RU2742077C1 - Method of localising hydrocarbon reserves in siliceous deposits of the late cretaceous - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention relates to geological survey work in terms of assessment of hydrocarbon reserves in siliceous deposits of sedimentary cover. Proposed method consists in determination of zonality of distribution of forms of silica, which composes Berezovsky suite and its analogues. According to the disclosed method, the strata of the opoka and opoka deposits are correlated using geophysical survey data. Structural map is constructed on the roof of siliceous deposits, which is corrected taking into account reduction of thickness of deposits due to Neogene-Quaternary washing. Minimum depths at which there is a transition from biogenic opal to recrystallized forms of chalcedony and quartz in siliceous deposits are determined. Three regions are separated on the territory of the region by boundary values of depths of transition of opal into chalcedony on the map of the paleodepths. Obtained results are monitored by a temperature factor with construction of a palaeotemperature map in the roof of siliceous deposits. Final matching of the high-promising, medium-perspective and hopeless distribution zones of the collector is obtained by combining paleotemperature and structural structures.

EFFECT: higher reliability of localization of zones of distribution of a non-traditional collector, which is represented by opoka and opoka clays, which enables to forecast hydrocarbon content in sediments of the Berezovsky suite.

1 cl, 2 dwg

Description

The invention relates to geological exploration in terms of assessing hydrocarbon reserves in siliceous sediments of the sedimentary cover.

A known method for determining the degree of crystallization of silica by changing the bulk density and partly neutron porosity based on the data of geophysical studies of wells (GIS) [Derevskova NA, Kravchenko TI, Lykova SB, Dryablov S.N. Regularities of changes in the lithological composition of the Pilskaya suite of about. Sakhalin in connection with the prospects for oil production from siliceous deposits // Scientific and technical bulletin of OAO NK Rosneft. 2014. Issue 37. No. 4. - p. 34-40]. The method makes it possible to divide reservoirs with a high silica content into highly porous (promising) and low porous (unpromising) according to the data of an extended set of geophysical well surveys (GIS).

The disadvantage of this method is the need for an extended GIS complex and the local nature of the forecast. The compared method does not allow mapping the boundary of the phase transition of amorphous opal to the crystalline state and, accordingly, a sharp deterioration of reservoir rocks on a regional scale.

There is a known method for predicting oil accumulations in carbotate-siliceous reservoirs of the Bazhenov formation, which arose under the influence of hydrothermal development of bazhenovites [RU 2596181 C1, IPC G01V 11/00, publ. 27.08.2016]. The essence of the method lies in the delineation by geophysical methods of zones of enhanced generation of hydrocarbons associated with temperature anomalies and hydrothermal development of rocks with a high carbon content, which are caused by acidic intrusions.

This method is inapplicable in the northern and central regions of Western Siberia, where there are no zones of local heating and discharge of fluids as a result of intrusions of acidic intrusions.

There is a method for localizing reserves in oil source strata by differentiating the section into lithotypes according to acoustic, density and petrophysical characteristics, analyzing the dependence of the properties and capacities of lithotypes on the starting flow rates of wells and building a map of effective oil-saturated densities [RU 2572525 C1, IPC G01V 1/48, G01V 1 / 50, G01V 11/00, publ. 01/20/2016]. The localization method involves the identification of promising areas within the field according to the interpretation of the results of geophysical and field tests, the construction of maps of effective oil-saturated capacities, porosity and distribution of the density of oil reserves.

The disadvantage of this method is the requirement of a good knowledge of the area by drilling and the local nature of the forecast of the distribution of oil reserves.

