Project Description

 

The project is aimed at creation of technologies complex to provide optimal and monitorable development of structurally complex and challenged hydrocarbon deposits including oil and gas shales deposits as well as secondary recovery of highly watered deposits based on use of micro-seismic monitoring methods, supercomputer signal processing and mathematical methods for solving seismic inverse amplitude problems.

 

Since in structurally complex hydrocarbon deposits decompression zones in which fractures were formed during the most recent tectonic processes are the most promising sites for development, the first stage, as the technologies complex suggests, is detecting primary fractures using active seismic methods. As such, it is proposed that carrying out seismic prospecting using the 3D common depth point method should be used. However, in contrast to standard seismic prospecting, in processing and interpretation of seismographic records a new processing method based on selecting a scattered component from 3D common depth point data and oriented towards search of fractured, fissured cavernous and porous-fissured reservoirs is proposed to use. This method was elaborated with the support of The Ministry of Education and Science of the Russian Federation grant in 2008-2010 and was called the Common Scattering Point method (the CSP method).

 

Unlike other ways to approach the problem of fractured reservoirs search, the CSP method implements a new strict solution of the reverse task of division the full wavefield into the reflected and scattered components. This fact sets the CSP method apart from other methods of scattered seismic waves processing. Mathematically correct division of the waves allows principally new geological information to be retrieved from seismic records and visualize scattering elements which are invisible when being processed by other methods.

 

Figure 1 presents the result of the CSP method processing of seismic 3D common depth point data for one of the areas in the Western Siberian oil and gas province (the diffractors are red coloured). Figure 2 shows the position of two wells in vertical time sections of reflectors (the upper part of the figure) and diffractors (the lower part of the figure). The figure clearly shows that these wells lie in the areas with increased values of diffractors, i. e., with increased scattering properties.

 

Figure 1. CSP-diffractors cube combined with CSP-reflectors cube. The Western Siberian oil and gas province.

 

 

Figure 2. The production wells position in time sections of reflectors (the upper part of the figure) and diffractors (the lower part of the figure).

 

 

The CSP method allows for determination of geometry and spatial distribution of acoustic heterogeneities areas connected with fissured cavernous collector using the diffraction component of registered seismograms. In this case, the amplitude of diffractors reflects the fractures intensity (the number of cracks per unit volume) and width. The use of the CSP method will make it possible to construct an adequate digital geological model of reservoirs comprising hydrocarbons in oil and gas shales using the diffractors cube.

 

At the second stage of development of structurally complex hydrocarbon deposits with challenged reserves, it is proposed that methods of on-line micro-seismic monitoring of geologic-technological procedures (including hydraulic fracturing) should be used. These methods are designed to provide the information tracking of geologic-technological procedures and three dimensional mapping of secondary (man-made) fractures areas which have appeared in the process of geologic-technological procedures. In order to achieve this objective, modern techniques of micro-seismic emission data recording and processing are proposed to be used. When recording micro-seismic events on land, it is suggested that recording systems positioned on the daylight surface and in single wells should be applied. Monitoring of the continental shelf deposits implies using the bottom systems with fiber-optic recorders.

 

Real-time monitoring data processing is possible only on the basis of seismic acoustic inversion carried out with the help of specialized software which performs high-level of parallelization using super computers. Recording and preliminary processing can be practiced on the basis of a transportable hardware and software system which is used to monitor hydraulic fracturing and a waterflood operation. А transportable hardware and software system allows for real-time monitoring of the spatial location of micro-seismic activity areas during hydraulic fracturing and optimizes performance of hydraulic fracturing.

 

Micro-seismic monitoring of hydrocarbon deposits is aimed to define the source (hypocenter) of micro-seismic emission in a hydrocarbon deposit and dynamic parameters of stress distribution in the sources. Micro-seismic monitoring research is based on passive observation schemes. Recording is carried out by a seismic antenna (a set of seismic sensors) on the daylight surface or in a well. The methods of processing and interpretation of records used in the technique of passive seismic monitoring of hydrocarbon deposits are capable of attaining the following objectives:

to define the sources (hypocenters) of micro-seismic emission;

to define the energy characteristics and the spatial orientation of the forces in the sources (the seismic moment tensor);

to analyze the intensity change of energy emission which takes place in the process of field development;

to analyze the correlation between micro-seismic activity and the intensity of fluid injection frontal advance;

to estimate changes in the configuration of canals of fluid filtration;

to identify active fault zones, fractured zone etc.

