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1

Productivity stimulation of depleted reservoirs by applying new technologies to open the productive layers

Vlasin I., Stefanescu D.-P., Sutoiu F.

AGH Drilling, Oil, Gas

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2017

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Vol. 34, no. 2

569--576

EN

The greatest natural gas fields belonging to Romgaz company are characterized by an advanced stage of exploitation, which actually involves a special approach, from the perspective of the works performed in the wells. As part of the most recently Romgaz strategy, for these fields have been created new geological models based on 3D seismic acquisitions, which allowed identifying some new less drained or even undrained zones. This aspect created the premises for developing the opportunities for capitalization of the new reserves volumes, by applying the advanced technologies of opening productive layers by perforation and reperforation operations with deep penetration guns, using also underbalance conditions. We mention also that new cased hole geophysical methods like PNN and RCI consisted also important elements in establishing the perforation intervals and identifying the by-passed layers. The paper contains some relevant case studies, which illustrates the efficiency of these new methods.

2

Controls on basal Zechstein (Wuchiapingian) evaporite deposition in SW Poland

Dyjaczyński K., Peryt T. M.

Geological Quarterly

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2014

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Vol. 58, No. 3

485--502

EN

The development of basal Zechstein (Wuchiapingian) strata inSW Polandindicates the existence of a diversified relief inherited after the flooding of the pre-existing depression by the transgressing Zechstein sea. The deeper parts of the basin were the place of development of thin basinal Zechstein Limestone showing sedimentary condensation manifested by bored and encrusted grains and thick evaporites (mostly halite), and in shallow parts Zechstein Limestone reefs followed by thinner evaporite sequences (dominated by anhydrite) occur. The analysis of 3D seismic sections showed that instead of three conventionally recognized evaporite units of stratigraphic potential in the PZ1 cycle, five units occur (from the base to the top: Lower Anhydrite, Lower Oldest Halite, Middle Anhydrite, Upper Oldest Halite, Upper Anhydrite). In a particular place their number may vary from two (Lower Anhydrite at the base of the PZ1 cycle and Upper Anhydrite at the top of the PZ1 cycle) to five. There are two complexes of Lower Anhydrite occurring throughout the platform and basinal zones showing deepening-upward (transgressive) trend. The halite sedimentation in the deepest parts of salt basins began shortly after the deposition of the upper Lower Anhydrite complex while in the sulphate platform areas the sulphate deposition lasted still for a long time. The Lower Oldest Halite deposits occur in the depressions. Between the halite basins, anhydrite platforms occur, and the thickness of anhydrite platform deposits is smaller than it is observed in salt basins. The Upper Oldest Halite in turn is recorded above the anhydrite platform. The two halite units represent different phases of development of halite basins. The Lower Oldest Halite basins are related to the pre-Zechstein depressions, although in some cases their syndepositional subsidence was controlled by reactivation, during the deposition of basal Zechstein strata, of former faults. In turn, the Upper Oldest Halite basins used the accommodation space created due to anhydritization of the Lower Anhydrite deposits composed originally of selenitic gypsum. The 3D seismics evidences that the PZ1 evaporites inSW Polandhave been deposited in far more complex and dynamic system than it was assumed before.

3

Application of seismic methods to identify potential gas concentration zones at the Zechstein Limestone Level in the "Rudna" mining area, SW Poland

Dec J., Pietsch K., Marzec P.

