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Nafta i Plin, Vol. 40 No. 166, 2020.

Stručni rad

Remained hydrocarbon saturation evaluation using C/O (Carbon/Oxygen) method

Zdravko Kosovec orcid id orcid.org/0000-0002-5006-6353 ; INA-Industrija nafte, d.d.
Hrvoje Pavičić orcid id orcid.org/0000-0001-7903-8383 ; INA-Industrija nafte, d.d.
Zoran Čogelja orcid id orcid.org/0000-0002-6360-320X ; INA-Industrija nafte, d.d.

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Sažetak

With the large base of existing wells in mature producing fields in Croatia, as well as the potential for future wells, the need for logging in cased-hole wells for remained hydrocarbon saturation evaluation, finding bypassed pay and changing fluid contacts is clear. This logging also reduces the risk by enabling formation evaluation when open hole logs are not avaliable.
Neutron logging has been proved as the most practical and reliable logging in cased hole wells. For this purpose, we use tools with the artificial neutron source (generator). Its practicality is that it isn't active until it is turned on, and it gives much stronger neutron source then a natural radioactive source.
These tools have two logging modes: Pulse neutron capture (PNC) and carbon and oxygen ratio mesurement.
Compared to the previously used pulse neutron capture method, C/O method, although more demanding (very slow logging speed at 1 m/min with at least three logging passes for statistical accuracy) is far less sensitive to low salinity formation water layers.
The operating physics of the pulsed neutron spectrum logging is based on the detection of gamma rays and their associated energy distributions. These gamma rays result from the inelastic capture and interaction of the tool generated, high-energy neutrons within the media surrounding the logging tool, including the wellbore and the near wellbore formation. Inelastic interactions within the logging environment produce gamma rays with energy characteristics related to the specific materials encountered by the nuclear cloud emitted by the downhole neutron generator. These interactions are useful in determining the presence of carbon, oxygen, calcium, and silicon.
The ratio of carbon to oxygen helps identify and distinguish between oil and water. Hydrocarbons are simply speaking chemical compounds of carbon and oxygen. Accepting this simplification a hydrocarbon molecule can be written as CxHy. Another usual reservoir fluid is water (H2O). By observing the relative abundance of carbon and oxygen we can determine the presence of oil and water through casing and within the wellbore.
Similarly, neutron collisions with the formation and cement cause gamma ray emissions with the energy distribution related to calcium and silicon. The detection of the contribution of energy levels related to calcium and silicon enables the interpretation of the quantity of cement behind casing, limestone, sandstone and minerals containing calcium and silicon, as well as the indication of the reservoir cementation containing calcium.

Ključne riječi

Identification of Residual Hydricarbons; Carbon/Oxygen method; SIGMA Method; SATG method

Hrčak ID:

249936

URI

https://hrcak.srce.hr/249936

Datum izdavanja:

14.1.2021.

Podaci na drugim jezicima: hrvatski

Posjeta: 850 *

Publication date: 18 January 2021

Volume: 40

Issue: 166.

Pages: 50-57

DOI:

Article Information (continued)

Categories:

Subject: Stručni rad

Categories:

Subject: Professional Paper

Keywords:

Keyword: identifikacija prostalih i zaobiđenih ugljikovodika

Keyword: metoda ugljik/kisik

Keyword: SIGMA metoda

Keywords:

Keyword: Identification of Residual Hydricarbons

Keyword: Carbon/Oxygen method

Keyword: SIGMA Method

Keyword: SATG method

Procjena preostalog zasićenja ugljikovodicima korištenjem metode ugljik/kisik (c/o Carbon/Oxygen)

Translated Title (en): Remained hydrocarbon saturation evaluation using C/O (Carbon/Oxygen) method

[ORCID] Zdravko Kosovec[1]

Email: zdravko.kosovec@ina.hr

 

INA-Industrija nafte, d.d. INA-Industrija nafte, d.d. Av. Večeslava Holjevca 10, 10000, Zagreb

