RU2012905C1 - Method of revealing zones of natural brines - Google Patents

Abstract

FIELD: gas and oil prospecting. SUBSTANCE: complex of field geographic testings is carried out, structural plans of above- and under salt deposits are drawn, then holes are bored in the contour of arch of anticlinal raising outside joint of arch in the section, where thickness of salt formations is no less than one third of its maximal value. EFFECT: improved reliability. 1 dwg

Description

 The invention relates to field geophysics and can be used for prospecting and exploration of oil and gas fields, as well as mineralized waters in the areas of development of salinity deposits.

 A known method for predicting zones of occurrences by constructing maps of thicknesses of salt formations and identifying zones of occurrences with local blowouts of thicknesses of salts in the near-arch and arch sections of modern structures [1].

 The disadvantage of this method is its low reliability, due to the possibility of only qualitative assessments with the potential spread of anticlinal salt structure.

 There is a method (prototype) for identifying zones of high pressure and high moisture saturation of a section by conducting a complex of geophysical studies, isolating anticlinal uplift with offset structural plans of over- and subsalt deposits, determining the contour of its arch of drilling a well, conducting a well logging complex and determining a zone of developmental events [2].

 The disadvantages of this method are related to the impossibility of taking into account the real lithological conditions of the saline section and the identification of the intervals of occurrence of zones of developmental occurrences associated with the presence in the section of inter-salt rocks - host rocks.

 The aim of the invention is to increase the reliability of identifying zones of manifestations.

 The goal is achieved by the fact that, within the identified anticlinal uplift with shifted structural plans of the over- and sub-salt deposits, the wells are additionally drilled outside the arch lock, intersalt saturated reservoirs are identified and traced according to a complex of geophysical studies, with areas of spatial development in the contour of the arch of the anticline uplift conducted according to the last closed isogypsum along the roof of subsalt deposits, the zones of development are identified.

 Under the "zone of development" in the claimed method is meant located in saline sediments, a cluster of highly mineralized high-pressure brines (brines), confined to the inter-salt lithologically separated formation - a pore-fracture type reservoir. Rapa in a decompressed, fractured, predominantly terrigenous rock is contained under conditions of abnormally high reservoir pressure (AAP), which determines its ability to self-flow through the wellhead. The rapeseed formation always lies between the fluid-resistant formations of dense anhydrites and rock salt, which represent a lithological permeability barrier (pressure barrier). In the context of saline sediments, there may be several hydrodynamically isolated hydrated reservoirs; within the area development of each of them, in turn, there may be several “zones of development”. When a well-saturated formation is opened by a well, development can occur only if the well enters the contour of the arch of the anticlinal uplift.

The arrival of brine into the well is noted by the following signs: an increase in the level of drilling fluid in the receiving tanks, a drop in pressure on the riser, a sharp change in the parameters of the flushing fluid (a decrease in density, viscosity of the pH value, an increase in water loss), an increase against the background gas content in the flushing fluid, and an increase in concentration ions K ⁺ , Mg ²⁺ , Ca ²⁺ , SO ₄ ^2- and trace elements Sr, Rb, Cs, Li, Br, B, I, F in the mud filtrate. In case of development, mud overflow is usually observed through the wellhead.

 In the study area, within the distribution of saline sediments, field geophysical studies are carried out, including seismic exploration. Having compiled structural plans for over- and subsalt sediments, the spatial position of the saline stratum is determined and an anticlinal elevation with displaced structural plans over and subsalt sediments is determined, the arch contour of which is drawn along the last closed isogypsum along the roof of subsalt sediments.

 Then, a search well is drilled for subsalt deposits in the arch contour of the anticline elevation outside the arch lock. In FIG. 1 is a schematic geological section, where saline deposits 1, gas-saturated rocks 2, arch 3 of anticlinal uplift, saturated reservoir 4, stratigraphic boundaries 5, well 6.

 A well is laid at a point where the thickness of the salt deposits is at least one third of its maximum value. This is due to the fact that in the areas of a sharp decrease in salt thickness (in troughs), the inter-salt reservoir layers containing brine are usually absent, and in the castle castle of the anticlinal uplift there is a high probability of intense developmental manifestations, which often lead to liquidation of wells.

