Reservoir Characteristics And Favorable Belt Evaluation Of Chagan Sag In Yin-E Basin In Inner Mongolia

Guided by petroleum and natural gas geology, seismic stratigraphy, sequence stratigraphy and reservoir geology and on the basis of drilling data and logging data on hand, seismic data has been fully used and study on seismic stratigraphy and sequence stratigraphy has also been done in this paper so as to carry out sedimentary facies study and depositonal system study of primary target strata in the block. A lot of analytical assay work of drilling core data has been done to carry out research on lithological property of clasolite reservoir for primary target strata, reservoir bed diagenesis, petrophysical property of reservoir bed and its influential factor, with which reservoir bed classification evaluation and favorable reservoir belt prediction have been done successfully.In this paper the primary exploration targets of lower Cretaceous are divided into 6 third-class sequences and 14 systems, among which Bayingebi formation is divided into 2 sequences, Suhongtu formation into 3 sequences and Yingen formation 1 sequence. Study suggests the strata of this block are of the following feature: various sequence interface types, first-class fault and tectonic movement control strata framework styles; formation and evolution of Maodun sub-high makes single-lined fault dustpan-type depression complicated to produce unsymmetrical grabens and igneous rock, which influences detrital rock infilling pattern in the depression.Strata sequence of this block has 4 types of infilling pattern: faulted slope of Hule-Egen sub-depression actic region, glacis slope of single-lined fault dustpan-type lake basin, trough fault infilling of double faulted graben and central Maodun sub-high.5 types of sedimentary facies have been classified in this paper after facies attribute study: alluvial fan facies, fluvial facies, sub-marine fan facies, fan delta facies and lacustrine facies. On the basis of planar sedimentary facies analysis for key layers, it is thought 2 depositional models were mainly developed in this block: single-lined fault dustpan-type lake basin depositional model and double faulted graben lake basin sedimentary model. This paper also tells us clasolite reservoir of lower Cretaceous is generally of the following lithological characteristics: low component maturity, low structural maturity, high cuttings content, high infilling content, various infilling composition, various cementation types, near source, rapid accumulation speed and polytropic lithologic genesis. Clasolite diagenetic stage can be divided into: B period of early diagenetic stage, A1 period of middle diagenetic stage, A2 period of middle diagenetic stage and B period of middle diagenetic stage.Petrophysical property of the reservoir bed, which is of too low porosity and permeability, is commonly poor in this block. The influential factors are: horizon, different system in strata sequence framework, clast composition, structure, matrix quality in source area, sedimentary facies belt, diagenesis, volcanics distribution and pressure distribution.Comprehensive study shows, vertically, reservoir bed of Chagan sag mainly developed fan delta, fluvial fan and submarine fan sand body deposits of Bayingebi formation and shore mere facies sand deposits in interval Su 1 and Su 2. Among all sequence strata of exploration target, it mainly developed medium-coarse clastic arkose in high water system, which overlies and underlies the primary sequence interface (unconformity) as well. On the plane, deposits mainly distribute on the sides of the depression, especially submarine sand body of downthrow block of Tugege fault and Hule fault and sand body inside the depression. Generally these sand bodies are of big area and thickness. They are also favorable objectives for further exploration.