How drilling a well for water identifies waterless tectonic zones

Today we will talk about this drilling a well for water topic - the relationship between "tectonic compression zone" and groundwater.

drilling a well for water look for faults, there are faults, there is groundwater, this view seems to have become a consensus, but not completely correct. For one thing, it is not uncommon to find faults in mudstone, but it is difficult to make the mudstone fracture, if there is no brittle other rock interlayer in the stratum is generally waterless.

Each fault has its own mechanical cause, and the water-richness of faults with different mechanical properties varies greatly. Here we do not discuss more other mechanical properties of the fault problem, only to talk about the black sheep of the fault - the problem of tectonic extrusion zone. drilling a well for water should try to avoid the extrusion zone and go to the more complete "influence zone" at the edge of it. "drilling a well for water.

Fault is called "rupture structural surface" in geomechanics, and the compressive rupture structural surface has many microscopic features, such as recoil rubbing, traction phenomenon tectonic lens body, plume joints, "into the word branch fracture, etc. (see Figure 1), which is difficult for non-geological professionals to understand.

According to Mr. Li Siguang's geomechanical theory combined with our field work experience, it is not difficult to judge the macroscopic fault extrusion zone, which mainly has the following six characteristics.

First, "rock fragmentation". In the exposed rocks, large areas of rock are broken into pieces (see Figure 2). drilling a well for water has to be found in places where there are many large fissures, and it is difficult to have large fissures in places where the rocks formed by extrusion are very broken, so it is difficult to have water.

Secondly, the "production of upright", the formation of a large area of upright rock belt. Upright rock belt is mostly formed by strong extrusion.

Third, "lithology is disordered". Figure 3 shows a fault breccia in an extrusion zone, which can be composed of several rocks in two plates of the same rock (fault breccia, also called tectonic breccia or crushed breccia, is a kind of breccia formed after the original rock is broken by dynamic metamorphism. It consists mainly of angular primary rock breccias of varying sizes, cemented by microfine fragments of the same composition. (Often distributed along the fracture zone, is one of the distinctive signs of the fracture zone).

The fourth is "variable tendency". This is due to the fact that there are many folds in the extrusion zone, whether it is back-sloping to oblique, the tendency of its two wings are reversed.

Fifth, "large scale". Upright rock belt width can reach tens of meters or several kilometers, some are called "deep large fracture", often groundwater poor many control of large faults are often compressive structural surface.

Sixth, the fault extrusion zone in the sky electrogram is often expressed as a wider low value band, if the point distance is very small, not many measurement points is difficult to identify the extrusion zone. It is better to avoid the extrusion zones that are already visible in the rock outcrop when choosing the measurement line.

To identify the extrusion zone, it is necessary to accumulate more geological knowledge and observe more rock outcrops, and it is difficult to analyze the drawings alone. If the rocks are not exposed at all, the above characteristics are not visible, the measured map looks good, the verification work has been done, the hole is even collapsed or stuck, and it is not a soft rock stratum, but still playing dry eyes without water, you should suspect whether to encounter the tectonic extrusion zone.