Geological Characteristics Of The Changxing Formation Reef Gas Reservoir In Longgang Donglong Site And Tieshan Area And Optimization Of Favorable Area

In this paper, reef reservoir of upper Permian Changxing Formation in the Longhuichang-Tieshan area is the main research subjects. It is guided by the principle and methods of petroleum geology, carbonate sedimentology, reservoir geology, geochemistry, Using logging data, logging, seismic, production performance data, the existence of Dalong Formation is proved on the basis of a large number of cores observations, rock slices identification, paleontological features analysis, regional stratigraphic correlation and previous research achievements. The Permian-Triassic boundary and Trough border has been readjusted. The characteristics and differences of Dalong Formation and the Longtan Formation (Wujiaping formation) are summarized.This paper has redrew the platform margin boundary. The Changxing formation sedimentary facies types and the distribution of reefs has been found out. The sedimentary system is further divided into such fancies as open platform, platform margin fancies and slope-trough phase. Reefs in the study area belong to platform margin reef, which distributed like band. The organic reef-bank complex can be divided into reef core, reef beach and reef-cap fancies on the longitudinal. The reef beach is further divided into reef base beach, inter-reef beach and top-reef beach.The characteristics and main controlling factor of Reef reservoir development and distribution has further studied in this paper. The study points out that platform margin shoals and organic reefs are the best favorable fancies belts of reservoirs, and reef dolomite and grain dolomite are the favorable reservoir rocks of reservoirs. The main type of reservoir is fracture-pore, but some caves also develops in local intervals. The main types of reservoir space include intergranular dissolved pore, intracrystalline dissolved pore, which are created by dolomitization and dissolution. The reservoir is low porosity and low permeability,but some local depth sections is high porosity and high permeability. The reservoir is controlled by deposition, diagenesis, and structural factors., and is profoundly affected by dolomitization, dissolution and cementation.Typical reef gas reservoir were analyzed in the researched region, and the origin types of gas reservoir is further confirmed. The promising exploration belts were located which is classified as class Ⅰ and class Ⅱ favorable areas. The research has guided the successful LongHui002-X2drilling, which is a milestone to the reef reservoir exploration in Longhuichang.