 Since the filtration-capacitive properties of the inter-salt rocks are controlled mainly by the tectonic factor, the occurrence of rock is most likely when opening the saturated reservoirs located in the arches of the intra-salt folds, where, due to tensile forces, the opening of the cracks is maximum and the least probable on the wings of the folds and in the inter-arch parts (syncline) where brine is contained in pore space and in limited quantities.

 A complex of geophysical well surveys (GIS) is carried out using electrical methods (apparent resistivity method (CC) or lateral logging (BK), radioactive methods (gamma-ray logging (GK), neutron gamma-ray logging (NGC), and the acoustic method (acoustic logging ( AK)), thermometry, measuring the diameter of the wellbore (cavernometry (HF)), as well as mechanical and gas logging), and intersalt-saturated intersalt formations are distinguished in the opened saline section.

 PRI me R. Based on the materials of field geophysical studies on the studied area, an anticlinal uplift with displaced structural plans of the over- and sub-salt deposits is revealed, the arch of which is drawn along the last closed isogypsum - 4700 m along the roof of the subsalt deposits.

 A search well is drilled on the wing of the anticlinal structure and a saline stratum is uncovered in the depth interval of 1491-4362 m, a saturated reservoir in the depth interval of 3957-3968 m in its submerged part (in the syncline), under conditions of deterioration of the capacitance-filtration properties of rock-host rocks.

In the process of drilling, brine entering the well is noted (an increase in the mechanical penetration speed from 0.67 to 9.3 m / h. A decrease in the density of the drilling fluid from 1850 to 1780 kg / m ³ , an increase in gas readings to 2.1%, an increase in the volume of the drilling fluid in receiving tanks of 8 m ³ After the drilling fluid was heavier to 1940 kg / m ^{3 there were} no signs of brine manifestation.

 Simultaneously with the study of GIS materials, seismic data are being processed. Binding of the saturated reservoir opened by the well is made to the reflecting horizon recorded on the reference seismic section passing through the borehole.

 Reflected horizons linked to the GIS are tracked throughout the seismic section.

 Produce correlation linking of adjacent sections.

 Clarify the structural plans of suprasalt and subsalt deposits. Structural maps are constructed along intersalt reflecting horizons in the contour of the arch of anticlinal uplift.

By the coincidence of the seismic images of the reflecting horizons, R _a and R _b predict the development on the area of two homogeneous saturated reservoirs.

The zone of developmental occurrences confined to the saturated reservoir R _b is identified with the region of spatial development of this formation in the contour of the arch of the anticlinal uplift, i.e., it is limited by the line of wedging out of the saturated reservoir and the isoline is 4700 m along the last closed iso gypsum along the roof of subsalt deposits.

For raponasyschennogo reservoir R _and construct a similar map - circuit rapoproyavleny zone.

 The proposed method outlines the development area of the development zone significantly more accurately (≈ 30-40%) relative to the prototype, which avoids complications when drilling wells in saline sediments.

 Confirmation is a well drilled in the same area, in the arch of the subsalt uplift, revealed the saline layer without complications and confirmed the absence in the section of a saturated reservoir, not previously identified in seismic sections.

 Using the proposed method allows to increase the reliability of identifying zones of developmental occurrences both in terms of the area of development of saline thickness and its section, combining this task with the search for hydrocarbon deposits.

Claims (1)

 METHOD FOR IDENTIFYING ZONE OF DEVELOPMENT, including field geophysical surveys, drawing up structural plans for over- and sub-salt deposits, drilling a well, conducting a complex of geophysical surveys in it and judging by the data obtained on the presence of development zones, characterized in that, in order to improve the accuracy of the method, a well is drilled in the contour of the arch of the anticlinal uplift outside the castle vault in the area where the thickness of saline deposits is at least one third of its maximum value, according to the ge In official studies, intersalt-saturated, saturated layers are identified, the areas of spatial development of which are located in the contour of the arch of the anticlinal uplift and bounded by the last closed isogypsum roof of subsalt deposits, are identified with the zone of development.

Images