89 research outputs found
SREDNJE MIOCENSKI TALOŽNI MODEL U DRAVSKOJ DEPRESIJI OPISAN GEOSTATISTIÄKIM MAPAMA POROZNOSTI I DEBLJINE (POLJE: STARI GRADAC-BARCS NYUGAT)
Neogene depositional environments in the Drava depression can be classified in two groups. One group is of local alluvial fans, which were active during the period of Middle Miocene (Badenian) extension through the entire Pannonian Basin. The second group is represented by continuous Pannonian and Pontian sedimentation starting with lacustrine environment of partly deep water and partly prodelta (turbidity) fans and terminating at the delta plain sedimentation. The coarse-grained sediments of alluvial fans have the great hydrocarbon potential, because they often comprise reservoir rocks. Reservoir deposits are mostly overlain (as result of fan migration) by pelitic seal deposits and sometimes including organic rich source facies. That Badenian sequences are often characterised by complete petroleum systems, what is confirmed by large number of oil and gas discoveries in such sediments in the Drava and other Croatian depressions. Alluvial environments are characterised by frequent changes of petrophysical properties, due to local character of depositional mechanism and material sources. In the presented paper, Stari Gradac-Barcs Nyugat field is selected as a case study for demonstrating the above mentioned heterogenic features of the Badenian sequences. Structural solutions are compared by maps of parameters related to depositional environment, i.e. porosity and thickness maps. Geostatistics were used for spatial extension of input dataset. The spatial variability of porosity values, i.e. reservoir quality, is interpreted by transition among different sub-environments (facies) in the alluvial fan system.Neogenski taložni okoliÅ”i u Dravskoj depresiji mogu se podijeliti u dvije skupine. Prva skupina obuhvaÄa lokalne okoliÅ”e aluvijalnih lepezi, koje su bile aktivne u razdoblju srednjomiocenske (badenske) ekstenzije u cijelom Panonskome bazenu. Druga skupina predstavljena je kontinuiranom panonskom i pontskom sedimentacijom u lakustriÄkom okoliÅ”u, koja je zapoÄela djelomiÄno s dubokovodnom, a dijelom taloženjem u prodeltnim lepezama (turbiditni facijesi). Taj ciklus zavrÅ”io je sedimentima karakteristiÄnim za deltne ravnice. Krupnozrnati sedimenti aluvijalnih lepezi karakterizirani su velikim naftnoplinskim potencijalom, jer vrlo Äesto obuhvaÄaju ležiÅ”ne stijene. Ti sedimenti uglavnom su prekriveni (a kao rezultat migracije aluvijalnog okoliÅ”a u vremenu i prostoru) pelitskim izolatorskim stijenama koje ponegdje sadrže i matiÄne facijese bogate organskom tvari. Zato takve badenske sekvence Äesto obuhvaÄaju cjelovite naftnoplinske sustave, Å”to je potvrÄeno otkriÄem velikog broja naftnih i plinskih ležiÅ”ta u tim sedimentima, kako unutar Dravske tako i u drugim depresijama u hrvatskom dijelu Panonskog bazena. Aluvijalni okoliÅ”i su karakterizirani Äestim promjenama petrofizikalnih svojstava, a zahvaljujuÄi lokalnom karakteru takvoga taložnog okoliÅ”a i izvora materijala. U prikazanom radu odabrano je polje Stari Gradac-Barcs Nyugat kao ogledni primjer, na kojemu je prikazana ranije spomenuta heterogenost badenskih sekvenci. Strukturna rjeÅ”enja su usporeÄena s karatama onih parametara Äije vrijednost ovisi o taložnom okoliÅ”u, tj. s kartama poroznosti i debljina. Geostatistika je upotrijebljena za prostornu analizu ulaznog skupa mjerenja. Prostorna varijabilnost vrijednosti poroznosti, tj. kvaliteta ležiÅ”ta, je objaÅ”njenja prijelazom izmeÄu razliÄitih podokoliÅ”a (facijesa) unutar sustava aluvijalne lepeze
Kriging, cokriging or stochastical simulations, and the choice between deterministic or sequential approaches
The data presented here for the first time in the Croatian geomathematical community, aims to establish several criteria which will aid in the selection of deterministic or stochastic geostatistical methods of estimation.
This review associates the theoretical background of kriging, cokriging or stochastic simulations with some results obtained by mapping Badenian clastic reservoirs in the Drava Depression. The selected reservoirs are located in the Stari Gradac-Barcs Nyugat field, in the Western part of the Drava Depression, and at the BeniÄanci field in the Eastern part of this depression.
Both datasets (each with 14 points) include mean porosity values taken from well log analysis in the reservoir interval at the well sites. This resulted in significant uncertainties in the variogram models, especially with the determination of range (at the secondary variogram axis).
