Application of Meshwork-Carpet Hydrocarbon Accumulation Theory in Carboniferous Reservoirs in Tazhong 4 Oilfield, Tarim Basin

Abstract

Tazhong 4 oilfield is located on the eastside of central fault horst belt, Tazhong low uplift in Tarim basin, with a petroliferous area of 50 km². The multistage tectonic movements, multi-type sedimentary system and diverse diagenesis in Tazhong area results in multistage accumulation, several reservoir-caprock assemblages, multiple traps and reservoirs in Carboniferous. There are heavy oil reservoirs in CIII Donghe sandstone, conventional crude with condensate gas cap in CIII pebbled sandstone, condensate gas in CII bioclast limestone and conventional crude in CI clasolite. This article explains the complex genesis of Tazhong 4 Carboniferous reservoirs with meshwork-carpet hydrocarbon accumulation theory. A complete meshwork-carpet hydrocarbon accumulation system consists of four parts. (1) Source channel meshwork, which is fault, unconformity or volcanic rock intrusion connecting source rock and storage layer, severs as vertical migration channel; (2) Middle storage layer, which is unconformity complex or continuous sand body beyond charging threshold, contains hydrocarbon to migrate horizontally and aggregate in suitable traps; (3) hydrocarbon adjustment meshwork, which is fault or unconformity connecting two storage layers, can adjust reservoir vertically to upper traps; (4) upper storage layer is merely different from middle storage layer in relative position. The combination of meshwork-carpet system can be classified into “Y-shape”, “T-shape” and “S-shape”. Processing the seismic data with methods of stratum reposition, coherent body, attribute pickup and plane-profile interaction, we clarified the tectonic history of Tazhong 4 area and concluded the accumulation history as: early charge of CIII happened in the late Hercynian though the thrust fault and the unconformity between Donghe sandstone and peddled sandstone; in early Himalayan oil in CIII adjusted to CI by faults, due to inferior reservoir properties, CII was not charged by then; in the late Himalayan cracking gas filled CIII and episodically broke through fault closure pressure and migrated form CIII to CII, forming the current reservoirs distribution pattern of“deep gas and shallow oil” in Carboniferous. According to the analysis, the integrity of meshwork-carpet system is the key influence of allothigenous source reservoir accumulation.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015