Annales Societatis Geologorum Poloniae

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2011

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Vol. 81, No 1

63-78

EN

A block development operation at the "Rudna" copper mine (KGHM Polska Miedź S.A.) encountered a "compressed gas trap" that caused the ejection of fragmented rock material into a drift. Faced with a new threat of gas ejection the mine needed to find methods to identify potential gas concentration zones prior to any further exploration work. Surface seismic surveying was chosen as a widely-accepted standard method of investigating rockmass structure and tectonics and pinpointing natural gas deposits. An area of one square kilometre was selected directly above the ejection site, a 3D seismic survey, known as Duża Wólka 3D, was performed and a survey well S-421A was drilled. The objective was to investigate the overall rock structure, especially the structure of Zechstein and top Rotliegendes formations, as well as to attempt identifying anomalous zones, which could be linked with the gas saturation of Ca1 dolomites, on the 3D seismic image at the P1 level (Zechstein/ Rotliegendes boundary). An interpretation of multi-scenario seismic modelling of the recorded data helped to: – recognize the structure and tectonics of the area, including minor faults cutting through the top-level Rotliegendes formations and floor-level Zechstein formations. Such faults could constitute migration channels for Carboniferous-period gases, – locate zones with nearly zero-reflection amplitude at the surface of the top-level Rotliegendes (P1 seismic boundary), which would suggest a reduction of elastic parameters of the Ca1 dolomite. This reduction could be linked to an increased porosity and fracturing of the dolomite and its saturation with gas (a reduction of the seismic wavelet propagation velocity). Credibility of this interpretation is already partly corroborated by data from wells drilled in the Zechstein limestone by the mine. The paper presents the first in the world attempt to use the surface seismic survey for location of zones with small gas concentration in porous rocks at the Zechstein/Rotliegendes boundary. Such zones should not be identified with gas pools that occur in the Zechstein Limestone (Ca1) in the area of the Fore-Sudetic Monocline.

4

Kryteria identyfikacji obiektów litofacjalnych jako potencjalnych pułapek złożowych w utworach dolomitu głównego (Ca2) u podnóża platform i mikroplatform węglanowych w środkowo-zachodniej Polsce

Kwolek K., Mikołajewski Z.

Przegląd Geologiczny

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2010

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Vol. 58, nr 5

426-435

EN

In terms of oil reserves of Poland, the Lubiatów oilfield in the Międzychód area is the second largest after BMB oilfield. The discovery of this structural-lithological trap in a toe-of-slope position in relation to the Main Dolomite (Ca2) carbonate platform opened a new hydrocarbon opportunities in this unit. One of the conditions for trap occurrence in the "Lubiatów-type" deposits of the toe-of-slope zone in relation to Ca2 carbonate platforms and microplatforms is the presence of appropriate reservoir facies. These facies are characterized by occurrence of thick packets of porous Main Dolomite rocks (Ca2 lithosomes) composed mostly of sublittoral, redeposited carbonate sands (packstones, floatstones, sporadic rudstones), deposited below wave-base and resulting from activity of traction and suspension currents and gravity flows. The only method to detect such facies is via high resolution seismic images, preferably from three-dimensional (3D) surveys. Unfortunately, intensive exploration studies carried out in this zone between 2005-2008 did not bring measurable effects, that is discovery of new hydrocarbon deposits. Several boreholes drilled in Ca2 lithosomes found water-bearing horizons only. In several other dry holes, none of the facies assumptions made prior to drilling were confirmed. Comparison of seismic images of area of those dry holes made it posssible to find a geometric criterion for seismic detection of Ca2 lithosomes located at the toe-of-slope of carbonate platforms and microplatforms. This geometric criterion, along with the seismological one, should constitute an important interpretational premise in identifying or excluding areas with potential hydrocarbon traps in the Main Dolomite rocks in the area under study.

5

Zdjęcie sejsmiczne Trzciana-Cierpisz-Zaczernie 3D asumptem dla renesansu prac poszukiwawczych w utworach miocenu i jego mezopaleozoicznego podłoża w środkowej części zapadliska przedkarpackiego

Syrek-Moryc C.