[ORCID] Zdravko Kosovec[*][1]

 

INA-Industrija nafte, d.d. INA-Industrija nafte, d.d. Av. Večeslava Holjevca 10, 10000, Zagreb

[ORCID] Hrvoje Pavičić[*][2]

 

INA-Industrija nafte, d.d. INA-Industrija nafte, d.d. Av. Večeslava Holjevca 10, 10000, Zagreb

[ORCID] Zoran Čogelja[*][3]

 

INA-Industrija nafte, d.d. INA-Industrija nafte, d.d. Av. Večeslava Holjevca 10, 10000, Zagreb

Author notes:

Correspondence to: [*] Zdravko Kosovec,INA-Industrija nafte, d.d.,Av. Večeslava Holjevca 10, 10000, Zagreb zdravko.kosovec@ina.hr

Abstract

Uz veliki broj postojećih bušotina na zrelim proizvodnim poljima u Hrvatskoj, kao i potencijalnih budućih proizvodnih bušotina, očita je potreba za mjerenjima u zacijevljenim bušotinama s ciljem procjene preostalih zasićenja, pronalaženja zaobiđenih zaliha i utvrđivanja promjene kontakta između fluida. Takva mjerenja također umanjuju rizik u situacijama kada nisu dostupni podaci iz nezacijevljenog kanala bušotine. Kao najpraktičnija i najpouzdanija mjerenja u zacijevljenom kanalu bušotine pokazala su se neutronska mjerenja. Za tu svrhu koriste se sonde s umjetnim izvorom (generatorom) neutrona, čija je praktičnost u tome da nisu aktivne do uključenja te daju mnogo jači izvor neutrona od prirodnih radioaktivnih izvora. Te sonde mogu imati dva moda mjerenja: metoda prihvata neutrona (PNC), tzv. Sigma () i mjerenje odnosa ugljika (carbon) i kisika (oxygen). Za razliku od dosadašnje korištene motode prihvata neutrona (PNC), metoda C/O iako zahtjevnija (potreba vrlo sporog mjerenja brzinom 1 m/min te ponavljanja barem 3 puta zbog statističke sigurnosti) daleko je manje osjetljiva na utjecaj niskog saliniteta slojne vode. Fizikalni princip mjerenja pulsno-neutronskog spektra se temelji na detekciji gama zraka i distribuciji njihove energije. Te gama zrake su rezultat neelastičnih prihvata i interakcije visoko energetskih neutrona generiranih izvorom s prostorom koji okružuje sondu, što uključuje kanal bušotine i blisku formaciju. Neelastične interakcije u mjerenom okolišu proizvode gama zrake s karakterisitikama energije vezanim uz specifične materijale koji se nađu u neutronskom oblaku emitiranom iz izvora (generatora). Te interakcije su korisne u determinaciji prisutnosti ugljika, kisika, kalcija i silicija. Odnos ugljika i kisika pomaže u identifikaciji i razlikovanju nafte i vode. O ugljikovodicima možemo pojednostavljeno razmišljati kao o spoju ugljika i vodika. Uz takvo pojednostavljenje, možemo prikazati molekulu ugljikovodika kao CxHy. Drugi uobičajeni fluid u rezervoaru je voda (H2O). Promatrajući relativne količine prisutnih ugljika i kisika, moguće je determinirati prisustvo nafte i vode kroz kolonu zaštitnih cijevi i unutar kanala bušotine. Slično tome, sudari neutrona s formacijom i cementom uzrokuju emisije gama zraka s distribucijom energije vezanom uz kalcij i slilicij. Detekcija doprinosa energije vezane uz kalcij i silicij omogućava interpretiranje količine cementa iza kolone, vapnenca, pješčenjaka i minerala koji sadrže kalcij i silicij, kao i indikaciju stijenskog veziva koje sadrži kalcij.

