which will provide technical support for karst groundwater exploration in Guizhou karst areas.

After two years of collecting and sorting out more than 20 items of geological, geophysical and drilling data1in different hydrogeological units in Guizhou karst area, as well as field work in 2229 comprehensive physical points, the following results have been achieved:

(1) Through the application of remote sensing technology, the distribution law of geological structures in Fenggang County and key areas has been found out, and the water exploration target area has been delineated. Combined with the comprehensive geophysical exploration work carried out by Guizhou Ershui and the project team, five suitable drilling positions were determined, and four wells were found to have water after drilling verification.

(2) The response characteristics of geophysical profile curves (audio-frequency geoelectric field method, combined profile method, electrical sounding method, induced polarization method, charging method, etc.) are studied through the analysis of groundwater exploration data of various geophysical methods in karst areas and the experimental research and effect analysis of geophysical exploration techniques for different types of karst groundwater. ) In different water storage structures, the water-rich lithology, geophysical response characteristics and structural characteristics such as dolomite and limestone are summarized, providing technical experience for future work.

(3) Through the comprehensive analysis of the collected data and the measured data, the comprehensive geophysical exploration technology modes of different types of groundwater in Guizhou are summarized, which can provide technical guidance for groundwater exploration in similar areas.

(4) The spectrum IP parameter extraction technology, data processing technology and model parameter inversion technology for distinguishing the properties of karst pipeline fillings are studied, which provides a theoretical basis for effectively using relaxation time t and imaginary part resistivity to study the properties of karst fillings, eliminate electromagnetic coupling effects and accurately calculate IP parameters.

(5) The spectrum response characteristics of amplitude, phase and virtual resistivity components are analyzed and summarized through the experiments of eight artificial specimens and the experimental data of soil tanks with different compositions and mass ratios. Through the analysis of experimental data, it is considered that the time constant T when filled with mud and water is much larger than that when filled with hollow and solid T. Compared with when filled with mud, the virtual resistivity component in the frequency range of T slightly larger than T, M slightly smaller than M, and C slightly smaller than C..0.0 1 ~ 1 Hz is an effective parameter to judge the properties of karst pipeline fillers.

(6) Through the known hole test in the field, the characteristics of karst water strengthening parameters judgment of underground pipelines in limestone area of Guizhou are summarized, that is, the time constant t value is obviously increased compared with the background value (generally two orders of magnitude, the size is n ~10× n); The charging rate m is moderate (about 0.05) and the frequency correlation coefficient c is small (0.0 1 ~ 0.04), which provides a new technical means for detecting karst pipeline groundwater.

(7) Based on the existing geological data and drilling data, through the analysis of geological structure and rock mechanical properties of carbonate strata (bedrock wells, especially wells involving karst mountains), the engineering geological and hydrogeological characteristics factors such as stress and strain that affect the hydraulic fracturing effect are found out, which lays the foundation for hydraulic fracturing rock mechanical analysis and calculation, fracturing simulation and optimal design of fracturing technology.

(8) According to the typical carbonate strata and roof and floor conditions, a mathematical model of fracture development is established, which is consistent with the change of actual strata conditions during hydraulic fracturing. On this basis, a quasi-three-dimensional visual simulation software for hydraulic fracturing of water wells in carbonate formation is developed by using the interactive scientific calculation and graphic development platform of Visual c++ and OpenGL. It can dynamically demonstrate the development direction, length and width of fractures in real time, and display the length and width of hydraulic fracturing fractures in water wells at this time. It provides a technical means for dynamic prediction of hydraulic fracturing fractures in carbonate water wells.

(9) Through a large number of indoor experiments, the successfully developed water-based fracturing fluid has the advantages of low price, good performance, non-toxicity, no pollution to aquifer and strong operability, which can meet the requirements of hydraulic fracturing fluid for bedrock wells.

(10) Single-pipe top pressure and double packer sealing seats can realize single-well local borehole fracturing and multi-stage fracturing, which makes fracturing equipment miniaturized and pipeline system simplified, and creates conditions for the popularization and application of fracturing water increasing technology in bedrock water wells.

(1 1) It is the first time to introduce hydraulic fracturing stimulation technology into the field of basic rock wells with relatively shallow completion depth and less investment, which can provide effective technical measures for increasing production of small wells in arid and semi-arid mountainous areas in China, especially in karst mountainous areas in southwest China. It fills the research blank of hydraulic fracturing stimulation of basic rock wells in China.

2. Technical characteristics

(1) According to the characteristics of groundwater geophysical exploration in different hydrogeological units in Guizhou karst area, the combination scheme of groundwater geophysical exploration in different hydrogeological units is systematically summarized by integrating conventional geophysical exploration methods and new technologies and methods, which not only improves the efficiency of groundwater geophysical exploration in this area, but also facilitates popularization and application.