The critical advantage was the availability of a seismic attribute that could be used as a secondary and co-regionalized variable (porosity is the primary variable). In the first example (the BeniÄanci field) the seismic attribute was correlated with the average logged porosities. This made it possible to apply the cokriging method as the best interpolation option. The cross-validation result was 2.19 for 14 wells.
In contrast, the existence of only a primary variable at the Stari Gradac-Barcs Nyugat field, forced the application of stochastic simulations as the better estimation tool, which can better describe the porosity changes in inter-well areas
Stochastical approach in deterministic calculation of geological risk - theory and example
Za izraÄun geoloÅ”koga rizika (ili vjerojatnosti, engl. skr. POS) otkriÄa ugljikovodika u postojeÄem ili novome stratigrafskom intervalu ili izglednom podruÄju unutar Dravske depresije upotrijebljen je dobro poznati deterministiÄki postupak. Isti se može primijeniti, uz male dorade, za gotovo sve litologije ležiÅ”ta u bilo kojem naftno-plinskom bazenu ili depresiji. Takav izraÄun, iako veÄ pomalo zastario, predstavlja pouzdani alat te, zahvaljujuÄi tomu, joÅ” uvijek ga primjenjuju brojne nafto-plinske tvrtke i konzultantske kuÄe.
Analiza je naÄinjena u najmlaÄem dijelu ležiÅ”ta (obuhvaÄa Äetiri litofacijesa) u polju Stari Gradac-Barcs Nyugat koji je predstavljen krupnoklastiÄnim sedimentima badenske starosti. To polje je odabrano s obzirom da su tamo veÄ naÄinjene odreÄene procjene postojanja dodatnih koliÄina ugljikovodika u \u27skrivenim\u27 zamkama, ali i brojne geostatistiÄke analize na podatcima poroznosti iz svih ležiÅ”nih litofacijesa. Naravno, najmlaÄi i najpliÄi litofacijes obuhvatio je najveÄi broj takvih mjerenja, a ujedno je to (uz sljedeÄi dublji litofacijes) ujedno dio ležiÅ”ta s najveÄim rezervama ugljikovodika.
DeterministiÄki pristup izraÄuna POS-a nadograÄen je u deterministiÄko-stohastiÄki, upotrebom geostatistiÄkih karata poroznosti gdje je ona izražena kroz tri moguÄe realizacije (minimalnom, medijanskom i maksimalnom) za analizirani badenski litofacijes.
Ukupni POS ostao je isti kao i onaj dobiven iskljuÄivo deterministiÄki (POS=0,375). Razlog tomu je Å”to srednja poroznost u analiziranim badenskim klastitima varira u uskome intervalu te ne utjeÄe na procjenu vjerojatnosti postojanja novih koliÄina ugljikovodika. No, u dubljim litofacijesima, gdje je litologija heterogenija i/ili znatnije raspucana varijacije poroznosti su znatno veÄe te bi uvoÄenje deterministiÄko-stohastiÄkog pristupa dovelo do promjena u vrijednostima POS-a, ovisno o tomu koja je stohastiÄka realizacija odabrana kao reprezentativna.Calculation of geological risk (or Probability Of Success; abbr. POS) of hydrocarbon discovery in existing or new play or prospect in the Drava depression has been done using well-known deterministical procedure. Such approach, with slightly modifications, can be used in almost all reservoir lithologies in any hydrocarbon basin or depression. This calculation, although already an old-fashion tool, represent reliable tool and it is why it is still applicable in many oil and gas companies or consulting firms.
Analysis is performed in the youngest part of reservoir (which encompasses four lithofacies) in the Stari Gradac-Barcs Nyugat field. It is represented by coarse-grained sediments of Badenian age. This field is selected regarding there are already done some estimations of existence of additional hydrocarbon reserves in the āsubtleā traps, but also numerous geostatistical analysis with porosity data taken from all reservoirās lithofacies. Of course, the youngest and the shallowest lithofacies included the most such measurements, and also it is (together with the next, deeper lithofacies) reservoirās part with the largest hydrocarbon reserves.
Deterministical approach in POS calculation had been improved in deterministical-stochastical, by using geostatistical porosity maps, where this variable is expressed through three possible realizations (minimal, median and maximal) for analysed Badenian lithofacies.