A known method for localizing hydrocarbon deposits is described in [RF Bulgakov, AE Zharov, VE Korablinov, O. Krovushkina, A.A. Tereshchuk. Criteria for identification of siliceous strata and sandy reservoirs in sedimentary sections of the Okhotsk shelf based on well and seismic data // Materials of the Russian Technical Oil and Gas Conference and Exhibition SPE, October 26-28, 2010, Moscow, Russia] on the study of siliceous strata on the shelf of Northern Sakhalin. The method is based on the analysis of seismic data, the localization is carried out by dividing areas (layers) according to the degree of transformation of siliceous matter into poorly transformed with opal, crisstabalite and tredimite OCT (promising) and strongly transformed with silica (unpromising). The boundaries of the plots correspond to the transition zones between the silica modifications and are sometimes manifested by a paired diagenetic section. The boundary of the transition of OCT to chalcedony has certain morphological features, which on seismic sections are manifested by one or two subhorizontal, extended reflective boundaries, subconcordant or obliquely intersecting rhythmically alternating phases of different amplitudes.

This method assumes the availability of regionally linked seismic data of good quality, which is often impossible and expensive.

The studied supra-Cenomanian complex occurs at shallow depths (400-1000 m, maximum depths do not exceed 1500 m). Therefore, the processing of seismic materials must necessarily take into account the presence of permafrost rocks on the territory of the West Siberian plate with a complex mosaic structure, which significantly complicate the work with seismic data. Underestimation of the permafrost layer, or incorrectly entered corrections often distort the wave field on time seismic sections.

However, even a locally undercut acoustic density anomaly on the time section makes it possible to determine or clarify the depth boundary of the transition of OCT to chalcedony.

In the geological section about. Sakhalin, the study of a number of continuous siliceous strata in the sea areas of Khanguzinskaya, Magadanskaya, Khmit'evskaya in Aniva and Terpeniya bays, in a number of areas of the Tatar trough, as well as fragmentary sections, made it possible to reveal the zoning in the distribution of silica forms depending on the depths of maximum subsidence of the bottom of the paleobasin and the paleotemperature [ N.A., Kravchenko T.I., Lykova S.B., Dryablov S.N. Regularities of changes in the lithological composition of the Pilskaya suite of about. Sakhalin in connection with the prospects for oil production from siliceous deposits // Scientific and technical bulletin of OAO NK Rosneft. 2014. Issue 37. No. 4. - p. 34-40]. The first indicator was determined by typical curves of changes in physical properties (density, open porosity) of clay rocks, and paleotemperature - by the reflectivity of vitrinite. Organogenic opal-α (organogenic diatom structure) remains up to a depth of immersion of 1250-1300 m at paleotemperatures less than 50 ° C, opal-KT and α-cristobalite in chalcedony - 1800-2000 m (depending on clay material in flasks) at temperatures above 70 ° С α-Cristobalite has a narrow range of existence, it is not always determined, and its deep confinement has not yet been precisely established.

The results obtained in the study of siliceous deposits at O. Sakhalin are considered acceptable for the deposits of Western Siberia and are taken as an analogue.

A technical problem when using the claimed invention is: mapping the position of the boundary of the transition of amorphous opal into a crystalline state, which allows localizing the development zone of a promising siliceous reservoir and, accordingly, cutting off areas characterized by the propagation of recrystallized forms of opal (non-collector).

Implementation of the claimed technical solution allows to achieve a technical result, which consists in increasing the reliability of localization of the zones of distribution of an unconventional reservoir, represented by opokas and opoka-like clays, which makes it possible to predict the content of hydrocarbons in the deposits of the Berezovskaya suite.

The specified technical result is achieved by the fact that the method for localizing hydrocarbon reserves in the Upper Cretaceous sediments includes conducting geological-geophysical and field studies of wells, a comprehensive analysis of their results, characterized in that the correlation of the formations of opokas and opoka-like sediments using data from geophysical studies of wells, evenly located over the area, siliceous potentially productive strata to seismic horizons, a structural map is built along the top of siliceous deposits, which is corrected taking into account the decrease in the thickness of the deposits due to Neogene-Quaternary erosion, determination of the minimum depths at which the transition from biogenic opal to recrystallized forms occurs chalcedony and quartz in siliceous sediments, three zones are distinguished on the territory of the region according to the boundary values of the depths of the transition from opal to chalcedony on the map of paleo-depths; control of the obtained results by the temperature factor, for which a map of paleotemperatures in the top of siliceous deposits is built as the sum of the current reservoir temperatures, according to the data of actual measurements in wells, and the values of rock cooling for the Neogene-Quaternary time, by combining paleotemperature and structural constructions, the final corrected boundaries of the highly promising , medium-promising and unpromising reservoir distribution zones.

