FILTRATION FLOW TRACING

 

Efficiency of further development of oil deposits and the choice of stimulation methods in order to achieve oil recovery enhancement is highly dependent on information fidelity about formation reservoir properties. It is filtration flow tracing that gives the most reliable information about the current state of oil reservoir development.

 

This method enables to determine real speed and direction of injected water, reservoir characteristics in conditions of natural occurrence, flow distribution between reservoirs and between separate wells, as well as sources of water encroachment, hydrodynamic connection of wells, inhomogeneity of deposits, efficiency of oil displacement process, current state of the reservoir, etc. [1-3]. The main advantage of this method is the opportunity to define a number of geological and physical reservoir characteristics directly in the reservoir conditions with the coverage of a considerable volume of geological material and also a differentiated presentation of the reservoir structure in the interwell space.

 

Filtration flow tracing lies in the injection of indicator solutions to the injection wells together with the injected water, drawing of samples from the neighboring production wells on a periodic predetermined base, determining presence and concentration of indicators in the samples of selected water. Chemical elements, salts of chemical compounds, colouring agents, stable radicals, isotopes, food products and their waste are used as indicators. Poly-indicator methods are applied to evaluate the influence of the neighboring injection wells on the same production wells: solutions of different indicators are pumped into the neighboring injection wells. Tracing results analysis is carried out with the help of a software system, developed by BelNIPIneft according to the calculation model described by E.V.Sokolovsky et al. [1].

 

For a number of years BelNIPIneft has been caring out research on filtration flow tracing not only in the fields of the Republic of Belarus, but also in Western Siberia and the Komi Republic. During these years broad research and practice experience has been gained in applying such indicators as fluorescein, ammonium nitrate (nitre), carbamide (urea), thiourea, ammonium thiocyanate, etc. Scientists of the institute are constantly looking for new indicators and are developing new methods of their application in various geological and physical environments. In particular, a new filtration flow tracing method, which is based on introduction of a tracer fluid into the flow-deflecting compound, is being worked out at present.

 

PRODUCTION ENHANCEMENT (PE)

 

BelNIPIneft personnel is constantly carrying out research on upgrading the existing technologies and compositions aimed at production enhancement and are developing new ones in the following direction:

At present all programs on PE include two compulsory stages: pre-operational and post-operational tracing. Pre-operational tracing on PE enables to make a well-grounded choice of the exposed targets, kinds and volumes of flow-deflecting compounds. Post-operational tracing on PE gives an opportunity to evaluate the degree and effectiveness of the exposure on the reservoir, and, if required, to give reasons for repeated implementation of operations aimed at PE. Efficiency of the latter is proved by the experience in the subsalt reservoir of the Vishanskoye field, intersalt reservoir of the Rechitskoye field and a number of other fields in Belarus.

 

Analysis of PE operations carried out on the Vishanskoye field [4] has shown that maximum efficiency is observed when periodicity of these operations is less than 1 year. On this site practical field operations were carried out in four stages, each including tracing, injection of flow-deflecting reagents, repeated tracing. As a result, total effect by January,1,2008 was 26,824 tonnes of oil, with the returns of investment more than 400 per cent.

 

BelNIPIneft specialists have worked out the "Advanced Program for Production Enhancement of RUP PO Belorusneft fields, using physicochemical and microbiological methods, for 2007-2015", which anticipates systematical carrying out of such activities. The activities are at the stage of laboratory research.

 

During development of fields with several rows of production wells formation of filtration system takes place, which is determined by the zone of low reservoir pressure (depression cone). The negative factor in this situation is that further rows of wells are being watered out after the first row wells are excluded from development. In this case operations, aimed at injecting flow-deflecting reagents only through injection wells and carried out in order to gain conformance control and, consequently, production enhancement, do not always prove to be effective.

 

Wide-covering exposure technology has been introduced in order to improve operational efficiency. Its essence is the following: flow-deflecting reagents get into the pay zone not only through injection wells, but also through inspection idle production (intermediate) wells. Spaciotemporal reservoir system of flow-deflecting reagents injection is designed so (particularly with the help of hydrodynamic computer models) that several stream redistribution frontiers from fully-washed, highly porous interlayers to less washed more oil-saturated  ones could be created on the ways of oil filtration.

 

It should be also noted that all wide-covering reservoir exposure operations are preceded by filtration flow tracing through idle production wells, and in some cases - through injection wells.

 

For the sake of testing and developing separate stages of wide-covering reservoir exposure technology and also working out optimal systems of PE for various conditions of oil reservoirs development, practical field operations were carried out in four sites (semiluksky reservoir of Zolotukhinskoye field, subsalt reservoir of Vishanskoye field, voronezsky reservoir of the eastern block of Tishkovskoye field, eletsko-zadonsky reservoir of the third block of Beresinskoye field) in 2007.