Prace Instytutu Nafty i Gazu

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2008

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nr 150 wydanie konferencyjne

87--95

PL

Zdjęcie sejsmiczne Trzciana—Cierpisz—Zaczernie 3D zrealizowano w latach 2006-2007. Inspiracją dla jego wykonania było odkrycie w rejonie zdjęcia w 2004 roku, po wielu latach braku zainteresowania poszukiwawczego rejonem, zasobnego złoża gazu ziemnego Cierpisz w cienkowarstwowych utworach miocenu. Złoże rozpoznano w sąsiedztwie złoża Czarna Sędziszowska, po uprzedniej analizie materiałów sejsmicznych 2D z lat 1981-2000. Odkrycie złoża wraz z wynikami wspomnianej analizy dało podstawę do przypuszczeń o istnieniu w rejonie nie odkrytych jeszcze zasobów węglowodorów. Identyfikację istnienia zasobów oparto o zdjęcie sejsmiczne 3D Trzciana—Cierpisz—Zaczernie, którego wyniki potwierdziły spodziewane w tym zakresie oczekiwania. Rezultatem zdjęcia było udokumentowanie 20 potencjalnych pułapek złożowych w utworach miocenu i jego mezopaleozoicznego podłoża. Dodatkowym efektem było też nowe doświadczenie w zakresie identyfikacji mioceńskich osadów kanałowych, których penetracja wiertnicza stanowić może przyszłościowy kierunek prac poszukiwawczych w obszarze zapadliska. Różno- rodność i ilość wydzielonych w rejonie potencjalnych obiektów złożowych, z zasobami na poziomie 7 mld m3 gazu ziemnego, wskazały na jego znaczną perspektywiczność, wymagającą potwierdzenia nowym zakresem prac poszukiwawczych. Potwierdzenie nasycenia węglowodorami obiektów przyczynić się winno da znacznego przyrostu zasobów w tej części zapadliska, a sposób ich rozpoznania i udokumentowania inspirować podobne działania w innych partiach jego obszaru. Rejon Trzciana — Cierpisz — Zaczernie stanowi fragment środkowej części zapadliska przedkarpackiego, usytuowanej bezpośrednio na północ od brzegu nasunięcia karpacko-stebnickiego, w strefie pomiędzy południkami Sędziszowa i Rzeszowa. Rejon ten przez wiele lat nie był objęty programem prac poszukiwawczych z uwagi na brak przesłanek o możliwości występowania w nim nagromadzeń węglowodorów o znaczeniu przemysłowym. Odkryte w latach 1966-1969 mioceńskie złoże gazu ziemnego Czarna Sędziszowska wydawało się stanowić jedyną, znaczącą w rejonie akumulację węglowodorów. Podstawą takiej oceny były wyniki wykonanych w rejonie nielicznych wierceń poszukiwawczych oraz wyniki prac sejsmicznych 2D przeprowadzonych w latach 1985-1987 i 1995-1996. Ocena ta nie korespondowała jednak z pozytywnymi efektami złożowymi, uzyskanymi w międzyczasie w sąsiednich rejonach zapadliska, charakteryzujących się analogicznym jak rejon Trzciana — Cierpisz — Zaczernie

EN

The 3D seismic survey Trzciana—Cierpisz—Zaczernie was carried out within the years 2006 and 2007. After many years of the lack of interest in the region, a discovery of Cierpisz, a rich natural gas reservoir accumulated in the thin strata of Miocene sandstone and mudstone deposits, in the area of the survey in 2004, became a source of inspiration for conducting the survey. The deposit was recognized in the neighbourhood of the Czarna Sędziszowska deposit, after 2D seismic materials from 1981-2000 had been analysed. The discovery of the deposit along with the results of the above mentioned analysis have formed the assumption that undiscovered hydrocarbons' deposits might exist in the area. An identification of the deposits existence was supported by the 3D seismic survey Trzciana—Cierpisz—Zaczernie, the outcome of which proved the hypothesis. As a result, 20 potential hydrocarbon traps in the strata of Miocene and its mezopaleosoic substratum were documented. A new experience concerning an identification of channel deposits of Miocene, the exploratory work of which may constitute a future direction in exploratory drilling in the area of foredeep became an additional positive result of the survey. Both the diversity and the amount of potential deposit objects marked off in the area, with the resources of about 7 milliard cubic of natural gas, pointed to its considerable perspectivity requiring confirmation in a new area of exploratory works. The confirmation of hydrocarbons' saturation of the objects should contribute to a considerable growth of deposits in this part of foredeep, and the way they were recognized and substantiated should encourage to similar actions in other parts of its area.