An example of a specific implementation of the method is shown in the following illustrations:

FIG. 1. The zoning of the territory with the use of boundary values is presented (a fragment of the paleo-depth map along the roof of the Nizhneberezovskaya suite in the area of the Beregovoye and Kharampurskoye deposits).

FIG. 2. Comparative analysis of flask of formation NB1 in thin sections of Kharampurskaya and Beregovoy wells.

Upper Cretaceous siliceous and siliceous-argillaceous deposits have a regional distribution within almost the entire West Siberian sedimentary basin, with the exception of the eastern and northeastern margins. In 2016-2018, gas deposits were first discovered in these deposits at the Medvezhye and Kharampurskoye fields. Resources nadsenomanskogo complex, estimated by different researchers for the entire territory of Western Siberia are enormous, but due to poor knowledge of a considerable spread of 6.5 to 50 trillion ^m3. Estimation of reserves directly depends on the volume of the reservoir. In the process of compaction, dehydration, and lithogenesis under the influence of paleothermobaric conditions, organogenic opal transforms into opal-KT, then into cristobalite, and then into chalcedony and quartz. Opal crystallization leads to a complete loss of reservoir properties of rocks.

All siliceous layers have reservoir features: the presence of penetration on the resistivity curves at different depths, a clay cake according to caliper data, negative PS curve anomalies, and extremely low radioactivity values.

It is possible to divide siliceous rocks into opokovy non-crystallized reservoirs and crystallized crystallized crystallized-chalcedony non-reservoirs according to their physical properties: porosity, rock density, and propagation velocity of longitudinal waves.

The proposed method consists in determining the zonation of the distribution of forms of silica that composes the Berezovskaya suite and its analogues.

The proposed method is based on the use of regional maps of paleo-depths and paleotemperatures of siliceous deposits of the West Siberian sedimentary basin, taking into account the cutoff by the boundary values.

The method is carried out as follows.

Correlation of flasks and opoka-like deposits is carried out using the data of geophysical studies for at least 100 reference wells, located evenly over the area, with the binding of potentially productive layers to seismic-reflecting horizons. On the territory of Western Siberia, the Kheyakhin member (confined to the roof of the Nizhneberezovskaya subformation), composed mainly of opokas, is a regional benchmark, which is confidently monitored both according to well logging data (the main criterion is low radioactivity values) and on seismic sections. On the basis of the data obtained, the structural surface of the modern relief of the siliceous strata in the section of the supra-Cenomanian complex of Western Siberia is constructed.

The constructed structural map for the top of the siliceous deposits is corrected taking into account the decrease in the thickness of the deposits due to the Neogene-Quaternary erosion of the upper part of the sedimentary cover. As a result, a paleo-depth map is obtained along the top of siliceous rocks.

The minimum depths at which the transition from biogenic opal to recrystallized forms of chalcedony and quartz in siliceous sediments is recorded have a range of values from 1250 m to 1300 m, which creates a zone of uncertainty. When the boundary values (1250 m and 1300 m) are crossed with the paleo-depth map, two contours are obtained, which in terms of plan divide the territory into three zones.

The zone of depths above 1250 m, characterized by the distribution of unaltered biogenic opal, i.e. the zone of maximum prospects with the highest probability of the presence of rocks with reservoir properties.

The zone of uncertainty, with a depth interval of 1250-1300 m, where opal is already subject to crystallization processes. The mid-prospect zone, where there is a risk of detecting low-permeability siliceous rocks, requires additional study.