 

During hydraulic fracturing operations, seismo-acoustic emission is being synchronically recorded using a seismic antenna above the well bottom in which the hydraulic fracturing is being executed. Application of special methods for records processing makes it possible to select spatial zones of micro-seismic activity, define their changes in intensity during hydraulic fracturing operations, estimate the correlation between micro-seismic activity and the intensity of fluid injection into a deposit and other geologic-technological procedures. Monitoring hydraulic fracturing (definition of length and direction of fractures) allows one to ensure forecast for man-made fractures, select the zones of canals of fluid filtration and thus decrease unproductive drilling costs.

 

Monitoring of hydraulic fracturing has been undertaken with OJSC «Yuganskneftegaz», OJSC «RITEK», Salym Petroleum Development, Schlumberger (hydraulic fracturing oilfield service companies: MeKaMineft, KATKOneft, Schlumberger, NewCo, Well Service) at the following oilfields: Prirazlomnoe oilfield, the West Malo Balykskoe oilfield, Galyanovskoe oilfield, the Mid Nazymskoe oilfield, the West Salym oil field.

 

Figure 3 presents the system of collection, transmitting and processing of data of development micro-seismic monitoring based on the transportable hardware and software system (THSS).

Figure 4 represents an example of parameters definition of a crack that appeared in the process of hydraulic fracturing at one of the wells of Priobskoe oilfield in the Khanty-Mansiysk Autonomous Area. Figure 5 shows micro-seismic events density in the process of a waterflood operation.

 

 

Figure 3. The system of micro-seismic monitoring data collection, transmitting and processing (THSS).

 

 

 

Figure 4. Seismic emission of the main hydraulic fracturing in a well perforation zone at one of the the Khanty-Mansiysk Autonomous Area deposits.

Coordinate axes are expressed in meters, colouring corresponds to the certainty of micro-events.

 

 

Figure 5. Density of micro-seismic events that occur in the process of a waterflood operation at one of the well sites of the Priobskoe oilfield in the Khanty-Mansiysk Autonomous Area.

 

 

Oil and gas industry has been applying passive seismic monitoring (PSM) since 1960s. Abroad PSM was actively developed in the 90s of the 20th century. To demonstrate the principal possibility of the passive methods of seismic exploration use, a number of experiments were undertaken. Mention may be made of the research of the Yibal oilfield which was executed for Shell/PDO by Vetco Gray company [Teanby N., Kendall
J. M., Jones R. H., Barkved O. Stress induced temporal variations in seismic anisotropy observed in microseismic data // Geophys. J. №156, 3, 2004. pp. 459-463], «Peace River» project – a water injection monitoring project carried out by Shell Canada.

 

The vast majority of research was focused on hydraulic fracturing study. For instance, on land – Cotton Valley [Rutledge J. T., Phillips W. S. Hydraulic simulation of natural fractures as revealed by induced microearthquakes, Carthage Cotton Valley gas field, East Texas // Geophysics, 68, pp. 441-452], fields in Oman [Zhang H., Sarkar S. Passive Seismic Tomography Using Induced Seismicity…// Geophysics Imagine 05.2009], offshore – Ekofisk, Valhall and others]. In these studies seismic emission sources are used to map hydraulic fracturing cracks during reservoir stimulation. In the majority of cases geophones were disposed in the wells [Maxwell S. Assessing the Impact of Microseismic Location Uncertainties On Interpreted Fracture Geometries // This paper was prepared for presentation at the 2009 SPE Annual Technical Conference and Exhibition held in New Orleans, Louisiana, USA, 4-7 October 2009].

 

The performed experiments have shown the feasibility of passive seismic studies and allowed for position detection of microseismic events sources on the basis of recorded data. Currently, several big national and international companies – Saudi Aramco, BP, Anadarko, TCO/Chevron Texaco, Shell Canada, Exxon Mobil, Pemex, Schlumberger and other companies – conduct surveys using the method of passive monitoring.

