BGHMS: A Geohistory Modeling System for Cratonic Basins

The BGHMS system described in this paper was designed to model the geohistory for cratonic basins and written in turbo BASIC language with a user-friendly interface for data inputs and outputs on IBM PC-compatible computers. The major mathematical models in this system include the models of compaction correction. unconformity restoration. sea-level change and paleo-water-depth correction. and tectonic subsidence modeling. Two geological events of sediment compaction and erosion are considered in this system. It consists of three modules for data input, geohistory modeling and graph conversion and output. containing more than twenty subroutine programs, is an easy-to-use. menu-driven program system with many obvious advantages, and is a useful tool for hydrocarbon geologists to make quantitative studies on geohistory and to make exploration decisions in regional evaluation.

Investigation of plateau basin crustal structures and thickening mechanisms in the northeastern margin of the Tibetan plateau

This paper uses deep seismic sounding （DSS） data to contrast and analyze the crustal structures of three plateau basins （Songpan-Garze, Qaidam, Longzhong） in the northeastern margin of the Qinghai-Xizang （Tibetan） plateau, as well as two stable cratonic basins （Ordos, Sichuan） in its peripheral areas. Plateau basin crustal structures, lithological variations and crustal thickening mechanisms were investigated. The results show that, compared to the peripheral stable cratonic basins, the crystalline crusts of plateau basins in the northeastern margin are up to 10 15 km thicker, and the relative medium velocity difference is about 5% less. The medium velocity change in crustal layers of plateau basin indicates that the upper crust undergoes brittle deformation, whereas the lower crust deforms plastically with low velocity. The middle crust shows a brittle-to-plastic transition zone in this region. Thickening in the lower crust （about 5 10 km）, and rheological characteristics that show low- medium velocity （relatively reduced by 7%）, suggest that crustal thickening mainly takes place in lower crust in the northeastern margin of the Tibetan plateau. The crust along the northeastern margin shows evidence of wholesale block movement, and crustal shortening and thickening seem to be the main deformation features of this region. The GPS data show that the block motion modes and crustal thickening in the Tibetan plateau is closely related to the peripheral tectonic stress field and motion direction of the Indian plate. The Mani-Yushu- Xianshuihe fold belt along the boundary between the Qiangtang block and the Bayan Har block divides the different plateau thickening tectonic environments into the middle-western plateau, the northeastern margin and the southeastern plateau.

Petroleum Exploration of Craton Basins in China

Craton basins are a significant petroliferous provenance. Having undergone multiple open- dose tectonic cycles and strong reworking of the late Cenozoic tectonic movement, the craton basins in China are highly broken. This has resulted in multi-source and multiphase hydrocarbon generation and later hydrocarbon accumulation so that a complicated spatial assemblage of primary, paraprimary and secondary oil-gas pools has been formed. The primary factors controlling hydrocarbon accumulation include hydrocarbon-generating depressions, paleouplifts, paleoslopes, unconformity surfaces, paleo-karst, faults and fissure systems as well as the later conservation conditions. In consequence, the strategy of exploration for China＇s craton basins is to identify the effective source rocks, pay attention to the different effects of paleohighs and late reworking, enhance studies of the secondary storage space, attach importance to the exploration of lithologic oil-gas reservoirs and natural gas pools, and approach consciously from the secondary oil pools to the targets near the source rocks. At the same time, a complete system of technologies and techniques must be built up.

Characteristics of the crystalline basement beneath the Ordos Basin:Constraint from aeromagnetic data

Aeromagnetic anomaly zonation of the Ordos Basin and adjacent areas was obtained by processing high-precision and large-scale aeromagnetic anomalies with an approach of reduction to the pole upward continuation. Comparative study on aeromagnetic and seismic tomography suggests that aeromagnetic anomalies in this area are influenced by both the magnetic property of the rock and the burial depth of the Precambrian crystalline basement. Basement depth might be the fundamental control factor for aeromagnetic anomalies because the positive and negative anomalies on the reduction to the pole- upward-continuation anomaly maps roughly coincide with the uplifts and depressions of the crystalline basement in the basin. The results, together with the latest understanding of basement faults, SHRIMP U-Pb zircon dating of metamorphic rock and granite, drilling data, detrital zircon ages, and gravity data interpretation, suggest that the Ordos block is not an entirety of Archean.

Oil-gas microseapage and shallow hydrocarbon anomaly in craton basin

Although it has been accepted that oil and gas can migrate a long distance throughfaults, surface of unconformity and fractures in vertical and horizontal directions, it isuncertain whether deep oil-gas can reach the surface in stable craton basin in which faultsand fractures are poorly developed. The vertical changes of pyrolysis hydrocarbon,