The zone of depths above 1300 m, obviously unfavorable for the detection of the reservoir. The presence of recrystallized forms of chalcedony is expected.

The results obtained are controlled by the temperature factor. To do this, build a map of paleotemperatures in the top of siliceous sediments as the sum of modern reservoir temperatures, according to actual measurements in wells and values of rock cooling for the Late Oligocene-Quaternary time in the top of Cenomanian sediments [Kurchikov A.R., Stavitsky B.P. Geothermy of oil and gas bearing regions of Western Siberia M: Nedra. 1987. 134 pp.]. The temperatures at which the transformation of opal occurs vary in the range of 50-70 ° C [Bulgakov RF, Zharov AE, Korablinov VE, Krovushkina O.., Tereshchuk AA. Criteria for identifying siliceous strata and sandy reservoirs in sedimentary sections of the Okhotsk shelf based on well and seismic data // Proceedings of the Russian Technical Oil and Gas Conference and Exhibition SPE, October 26-28, 2010, Moscow, Russia]. The intersection of the accepted boundary values of temperatures (50 ° C and 70 ° C) with the paleotemperature map, by analogy with deep constructions, forms three zones. The overlapping of temperature and depth zones allows to obtain the final corrected boundaries of highly promising, medium promising and unpromising reservoir distribution zones.

FIG. 1 shows an example of the application of the proposed method for localizing an unconventional reservoir in siliceous deposits near the Kharampursky and Beregovoy areas. According to the values of paleotemperatures and paleo-depths, the Coastal area belongs to the border zone of crystallization of opokas, which explains the deterioration of filtration-capacity properties in comparison with the Kharampur deposit located to the south.

Thus, the actual measurements of the bulk density from the core of the Nizhneberezovskaya suite in the Kharampurskaya area amounted to 1.55-1.65 g / cm ³ , on the Beregovoy area 1.88-2 g / cm ³ (Western Siberia). In a comparative analysis of flasks in thin sections from the wells of the Kharampurskaya and Beregovoy areas (Fig. 2), Beregovaya is characterized by reduced values of porosity, permeability, quartz content, the sum of clays and montmorillonite; increased values of the bulk density and the proportion of illite (as a derivative of the transformation of montmorillonite in catagenesis).

FIG. 2 shows the different degree of transformation of the siliceous material of the NB1 formation in thin sections of the Kharampurskaya and Beregovoy wells. The core from the NB1 reservoir in the wells of the Kharampursky license area is, in general, similar to the core from the wells of the Beregovoye license area, but the interlayers of thickening of clay layers of compaction in the wells are observed relatively more often and have a noticeably more pronounced character.

Thus, the peculiarities of the distribution of the reservoir rocks and the ratio of clay minerals indicate an increased degree of catagenetic transformation of the flasks, with a deterioration in reservoir properties, which is confirmed by the test results in these two areas.

Claims (1)

A method for localizing hydrocarbon reserves in Upper Cretaceous siliceous sediments, including conducting geological-geophysical and field studies of wells, a comprehensive analysis of their results, characterized in that they correlate the formations of opoka and opoka-like deposits using geophysical data from wells located evenly over the area, siliceous of potentially productive formations to seismically reflecting horizons, a structural map is constructed along the top of siliceous deposits, which is corrected taking into account the decrease in the thickness of deposits due to Neogene-Quaternary erosion, the minimum depths are determined at which the transition from biogenic opal to recrystallized forms of chalcedony and quartz in siliceous deposits is determined , distinguish three zones on the territory of the region according to the boundary values of the depths of transition of opal into chalcedony on the map of paleo-depths, control the obtained results by the temperature factor, for which a map of the paleotempe is constructed temperatures in the top of siliceous deposits as the sum of modern reservoir temperatures according to actual measurements in wells and rock cooling values for the Neogene-Quaternary time, by combining paleotemperature and structural constructions, the final corrected boundaries of highly promising, medium promising and unpromising reservoir zones are obtained.

Images