Intra-platform Shoal Research Articles

Reservoir characteristics and main controlling factors of the Longwangmiao Formation in the Moxi area, central Sichuan Basin, China

The Longwangmiao Formation in the Lower Cambrian is one of the key petroleum systems in Sichuan Basin. Especially with the great breakthrough of the Longwangmiao Formation in the central Sichuan Basin, it shows a giant exploration potential. Using various data and approaches including core and petrographical analysis, petrophysical properties, SEM, and cathodoluminescence emission, the reservoir characteristics and the main controlling factors of the Longwangmiao Formation (in the Moxi area) are evaluated. This study shows that the reservoir of the Longwangmiao Formation developed very well. It is mainly composed of dolarenite and fine crystalline dolostone. The most dominant pore types are dissolved enlarged intergranular and intercrystalline pores or vugs. The reservoir properties of the Longwangmiao Formation were varying respectively, from 0.5 to 12 % and 0.001 to 1000 mD. The main reservoir controlling factors are deposition, diagenesis, and tectonism. Deposition laid a foundation to reservoir development, especially the intraplatform shoals deposited in an environment with relatively high energy and platform flat located in the highland with low energy. In the early Cambrian Longwangmiao period, two episodes of transgression and regression process had occurred, and reservoir intervals are developed in the end of each episode. Meanwhile, diagenetic alterations are keys to reservoir evolution; three kinds of dissolution played an effective role in the generation and development of the pore system. Compaction and cementation caused many damages to the reservoir porosity. Fractures caused by structural breakages can improve the reservoir permeability and provide fluid migration pathways to the late dissolution, which formed solution-enlarged fractures as reservoir and percolation spaces.

Characteristics and controlling factors of carbonate intra-platform shoals in the Tarim Basin, NW China

Abstract Intra-platform shoals are widely developed in the Cambrian-Ordovician of the Tarim Basin, western China, and are prospective for hydrocarbon exploration. Early Paleozoic tectonic evolution of the Tarim Basin was one of the extensions and was followed by compression. The dynamic transformation of the regional plate margins caused differentiation of the intra-platform paleogeomorphology, which imposed changes in the development of sedimentary facies contemporaneous with the development of intra-platform shoals. An integrated model for the recognition of intra-platform shoals was established through outcrop investigation, core observation, logging analysis and seismic data interpretation. Ordovician intra-platform shoals in the Tarim Basin occur as ‘shoal containing reefs’, ‘shoal covering reefs’ as well as ‘shoal wrapping reefs’ and show different characteristics at different periods. Few but large intra-platform shoals are developed in the Penglaiba Formation. Large numbers of small-scale intra-platform shoals are widely developed in the lower member of the Yingshan Formation, whereas larger and thicker intra-platform shoals are widely developed in the upper member of the Yingshan Formation. Intra-platform shoals show successive development characteristics from Penglaiba to Yingshan Formations. This study indicates that the development of intra-platform shoals is controlled by many factors such as platform structure, sea-level change, paleodepth, hydrodynamic condition, and paleogeomorphology, among which sea-level changes and micro-paleogeomorphology play the most significant role. The shoals are found mainly in highstand system tracts of high-frequency depositional cycles. The ideal locations for the development of intra-platform shoals are over micro-uplifts and facing windward paleoslopes.

Intra-platform tectono-sedimentary response to geodynamic transition along the margin of the Tarim Basin, NW China

The Tarim Basin has experienced three tectonic evolutionary phases from the Cambrian to Ordovician: (1) Regional extension from the late Neoproterozoic to Mid-Early Cambrian, (2) Relatively weak regional compression from the Late Cambrian to Mid-Early Ordovician, and (3) Regional compression during the Late Ordovician. Intra-platform tectonic and sedimentary characteristics indicate a clear linkage to the tectonic evolution of the basin margin during early Paleozoic time. During the Cambrian, small intra-platform rift-related depressions formed during an extensional setting. During the Mid-Early Ordovician, a transition from extension to compression caused formation of the Tazhong and Tabei paleo-uplifts and major unconformities T74 (base of the Late Ordovician). The evolving paleo-geomorphology led to differentiation of sedimentary facies, and numerous intra-platform shoals formed during deposition of the Early Ordovician Yingshan Formation. During the Late Ordovician, regional compression began, which changed the platform margin slopes into four slopes that surrounded the three isolated island uplifts of Tabei, Tazhong, and Tangnan in the Late Ordovician. Simultaneously, the basin margin dynamic conditions also changed the relative sea level and filling pattern of the basin. In the Early and Middle Cambrian, the Tarim Basin mainly developed a progradational ramp-type platform due to relative sea level fall. From the Late Cambrian to Early Ordovician the relative sea level began to rise, resulting in an aggradational—retrograding rimmed margins-type platform. In the Late Ordovician, along with a further rise in relative sea level, the basin mainly developed isolated platform.

