CONFIGURATION OF THE LOWER PALAEOZOIC SOURCE AND RESERVOIR UNITS IN THE GUCHENGXU HIGH,TARIM BLOCK

Multiple tectonic deformations result in a monocline structure in the Guchengxu Well Block,eastern Central High of the Tarim Block.Sequences throughout the Cambrian to Middle Ordovician along the northward Mangaer Depression are considered as source rocks.Potential region for hydrocarbon accumulation shows a transitional distribution adjacent to the Tazhong Lower Uplift to the west.Sedimentary as well as tectonic patterns show optial spatial configurations of the source rocks and reservoirs.Three types of carbonates and one type of sandstone are considered as ideal Ordovician reservoirs.These are the reef complexes of the platform margin from the Middle Ordovician Yijianfang Formation;karst crusts of the Yijianfang Formation;Lower-Middle Ordovician inner karst units;turbidite fans of the out-shelf and basin facies of the Querquek Formation.Of these rock types,the first is considered the best.Reservoir-cap associations occur in the Querquek and Yishan formations;in the Yijianfang Formation limestone capped by the overlying Qiaerbaq Formation limestone or Querquek Formation mudstone;and the Tursaq Formation muddy limestone overlain by the Heituao Formation mudstone.