Prospects of oil deposits mapping by the SSP1 method
The spectral-seismic profiling method (SSP) does not allow to receive the information from very big depths. In examples of use of SSP method the depths exceeding 300 m are not meeting almost. A lot more depth are of interest for searches of deposits.
It is considered that the geological objects which are taking place on small depth, can be of interest only at engineering researches when it is necessary to reveal objects which influence constructions. These are quicksands, karsts, and some other things.
In this direction we worked, trying to see dependences between SSP-sections received by us and the available geological information. It frequently happens in a science, results of these researches was found unexpected.
So, at researches near sites of constructions destructions, in these zones on SSP-section arise funnel-shaped (V-shaped) objects or one element of these objects. In search of a nature of these objects (V-shaped) we began to carry out the researches in the regions where thickness of a sedimentary rock are different. From Kola Peninsula and the Vyborg's area of Leningrad Region where depth of roof of crystal rock is from zero up to a few tens of meters, and up to such regions of Western Siberia where thickness of a sedimentary rock achieves 8 km.
In result, we managed to ascertain, that V-shaped objects observed on SSP-sections unequivocally correspond to zones of tectonic dislocations in crystal rock. It turned out, that depth of these objects on SSP-sections is from 30-50 up to 200-500 (and sometimes and more) meters and does not depend on thickness of a sedimentary rock. On fig.1 it is given more or less typical example of such object. The knowledge of parameters of this object allows to predict reliability of the constructions which have got in a zone of tectonic dislocations.
The V-shaped object on the SSP-section is a steady attribute of presence of a zone of tectonic dislocation, and properties of rock in this zone considerably differ from properties of the rock which are taking place outside of this zone. Having an opportunity now, as a result of application of SSP to reveal these zones, we can explain a number of the moments, that did not having the explanation before. So, it is known, that sometimes there are places where at realization of exploration drilling it is not possible to take a core. Rock in these zones are in so broken condition, that at drilling they completely collapse. The drill tool in such zones does not meet resistance, but even comes down abruptly. In these zones even on significant depths there can be emptiness.
From the point of view of physics of influence of tectonic dislocation on constructions of us has interested, that with increase of size of thickness of a sedimentary rock the influence of tectonic dislocation on constructions does not decrease. It is one more proof of that rocks are not elastic solids, and if to influence on them at long time there will not a bend of rocky layers, but it will development of destruction. In other words, all deformations in rocky thickness occur not due to elastic properties of rock, and owing to their destruction. And, hence, all motions that occured on somehow big depths, traces of them will be visible on all thickness of rock, down to near-surface layers.
Thereby, if dislocations in rock occur on any depths, to see traces of these dislocations is possible in near-surface layers of rock.
For test of this idea a some of the objects having a magmatic origin was investigated. Namely, kimberlite and another pipes.
In zones of tectonic dislocations the disturbances in rocks develops owing to micromovings of particles from the top downward, and on SSP-sections funnel-shaped objects have an spike downwards. In zones of output of magma, on the contrary, micromotions of rocky particles go from below to upwards and as the magmatic material should slide apart rock material the traces of motions should look like a dome.
Potentially diamondiferous structures surveyed by a SSP method, are in territory of the Arkhangelsk area, on peninsula Yamal, on archipelago New Land, and also in Leningrad region. Despite of distinctions in conditions being these structures, all of them on SSP-sections are shown by domes which appear on the depths which are not exceeding 300 m. One of such domes (received at profiling through tube Pomorskaya) is given on fig.2.
And, at last, about petroliferous structures.
Depth of petroliferous layers can be very big. Down to 8 km it takes place in some regions of Western Siberia. It is natural, that all efforts of geophysicists are directed to creating such geophysical method with which help it would be possible to glance on these depths, and somehow to increase efficiency of searches of deposits of hydrocarbons. Alas, it is necessary to recognize, that for today of such methods is not present. In USA it have recognized, and search for hydrocarbons only by drilling.
To my greatest surprise, oilmen at all do not receive from geophysicists the information on zones of tectonic dislocations. And a lot of failures at drilling chinks because that they get in tectonics.
Thus, even if the information which could be received by a SSP method was limited only by mapping of tectonics and in this case the efficiency at drilling on petroleum essentially would increase. However, as appeared, it is not all.
On fig.3 SSP-section received by researching along a line through the oil-extracting oil well is given. When we have moved off from the hole on 430 meters, we were in system of tectonic dislocations that follows from two V-shaped objects. But on a site of 440-390 m the line with decreasing steepness with distance from a zone of tectonic dislocation is shown. To understand, than this line is caused, we shall consider the following model.
As rock in a zone of tectonic dislocation have the increased permeability, petroleum is squeezed out from a petroliferous layer into these pervious rock. Petroleum trickles downwards, along cracks of tectonic infringement. Pairs of it leave to a surface, being shown sometimes on surface those or other attributes of a oil deposit2. Layer, being exempted from a petroleum and being under pressure of overlying rock smoothly reduces the thickness as approaching a zone of tectonic dislocation. On as much as, on how decreases a thickness of layer (from where oil is squeezed out ), will be lowered and all rock layers, that are higher its. Hence, in a zone adjoining to tectonic dislocation, all rocky column is exposed to motions, basically, the same character, as rock in a zone of tectonic dislocation.
To differ these motions should on character of a portrayal on the SSP-section. And if an attribute of tectonic dislocation - funnel-shaped object the border of a petroliferous layer should be shown by one forming V-shaped object which steepness should decrease (plateau) in process of moving off from a zone of tectonic dislocation. That is such line as is shown on fig.3 in an interval of a structure of 440-390 m, is an attribute of presence of a petroliferous layer.
Or, in other words, an attribute of presence of petroliferous structure at use of SSP method is presence of one branch of V-shaped object with a varied steepness on border with a zone of tectonic dislocation.
Precisely the same as on parameters of the V-shaped objects arising on SSP-section appeared possible(probable) to do(make) the forecast of destructions of constructions, under characteristics of SSP-section in due course it will be possible not only mapping petroliferous layers but also to assess operational characteristics of these structures.
- SSP – spectral-seismic profiling. Physics and practice of spectral seismics - on website www.newgeophys.spb.ru
- On base of these attributes Gubkin has opened one of oil fields.