SeqÃÃncias siluro-devoniana e eocarbonÃfera da Bacia do ParnaÃba, Brasil, como anÃlogos para a explotaÃÃo de hidrocarbonetos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The present study was applied to understanding the similar hydrocarbon reservoirs on the Silurian, Devonian and Early Carboniferous sequences of the ParnaÃba Basin. The exposure investigated are located in the central area in the Piauà state. These outcrops are geologicaly inserted in the southeastern border of the ParnaÃba Basin. Three outcrops constituited on the Silurian strata of the Serra Grande Group (Ipà 1, JaicÃs 1 and 3) and the others exhibit Devonian (Itaim-Pimenteiras 1 and 2, CabeÃas 1 and 2) and Early Carboniferous strata of the, Poti 1, 2 and 3), all of the Canindà Group. The sedimentary sequences confirm two different cycles in the basin, dominated by eustatic levels variations the inland: one a Devonian other a Devonian-Early Carboniferous sequences. The first sequence is represented by the CabeÃas Formation, deposited in a proximal deltaic front, dominated by channels and sigmoids. The Devonian-Early Carboniferous sequence is composed by the deposicional succession of fluvial-deltaic shallow platform, where the proximal facies belong to the Poti Formation and, the distal, to the Longà Formation. The Poti Formation was deposited on the fluvial meandering system in extensive flood plain with certain marine and storms influence. Eight sedimentary facies were identified: conglomerate clast supported (Gcm), sandstones with crossed bedding of low angle (Sl), sandstones with crossed bedding to glide (Sp), sandstones with channeled crossed bedding (St), sandstones with ripples or hummocky (Sr), sandstones with plan-parallel bedding or climbing ripples (Sh), and siltstones to very fine stratified sandstones with ripples (Fl). The Ipà Formation, visualized in IP-1outcrop, presents four facies with represent of longitudinal bars of braided fluvial beds of a submerged fandelta. The JaicÃs Formation, with great lateral continuity and tabulate geometry, was analyzed in two outcrops (JC-1 and JC-2), showing four different facies of fluvial channels of low energy with migration of truncated longitudinal bars by shallow channels. The Itaim and Pimenteiras Formations present five sandy facies: the outcrop ITP-1 suggest a deposition from a retrogradational deltaic front to a progradational high energy environment, and the outcrop ITP-2, with the largest facies variety in the Canindà sequence, a estuarine deposition of coastal areas with interference of low energy currents. The CabeÃas Formation, analyzed in two outcrops of wide lateral continuity (CAB-1 and CAB-2), showed three sandy facies attributed to the deposition in deltaic plain with channels, bars, and lobes. The regressive sequence between Longà and Poti Formations was evaluated in three extensive outcrops (PT-1, PT-2 and PT-3), revealing four facies related to a fluvial meandring environment with lateral accretion of bars, and periodic variations of the speed of currents. Three main types of depositional systems were identified: platformal deposits constituted by laminated pelites and fine sandstones, with planparallel or cross bedding hummocky (in all formations); coastal deposits of fine to medium sandstones with sigmoids, rhitmites related to tide plains, bioturbed sandstones, and siltstones with plan-parallel lamination (Itaim, CabeÃas and Poti Formations); and fluvial deposits mainly of the anastomosed type, composed by medium to conglomeratic sandstones with cross bedding of bars and dunes in braided sub-aqueous system (JaicÃs and Poti Formations). The correlation of outcrops with RG profiles made possible the identification of 52 electric or stratigraphical marks, being also defined three depositional sequences (from the base to the top): Devonian (from the Jaic mark to M200), Devonian-Early Carboniferous (from M200 to M015), and Early Carboniferous (from M015 to M010). The Devonian sequence shows a transgressive interval, corresponding to the Itaim Formation and part of the Pimenteiras Formation, and a regressive interval, corresponding to the Pimenteiras and CabeÃas Formations. It is possible to individualize parassequences that correspond to a shoaling upward facies, frequently covered for radioactive shales corresponding to the surface of flood of the parassequence. The Devonian-Early Carboniferous sequence presents a transgressive interval correspond lower part of the Longà Formation and it is formed by two parassequences, that represent a depositional system of platforms dominated by storms. The regressive interval corresponds to the Poti Formation, where two parassequences are individualized. A numeric simulation of the acquired data in the present study demonstrates that the detailed facies analysis of outcrops can offer interesting subsidies in the investigation of similar hydrocarbons reservoirs

ASSUNTO(S)

modelo numÃrico bacia parnaÃba anÃlogos estratigrafia geociencias reservatÃrios arquitetura

ACESSO AO ARTIGO

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