Translated Abstract

With the large base of existing wells in mature producing fields in Croatia, as well as the potential for future wells, the need for logging in cased-hole wells for remained hydrocarbon saturation evaluation, finding bypassed pay and changing fluid contacts is clear. This logging also reduces the risk by enabling formation evaluation when open hole logs are not avaliable. Neutron logging has been proved as the most practical and reliable logging in cased hole wells. For this purpose, we use tools with the artificial neutron source (generator). Its practicality is that it isn't active until it is turned on, and it gives much stronger neutron source then a natural radioactive source. These tools have two logging modes: Pulse neutron capture (PNC) and carbon and oxygen ratio mesurement. Compared to the previously used pulse neutron capture method, C/O method, although more demanding (very slow logging speed at 1 m/min with at least three logging passes for statistical accuracy) is far less sensitive to low salinity formation water layers. The operating physics of the pulsed neutron spectrum logging is based on the detection of gamma rays and their associated energy distributions. These gamma rays result from the inelastic capture and interaction of the tool generated, high-energy neutrons within the media surrounding the logging tool, including the wellbore and the near wellbore formation. Inelastic interactions within the logging environment produce gamma rays with energy characteristics related to the specific materials encountered by the nuclear cloud emitted by the downhole neutron generator. These interactions are useful in determining the presence of carbon, oxygen, calcium, and silicon. The ratio of carbon to oxygen helps identify and distinguish between oil and water. Hydrocarbons are simply speaking chemical compounds of carbon and oxygen. Accepting this simplification a hydrocarbon molecule can be written as CxHy. Another usual reservoir fluid is water (H2O). By observing the relative abundance of carbon and oxygen we can determine the presence of oil and water through casing and within the wellbore. Similarly, neutron collisions with the formation and cement cause gamma ray emissions with the energy distribution related to calcium and silicon. The detection of the contribution of energy levels related to calcium and silicon enables the interpretation of the quantity of cement behind casing, limestone, sandstone and minerals containing calcium and silicon, as well as the indication of the reservoir cementation containing calcium.

Za rješavanje problema preostalih zasićenja ugljikovodicima u ležištima u zacijevljenim bušotinama, u Ini se od 1999. godine koristila Pulsno neutronska metoda prihvata neutrona (PNC), tzv. Sigma (), koja je i razvijena u Ini. Postojeću tehnologiju i opremu za ta mjerenja je posjedovao Crosco kao servisna kompanija. Ta je metoda () uvelike ovisna o salinitetu slojne vode (otežano je razlučivanje ugljikovodika i vode niskog saliniteta, dok je kod slojnih voda visokog saliniteta razlučivanje izvrsno). Budući da se na Ininim zrelim poljima uz inače relativno nizak salinitet korištenjem sekundarnih metoda pridobivanja utiskivanjem vode (koja je obično nižeg saliniteta) i CO2 (EOR) dodatno snižava salinitet, odlučeno je sa servisnom kompanijom uvesti mjerenje koje je neovisno o salinitetu slojne vode pri rješavanju zasićenja ugljikovodicima u bušotinama. Stoga je u suradnji s vodećim proizvođačem opreme za karotažna mjerenja (Halliburton) i servisne kompanije (Crosco) uvedena nova metoda korištenja Pulsno-neutronskih mjerenja na temelju odnosa ugljika i kisika (Carbon/Oxygen) kao nadogradnja dosadašnje korištene tehnologije. Crosco je od Halliburtona nabavio opremu, a INA software i obuku za primjenu. Napravljena su tri pokusna mjerenja u suradnji s Halliburtonom (mjerenja i analize), a nakon toga samostalno smo pristupili mjerenjima i analizama izmjerenih podataka. Dobiveni rezultati u suradnji s geolozima i inženjerima za fizikalnu razradu doprinose boljem razumijevanju sadašnjeg stanja preostalog zasićenja ugljikovodicima u ležišnoj stijeni.

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