Exploration of hot spring well prices

Exploration of hot spring well prices

The occurrence and development of karst are influenced by various factors. In general, the basic conditions for karst development include: solubility of rocks, permeability of rocks, solubility of water, and fluidity of water. The first two are the internal factors that generate karst, while the latter two are the external conditions that lead to karst occurrence.

Exploration of hot spring well pricesSolubility of rocks

Composition of rocks: The solubility of rocks varies depending on their composition. According to their composition, they can be divided into halide salt rocks (rock salt, potassium salt, etc.), salt rocks (gypsum, hard gypsum, etc.), and carbonate rocks (limestone, dolomite, dolomite, dolomite, marble, etc.). Among these three types of rocks, halogenated salt rocks have the highest solubility, followed by salt rocks, while carbonate rocks have the lowest solubility. However, in nature, halide salt rocks and salt rocks are not common, far less widespread than carbonate rocks. In terms of karst phenomena, carbonate rocks have the greatest practical significance.

Carbonate rocks are composed of different proportions of calcite and dolomite, and contain impurities such as mud and silica. Research data shows that the dissolution rate of calcite is much higher than that of dolomite, therefore limestone is more easily dissolved than dolomite; Baiyun limestone and calcareous dolomite, the first to dissolve is calcite, leaving dolomite behind, blocking the fissures, and weakening karstification; Mudstone contains many clay minerals, and after dissolution, the residual clay particles on its surface can also block the pores, hinder water flow, and affect the continuation of karstification. Therefore, generally pure limestone has more developed karst, while mudstone, cassiterite limestone, etc. have poorer karst development. For example, the Devonian, Carboniferous, Permian, Triassic limestone distributed in southern China and the Middle Ordovician limestone in northern China generally have relatively pure lithology and well-developed karst; However, the siliceous limestone of the Northern Cambrian and the dolomitic limestone of the Lower Ordovician have poor karst development.

The structure of rocks: The structure of rocks has a significant impact on karst. The size, shape, and crystallization status of mineral particles all control the porosity of rocks. Generally, the grain size is coarse or uneven, and due to poor weathering resistance and developed joint fissures, it is prone to dissolution; And rocks with finer grains and uniform density are less prone to dissolution; For bioclastic rocks and oolitic limestone, they are mainly composed of bioclasts, with large pores and well-developed karst features; The recrystallized bright crystalline limestone has a small porosity and is not easily dissolved. In Shandong Province, China, some dolomite and mudstone have more karst development than pure limestone. This is because the structure of these rocks is mainly composed of bioclastic limestone and oolitic limestone, with high porosity and developed karst pores.

Drilling technology

Protecting the water bearing fractures in the target layer during geothermal deep well construction is a key step in well completion. Currently, the vast majority of geothermal construction teams still rely on traditional mud circulation comprehensive drilling technology, which brings many unfavorable factors to the later stage of geothermal deep well completion. Firstly, when the well depth is large, the mud column pressure is too high during drilling in the target layer, which can easily push mud and rock powder into the water bearing fractures, block the water outlet channel, and make it easier for undeveloped micro fractures to be blocked; The second is that high molecular weight polymers such as cellulose and amine salts in the mud form a highly cohesive complex with clay and rock powder in the cracks, which is difficult to destroy during well washing operations and becomes a fatal factor affecting water output. To protect the water bearing cracks in the target layer, the following measures can be taken:

(1) The target layer is drilled using gas lift reverse circulation clean water drilling. This technology is part of the "Seventh Five Year Plan", "Eighth Five Year Plan", and "Ninth Five Year Plan" scientific and technological achievement promotion projects of the Ministry of Geology and Mineral Resources, and is also listed as a "National Key Science and Technology Achievement Promotion Plan Project". At present, this technology has been widely applied and promoted in water well and hydrogeological drilling construction, with drilling depths exceeding 3000m and mature experience. Due to the fact that gas lift reverse circulation drilling can use clean water as the circulating medium, and the medium has a fast upward velocity and strong ability to carry rock powder, it can effectively protect fractures from being blocked and protect aquifers, greatly reducing the difficulty of well flushing work.

(2) If mud is used for normal circulation drilling in the water intake target layer, the drilling fluid should be solid free lightweight mud, with a mud funnel viscosity of 19-22s, a density of 1.05-1.10g/cm3, and an API water loss of 10-15ml/30min, in order to minimize the damage of mud to the aquifer.

(3) Before starting to drill into the target layer for water intake, it is necessary to carry out drilling, casing installation, and cementing work on the upper section of the well to prevent a large amount of rock powder during drilling, cement during cementing operations, and sawdust generated by sweeping open the wooden plugs used to make false bottom holes from entering the target section of the well and blocking water containing cracks.

Distribution of thermal reservoirs

The thermal reservoirs in Guizhou Province are mainly composed of multiple water bearing thermal fluid storage structures formed by the interaction and stacking of carbonate rocks and clastic rocks. From the Proterozoic to the Triassic, they can be divided into five major reservoirs. Currently, the main thermal reservoir structures being developed and utilized are the Sinian and Cambrian Ordovician systems, with a small amount of other thermal reservoirs also being exploited.

Deep geothermal reservoirs in Guizhou Province are generally composed of carbonate rock formations with developed caves, fissures, and fractures, and some formations contain mud. In addition, to ensure sufficient groundwater recharge channels in the formation, geothermal drilling is generally selected in structural fault zones, where the thermal reservoir formation is often fragmented and has poor uncertainty. During the drilling process of thermal reservoirs, it is necessary to ensure the stability of the formation and prevent contamination of the formation and groundwater, which requires a high level of drilling fluid.

Drilling rig type

Deep geothermal drilling in Guizhou Province generally uses petroleum drilling rigs or water source drilling rigs, with vertical axis drilling rigs and rotary drilling rigs initially used. However, due to the low power of vertical drilling rigs and the small displacement of conventional mud pumps, it is difficult to meet the requirements of deep geothermal drilling. Nowadays, rotary drilling rigs are basically used.

However, rotary drilling machines also have their shortcomings, such as relatively poor guidance and orientation performance, high rotary torque, which affects the increase of rotational speed.

At present, the commonly used deep geothermal drilling rigs in Guizhou Province include several series such as RPS series and SPS series. At present, some other provinces in China have begun to update their deep geothermal drilling equipment, such as introducing top drive drilling rigs and combining oil drilling with core drilling technology to improve drilling efficiency. However, Guizhou Province has not yet seen relevant research information