Total POS remained the equal as such value calculated only deterministically (POS=0.375). It is because average porosity in analysed Badenian clastics varying in narrow interval, and its selection from stochastical results did not have influence on estimation of probability of new hydrocarbon reserves existence. But, in deeper lithofacies, where lithology is more heterogeneous and/or more cataclised, variations in porosity are significantly higher. In such case, introducing of deterministical-stochastical approach could result in changes in POS values, depending on which stochastical realization had been selected as representative
Linearity and Lagrange Linear Multiplicator in the Equations of Ordinary Kriging
Analizirane su jednadžbe jednostavnoga i obiÄnoga kriginga kako bi se uoÄila razlika u izraÄunu procjene u toÄki, te zorno prikazalo na koji naÄin se Lagrangeov multiplikator iskazuje kao veliÄina u tehnici obiÄnoga kriginga koja minimizira varijancu procjene. Detaljnom analizom matrica i linearnih jednadžbi, koje se inaÄe automatski izraÄunavaju u pozadini raÄunalnih programa za kartiranje, prikazana je važnost geomatematike u jednoj od temeljnih geoloÅ”kih djelatnosti ā kartiranju. Nadalje, izvoÄenjem niza jednadžbi kroz Älanak pruža se na inženjerski naÄin razumijevanje algoritama jednostavnoga i obiÄnoga kriginga, koje su danas dvije najÄeÅ”Äe koriÅ”tene geostatistiÄke tehnike (uz indikatorski kriging kao treÄe). U zakljuÄku su predloženi postupci kojima se može odrediti najprimjerenija vrijednost Lagrangeovog multiplikatora za bilo koju jednadžbu obiÄnoga kriginga.The equations of Simple and Ordinary Kriging are compared to outline their differences in the estimation procedure. Emphasis is given to the Lagrange multiplicator as a variable that allows the minimization of variance in Ordinary Kriging. The matrices and linear systems of kriging, which are most often performed in the background of the computer mapping algorithm, are analyzed and presented in detail. The intention is to show the importance of geomathematics in one of the basic geological tasks, mapping. Furthermore, a detailed presentation of equation sets provides a better understanding of the Simple and Ordinary Kriging algorithms for geological engineers, as the two most-used geostatistical techniques (included Indicator Kriging as the third). The conclusion includes proposals, presented in four steps, for the determination of the Lagrange multiplicator value in any Ordinary Kriging equation
Stochastic simulations of dependent geological variables in sandstone reservoirs of Neogene age: A case study of KloŔtar Field, Sava Depression
The research presented herein is the first attempt to perform geostatistical simulations on three geologic variables, porosity, thickness, and depth to reservoir, in the Croatian Pannonian basin. The data were collected from a reservoir of Lower Pontian age in KloŔtar Field, located in the western part of the Sava Depression.
All three variables were analyzed using sequential Gaussian simulations (SGS). Information regarding present-day depth, thickness, and locations of areas with higher porosity values were used to reconstruct paleo-depositional environments and the distribution of different lithotypes, ranging from medium-grained, to mostly clean sandstones and to pure, basin marls. Estimates of present-day thickness and depth can help to define areas of gross tectonic displacement and the role of major faults that have been mapped in the field. However, since mapping of the raw data (including porosities) does not allow the reconstruction of paleo-depositional environments, sequential indicator simulations (SIS) were applied as a secondary analytical tool. For this purpose, several cutoff values for thickness were defined in an effort to distinguish the orientation of depositional channels (main and transitional). This was accomplished by transforming porosities to indicator values (0 and 1) and by applying a non-linear āindicator krigingā technique as the āzeroā map for obtaining numerous indicator realizations by SIS.