 

Schlumberger, joint stock company «Central Geophysical Expedition» [Alexandrov S., Gogonenkov G., Mishin V. Passive seismic monitoring application for controlling hydraulic fracturing parameters // Oil Industry Journal, №5, 2005]. JSC «Nazygeodobycha», «SINAPSE» [Chebotareva I. New algorithms of emission tomography for passive seismic monitoring of hydrocarbon production fields. Part I: Processing algorithms and  numerical simulation // Journal of Physics of the Earth, №3, March 2010, pp. 7-19], Institute of New Oil & Gas Technologies [Kuznecov O., Chirkin I., Rurjanov J., Rogotskij G., Dyblenko V. Seismic acoustics of porous and fractured geological environment. Experimental studies // M.: State Research Centre of the Russian Federation – All-Russian Research Institute of Geological, Geophysical, and Geochemical Systems (VNIIGEOSYSTEM), 2004. V. 2, 362 pages], Institute of New Oil & Gas Technologies [Kuznecov O., Chirkin I., Firsov V. and others The forecast for complication risks of drilling based on the information about the near-well area fractures  available from Seismic Sidescan Detector data // International Conference Papers. EAGE 65th Conference and Exhibition – Stavanger, Norway, 2-5 June, 2003].

 

Most of the studies are experimental. Some of the recent studies were focused on creation of passive seismic monitoring systems using elastic waves registration on the daylight surface. There is a well-known in Russia technology which uses the effect of stimulated infra-low-frequency seismic emission over hydrocarbon fields. Low resolution capacity of the technology delimits its applications and, therefore, the technology is used at the exploration stage and is not intended for field monitoring during field development. To study seismic emission in exploration areas and production fields, a passive seismic technology has been created – Seismic Detection of Emission Sources (SDES) [Kuznetsov, Chirkin, Smirnov and others] which is a modification of Seismic Sidescan Detector (SSD). The SSD technology was developed in the early 1990s to select scattered waves and man-caused noise. The result of SDES seismic data processing is a 3D matrix of seismic emission sources energy the meanings of which are in direct proportion to the intensity of radiation of seismic emission sources.

 

We should also note that in the West Siberia it is difficult to rig up a seismic array antenna with a large amount of recording lines in the short term. It is related to the fact that the area is heavily waterlogged and includes considerable forest cover. Therefore, rigging up such a seismic array antenna implies undertaking preparatory works similar to line clearance in seismic survey: employing heavy equipment, felling etc. and thus makes additional expenditures necessary.

 

There is a well-known technique which has been developed at Joint Institute of Physics of the Earth of the Russian Academy of Sciences     (JIPE RAS) that enables one to detect weak impulsive signals whose amplitude is comparable to the amplitude of natural seismic noise by a small aperture group with no use of man-made seismic radiation sources. The technique is based on detecting areas (sources of impulsive seismic events) radiating signals in space. The benchmark data is endogenous seismic radiation (seismic emission) that is represented by microseisms and weak events. Frequency content of oscillations falls into medium frequency range – a bandwidth of 0.5-40 Hz.

 

Emission tomography is a method which is actively used in seismic survey and that allows one to retrieve information about subsurface state and structure on the basis of seismic emission recording. Galperin E. and Gamburtsev G. were the originators of the emission tomography method. Principles of the emission tomography method were taken from the seismic tomography method, however, approaches to inversion of these methods are different and that is related to differences in the source-to-detector schemes.

 

The mathematical apparatus of seismic tomography is an inverse travel time problem relying on Radon transformation which underlies X-ray, magnetic resonance and ultrasonic industrial tomographs used for a variety of applications. The methods of seismic tomography inversion are described in Gruzman I. Mathematical problems of computerized tomography // the Soros Educational Journal, V. 7, №5, 2001.