(2) Aiming at the technical problems existing in the development and utilization of groundwater in Guizhou karst area, the research and application of spectral induced polarization method and new technology of hydraulic fracturing of water wells have been carried out, which has effectively promoted the development of new technologies.

Second, the scope of application and application examples

1. Scope of application

This project is a demonstration study in Guizhou karst area. There are many types of karst areas in Guizhou, which can represent different types of karst hydrogeological units in southwest karst areas. Therefore, its application scope can cover different types of groundwater exploration in karst areas in southwest China.

2. Application example

(1) Comprehensive Geophysical Exploration of Pipeline Groundwater

Dalu Village, Shatu Town, Jinsha County is a peak cluster valley, and the exposed strata are as follows from top to bottom: ① Quaternary eluvial layer (Q): yellowish brown red clay, with plant roots on the surface, distributed on hillsides, valleys and flat terrain, with a thickness of 0 ~ 5.0m..② ② Middle Triassic Songzikan Formation (T2s): distributed in the south of the site, with gray, grayish-white medium-thick dolomite and limestone mixed with mudstone. ③ Lower Triassic Maocaopu Formation (T 1m): it is distributed throughout the site, and the lithology is gray and dark gray medium-thick microcrystalline limestone and dolomitic limestone, with dark gray and dark gray argillaceous limestone and mudstone mixed locally.

Geophysical exploration methods selected in this work area include high density resistivity method, induced polarization method, audio magnetotelluric method and audio magnetotelluric method. Audio geoelectric field method shows a low-value anomaly zone in northeast China; The high density resistivity has a low resistance body at a buried depth of about 70m, which may be a karst pipeline. In induced polarization method, the half-life and polarizability are obviously abnormally high at AB/2 = 120 ~ 160, indicating that it is a water-bearing structure. Audio-frequency magnetotelluric method shows that there are two underground pipelines, one is about 20m in the shallow layer and the other is 90 ~ 1 15m in the middle and deep layer. According to lithology analysis, the shallow layer is covered by Quaternary sandy clay, and the resistivity is low. The lower low-resistivity zone is mainly composed of water-filled zone and argillaceous limestone in structural fracture zone or pipeline crack, in which the high-resistivity zone is mainly Triassic limestone and dolomite limestone, and the resistivity of middle-thick dolomite limestone exceeds1000Ω m.

The anomalies of middle and deep pipelines reflected by the above four geophysical prospecting results are basically consistent with the data of known wells. Therefore, the following two points can be explained: first, the selected method is effective under the geological conditions in this area. Secondly, the half-life and polarizability of induced polarization parameters have high values, which should be effective parameters to judge the properties of karst pipeline fillers.

(2) Spectrum induced polarization method is used to identify the properties of karst pipeline fillers.

Fig. 1 and fig. 2 are the application examples of spectrum induced polarization method for filling water and mud in karst water-bearing medium in Bijie area of Guizhou province.

Figure 1 m, t and c values at different depths when the filling is water.

It can be seen from Figure 1 and Figure 2 that the time constant t of the induced polarization parameter changes obviously when the karst water-bearing medium is filled with water, which is larger at the depth of point 5 and point 6, indicating that the stronger the permeability coefficient, the greater the water yield. When the filling material is mud, the time constant t of induced polarization parameter changes irregularly, indicating that the permeability coefficient is poor and the water yield is small or zero. Consistent with the actual situation.

Fig. 2 m, t and c values of different depths when the filler is mud.

Fig. 3 Comparison diagram of pumping test water level before and after fracturing in Shanyangzhuang demonstration hole in Tangxian County.

(3) Application of hydraulic fracturing technology in water wells.

The lithology of the water well in Shanyangzhuang Village, Gaochang Town, Tang County is gneiss, with a depth of 80m, a diameter of 220mm and a static water level of 9.1m.. Before fracturing, the sunrise water volume of this well is only 6.26m3, which is a dry well. Before fracturing the oil well, use the MicroLogger 2 digital logging tool for electrical logging. According to the logging results, the first fracturing interval is 44.5~54m, the second fracturing interval 19.8 ~ 29m, the opening pressure of the first fracturing interval is 7.0 MPa, and the water inflow is 9.87m3; the maximum pump pressure of the second fracturing interval is 5. 1 MPa, and the water inflow of * * * is 6.6m3 After fracturing, the pumping test shows that Fig. 3 is a comparison diagram of water level in the hole before and after fracturing.

Third, promote the transformation mode.

Conference exchange, technical consultation, personnel training, on-site service, publicity and reporting, etc.

Technical support unit: Hydrogeological Environmental Geological Survey Center of China Geological Survey.

Contact: Wei Yumei Wu Yi

Mailing address: No.0/305, Qiyi Middle Road, Baoding City, Hebei Province.

Postal code: 07 105 1

Tel: 03 12-59085 10

E-mail :weiyumei@chegs.cn