6

New stratigraphic scheme for Zechstein rocks in the Pogorzela High (Foresudetic Monocline) and its significance for hydrocarbon exploration

Kwolek K., Mikołajewski K.

Przegląd Geologiczny

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2007

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Vol. 55, nr 12/1

1037-1047

EN

Results of an analysis of new 3D seismic data, obtained from the part of the Wolsztyn High in the Pogorzela High area (SW Poland), allow to test the existing knowledge regarding the geologic framework of the Zechstein rocks in this area. A characteristic arrangement of seismic reflectors within pinched-out Zechstein deposits on slopes of the high shows that they are overlapped in relation to the distinct surface of angular unconformity related to the base of the Zechstein-the Z1'seismic boundary. 3D seismic data seems to show that PZ1 strata are absent in the close vicinity of the Pogorzela High with the lower part of the PZ2 cyclothem also absent across the crest. This suggests that the interpretation of the stratigraphy of Zechstein deposits in the Pogorzela-1 and Pogorzela-2 wells (located on the crest of the high) is, in the light of 3D seismic data, questionable. Probably, the initial stages of the Zechstein transgression did not reach the most elevated part of the high, so that the Carboniferous basement is directly overlain by rocks of the Main Dolomite (Ca2), not by the Zechstein Limestone (Ca1) as was previously thought. The lack of Ca1 strata across the crest of the Pogorzela High opens new exploration perspectives in this interval and explains the apparent negative results of boreholes drilled in 1970s. Presumably it also explains differences in formation of these rocks in comparison with the central and western part of the Wolsztyn High (the Kościan-Nowy Tomyśl area).

7

Nowa jakość danych sejsmicznych kluczem do odkrycia pułapek niestrukturalnych w rejonie Gorzów Wielkopolski — Międzychód

Górska W., Łukaszewski M., Grzywa E.

Prace Instytutu Nafty i Gazu

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2004

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nr 130

243--247

PL

Głównym przedmiotem poszukiwań w rejonie Gorzowa były osady dolomitu głównego. Dotychczasowe badania skoncentrowano na utworach Ca2 zdeponowanych w strefie bariery oraz wewnętrznej laguny i dla tychże obszarów przypada zdecydowana większość powierzchni wykonanych zdjęć 3D. Jednakże ostatnie odkrycia złóż ropy naftowej poza rejonem platformy węglanowej odsłaniają nowe możliwości, co do powiększenia naftowej perspektywiczności basenu permskiego. Odkryte na podstawie danych sejsmiki 3D akumulacje węglowodorów (Lubiatów, Sowia Góra) stanowią pułapki niestrukturalne w poziomie dolomitu głównego zlokalizowane u podnóża platformy anhydrytowo-węglanowej. Mimo iż jest to strefa o niskim stopniu poznania, wysoka jakość danych sejsmicznych 3D oraz właściwa interpretacja litofacjalna pozwoliła nie tylko na zdefiniowanie geometrii pułapek, które stały się przedmiotem spektakularnych odkryć, ale i na wskazanie optymalnej lokalizacji otworów. Efekt ten osiągnięto dzięki zintegrowaniu wysokiej klasy bloku sejsmicznego z pozostałymi dostępnymi rodzajami danych, co było kluczem do oceny zmienności litofacji w obszarze pułapki i ilościowego oszacowania zmian porowatości.

EN

Our aim is to present some examples of porous carbonate slumps occurrence. They were encountered based on seismic interpretation combined with seismic amplitude examination and seismic inversion by means of 3D seismic data. Basinward location cited traps in the vicinity of the carbonate platform not always encourage geologists to explore them. However the latest commercial oil discovery will promote The Main Dolomite aged carbonate slumps as promising hydrocarbon traps as well as potential future exploration targets.