 

The method of seismic tomography is used for hydrocarbon deposits exploration, studying the geological structure between wells in order to reconstruct a real volumetric pattern of oil saturated layers distribution. Seismic tomography is based on velocity measurement of bodily seismic waves directed in such a way that they can “illuminate” an opaque body which is of interest to geologists, for instance, rock mass that is impossible to observe directly. In this case, rock mass is motionless and the same is true for seismic waves sources and detectors. Information source is total seismic wave field, all types of waves are used, wave values are used integrally.

 

There is a known method of micro-seismic monitoring based on the method of seismic emission tomography  [Chebotareva I., Rozhkov M., Tagizade T., Erokhin G. A technique for micro-seismic monitoring of spatial distribution of the sources of emission of scattered radiation and a device for its implementation // RF patent No. №2278401 C1 20.06.2006]. Areal data collection system is rigged up on the daylight surface over the object under study (in the area of projection onto the daylight surface, for instance, the well bottom projection onto the daylight surface). Detectors are rigged up at up to 10 m depth that makes it possible to reduce the level of surface noise and thus to proportionally increase sensitivity of the method. The method includes wave field recording using one-component or three-component seismic detectors.

 

The discussed methods of seismic emission sources research have the following disadvantages:

artificial seismic sources use causes additional expenses;

observation well use, which is almost impossible, that is why the works are mainly experimental;

the necessity of rigging up seismic antennas with a big number of sensors on the daylight surface (Seismic Sidescan Detector – up to 600) that is, firstly, impossible to do everywhere and, secondly, leads to poor efficiency of seismic surveys;

small number of used sensors (less than 10) that considerably affects the resolution capacity of the method and reliability of objects detecting;

use of principles and seismic methodical techniques bases on the use of  Geiger’s method (earthquake focus definition) which doesn’t allow to define the coordinates of the focus accurately enough.

 

The methods for breakage parameters definition during hydraulic fracturing, which are similar to the ones presented by the project’s authors, are patented (Kochenev, Polyakov, Murtaev and others. RF patent No. 2282876 «The method for seismic survey of the formations fissuring zones during hydraulic fracturing», published 27.08.2006). This method differs from the one presented in the project by using multi-channel station and a 600 channel antenna. The micro-seismic data processing methods are also different.

 

Among foreign companies, the three patents of Schlumberger Technology may be noted:

Patent № 2324810 (Thiercelin Marc (FR) «The method for hydraulic fracturing breakage definition», published 20.12.2007) – hydraulic-fracture crack length and width are defined on the basis of hydrofracturing fluid measuring using numerical simulation of hydrofracturing fluid displacement from the hydraulic-fracture crack.

Patent № 2327154 (Segal Arkady (RU), Thiercelin Marc (FR) «Method and system for monitoring of fluid-filled domains in a medium based on interface waves propagating along their surfaces», published 10.10.2005). Standing interface waves propagating along cracks are used, the typical size of the crack is defined by the velocity of interface waves propagation.

Patent № 2318223 (Thiercelin Marc (FR), Segal Arkady (RU) «Passive seismic monitoring optimization via reactivation of shear faults by pressure pulsing», published 27.02.2008). The surface boundary of hydraulic-fracture crack is estimated by pressure pulsing into the well with the amplitude sufficient to open shear faults during hydraulic fracturing or after it; in the adjacent well, seismic signals from acoustic events associated with shear faults opening are registered.

The disadvantages of the methods described above are:

they can’t determine the direction of hydraulic-fracture crack;

insufficient accuracy of crack’s size definition.

 And, finally, at the third stage – the stage of oil and gas shales field development itself – it is supposed that constantly acting seismic and micro-seismic 4D monitoring of fields development is being performed. Therefore, it is a case of two methods – the active method of 3D common depth point method (3D CDPM) sensing of the Earth and the passive method of volumetric micro-seismic monitoring similar to the one that is used for hydraulic fracturing monitoring.

 

The general structure of the technology complex is represented in the scheme below:

 

Within the scope of the proposed project, it is expected to conduct series of interconnected research and developmental work for creation the technologies of micro-seismic monitoring of the hydrocarbon deposit during all stages of its production. It is assumed that the study will be largely based on the results of the previous research and developmental works on this subject and that these approaches will be developed in scientific and technological aspects.