 

Implementation of this technology resulted in increase of coverage of these reservoirs by forcing-out horizontally and vertically, involvement into development of additional zones and oil-saturated thickness, which were earlier not exposed. In the future it will help to achieve maximum possible oil recovery factor and to improve technical and economic characteristics of the reservoir development. Success of the conducted activities made it possible to continue activities on mastering this technology in 2008 in accordance with the approved program aimed at wide-covering exposure to the pay-zone in order to achieve PE.

 

Conventional PE technologies ensure only coverage coefficient increase and are based on redistribution of filtration flows in the course of reservoir flooding, resulting in the situation when stagnant (relatively low-porous) oil-saturated zones are included in the development. Still, the problem of displacement of capillary -held and filmed oil, contained in the porous medium, remains unsolved.

 

In order to tackle this problem BelNIPIneft specialists have developed a complex technology of formation stimulation which consists in injection of flow-deflecting and oil-washing compositions into the injection wells. Practical and field operations on mastering of the complex technology on the basis of polyacrylamide gels and surface-active substance "Don-96" are scheduled in the third quarter of the current year.

 

In the period from 1983 to 2006 while conducting operations aimed at production enhancement the following substances were used as residuum-and-gel-processing reagents [5]: caustic soda, ash of soda, gel composition, simusan, suspension BMZ wastage, SPS, soluble glass, hydrolyzed polyacrylonitrile, renivol, lingopol, OVP-1, polyacrylamide (PAA), etc. The main principle of operation of majority of them involves the fact that in the course of interaction of solutions and compositions of chemical reagents with ions Са2⁺ and Мg²⁺, concentration of which in oil-field water is up to 70-80 g/l, residuum and gels are formed which reduce permeability of highly porous channels to a considerable extent.

 

During 2006-2007 practical and field tests of flow-deflecting compositions (for PE) on the basis of diluted water solutions "OVP-1" and natrium soluble glass (Na₂O·mSiO₂), and also "OVP-1" and ash of soda (Na₂CO₃) were carried out at six reservoirs. Operations at zadonsky reservoir (forth bench) proved to be the most successful, resulting in more than 2.8 th. tonnes of  incremental ultimate recovery [6].

 

Lately composition of chemical reagents (polymer-polymer, organic-mineral, compounded  polymer compositions, etc.) has been one of the major directions in improvement, development and implementation of new compounds, which enables to create solutions and plugging materials with required properties without substantial extra expenditures on the synthesis of new reagents.

 

At present there are compositions with adjusted time of gellation on the basis of PAA (TR-1516, Alcoflood-955) and chrome acetate (stitcher) at the stage of implementation. These compositions have given a good account of themselves in laboratory and model studies and differ from those previously used in lower cost and fabricability of preparation, as they can be composed using both fresh and salt water, which presupposes all-the-year-round operating mode.

 

It is also worth mentioning that there is the PAA+ soluble glass composition for high-temperature wells (over 80°С (176°F)) in the stage of implementation. This composition is recommended considering new experimental results in gellation kinetics and heat stability of polyacrylamide gels, obtained in the course of research on state-of-the-art equipment.

 

Implementation of new highly-effective complex technologies of production enhancement combined with existing technical, economic and intellectual asserts will allow to gain maximum possible oil recovery factor in Belarusian fields and improve technical and economic characteristics of reservoir development, which will ensure slowing down the rate of oil production decline for the coming 20-30 years.

 

REFERENCES

 

1. Sokolovsky E.V., Solovjov G.B., Trenchikov Yu.I. Indicator methods of oil-and-gas-bearing formation studying. M., Nedra, 1986.

2. Chernorubashkin A.I. Study of motion work of injected water with the help of indicators in fractured reservoirs. - Abstract of research-and-technology collected volume, series Petroleum engineering, 1979, № 10.

3. Application of indicator methods to control development of oil fields. - Abstract of research-and-technology collected volume, series Petroleum engineering 1985, № 10.

4. Integrated approach to activities aimed at production enhancement on the example of subsalt reservoir of Vishanskoye field. / Limar I.V., Demianenko N.A., Pirozhkov V.V., Pisenkov V.G. et al. Collection of scientific papers "Search and developing of oil resources of the Republic of Belarus", Gomel, 2004, p. 16-26.

5. Technical and economic efficiency of activities on regulating reservoir conformance on the oil reservoirs of RUP PO Belorusneft fields / Demianenko N.A., Pisenkov V.G., Pirozhkov V.V., Ageenko E.V., Limar I.V., Tishchenko N.V. Materials of scientific-practical conference "Problems of oil and gas resources development in Belarus and ways of solving them", Gomel, 2002, p. 365-375.

6. Reagent "OVP-1" - application in technologies of water production restraining and production enhancement / Makarevich A.V., Pisenkov V.G., Limar I.V., Pirozhkov V.V., Parkalova E.I., Melguj A.V., Danishevsky V.N., Riazantseva A.A., Senchuk N.V. // Petroleum engineering. - 2008. - № 2. - p. 26-29.