Ordovician intra-platform shoal reservoirs in the Tarim Basin, NW China: Characteristics and depositional controls

Research Article| March 01, 2013 Ordovician intra-platform shoal reservoirs in the Tarim Basin, NW China: Characteristics and depositional controls Zhi-qian Gao; Zhi-qian Gao Key Laboratory for Marine Reservoir, Evolution and Hydrocarbon Accumulation Mechanism, Ministry of Education of China China, University of Geosciences, Beijing 100083, China, gzq@cugb.edu.cn Search for other works by this author on: GSW Google Scholar Tai-liang Fan Tai-liang Fan Key Laboratory for Marine Reservoir, Evolution and Hydrocarbon Accumulation Mechanism, Ministry of Education of China, China University of Geosciences, Beijing 100083, China, ftl@cugb.edu.cn Search for other works by this author on: GSW Google Scholar Bulletin of Canadian Petroleum Geology (2013) 61 (1): 83–100. https://doi.org/10.2113/gscpgbull.61.1.83 Article history received: 05 Mar 2012 accepted: 29 Jan 2013 first online: 12 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Zhi-qian Gao, Tai-liang Fan; Ordovician intra-platform shoal reservoirs in the Tarim Basin, NW China: Characteristics and depositional controls. Bulletin of Canadian Petroleum Geology 2013;; 61 (1): 83–100. doi: https://doi.org/10.2113/gscpgbull.61.1.83 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract Intra-platform shoal reservoirs are widely developed in the Ordovician of the Tarim Basin, western China and are prospective for hydrocarbon exploration. Early Paleozoic tectonic evolution of the Tarim Basin was one of extension and followed by compression. The dynamic transformation of the regional plate margins caused differentiation of the intra-platform paleogeomorphology, which imposed changes on the development of sedimentary facies contemporaneous with the development of intra-platform shoals. An integrated model for recognition of intra-platform shoal reservoirs was established through outcrop investigation, core observation, logging analysis and seismic data interpretation. Ordovician intra-platform shoals in the Tarim Basin occur as ‘shoal deposits containing small reefs’, ‘shoal deposits covering large reefs’, as well as ‘reef-dominated shoal deposits’. Each of these types tend to dominate at different stratigraphic levels. Few but large intra-platform shoals are developed in the Penglaiba Formation. Large numbers of small-scale intra-platform shoals are widely developed in the lower member of the Yingshan Formation, whereas larger and thicker intra-platform shoals are widely developed in the upper member of the Yingshan Formation. This study indicates that the development of intra-platform shoals is controlled by many factors such as platform structure, sea-level change, paleodepth, and paleogeomorphology, among which the sea-level changes and micro-paleogeomorphology play the most significant role. The shoals are found mainly in highstand system tracts of high-frequency depositional cycles. The ideal locations for the development of intra-platform shoals are over micro-uplifts and facing windward paleoslopes. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Structural characteristics of intra-platform shoal in the Leikoupo Formation in the transitional zone of the central and southern Sichuan Basin

Abstract Through comprehensive research on drilling, logging and core data of T 2 l 1 1 sub-member, which is the major pay of the Leikoupo Formation in the transitional zone of the central and southern Sichuan Basin, the structural characteristics, distribution regularity and its major controlling factors of intra-platform shoal are studied. The major rocks of intra-platform shoal in T 2 l 1 1 sub-member include oosparite, residual oolitic dolostone, sparrenite, residual doloarenite and sparry doloarenite, sparry bioclastic limestone and residual bioclastic dolostone, which constitute oolitic shoal, arene shoal and bioclastic shoal. The intra-platform shoal is characterized vertically by shallowing-upward sequences, and consists of three sedimentary units, namely shoal base, shoal core and shoal cap. Besides, three microfacies can be distinguished laterally, shoal core, shoal edge and intershoal sea. The variation of water depth and hydrodynamic conditions caused by sea level change control the characteristics and superposed pattern of shoal body. Meanwhile, the palaeogeomorphology with alternating uplifts and depressions defines the differential distribution and lateral combination pattern of intra-platform shoal body.

Geochemical characteristics and genetic model of dolomite reservoirs in the eastern margin of the Pre-Caspian Basin

The widespread Carboniferous KT-I dolomite in the eastern margin of the Pre-Caspian Basin is an important hydrocarbon reservoir. The dolomite lithology is dominated by crystalline dolomite. The δ18O values range from −6.71‰ to 2.45‰, and average 0.063‰, obviously larger than −2.5‰, indicating low-temperature dolomite of evaporation origin. Stable strontium isotope ratios (87Sr/86Sr) range from 0.70829 to 0.70875 and average 0.708365, very consistent with 87Sr/86Sr ratios in Carboniferous seawater. Chemical analysis of Ca and Mg elements shows that the dolomite has 9.1 mole% excess Ca or even higher before stabilization. The degree of order of dolomite is medium-slightly poor, varying in a range of 0.336–0.504 and averaging 0.417. It suggests that the dolomite formed under near-surface conditions. There are two models for the origin of the Carboniferous KT-I dolomite reservoir. These are 1) the evaporation concentration — weathering crust model and 2) the shoal facies — seepage reflux model. The former is mainly developed in restricted platforms — evaporate platforms of restricted marine deposition environments with a representation of dolomite associated with gypsum and mudstone. The latter mainly formed in platform edge shoals and intra-platform shoals and is controlled by dolomitization due to high salinity sea water influx from adjacent restricted sea or evaporate platform.