| The Cambrian in Ordos Basin has the potential for natural gas exploration. To clarify the distribution pattern
of favorable sedimentary facies zones and reservoirs，by comprehensively analysing core, outcrop and seismic data，two
types of sequence boundaries, unconformities and lithological transition surfaces are have been identified in the Cambrian
of the Ordos Basin.The Cambrian strata can be divided into two 2nd-order sequences (SS1, SS2) and eight 3rd-order
sequences (SQ1-SQ8), each 3rd-order sequence consists of a TST and a HST, lacking a LST. The unconformity surfaces
of the bottom and top of the Cambrian system serve as the bottom and top boundaries of SS1 and SS2. The lithological
transition surface is the 3rd-order sequence boundary. Eight lithofacies palaeogeoguaphic maps were systematically
compiled to analyze the lithofacies paleogeographic distribution characteristics under 3rd-order sequence stratigraphic
framework of Cambrian in Ordos Basin. The Cambrian in the Ordos Basin has gone through two sedimentary stages. SQ1-
SQ4 is the stage of transgression, developing carbonate ramp sedimentary system. SQ5-SQ8 is the stage of regression,
developing shallow water carbonate platform sedimentary system. Controlled by the evolution of sequence lithofacies
paleogeography, the Cambrian reservoirs in Ordos Basin are mainly distributed longitudinally in SQ6-SQ8, and the good
reservoirs of Cambrian in Ordos Basin include three types: dolomitizational oolitic shoal reservoir, supergene karst
reservoir and fault-dissolution reservoir. Due to the control of the platform margin and high-level system tract, as well as
the distribution and faulting of ancient uplifts, the oolitic shoal reservoir is mainly distributed in the western and southern
platform margin of the basin, the supergene karst reservoir is distributed in the periphery of the palaeouplift, and the faultdissolution reservoir is isolated in the basin. |
