| The extensive application of elemental capture spectroscopy logging in the exploration and development of unconventional oil and gas reservoirs has promoted its demand for sedimentary rock classification and its lithologic identification.However,there is no unified sedimentary rock classification standard(The terrigenous clastic rocks are mainly based on the size of the debris particles,and the classification of the internal clastic rocks are mainly based on the mineral composition.),which restricts the further development of formation element logging technology and also affects the exploration and development of unconventional oil and gas.Based on the analysis of a large number of sedimentary mineral content data,this paper initially proposes the main types of sedimentary rock based on mineral composition,and discusses the relationship between the mineral composition and granularity of sedimentary rocks and their characteristics of sedimentary lithologic combinations,and has achieved the following four aspects of understanding:(1)Main types of sedimentary rock based on mineral composition The relative mineral content of 9067 sedimentary rock samples from 13 major Chinese petroliferous basins was collected and analyzed.According to the “Classification And Nomenclature Of Sedimentary Rock”,the content of rock endogenous minerals or terrigenous debris is more than 50% to determine the basic name of the rock.The Regulations found that among the 9067 sedimentary rock samples,sedimentary rock major rock-forming minerals such as quartz,feldspar,calcite,dolomite,and clay minerals all contained sample points exceeding 50%.Among all the samples,there are 3271 samples containing more than 50% of quartz minerals,accounting for 36.1% of all samples;227 samples containing more than 50% of feldspar minerals,accounting for 2.5% of all samples;6329 samples containing more than 50% of quartz and feldspar minerals,accounting for 69.8% of all samples;243 samples containing more than 50% of calcite minerals,accounting for 2.7% of all samples;548 samples containing more than 50% of dolomite minerals,which accounted for 6.0% of all samples;949 samples containing more than 50% of calcite and dolomite minerals accounted for 10.5% of all samples;325 samples containing more than 50% of clay minerals,accounting for 3.6% of all samples.In all samples,the amount of clay mineral components such as illite,montmorillonite,kaolinite,and chlorite containing more than 50% of relative content is relatively small,and there is 1 sample with greater than 50% relative content of illite account for 0.01% of all samples;3 samples with relative content of montmorillonite greater than 50% account for 0.03% of all samples;3 samples with relative content of kaolinite greater than 50%,accounting for 0.03% of all samples;0 samples with relative content of chlorite more than 50%.Among all the samples,there are 3 samples with a gypsum and anhydrite content greater than 50%,accounting for 0.03% of the total sample;and 4 coal samples,accounting for 0.04% of the total sample.Among the 9067 sedimentary rock samples,7610 samples accounted for more than 50% of the main rock-forming minerals,accounting for 83.9% of the total samples;1457 samples accounted for 16.1% of all samples with the main rock-mineral content less than 50%.Based on the above research,according to the percentage of rock mineral content and the origin similarity of major rock-forming minerals,combined with previous research results on gypsum rock,salt rock and coal,the sedimentary rock was classified into 7 major categories as clastic rock,carbonate rock,clay rock,complex rock,gypsum rock,salt rock and coal.The sedimentary rock with a content of quartz minerals and feldspar minerals greater than 50% are classified into one type,which is named clastic rock.;The sedimentary rock with a content of calcite minerals and dolomite minerals greater than 50% are classified as one type and named as carbonate rock;The sedimentary rock with a content of clay minerals more than 50% are classified into one group and named as clay rock.The sedimentary rock with less than 50% of the main rock-forming minerals are classified into one group and named as complex rock.Gypsum,anhydrite and halite can all be diagenetic separately,so the sedimentary rock with a content of gypsum or anhydrite greater than 50% is classified as a type and named as gypsum rock.The sedimentary rock with a content of halite greater than 50% is classified as a type and named salt rock.In the classification of sedimentary rock based on mineral composition,clastic rock,carbonate rock and complex rock are divided into 2,2,4 sub-categories respectively.The sub-classes classification of sedimentary rock is based on the content of major rock-forming minerals.For example,the clastic rock in which the content of quartz minerals is larger than the content of feldspar mineral is named as quartz clastic rock,conversely it is named as feldspar clastic rock.The clastic rock is divided into quartz clastic rock and feldspar clastic rock;The carbonate rock is divided into calcite carbonate rock and dolomite carbonate rock;The complex rock has a complex composition,according to the highest mineral content in the complex rock,the complex rock is divided into quartz and feldspar complex rock,calcite complex rock,dolomite complex rock and clay complex rock.(2)Granularity characteristics of sedimentary lithology based on mineral composition The casting thin slices of sedimentary rock samples from typical petroliferous basins were collected and analyzed to observe the Granularity characteristics of sedimentary rock.In the sedimentary rock samples with a grain size greater than 0.1 mm,the rocks containing more than 50% of the major rock-forming minerals are quartz clastic rock,feldspar clastic rock,calcite carbonate rock and dolomite carbonate rock,and the rocks containing less than 50% of the main rock-forming minerals is quartz and feldspar complex rock.In the sedimentary rock samples with a grain size less than 0.1 mm,the rock containing more than 50% of the major rock-forming minerals are quartz clastic rock,feldspar clastic rock,calcite carbonate rock,dolomite carbonate rock and clay rock,and the rocks containing less than 50% of the main rock-forming minerals are quartz and feldspar complex rock,calcite complex rock,dolomite complex rock,clay complex rock,gypsum rock,salt rock and coal.Analysing a variety of the granularity grading schemes of sedimentary rock at home and abroad,it is recommended that using 0.1mm as the granularity limit.The fine sand,sand and gravelly sand which particle size larger than 0.1mm are divided into coarse-grained sedimentary rock,the silt and clay which particle size less than 0.1mm is divided into fine-grained sedimentary rock.(3)Main sedimentary lithologic combinations of sedimentary rock based on mineral composition and granularity Based on the mineral composition and granularity characteristics of sedimentary rock,combined with the structure and mechanical properties of rock,the 4 types of sedimentary lithologic combinations in major petroliferous basins are preliminarily divided :The complex sedimentary rock combination,The fine-grained sedimentary rock combination,The coarse-grained and fine-grained sedimentary rock combination,The coarse-grained and fine-grained sedimentary rock with base rock combination.In addition,some of these sedimentary lithologic combinations were further divided,and on this basis,the above-mentioned relationship between sedimentary lithologic combinations and sedimentary facies was preliminarily established.(4)Characteristics and distribution of sedimentary lithologic combinations in typical petroliferous basins Based on the above studies,we analyzed the characteristics and distribution of sedimentary lithologic combinations in different strata of 3 typical petroliferous basins,which are Mesozoic-Cenozoic in Qaidam Basin,Ordovician and Upper Paleozoic in Ordos Basin,Mesozoic-Cenozoic in Zhanhua Sag of Bohai Bay Basin.It lays a foundation for further research on the unity,difference and correlation of unconventional and conventional hydrocarbon accumulation. |
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