In the SGS and the SIS approaches, the simulations encompassed 100 realizations. A representative realization was then selected using purely statistical criteria, i.e., two realizations were almost always chosen in accordance with the order of calculation. The 1st and 100th realizations were selected for each variable in the SGS and SIS and five āindicator krigingā maps were chosen for the thicknesses cutoffs
Miljenko Lapaine i DuÅ”an MarjanoviÄ (Ed.): Elementa Geometriae Practicae, Zemlyomirje, Introduction to Practical Geometry / Surveying
It has been my pleasant task to write a review of a very interesting book with its attractively archaic appearance of the cover and a layout which, it needs to be said, completely matches its contents. Furthermore, it is interestingly conceptualized; a working result of scientific teams from Croatia and Hungary within a framework of bilateral project Najstariji hrvatski udžbenik geodezije (The oldest Croatian textbook of Geodesy) in a way that its preface and abstract have been written trilingually ā in Croatian, Hungarian and English. The results of the project work have been conjoined, in a fitted final whole, by the bookās editors Miljenko Lapaine and DuÅ”an MarjanoviÄ
Production of a Porosity Map by Kriging in Sandstone Reservoirs, Case Study from the Sava Depression
Variogramske analize te upotreba geostatistiÄke
interpolacije predstavljaju u zadnjih pet godina
standardni alat u hrvatskoj geologiji. Takve analize
posebno su primjenjivane prilikom kartiranja naftnogeoloŔkih
podataka. U ovome Älanku opisani su prostorno
modeliranje podataka poroznosti te kartiranje s
pomoÄu krigiranja naÄinjeno za relativno veliki ulazni
skup vrijednosti prikupljenim na naftnom polju smjeŔtenom
u hrvatskom dijelu Panonskoga bazena, tj. u
podruÄju Savske depresije. Analizirani skup podataka
obuhvatio je vrijednosti poroznosti u pjeÅ”ÄenjaÄkom
ležiÅ”tu panonske starosti. Izvorni podaci, svojom brojnoÅ”Äu,
rijetko su obiman skup vrijednosti poroznosti
dostupnih u ležiŔtima ugljikovodika u Hrvatskoj. To je
omoguÄilo vrlo pouzdano semivariogramsko modeliranje
te interpolaciju tih podataka krigiranjem. Krigeova
metoda (krigiranje) istaknuta je kao najprimjerenija
interpolacijska tehnika za poroznost, ali i druge geoloŔke
podatke u pjeÅ”ÄenjaÄkim ležiÅ”tima miocenske starosti.Variogram analyses and usages of geostatistical
interpolations have been standard analytical
tools in Croatian geology in the last five years. Such
analyses have especially been applied in the mapping
of petroleum geological data. In this paper, spatial modelling
of porosity data and, consequently, kriging mapping
are described for a relatively large dataset obtained
at an oil field located in the Croatian part of
Pannonian basin (Sava depression). Analyzed datasets
included porosity values measured in a sandstone
reservoir of Pannonian age. The original dataset can
be considered as a rare extensive porosity set available
for Croatian hydrocarbon reservoirs. It made possible
very reliable semivariogram modelling and kriging
interpolation of porosity. The obtained results point
out kriging as the most appropriate interpolation approach
for porosity, but also for other geological data
in sandstone reservoirs of Miocene age
The Bjelovar Subdepression as an Area with Conventional and Unconventional Hydrocarbon and Geothermal Reserves
Bjelovarska subdepresij a, kao geoloÅ”ki odreÄen prostor, sadrži ā uz dokazane rezerve ugljikovodika ā i njihove potencij alne rezerve te rezerve geotermalne energij e. Dan je pregled pridobivanja i uporabe takvih energenata, a zatim sastav, dubina i rasprostranjenost takvih ležiÅ”ta u dij elovima gdje su istraživana i pretpostavljena. Geotermalno ležiÅ”te izuÄavano je u prostoru mezozojskih karbonata te donjomiocenskih i srednjomiocenskih krupnih klastita u sinklinali Velika Ciglena, najveÄoj pojedinaÄnoj strukturi u subdepresij i. Dokazano je postojanje termalne vode na dubinama od oko 2.500 m, no do danas nij e privedena pridobivanju na povrÅ”inu i uporabi bilo za proizvodnju struje bilo za grij anje. Nekonvencionalna ležiÅ”ta takoÄer su pretpostavljena u tom istom prostoru, unutar gornjobadenskih, sarmatskih i donjopanonskih matiÄnih stij ena, koje su dostigle termalnu zrelost. No, takvih ležiÅ”ta, posebice plina, moglo bi se naÄi i na rubu subdepresij e, u Bilogorskoj zoni, unutar struktura gdje nisu dokazana konvencionalna ležiÅ”ta ugljikovodika (CremuÅ”ina, Gakovo), no opažene su pojave plina i naft e u slabopropusnim pjeÅ”Äenjacima gornjega miocena.The Bjelovar Subdepression is geologically very well defi ned area where are discovered proven hydrocarbon reserves. However, there are assumed as well potential hydrocarbon and geothermal reserves. Here is fi rstly given review of forming and application of fossil fuels and geothermal energy. It is followed by review of lithologies, depths and distributions of unconventional and geothermal reservoirs in subdepression parts where they are explored and assumed. Geothermal reservoir is studied in Mesozoic carbonates and Karpatian to Badenian coarse grained clastics in Velika Ciglena Syncline. It is the largest single structure in Velika Ciglena Syncline, where is proven geothermal water at depth more than 2500 m. However, it still is not proven and used for electricity of thermal applications. Unconventional hydrocarbon reservoirs are also assumed in the same area, i.e. in Upper Badenian, Sarmatian and Lower Pannonian sediments in the thermal mature phase. Also, such unconventional reservoirs, especially of gas, could be proven at subdepression margin, in the Bilogora Zone, in structures where conventional reservoirs are not proven (CremuÅ”ina, Gakovo), but are registered oil and gas shows in weakly permeable Upper Miocene sandstones
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